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If these are example addresses, they should be changed. -- The document has examples using IPv4 documentation addresses according to RFC6890, but does not use any IPv6 documentation addresses. Maybe there should be IPv6 examples, too? Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- Couldn't find a document date in the document -- date freshness check skipped. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '1' on line 7650 -- Looks like a reference, but probably isn't: '2' on line 7659 -- Looks like a reference, but probably isn't: '3' on line 7668 -- Looks like a reference, but probably isn't: '4' on line 7738 -- Looks like a reference, but probably isn't: '5' on line 7737 -- Looks like a reference, but probably isn't: '6' on line 7731 -- Looks like a reference, but probably isn't: '7' on line 7740 -- Possible downref: Non-RFC (?) normative reference: ref. 'MIDI' -- Possible downref: Non-RFC (?) normative reference: ref. 'MPEGSA' ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) -- Possible downref: Non-RFC (?) normative reference: ref. 'MPEGAUDIO' -- Possible downref: Non-RFC (?) normative reference: ref. 'DLS2' ** Obsolete normative reference: RFC 2616 (Obsoleted by RFC 7230, RFC 7231, RFC 7232, RFC 7233, RFC 7234, RFC 7235) ** Obsolete normative reference: RFC 3388 (Obsoleted by RFC 5888) -- Possible downref: Non-RFC (?) normative reference: ref. 'RP015' ** Obsolete normative reference: RFC 4288 (Obsoleted by RFC 6838) -- Obsolete informational reference (is this intentional?): RFC 2326 (Obsoleted by RFC 7826) -- Obsolete informational reference (is this intentional?): RFC 2818 (Obsoleted by RFC 9110) Summary: 5 errors (**), 0 flaws (~~), 2 warnings (==), 18 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT J. Lazzaro 3 February 3, 2009 J. Wawrzynek 4 Expires: August 3, 2009 UC Berkeley 5 Intended Status: Proposed Standard 7 RTP Payload Format for MIDI 9 11 Status of This Memo 13 This Internet-Draft is submitted to IETF in full conformance with the 14 provisions of BCP 78 and BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering Task 17 Force (IETF), its areas, and its working groups. Note that other 18 groups may also distribute working documents as Internet-Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six months 21 and may be updated, replaced, or obsoleted by other documents at any 22 time. It is inappropriate to use Internet-Drafts as reference material 23 or to cite them other than as "work in progress." 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/1id-abstracts.html 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html 31 This Internet-Draft will expire on August 3, 2009. 33 Copyright Notice 35 Copyright (c) 2009 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (http://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with 43 respect to this document. 45 Abstract 47 This memo describes a Real-time Transport Protocol (RTP) payload 48 format for the MIDI (Musical Instrument Digital Interface) command 49 language. The format encodes all commands that may legally appear on 50 a MIDI 1.0 DIN cable. The format is suitable for interactive 51 applications (such as network musical performance) and content- 52 delivery applications (such as file streaming). The format may be 53 used over unicast and multicast UDP and TCP, and it defines tools for 54 graceful recovery from packet loss. Stream behavior, including the 55 MIDI rendering method, may be customized during session setup. The 56 format also serves as a mode for the mpeg4-generic format, to support 57 the MPEG 4 Audio Object Types for General MIDI, Downloadable Sounds 58 Level 2, and Structured Audio. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 5 63 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 64 1.2. Bitfield Conventions . . . . . . . . . . . . . . . . . . . 6 65 2. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . . . 7 66 2.1. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 7 67 2.2. MIDI Payload . . . . . . . . . . . . . . . . . . . . . . . 12 68 3. MIDI Command Section . . . . . . . . . . . . . . . . . . . . . . 14 69 3.1. Timestamps . . . . . . . . . . . . . . . . . . . . . . . . 15 70 3.2. Command Coding . . . . . . . . . . . . . . . . . . . . . . 17 71 4. The Recovery Journal System . . . . . . . . . . . . . . . . . . . 24 72 5. Recovery Journal Format . . . . . . . . . . . . . . . . . . . . . 26 73 6. Session Description Protocol . . . . . . . . . . . . . . . . . . 30 74 6.1. Session Descriptions for Native Streams . . . . . . . . . 31 75 6.2. Session Descriptions for mpeg4-generic Streams . . . . . . 33 76 6.3. Parameters . . . . . . . . . . . . . . . . . . . . . . . . 35 77 7. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . . . 37 78 8. Congestion Control . . . . . . . . . . . . . . . . . . . . . . . 38 79 9. Security Considerations . . . . . . . . . . . . . . . . . . . . . 39 80 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 40 81 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 40 82 11.1. rtp-midi Media Type Registration . . . . . . . . . . . . 41 83 11.1.1. Repository Request for "audio/rtp-midi" . . . . . 43 84 11.2. mpeg4-generic Media Type Registration . . . . . . . . . . 45 85 11.2.1. Repository Request for Mode rtp-midi for 86 mpeg4-generic . . . . . . . . . . . . . . . . . . 48 87 11.3. asc Media Type Registration . . . . . . . . . . . . . . . 49 88 A. The Recovery Journal Channel Chapters . . . . . . . . . . . . . . 52 89 A.1. Recovery Journal Definitions . . . . . . . . . . . . . . . 52 90 A.2. Chapter P: MIDI Program Change . . . . . . . . . . . . . . 57 91 A.3. Chapter C: MIDI Control Change . . . . . . . . . . . . . . 58 92 A.3.1. Log Inclusion Rules . . . . . . . . . . . . . . . . 58 93 A.3.2. Controller Log Format . . . . . . . . . . . . . . . 60 94 A.3.3. Log List Coding Rules . . . . . . . . . . . . . . . 62 95 A.3.4. The Parameter System . . . . . . . . . . . . . . . 65 96 A.4. Chapter M: MIDI Parameter System . . . . . . . . . . . . . 67 97 A.4.1. Log Inclusion Rules . . . . . . . . . . . . . . . . 68 98 A.4.2. Log Coding Rules . . . . . . . . . . . . . . . . . 70 99 A.4.2.1. The Value Tool . . . . . . . . . . . . . . . 71 100 A.4.2.2. The Count Tool . . . . . . . . . . . . . . . 75 101 A.5. Chapter W: MIDI Pitch Wheel . . . . . . . . . . . . . . . 76 102 A.6. Chapter N: MIDI NoteOff and NoteOn . . . . . . . . . . . . 77 103 A.6.1. Header Structure . . . . . . . . . . . . . . . . . 78 104 A.6.2. Note Structures . . . . . . . . . . . . . . . . . . 79 105 A.7. Chapter E: MIDI Note Command Extras . . . . . . . . . . . 81 106 A.7.1. Note Log Format . . . . . . . . . . . . . . . . . . 82 107 A.7.2. Log Inclusion Rules . . . . . . . . . . . . . . . . 82 108 A.8. Chapter T: MIDI Channel Aftertouch . . . . . . . . . . . . 83 109 A.9. Chapter A: MIDI Poly Aftertouch . . . . . . . . . . . . . 84 110 B. The Recovery Journal System Chapters . . . . . . . . . . . . . . 86 111 B.1. System Chapter D: Simple System Commands . . . . . . . . . 86 112 B.1.1. Undefined System Commands . . . . . . . . . . 87 113 B.2. System Chapter V: Active Sense Command . . . . . . . . . . 90 114 B.3. System Chapter Q: Sequencer State Commands . . . . . . . . 91 115 B.3.1. Non-compliant Sequencers . . . . . . . . . . . 93 116 B.4. System Chapter F: MIDI Time Code Tape Position . . . . . . 94 117 B.4.1. Partial Frames . . . . . . . . . . . . . . . . . . 96 118 B.5. System Chapter X: System Exclusive . . . . . . . . . . . . 98 119 B.5.1. Chapter Format . . . . . . . . . . . . . . . . 98 120 B.5.2. Log Inclusion Semantics . . . . . . . . . . . 101 121 B.5.3. TCOUNT and COUNT Fields . . . . . . . . . . . 103 122 C. Session Configuration Tools . . . . . . . . . . . . . . . . . . . 105 123 C.1. Configuration Tools: Stream Subsetting . . . . . . . . . . 106 124 C.2. Configuration Tools: The Journalling System . . . . . . . 110 125 C.2.1. The j_sec Parameter . . . . . . . . . . . . . . . . 111 126 C.2.2. The j_update Parameter . . . . . . . . . . . . . . 112 127 C.2.2.1. The anchor Sending Policy . . . . . . . . . 113 128 C.2.2.2. The closed-loop Sending Policy . . . . . . . 113 129 C.2.2.3. The open-loop Sending Policy . . . . . . . . 117 130 C.2.3. Recovery Journal Chapter Inclusion Parameters . . . 119 131 C.3. Configuration Tools: Timestamp Semantics . . . . . . . . . 124 132 C.3.1. The comex Algorithm . . . . . . . . . . . . . . . . 124 133 C.3.2. The async Algorithm . . . . . . . . . . . . . . . . 125 134 C.3.3. The buffer Algorithm . . . . . . . . . . . . . . . 126 135 C.4. Configuration Tools: Packet Timing Tools . . . . . . . . . 128 136 C.4.1. Packet Duration Tools . . . . . . . . . . . . . . . 128 137 C.4.2. The guardtime Parameter . . . . . . . . . . . . . . 129 138 C.5. Configuration Tools: Stream Description . . . . . . . . . 131 139 C.6. Configuration Tools: MIDI Rendering . . . . . . . . . . . 137 140 C.6.1. The multimode Parameter . . . . . . . . . . . . . . 138 141 C.6.2. Renderer Specification . . . . . . . . . . . . . . 138 142 C.6.3. Renderer Initialization . . . . . . . . . . . . . . 141 143 C.6.4. MIDI Channel Mapping . . . . . . . . . . . . . . . 143 144 C.6.4.1. The smf_info Parameter . . . . . . . . . . . 143 145 C.6.4.2. The smf_inline, smf_url, and smf_cid 146 Parameters . . . . . . . . . . . . . . . . . 145 147 C.6.4.3. The chanmask Parameter . . . . . . . . . . . 146 148 C.6.5. The audio/asc Media Type . . . . . . . . . . . . . 147 149 C.7. Interoperability . . . . . . . . . . . . . . . . . . . . . 149 150 C.7.1. MIDI Content Streaming Applications . . . . . . . 149 151 C.7.2. MIDI Network Musical Performance Applications . . . 152 152 D. Parameter Syntax Definitions . . . . . . . . . . . . . . . . . . 161 153 E. A MIDI Overview for Networking Specialists . . . . . . . . . . . 168 154 E.1. Commands Types . . . . . . . . . . . . . . . . . . . . . . 170 155 E.2. Running Status . . . . . . . . . . . . . . . . . . . . . . 170 156 E.3. Command Timing . . . . . . . . . . . . . . . . . . . . . . 171 157 E.4. AudioSpecificConfig Templates for MMA Renderers . . . . . 171 158 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 159 Normative References . . . . . . . . . . . . . . . . . . . . . 176 160 Informative References . . . . . . . . . . . . . . . . . . . . 177 161 Change Log for . . . . . . . . . 180 162 1. Introduction 164 The Internet Engineering Task Force (IETF) has developed a set of 165 focused tools for multimedia networking ([RFC3550] [RFC4566] [RFC3261] 166 [RFC2326]). These tools can be combined in different ways to support a 167 variety of real-time applications over Internet Protocol (IP) networks. 169 For example, a telephony application might use the Session Initiation 170 Protocol (SIP, [RFC3261]) to set up a phone call. Call setup would 171 include negotiations to agree on a common audio codec [RFC3264]. 172 Negotiations would use the Session Description Protocol (SDP, [RFC4566]) 173 to describe candidate codecs. 175 After a call is set up, audio data would flow between the parties using 176 the Real Time Protocol (RTP, [RFC3550]) under any applicable profile 177 (for example, the Audio/Visual Profile (AVP, [RFC3551])). The tools 178 used in this telephony example (SIP, SDP, RTP) might be combined in a 179 different way to support a content streaming application, perhaps in 180 conjunction with other tools, such as the Real Time Streaming Protocol 181 (RTSP, [RFC2326]). 183 The MIDI (Musical Instrument Digital Interface) command language [MIDI] 184 is widely used in musical applications that are analogous to the 185 examples described above. On stage and in the recording studio, MIDI is 186 used for the interactive remote control of musical instruments, an 187 application similar in spirit to telephony. On web pages, Standard MIDI 188 Files (SMFs, [MIDI]) rendered using the General MIDI standard [MIDI] 189 provide a low-bandwidth substitute for audio streaming. 191 This memo is motivated by a simple premise: if MIDI performances could 192 be sent as RTP streams that are managed by IETF session tools, a 193 hybridization of the MIDI and IETF application domains may occur. 195 For example, interoperable MIDI networking may foster network music 196 performance applications, in which a group of musicians, located at 197 different physical locations, interact over a network to perform as they 198 would if they were located in the same room [NMP]. As a second example, 199 the streaming community may begin to use MIDI for low- bitrate audio 200 coding, perhaps in conjunction with normative sound synthesis methods 201 [MPEGSA]. 203 To enable MIDI applications to use RTP, this memo defines an RTP payload 204 format and its media type. Sections 2-5 and Appendices A-B define the 205 RTP payload format. Section 6 and Appendices C-D define the media types 206 identifying the payload format, the parameters needed for configuration, 207 and how the parameters are utilized in SDP. 209 Appendix C also includes interoperability guidelines for the example 210 applications described above: network musical performance using SIP 211 (Appendix C.7.2) and content-streaming using RTSP (Appendix C.7.1). 213 Another potential application area for RTP MIDI is MIDI networking for 214 professional audio equipment and electronic musical instruments. We do 215 not offer interoperability guidelines for this application in this memo. 216 However, RTP MIDI has been designed with stage and studio applications 217 in mind, and we expect that efforts to define a stage and studio 218 framework will rely on RTP MIDI for MIDI transport services. 220 Some applications may require MIDI media delivery at a certain service 221 quality level (latency, jitter, packet loss, etc). RTP itself does not 222 provide service guarantees. However, applications may use lower-layer 223 network protocols to configure the quality of the transport services 224 that RTP uses. These protocols may act to reserve network resources for 225 RTP flows [RFC2205] or may simply direct RTP traffic onto a dedicated 226 "media network" in a local installation. Note that RTP and the MIDI 227 payload format do provide tools that applications may use to achieve the 228 best possible real-time performance at a given service level. 230 This memo normatively defines the syntax and semantics of the MIDI 231 payload format. However, this memo does not define algorithms for 232 sending and receiving packets. An ancillary document [RFC4696] provides 233 informative guidance on algorithms. Supplemental information may be 234 found in related conference publications [NMP] [GRAME]. 236 Throughout this memo, the phrase "native stream" refers to a stream that 237 uses the rtp-midi media type. The phrase "mpeg4-generic stream" refers 238 to a stream that uses the mpeg4-generic media type (in mode rtp-midi) to 239 operate in an MPEG 4 environment [RFC3640]. Section 6 describes this 240 distinction in detail. 242 1.1. Terminology 244 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 245 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 246 document are to be interpreted as described in BCP 14, RFC 2119 247 [RFC2119]. 249 1.2. Bitfield Conventions 251 In this document, the packet bitfields that share a common name often 252 have identical semantics. As most of these bitfields appear in 253 Appendices A-B, we define the common bitfield names in Appendix A.1. 255 However, a few of these common names also appear in the main text of 256 this document. For convenience, we list these definitions below: 258 o R flag bit. R flag bits are reserved for future use. Senders 259 MUST set R bits to 0. Receivers MUST ignore R bit values. 261 o LENGTH field. All fields named LENGTH (as distinct from LEN) 262 code the number of octets in the structure that contains it, 263 including the header it resides in and all hierarchical levels 264 below it. If a structure contains a LENGTH field, a receiver 265 MUST use the LENGTH field value to advance past the structure 266 during parsing, rather than use knowledge about the internal 267 format of the structure. 269 2. Packet Format 271 In this section, we introduce the format of RTP MIDI packets. The 272 description includes some background information on RTP, for the benefit 273 of MIDI implementors new to IETF tools. Implementors should consult 274 [RFC3550] for an authoritative description of RTP. 276 This memo assumes that the reader is familiar with MIDI syntax and 277 semantics. Appendix E provides a MIDI overview, at a level of detail 278 sufficient to understand most of this memo. Implementors should consult 279 [MIDI] for an authoritative description of MIDI. 281 The MIDI payload format maps a MIDI command stream (16 voice channels + 282 systems) onto an RTP stream. An RTP media stream is a sequence of 283 logical packets that share a common format. Each packet consists of two 284 parts: the RTP header and the MIDI payload. Figure 1 shows this format 285 (vertical space delineates the header and payload). 287 We describe RTP packets as "logical" packets to highlight the fact that 288 RTP itself is not a network-layer protocol. Instead, RTP packets are 289 mapped onto network protocols (such as unicast UDP, multicast UDP, or 290 TCP) by an application [ALF]. The interleaved mode of the Real Time 291 Streaming Protocol (RTSP, [RFC2326]) is an example of an RTP mapping to 292 TCP transport, as is [RFC4571]. 294 2.1. RTP Header 296 [RFC3550] provides a complete description of the RTP header fields. In 297 this section, we clarify the role of a few RTP header fields for MIDI 298 applications. All fields are coded in network byte order (big- endian). 300 0 1 2 3 301 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 303 | V |P|X| CC |M| PT | Sequence number | 304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 305 | Timestamp | 306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 307 | SSRC | 308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 311 | MIDI command section ... | 312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 313 | Journal section ... | 314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 316 Figure 1 -- Packet format 318 The behavior of the 1-bit M field depends on the media type of the 319 stream. For native streams, the M bit MUST be set to 1 if the MIDI 320 command section has a non-zero LEN field, and MUST be set to 0 321 otherwise. For mpeg4-generic streams, the M bit MUST be set to 1 for 322 all packets (to conform to [RFC3640]). 324 In an RTP MIDI stream, the 16-bit sequence number field is initialized 325 to a randomly chosen value and is incremented by one (modulo 2^16) for 326 each packet sent in the stream. A related quantity, the 32-bit extended 327 packet sequence number, may be computed by tracking rollovers of the 328 16-bit sequence number. Note that different receivers of the same 329 stream may compute different extended packet sequence numbers, depending 330 on when the receiver joined the session. 332 The 32-bit timestamp field sets the base timestamp value for the packet. 333 The payload codes MIDI command timing relative to this value. The 334 timestamp units are set by the clock rate parameter. For example, if 335 the clock rate has a value of 44100 Hz, two packets whose base timestamp 336 values differ by 2 seconds have RTP timestamp fields that differ by 337 88200. 339 Note that the clock rate parameter is not encoded within each RTP MIDI 340 packet. A receiver of an RTP MIDI stream becomes aware of the clock 341 rate as part of the session setup process. For example, if a session 342 management tool uses the Session Description Protocol (SDP, [RFC4566]) 343 to describe a media session, the clock rate parameter is set using the 344 rtpmap attribute. We show examples of session setup in Section 6. 346 For RTP MIDI streams destined to be rendered into audio, the clock rate 347 SHOULD be an audio sample rate of 32 KHz or higher. This recommendation 348 is due to the sensitivity of human musical perception to small timing 349 errors in musical note sequences, and due to the timbral changes that 350 occur when two near-simultaneous MIDI NoteOns are rendered with a 351 different timing than that desired by the content author due to clock 352 rate quantization. RTP MIDI streams that are not destined for audio 353 rendering (such as MIDI streams that control stage lighting) MAY use a 354 lower clock rate but SHOULD use a clock rate high enough to avoid timing 355 artifacts in the application. 357 For RTP MIDI streams destined to be rendered into audio, the clock rate 358 SHOULD be chosen from rates in common use in professional audio 359 applications or in consumer audio distribution. At the time of this 360 writing, these rates include 32 KHz, 44.1 KHz, 48 KHz, 64 KHz, 88.2 KHz, 361 96 KHz, 176.4 KHz, and 192 KHz. If the RTP MIDI session is a part of a 362 synchronized media session that includes another (non-MIDI) RTP audio 363 stream with a clock rate of 32 KHz or higher, the RTP MIDI stream SHOULD 364 use a clock rate that matches the clock rate of the other audio stream. 365 However, if the RTP MIDI stream is destined to be rendered into audio, 366 the RTP MIDI stream SHOULD NOT use a clock rate lower than 32 KHz, even 367 if this second stream has a clock rate less than 32 KHz. 369 Timestamps of consecutive packets do not necessarily increment at a 370 fixed rate, because RTP MIDI packets are not necessarily sent at a fixed 371 rate. The degree of packet transmission regularity reflects the 372 underlying application dynamics. Interactive applications may vary the 373 packet sending rate to track the gestural rate of a human performer, 374 whereas content-streaming applications may send packets at a fixed rate. 376 Therefore, the timestamps for two sequential RTP packets may be 377 identical, or the second packet may have a timestamp arbitrarily larger 378 than the first packet (modulo 2^32). Section 3 places additional 379 restrictions on the RTP timestamps for two sequential RTP packets, as 380 does the guardtime parameter (Appendix C.4.2). 382 We use the term "media time" to denote the temporal duration of the 383 media coded by an RTP packet. The media time coded by a packet is 384 computed by subtracting the last command timestamp in the MIDI command 385 section from the RTP timestamp (modulo 2^32). If the MIDI list of the 386 MIDI command section of a packet is empty, the media time coded by the 387 packet is 0 ms. Appendix C.4.1 discusses media time issues in detail. 389 We now define RTP session semantics, in the context of sessions 390 specified using the session description protocol [RFC4566]. A session 391 description media line ("m=") specifies an RTP session. An RTP session 392 has an independent space of 2^32 synchronization sources. 393 Synchronization source identifiers are coded in the SSRC header field of 394 RTP session packets. The payload types that may appear in the PT header 395 field of RTP session packets are listed at the end of the media line. 397 Several RTP MIDI streams may appear in an RTP session. Each stream is 398 distinguished by a unique SSRC value and has a unique sequence number 399 and RTP timestamp space. Multiple streams in the RTP session may be 400 sent by a single party. Multiple parties may send streams in the RTP 401 session. An RTP MIDI stream encodes data for a single MIDI command name 402 space (16 voice channels + Systems). 404 Streams in an RTP session may use different payload types, or they may 405 use the same payload type. However, each party may send, at most, one 406 RTP MIDI stream for each payload type mapped to an RTP MIDI payload 407 format in an RTP session. Recall that dynamic binding of payload type 408 numbers in [RFC4566] lets a party map many payload type numbers to the 409 RTP MIDI payload format; thus a party may send many RTP MIDI streams in 410 a single RTP session. Pairs of streams (unicast or multicast) that 411 communicate between two parties in an RTP session and that share a 412 payload type have the same association as a MIDI cable pair that cross- 413 connects two devices in a MIDI 1.0 DIN network. 415 The RTP session architecture described above is efficient in its use of 416 network ports, as one RTP session (using a port pair per party) supports 417 the transport of many MIDI name spaces (16 MIDI channels + systems). We 418 define tools for grouping and labelling MIDI name spaces across streams 419 and sessions in Appendix C.5 of this memo. 421 The RTP header timestamps for each stream in an RTP session have 422 separately and randomly chosen initialization values. Receivers use the 423 timing fields encoded in the RTP control protocol (RTCP, [RFC3550]) 424 sender reports to synchronize the streams sent by a party. The SSRC 425 values for each stream in an RTP session are also separately and 426 randomly chosen, as described in [RFC3550]. Receivers use the CNAME 427 field encoded in RTCP sender reports to verify that streams were sent by 428 the same party, and to detect SSRC collisions, as described in 429 [RFC3550]. 431 In some applications, a receiver renders MIDI commands into audio (or 432 into control actions, such as the rewind of a tape deck or the dimming 433 of stage lights). In other applications, a receiver presents a MIDI 434 stream to software programs via an Application Programmer Interface 435 (API). Appendix C.6 defines session configuration tools to specify what 436 receivers should do with a MIDI command stream. 438 If a multimedia session uses different RTP MIDI streams to send 439 different classes of media, the streams MUST be sent over different RTP 440 sessions. For example, if a multimedia session uses one MIDI stream for 441 audio and a second MIDI stream to control a lighting system, the audio 442 and lighting streams MUST be sent over different RTP sessions, each with 443 its own media line. 445 Session description tools defined in Appendix C.5 let a sending party 446 split a single MIDI name space (16 voice channels + systems) over 447 several RTP MIDI streams. Split transport of a MIDI command stream is a 448 delicate task, because correct command stream reconstruction by a 449 receiver depends on exact timing synchronization across the streams. 451 To support split name spaces, we define the following requirements: 453 o A party MUST NOT send several RTP MIDI streams that share a MIDI 454 name space in the same RTP session. Instead, each stream MUST 455 be sent from a different RTP session. 457 o If several RTP MIDI streams sent by a party share a MIDI name 458 space, all streams MUST use the same SSRC value and MUST use the 459 same randomly chosen RTP timestamp initialization value. 461 These rules let a receiver identify streams that share a MIDI name space 462 (by matching SSRC values) and also let a receiver accurately reconstruct 463 the source MIDI command stream (by using RTP timestamps to interleave 464 commands from the two streams). Care MUST be taken by senders to ensure 465 that SSRC changes due to collisions are reflected in both streams. 466 Receivers MUST regularly examine the RTCP CNAME fields associated with 467 the linked streams, to ensure that the assumed link is legitimate and 468 not the result of an SSRC collision by another sender. 470 Except for the special cases described above, a party may send many RTP 471 MIDI streams in the same session. However, it is sometimes advantageous 472 for two RTP MIDI streams to be sent over different RTP sessions. For 473 example, two streams may need different values for RTP session-level 474 attributes (such as the sendonly and recvonly attributes). As a second 475 example, two RTP sessions may be needed to send two unicast streams in a 476 multimedia session that originate on different computers (with different 477 IP numbers). Two RTP sessions are needed in this case because transport 478 addresses are specified on the RTP-session or multimedia-session level, 479 not on a payload type level. 481 On a final note, in some uses of MIDI, parties send bidirectional 482 traffic to conduct transactions (such as file exchange). These commands 483 were designed to work over MIDI 1.0 DIN cable networks may be configured 484 in a multicast topology, which use pure "party-line" signalling. Thus, 485 if a multimedia session ensures a multicast connection between all 486 parties, bidirectional MIDI commands will work without additional 487 support from the RTP MIDI payload format. 489 2.2. MIDI Payload 491 The payload (Figure 1) MUST begin with the MIDI command section. The 492 MIDI command section codes a (possibly empty) list of timestamped MIDI 493 commands, and provides the essential service of the payload format. 495 The payload MAY also contain a journal section. The journal section 496 provides resiliency by coding the recent history of the stream. A flag 497 in the MIDI command section codes the presence of a journal section in 498 the payload. 500 Section 3 defines the MIDI command section. Sections 4-5 and Appendices 501 A-B define the recovery journal, the default format for the journal 502 section. Here, we describe how these payload sections operate in a 503 stream in an RTP session. 505 The journalling method for a stream is set at the start of a session and 506 MUST NOT be changed thereafter. A stream may be set to use the recovery 507 journal, to use an alternative journal format (none are defined in this 508 memo), or not to use a journal. 510 The default journalling method of a stream is inferred from its 511 transport type. Streams that use unreliable transport (such as UDP) 512 default to using the recovery journal. Streams that use reliable 513 transport (such as TCP) default to not using a journal. Appendix C.2.1 514 defines session configuration tools for overriding these defaults. For 515 all types of transport, a sender MUST transmit an RTP packet stream with 516 consecutive sequence numbers (modulo 2^16). 518 If a stream uses the recovery journal, every payload in the stream MUST 519 include a journal section. If a stream does not use journalling, a 520 journal section MUST NOT appear in a stream payload. If a stream uses 521 an alternative journal format, the specification for the journal format 522 defines an inclusion policy. 524 If a stream is sent over UDP transport, the Maximum Transmission Unit 525 (MTU) of the underlying network limits the practical size of the payload 526 section (for example, an Ethernet MTU is 1500 octets), for applications 527 where predictable and minimal packet transmission latency is critical. 528 A sender SHOULD NOT create RTP MIDI UDP packets whose size exceeds the 529 MTU of the underlying network. Instead, the sender SHOULD take steps to 530 keep the maximum packet size under the MTU limit. 532 These steps may take many forms. The default closed-loop recovery 533 journal sending policy (defined in Appendix C.2.2.2) uses RTP control 534 protocol (RTCP, [RFC3550]) feedback to manage the RTP MIDI packet size. 535 In addition, Section 3.2 and Appendix B.5.2 provide specific tools for 536 managing the size of packets that code MIDI System Exclusive (0xF0) 537 commands. Appendix C.5 defines session configuration tools that may be 538 used to split a dense MIDI name space into several UDP streams (each 539 sent in a different RTP session, per Section 2.1) so that the payload 540 fits comfortably into an MTU. Another option is to use TCP. Section 541 4.3 of [RFC4696] provides non-normative advice for packet size 542 management. 544 3. MIDI Command Section 546 Figure 2 shows the format of the MIDI command section. 548 0 1 2 3 549 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 551 |B|J|Z|P|LEN... | MIDI list ... | 552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 554 Figure 2 -- MIDI command section 556 The MIDI command section begins with a variable-length header. 558 The header field LEN codes the number of octets in the MIDI list that 559 follow the header. If the header flag B is 0, the header is one octet 560 long, and LEN is a 4-bit field, supporting a maximum MIDI list length of 561 15 octets. 563 If B is 1, the header is two octets long, and LEN is a 12-bit field, 564 supporting a maximum MIDI list length of 4095 octets. LEN is coded in 565 network byte order (big-endian): the 4 bits of LEN that appear in the 566 first header octet code the most significant 4 bits of the 12-bit LEN 567 value. 569 A LEN value of 0 is legal, and it codes an empty MIDI list. 571 If the J header bit is set to 1, a journal section MUST appear after the 572 MIDI command section in the payload. If the J header bit is set to 0, 573 the payload MUST NOT contain a journal section. 575 We define the semantics of the P header bit in Section 3.2. 577 If the LEN header field is nonzero, the MIDI list has the structure 578 shown in Figure 3. 580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 581 | Delta Time 0 (1-4 octets long, or 0 octets if Z = 1) | 582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 583 | MIDI Command 0 (1 or more octets long) | 584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 585 | Delta Time 1 (1-4 octets long) | 586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 587 | MIDI Command 1 (1 or more octets long) | 588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 589 | ... | 590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 591 | Delta Time N (1-4 octets long) | 592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 593 | MIDI Command N (0 or more octets long) | 594 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 596 Figure 3 -- MIDI list structure 598 If the header flag Z is 1, the MIDI list begins with a complete MIDI 599 command (coded in the MIDI Command 0 field, in Figure 3) preceded by a 600 delta time (coded in the Delta Time 0 field). If Z is 0, the Delta Time 601 0 field is not present in the MIDI list, and the command coded in the 602 MIDI Command 0 field has an implicit delta time of 0. 604 The MIDI list structure may also optionally encode a list of N 605 additional complete MIDI commands, each coded in a MIDI Command K field. 606 Each additional command MUST be preceded by a Delta Time K field, which 607 codes the command's delta time. We discuss exceptions to the "command 608 fields code complete MIDI commands" rule in Section 3.2. 610 The final MIDI command field (i.e., the MIDI Command N field, shown in 611 Figure 3) in the MIDI list MAY be empty. Moreover, a MIDI list MAY 612 consist a single delta time (encoded in the Delta Time 0 field) without 613 an associated command (which would have been encoded in the MIDI Command 614 0 field). These rules enable MIDI coding features that are explained in 615 Section 3.1. We delay the explanations because an understanding of RTP 616 MIDI timestamps is necessary to describe the features. 618 3.1. Timestamps 620 In this section, we describe how RTP MIDI encodes a timestamp for each 621 MIDI list command. Command timestamps have the same units as RTP packet 622 header timestamps (described in Section 2.1 and [RFC3550]). Recall that 623 RTP timestamps have units of seconds, whose scaling is set during 624 session configuration (see Section 6.1 and [RFC4566]). 626 As shown in Figure 3, the MIDI list encodes time using a compact delta- 627 time format. The RTP MIDI delta time syntax is a modified form of the 628 MIDI File delta time syntax [MIDI]. RTP MIDI delta times use 1-4 octet 629 fields to encode 32-bit unsigned integers. Figure 4 shows the encoded 630 and decoded forms of delta times. Note that delta time values may be 631 legally encoded in multiple formats; for example, there are four legal 632 ways to encode the zero delta time (0x00, 0x8000, 0x808000, 0x80808000). 634 RTP MIDI uses delta times to encode a timestamp for each MIDI command. 635 The timestamp for MIDI Command K is the summation (modulo 2^32) of the 636 RTP timestamp and decoded delta times 0 through K. This cumulative 637 coding technique, borrowed from MIDI File delta time coding, is 638 efficient because it reduces the number of multi-octet delta times. 640 All command timestamps in a packet MUST be less than or equal to the RTP 641 timestamp of the next packet in the stream (modulo 2^32). 643 This restriction ensures that a particular RTP MIDI packet in a stream 644 is uniquely responsible for encoding time starting at the moment after 645 the RTP timestamp encoded in the RTP packet header, and ending at the 646 moment before the final command timestamp encoded in the MIDI list. The 647 "moment before" and "moment after" qualifiers acknowledge the "less than 648 or equal" semantics (as opposed to "strictly less than") in the sentence 649 above this paragraph. 651 Note that it is possible to "pad" the end of an RTP MIDI packet with 652 time that is guaranteed to be void of MIDI commands, by setting the 653 "Delta Time N" field of the MIDI list to the end of the void time, and 654 by omitting its corresponding "MIDI Command N" field (a syntactic 655 construction the preamble of Section 3 expressly made legal). 657 In addition, it is possible to code an RTP MIDI packet to express that a 658 period of time in the stream is void of MIDI commands. The RTP 659 timestamp in the header would code the start of the void time. The MIDI 660 list of this packet would consist of a "Delta Time 0" field that coded 661 the end of the void time. No other fields would be present in the MIDI 662 list (a syntactic construction the preamble of Section 3 also expressly 663 made legal). 665 By default, a command timestamp indicates the execution time for the 666 command. The difference between two timestamps indicates the time delay 667 between the execution of the commands. This difference may be zero, 668 coding simultaneous execution. In this memo, we refer to this 669 interpretation of timestamps as "comex" (COMmand EXecution) semantics. 670 We formally define comex semantics in Appendix C.3. 672 The comex interpretation of timestamps works well for transcoding a 673 Standard MIDI File (SMF) into an RTP MIDI stream, as SMFs code a 674 timestamp for each MIDI command stored in the file. To transcode an SMF 675 that uses metric time markers, use the SMF tempo map (encoded in the SMF 676 as meta-events) to convert metric SMF timestamp units into seconds-based 677 RTP timestamp units. 679 The comex interpretation also works well for MIDI hardware controllers 680 that are coding raw sensor data directly onto an RTP MIDI stream. Note 681 that this controller design is preferable to a design that converts raw 682 sensor data into a MIDI 1.0 cable command stream and then transcodes the 683 stream onto an RTP MIDI stream. 685 The comex interpretation of timestamps is usually not the best timestamp 686 interpretation for transcoding a MIDI source that uses implicit command 687 timing (such as MIDI 1.0 DIN cables) into an RTP MIDI stream. Appendix 688 C.3 defines alternatives to comex semantics and describes session 689 configuration tools for selecting the timestamp interpretation semantics 690 for a stream. 692 One-Octet Delta Time: 694 Encoded form: 0ddddddd 695 Decoded form: 00000000 00000000 00000000 0ddddddd 697 Two-Octet Delta Time: 699 Encoded form: 1ccccccc 0ddddddd 700 Decoded form: 00000000 00000000 00cccccc cddddddd 702 Three-Octet Delta Time: 704 Encoded form: 1bbbbbbb 1ccccccc 0ddddddd 705 Decoded form: 00000000 000bbbbb bbcccccc cddddddd 707 Four-Octet Delta Time: 709 Encoded form: 1aaaaaaa 1bbbbbbb 1ccccccc 0ddddddd 710 Decoded form: 0000aaaa aaabbbbb bbcccccc cddddddd 712 Figure 4 -- Decoding delta time formats 714 3.2. Command Coding 716 Each non-empty MIDI Command field in the MIDI list codes one of the MIDI 717 command types that may legally appear on a MIDI 1.0 DIN cable. Standard 718 MIDI File meta-events do not fit this definition and MUST NOT appear in 719 the MIDI list. As a rule, each MIDI Command field codes a complete 720 command, in the binary command format defined in [MIDI]. In the 721 remainder of this section, we describe exceptions to this rule. 723 The first MIDI channel command in the MIDI list MUST include a status 724 octet. Running status coding, as defined in [MIDI], MAY be used for all 725 subsequent MIDI channel commands in the list. As in [MIDI], System 726 Common and System Exclusive messages (0xF0 ... 0xF7) cancel the running 727 status state, but System Real-time messages (0xF8 ... 0xFF) do not 728 affect the running status state. All System commands in the MIDI list 729 MUST include a status octet. 731 As we note above, the first channel command in the MIDI list MUST 732 include a status octet. However, the corresponding command in the 733 original MIDI source data stream might not have a status octet (in this 734 case, the source would be coding the command using running status). If 735 the status octet of the first channel command in the MIDI list does not 736 appear in the source data stream, the P (phantom) header bit MUST be set 737 to 1. In all other cases, the P bit MUST be set to 0. 739 Note that the P bit describes the MIDI source data stream, not the MIDI 740 list encoding; regardless of the state of the P bit, the MIDI list MUST 741 include the status octet. 743 As receivers MUST be able to decode running status, sender implementors 744 should feel free to use running status to improve bandwidth efficiency. 745 However, senders SHOULD NOT introduce timing jitter into an existing 746 MIDI command stream through an inappropriate use or removal of running 747 status coding. This warning primarily applies to senders whose RTP MIDI 748 streams may be transcoded onto a MIDI 1.0 DIN cable [MIDI] by the 749 receiver: both the timestamps and the command coding (running status or 750 not) must comply with the physical restrictions of implicit time coding 751 over a slow serial line. 753 On a MIDI 1.0 DIN cable [MIDI], a System Real-time command may be 754 embedded inside of another "host" MIDI command. This syntactic 755 construction is not supported in the payload format: a MIDI Command 756 field in the MIDI list codes exactly one MIDI command (partially or 757 completely). 759 To encode an embedded System Real-time command, senders MUST extract the 760 command from its host and code it in the MIDI list as a separate 761 command. The host command and System Real-time command SHOULD appear in 762 the same MIDI list. The delta time of the System Real-time command 763 SHOULD result in a command timestamp that encodes the System Real-time 764 command placement in its original embedded position. 766 Two methods are provided for encoding MIDI System Exclusive (SysEx) 767 commands in the MIDI list. A SysEx command may be encoded in a MIDI 768 Command field verbatim: a 0xF0 octet, followed by an arbitrary number of 769 data octets, followed by a 0xF7 octet. 771 Alternatively, a SysEx command may be encoded as multiple segments. The 772 command is divided into two or more SysEx command segments; each segment 773 is encoded in its own MIDI Command field in the MIDI list. 775 The payload format supports segmentation in order to encode SysEx 776 commands that encode information in the temporal pattern of data octets. 777 By encoding these commands as a series of segments, each data octet may 778 be associated with a distinct delta time. Segmentation also supports 779 the coding of large SysEx commands across several packets. 781 To segment a SysEx command, first partition its data octet list into two 782 or more sublists. The last sublist MAY be empty (i.e., contain no 783 octets); all other sublists MUST contain at least one data octet. To 784 complete the segmentation, add the status octets defined in Figure 5 to 785 the head and tail of the first, last, and any "middle" sublists. Figure 786 6 shows example segmentations of a SysEx command. 788 A sender MAY cancel a segmented SysEx command transmission that is in 789 progress, by sending the "cancel" sublist shown in Figure 5. A "cancel" 790 sublist MAY follow a "first" or "middle" sublist in the transmission, 791 but MUST NOT follow a "last" sublist. The cancel MUST be empty (thus, 792 0xF7 0xF4 is the only legal cancel sublist). 794 The cancellation feature is needed because Appendix C.1 defines 795 configuration tools that let session parties exclude certain SysEx 796 commands in the stream. Senders that transcode a MIDI source onto an 797 RTP MIDI stream under these constraints have the responsibility of 798 excluding undesired commands from the RTP MIDI stream. 800 The cancellation feature lets a sender start the transmission of a 801 command before the MIDI source has sent the entire command. If a sender 802 determines that the command whose transmission is in progress should not 803 appear on the RTP stream, it cancels the command. Without a method for 804 cancelling a SysEx command transmission, senders would be forced to use 805 a high-latency store-and-forward approach to transcoding SysEx commands 806 onto RTP MIDI packets, in order to validate each SysEx command before 807 transmission. 809 The recommended receiver reaction to a cancellation depends on the 810 capabilities of the receiver. For example, a sound synthesizer that is 811 directly parsing RTP MIDI packets and rendering them to audio will be 812 aware of the fact that SysEx commands may be cancelled in RTP MIDI. 813 These receivers SHOULD detect a SysEx cancellation in the MIDI list and 814 act as if they had never received the SysEx command. 816 As a second example, a synthesizer may be receiving MIDI data from an 817 RTP MIDI stream via a MIDI DIN cable (or a software API emulation of a 818 MIDI DIN cable). In this case, an RTP-MIDI-aware system receives the 819 RTP MIDI stream and transcodes it onto the MIDI DIN cable (or its 820 emulation). Upon the receipt of the cancel sublist, the RTP-MIDI- aware 821 transcoder might have already sent the first part of the SysEx command 822 on the MIDI DIN cable to the receiver. 824 Unfortunately, the MIDI DIN cable protocol cannot directly code "cancel 825 SysEx in progress" semantics. However, MIDI DIN cable receivers begin 826 SysEx processing after the complete command arrives. The receiver 827 checks to see if it recognizes the command (coded in the first few 828 octets) and then checks to see if the command is the correct length. 829 Thus, in practice, a transcoder can cancel a SysEx command by sending an 830 0xF7 to (prematurely) end the SysEx command -- the receiver will detect 831 the incorrect command length and discard the command. 833 Appendix C.1 defines configuration tools that may be used to prohibit 834 SysEx command cancellation. 836 The relative ordering of SysEx command segments in a MIDI list must 837 match the relative ordering of the sublists in the original SysEx 838 command. By default, commands other than System Real-time MIDI commands 839 MUST NOT appear between SysEx command segments (Appendix C.1 defines 840 configuration tools to change this default, to let other commands types 841 appear between segments). If the command segments of a SysEx command 842 are placed in the MIDI lists of two or more RTP packets, the segment 843 ordering rules apply to the concatenation of all affected MIDI lists. 845 ----------------------------------------------------------- 846 | Sublist Position | Head Status Octet | Tail Status Octet | 847 |-----------------------------------------------------------| 848 | first | 0xF0 | 0xF0 | 849 |-----------------------------------------------------------| 850 | middle | 0xF7 | 0xF0 | 851 |-----------------------------------------------------------| 852 | last | 0xF7 | 0xF7 | 853 |-----------------------------------------------------------| 854 | cancel | 0xF7 | 0xF4 | 855 ----------------------------------------------------------- 857 Figure 5 -- Command segmentation status octets 859 [MIDI] permits 0xF7 octets that are not part of a (0xF0, 0xF7) pair to 860 appear on a MIDI 1.0 DIN cable. Unpaired 0xF7 octets have no semantic 861 meaning in MIDI, apart from cancelling running status. 863 Unpaired 0xF7 octets MUST NOT appear in the MIDI list of the MIDI 864 Command section. We impose this restriction to avoid interference with 865 the command segmentation coding defined in Figure 5. 867 SysEx commands carried on a MIDI 1.0 DIN cable may use the "dropped 868 0xF7" construction [MIDI]. In this coding method, the 0xF7 octet is 869 dropped from the end of the SysEx command, and the status octet of the 870 next MIDI command acts both to terminate the SysEx command and start the 871 next command. To encode this construction in the payload format, follow 872 these steps: 874 o Determine the appropriate delta times for the SysEx command and 875 the command that follows the SysEx command. 877 o Insert the "dropped" 0xF7 octet at the end of the SysEx command, 878 to form the standard SysEx syntax. 880 o Code both commands into the MIDI list using the rules above. 882 o Replace the 0xF7 octet that terminates the verbatim SysEx 883 encoding or the last segment of the segmented SysEx encoding 884 with a 0xF5 octet. This substitution informs the receiver 885 of the original dropped 0xF7 coding. 887 [MIDI] reserves the undefined System Common commands 0xF4 and 0xF5 and 888 the undefined System Real-time commands 0xF9 and 0xFD for future use. 889 By default, undefined commands MUST NOT appear in a MIDI Command field 890 in the MIDI list, with the exception of the 0xF5 octets used to code the 891 "dropped 0xF7" construction and the 0xF4 octets used by SysEx "cancel" 892 sublists. 894 During session configuration, a stream may be customized to transport 895 undefined commands (Appendix C.1). For this case, we now define how 896 senders encode undefined commands in the MIDI list. 898 An undefined System Real-time command MUST be coded using the System 899 Real-time rules. 901 If the undefined System Common commands are put to use in a future 902 version of [MIDI], the command will begin with an 0xF4 or 0xF5 status 903 octet, followed by an arbitrary number of data octets (i.e., zero or 904 more data bytes). To encode these commands, senders MUST terminate the 905 command with an 0xF7 octet and place the modified command into the MIDI 906 Command field. 908 Unfortunately, non-compliant uses of the undefined System Common 909 commands may appear in MIDI implementations. To model these commands, 910 we assume that the command begins with an 0xF4 or 0xF5 status octet, 911 followed by zero or more data octets, followed by zero or more trailing 912 0xF7 status octets. To encode the command, senders MUST first remove 913 all trailing 0xF7 status octets from the command. Then, senders MUST 914 terminate the command with an 0xF7 octet and place the modified command 915 into the MIDI Command field. 917 Note that we include the trailing octets in our model as a cautionary 918 measure: if such commands appeared in a non-compliant use of an 919 undefined System Common command, an RTP MIDI encoding of the command 920 that did not remove trailing octets could be mistaken for an encoding of 921 "middle" or "last" sublist of a segmented SysEx commands (Figure 5) 922 under certain packet loss conditions. 924 Original SysEx command: 926 0xF0 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0xF7 928 A two-segment segmentation: 930 0xF0 0x01 0x02 0x03 0x04 0xF0 932 0xF7 0x05 0x06 0x07 0x08 0xF7 934 A different two-segment segmentation: 936 0xF0 0x01 0xF0 938 0xF7 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0xF7 940 A three-segment segmentation: 942 0xF0 0x01 0x02 0xF0 944 0xF7 0x03 0x04 0xF0 946 0xF7 0x05 0x06 0x07 0x08 0xF7 948 The segmentation with the largest number of segments: 950 0xF0 0x01 0xF0 952 0xF7 0x02 0xF0 954 0xF7 0x03 0xF0 956 0xF7 0x04 0xF0 958 0xF7 0x05 0xF0 960 0xF7 0x06 0xF0 962 0xF7 0x07 0xF0 964 0xF7 0x08 0xF0 966 0xF7 0xF7 968 Figure 6 -- Example segmentations 970 4. The Recovery Journal System 972 The recovery journal is the default resiliency tool for unreliable 973 transport. In this section, we normatively define the roles that 974 senders and receivers play in the recovery journal system. 976 MIDI is a fragile code. A single lost command in a MIDI command stream 977 may produce an artifact in the rendered performance. We normatively 978 classify rendering artifacts into two categories: 980 o Transient artifacts. Transient artifacts produce immediate 981 but short-term glitches in the performance. For example, a lost 982 NoteOn (0x9) command produces a transient artifact: one note 983 fails to play, but the artifact does not extend beyond the end 984 of that note. 986 o Indefinite artifacts. Indefinite artifacts produce long-lasting 987 errors in the rendered performance. For example, a lost NoteOff 988 (0x8) command may produce an indefinite artifact: the note that 989 should have been ended by the lost NoteOff command may sustain 990 indefinitely. As a second example, the loss of a Control Change 991 (0xB) command for controller number 7 (Channel Volume) may 992 produce an indefinite artifact: after the loss, all notes on 993 the channel may play too softly or too loudly. 995 The purpose of the recovery journal system is to satisfy the recovery 996 journal mandate: the MIDI performance rendered from an RTP MIDI stream 997 sent over unreliable transport MUST NOT contain indefinite artifacts. 999 The recovery journal system does not use packet retransmission to 1000 satisfy this mandate. Instead, each packet includes a special section, 1001 called the recovery journal. 1003 The recovery journal codes the history of the stream, back to an earlier 1004 packet called the checkpoint packet. The range of coverage for the 1005 journal is called the checkpoint history. The recovery journal codes 1006 the information necessary to recover from the loss of an arbitrary 1007 number of packets in the checkpoint history. Appendix A.1 normatively 1008 defines the checkpoint packet and the checkpoint history. 1010 When a receiver detects a packet loss, it compares its own knowledge 1011 about the history of the stream with the history information coded in 1012 the recovery journal of the packet that ends the loss event. By noting 1013 the differences in these two versions of the past, a receiver is able to 1014 transform all indefinite artifacts in the rendered performance into 1015 transient artifacts, by executing MIDI commands to repair the stream. 1017 We now state the normative role for senders in the recovery journal 1018 system. 1020 Senders prepare a recovery journal for every packet in the stream. In 1021 doing so, senders choose the checkpoint packet identity for the journal. 1022 Senders make this choice by applying a sending policy. Appendix C.2.2 1023 normatively defines three sending policies: "closed- loop", "open-loop", 1024 and "anchor". 1026 By default, senders MUST use the closed-loop sending policy. If the 1027 session description overrides this default policy, by using the 1028 parameter j_update defined in Appendix C.2.2, senders MUST use the 1029 specified policy. 1031 After choosing the checkpoint packet identity for a packet, the sender 1032 creates the recovery journal. By default, this journal MUST conform to 1033 the normative semantics in Section 5 and Appendices A-B in this memo. 1034 In Appendix C.2.3, we define parameters that modify the normative 1035 semantics for recovery journals. If the session description uses these 1036 parameters, the journal created by the sender MUST conform to the 1037 modified semantics. 1039 Next, we state the normative role for receivers in the recovery journal 1040 system. 1042 A receiver MUST detect each RTP sequence number break in a stream. If 1043 the sequence number break is due to a packet loss event (as defined in 1044 [RFC3550]), the receiver MUST repair all indefinite artifacts in the 1045 rendered MIDI performance caused by the loss. If the sequence number 1046 break is due to an out-of-order packet (as defined in [RFC3550]), the 1047 receiver MUST NOT take actions that introduce indefinite artifacts 1048 (ignoring the out-of-order packet is a safe option). 1050 Receivers take special precautions when entering or exiting a session. 1051 A receiver MUST process the first received packet in a stream as if it 1052 were a packet that ends a loss event. Upon exiting a session, a 1053 receiver MUST ensure that the rendered MIDI performance does not end 1054 with indefinite artifacts. 1056 Receivers are under no obligation to perform indefinite artifact repairs 1057 at the moment a packet arrives. A receiver that uses a playout buffer 1058 may choose to wait until the moment of rendering before processing the 1059 recovery journal, as the "lost" packet may be a late packet that arrives 1060 in time to use. 1062 Next, we state the normative role for the creator of the session 1063 description in the recovery journal system. Depending on the 1064 application, the sender, the receivers, and other parties may take part 1065 in creating or approving the session description. 1067 A session description that specifies the default closed-loop sending 1068 policy and the default recovery journal semantics satisfies the recovery 1069 journal mandate. However, these default behaviors may not be 1070 appropriate for all sessions. If the creators of a session description 1071 use the parameters defined in Appendix C.2 to override these defaults, 1072 the creators MUST ensure that the parameters define a system that 1073 satisfies the recovery journal mandate. 1075 Finally, we note that this memo does not specify sender or receiver 1076 recovery journal algorithms. Implementations are free to use any 1077 algorithm that conforms to the requirements in this section. The non- 1078 normative [RFC4696] discusses sender and receiver algorithm design. 1080 5. Recovery Journal Format 1082 This section introduces the structure of the recovery journal and 1083 defines the bitfields of recovery journal headers. Appendices A-B 1084 complete the bitfield definition of the recovery journal. 1086 The recovery journal has a three-level structure: 1088 o Top-level header. 1090 o Channel and system journal headers. These headers encode 1091 recovery information for a single voice channel (channel 1092 journal) or for all systems commands (system journal). 1094 o Chapters. Chapters describe recovery information for a 1095 single MIDI command type. 1097 Figure 7 shows the top-level structure of the recovery journal. The 1098 recovery journals consists of a 3-octet header, followed by an optional 1099 system journal (labeled S-journal in Figure 7) and an optional list of 1100 channel journals. Figure 8 shows the recovery journal header format. 1102 0 1 2 3 1103 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1105 | Recovery journal header | S-journal ... | 1106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1107 | Channel journals ... | 1108 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1110 Figure 7 -- Top-level recovery journal format 1112 0 1 2 1113 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 1114 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1115 |S|Y|A|H|TOTCHAN| Checkpoint Packet Seqnum | 1116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1118 Figure 8 -- Recovery journal header 1120 If the Y header bit is set to 1, the system journal appears in the 1121 recovery journal, directly following the recovery journal header. 1123 If the A header bit is set to 1, the recovery journal ends with a list 1124 of (TOTCHAN + 1) channel journals (the 4-bit TOTCHAN header field is 1125 interpreted as an unsigned integer). 1127 A MIDI channel MAY be represented by (at most) one channel journal in a 1128 recovery journal. Channel journals MUST appear in the recovery journal 1129 in ascending channel-number order. 1131 If A and Y are both zero, the recovery journal only contains its 3- 1132 octet header and is considered to be an "empty" journal. 1134 The S (single-packet loss) bit appears in most recovery journal 1135 structures, including the recovery journal header. The S bit helps 1136 receivers efficiently parse the recovery journal in the common case of 1137 the loss of a single packet. Appendix A.1 defines S bit semantics. 1139 The H bit indicates if MIDI channels in the stream have been configured 1140 to use the enhanced Chapter C encoding (Appendix A.3.3). 1142 By default, the payload format does not use enhanced Chapter C encoding. 1143 In this default case, the H bit MUST be set to 0 for all packets in the 1144 stream. 1146 If the stream has been configured so that controller numbers for one or 1147 more MIDI channels use enhanced Chapter C encoding, the H bit MUST be 1148 set to 1 in all packets in the stream. In Appendix C.2.3, we show how 1149 to configure a stream to use enhanced Chapter C encoding. 1151 The 16-bit Checkpoint Packet Seqnum header field codes the sequence 1152 number of the checkpoint packet for this journal, in network byte order 1153 (big-endian). The choice of the checkpoint packet sets the depth of the 1154 checkpoint history for the journal (defined in Appendix A.1). 1156 Receivers may use the Checkpoint Packet Seqnum field of the packet that 1157 ends a loss event to verify that the journal checkpoint history covers 1158 the entire loss event. The checkpoint history covers the loss event if 1159 the Checkpoint Packet Seqnum field is less than or equal to one plus the 1160 highest RTP sequence number previously received on the stream (modulo 1161 2^16). 1163 0 1 2 3 1164 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1166 |S| CHAN |H| LENGTH |P|C|M|W|N|E|T|A| Chapters ... | 1167 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1169 Figure 9 -- Channel journal format 1171 Figure 9 shows the structure of a channel journal: a 3-octet header, 1172 followed by a list of leaf elements called channel chapters. A channel 1173 journal encodes information about MIDI commands on the MIDI channel 1174 coded by the 4-bit CHAN header field. Note that CHAN uses the same bit 1175 encoding as the channel nibble in MIDI Channel Messages (the cccc field 1176 in Figure E.1 of Appendix E). 1178 The 10-bit LENGTH field codes the length of the channel journal. The 1179 semantics for LENGTH fields are uniform throughout the recovery journal, 1180 and are defined in Appendix A.1. 1182 The third octet of the channel journal header is the Table of Contents 1183 (TOC) of the channel journal. The TOC is a set of bits that encode the 1184 presence of a chapter in the journal. Each chapter contains information 1185 about a certain class of MIDI channel command: 1187 o Chapter P: MIDI Program Change (0xC) 1188 o Chapter C: MIDI Control Change (0xB) 1189 o Chapter M: MIDI Parameter System (part of 0xB) 1190 o Chapter W: MIDI Pitch Wheel (0xE) 1191 o Chapter N: MIDI NoteOff (0x8), NoteOn (0x9) 1192 o Chapter E: MIDI Note Command Extras (0x8, 0x9) 1193 o Chapter T: MIDI Channel Aftertouch (0xD) 1194 o Chapter A: MIDI Poly Aftertouch (0xA) 1196 Chapters appear in a list following the header, in order of their 1197 appearance in the TOC. Appendices A.2-9 describe the bitfield format 1198 for each chapter, and define the conditions under which a chapter type 1199 MUST appear in the recovery journal. If any chapter types are required 1200 for a channel, an associated channel journal MUST appear in the recovery 1201 journal. 1203 The H bit indicates if controller numbers on a MIDI channel have been 1204 configured to use the enhanced Chapter C encoding (Appendix A.3.3). 1206 By default, controller numbers on a MIDI channel do not use enhanced 1207 Chapter C encoding. In this default case, the H bit MUST be set to 0 1208 for all channel journal headers for the channel in the recovery journal, 1209 for all packets in the stream. 1211 However, if at least one controller number for a MIDI channel has been 1212 configured to use the enhanced Chapter C encoding, the H bit for its 1213 channel journal MUST be set to 1, for all packets in the stream. 1215 In Appendix C.2.3, we show how to configure a controller number to use 1216 enhanced Chapter C encoding. 1218 0 1 2 3 1219 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1221 |S|D|V|Q|F|X| LENGTH | System chapters ... | 1222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1224 Figure 10 -- System journal format 1226 Figure 10 shows the structure of the system journal: a 2-octet header, 1227 followed by a list of system chapters. Each chapter codes information 1228 about a specific class of MIDI Systems command: 1230 o Chapter D: Song Select (0xF3), Tune Request (0xF6), Reset (0xFF), 1231 undefined System commands (0xF4, 0xF5, 0xF9, 0xFD) 1232 o Chapter V: Active Sense (0xFE) 1233 o Chapter Q: Sequencer State (0xF2, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC) 1234 o Chapter F: MTC Tape Position (0xF1, 0xF0 0x7F 0xcc 0x01 0x01) 1235 o Chapter X: System Exclusive (all other 0xF0) 1237 The 10-bit LENGTH field codes the size of the system journal and 1238 conforms to semantics described in Appendix A.1. 1240 The D, V, Q, F, and X header bits form a Table of Contents (TOC) for the 1241 system journal. A TOC bit that is set to 1 codes the presence of a 1242 chapter in the journal. Chapters appear in a list following the header, 1243 in the order of their appearance in the TOC. 1245 Appendix B describes the bitfield format for the system chapters and 1246 defines the conditions under which a chapter type MUST appear in the 1247 recovery journal. If any system chapter type is required to appear in 1248 the recovery journal, the system journal MUST appear in the recovery 1249 journal. 1251 6. Session Description Protocol 1253 RTP does not perform session management. Instead, RTP works together 1254 with session management tools, such as the Session Initiation Protocol 1255 (SIP, [RFC3261]) and the Real Time Streaming Protocol (RTSP, [RFC2326]). 1257 RTP payload formats define media type parameters for use in session 1258 management (for example, this memo defines "rtp-midi" as the media type 1259 for native RTP MIDI streams). 1261 In most cases, session management tools use the media type parameters 1262 via another standard, the Session Description Protocol (SDP, [RFC4566]). 1264 SDP is a textual format for specifying session descriptions. Session 1265 descriptions specify the network transport and media encoding for RTP 1266 sessions. Session management tools coordinate the exchange of session 1267 descriptions between participants ("parties"). 1269 Some session management tools use SDP to negotiate details of media 1270 transport (network addresses, ports, etc.). We refer to this use of SDP 1271 as "negotiated usage". One example of negotiated usage is the 1272 Offer/Answer protocol ([RFC3264] and Appendix C.7.2 in this memo) as 1273 used by SIP. 1275 Other session management tools use SDP to declare the media encoding for 1276 the session but use other techniques to negotiate network transport. We 1277 refer to this use of SDP as "declarative usage". One example of 1278 declarative usage is RTSP ([RFC2326] and Appendix C.7.1 in this memo). 1280 Below, we show session description examples for native (Section 6.1) and 1281 mpeg4-generic (Section 6.2) streams. In Section 6.3, we introduce 1282 session configuration tools that may be used to customize streams. 1284 6.1. Session Descriptions for Native Streams 1286 The session description below defines a unicast UDP RTP session (via a 1287 media ("m=") line) whose sole payload type (96) is mapped to a minimal 1288 native RTP MIDI stream. 1290 v=0 1291 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 1292 s=Example 1293 t=0 0 1294 m=audio 5004 RTP/AVP 96 1295 c=IN IP4 192.0.2.94 1296 a=rtpmap:96 rtp-midi/44100 1298 The rtpmap attribute line uses the "rtp-midi" media type to specify an 1299 RTP MIDI native stream. The clock rate specified on the rtpmap line (in 1300 the example above, 44100 Hz) sets the scaling for the RTP timestamp 1301 header field (see Section 2.1, and also [RFC3550]). 1303 Note that this document does not specify a default clock rate value for 1304 RTP MIDI. When RTP MIDI is used with SDP, parties MUST use the rtpmap 1305 line to communicate the clock rate. Guidance for selecting the RTP MIDI 1306 clock rate value appears in Section 2.1. 1308 We consider the RTP MIDI stream shown above to be "minimal" because the 1309 session description does not customize the stream with parameters. 1310 Without such customization, a native RTP MIDI stream has these 1311 characteristics: 1313 1. If the stream uses unreliable transport (unicast UDP, multicast 1314 UDP, etc.), the recovery journal system is in use, and the RTP 1315 payload contains both the MIDI command section and the journal 1316 section. If the stream uses reliable transport (such as TCP), 1317 the stream does not use journalling, and the payload contains 1318 only the MIDI command section (Section 2.2). 1320 2. If the stream uses the recovery journal system, the recovery 1321 journal system uses the default sending policy and the default 1322 journal semantics (Section 4). 1324 3. In the MIDI command section of the payload, command timestamps 1325 use the default "comex" semantics (Section 3). 1327 4. The recommended temporal duration ("media time") of an RTP 1328 packet ranges from 0 to 200 ms, and the RTP timestamp 1329 difference between sequential packets in the stream may be 1330 arbitrarily large (Section 2.1). 1332 5. If more than one minimal rtp-midi stream appears in a session, 1333 the MIDI name spaces for these streams are independent: channel 1334 1 in the first stream does not reference the same MIDI channel 1335 as channel 1 in the second stream (see Appendix C.5 for a 1336 discussion of the independence of minimal rtp-midi streams). 1338 6. The rendering method for the stream is not specified. What the 1339 receiver "does" with a minimal native MIDI stream is "out of 1340 scope" of this memo. For example, in content creation 1341 environments, a user may manually configure client software to 1342 render the stream with a specific software package. 1344 As in standard in RTP, RTP sessions managed by SIP are sendrecv by 1345 default (parties send and receive MIDI), and RTP sessions managed by 1346 RTSP are recvonly by default (server sends and client receives). 1348 In sendrecv RTP MIDI sessions for the session description shown above, 1349 the 16 voice channel + systems MIDI name space is unique for each 1350 sender. Thus, in a two-party session, the voice channel 0 sent by one 1351 party is distinct from the voice channel 0 sent by the other party. 1353 This behavior corresponds to what occurs when two MIDI 1.0 DIN devices 1354 are cross-connected with two MIDI cables (one cable routing MIDI Out 1355 from the first device into MIDI In of the second device, a second cable 1356 routing MIDI In from the first device into MIDI Out of the second 1357 device). We define this "association" formally in Section 2.1. 1359 MIDI 1.0 DIN networks may be configured in a "party-line" multicast 1360 topology. For these networks, the MIDI protocol itself provides tools 1361 for addressing specific devices in transactions on a multicast network, 1362 and for device discovery. Thus, apart from providing a 1- to-many 1363 forward path and a many-to-1 reverse path, IETF protocols do not need to 1364 provide any special support for MIDI multicast networking. 1366 6.2. Session Descriptions for mpeg4-generic Streams 1368 An mpeg4-generic [RFC3640] RTP MIDI stream uses an MPEG 4 Audio Object 1369 Type to render MIDI into audio. Three Audio Object Types accept MIDI 1370 input: 1372 o General MIDI (Audio Object Type ID 15), based on the General 1373 MIDI rendering standard [MIDI]. 1375 o Wavetable Synthesis (Audio Object Type ID 14), based on the 1376 Downloadable Sounds Level 2 (DLS 2) rendering standard [DLS2]. 1378 o Main Synthetic (Audio Object Type ID 13), based on Structured 1379 Audio and the programming language SAOL [MPEGSA]. 1381 The primary service of an mpeg4-generic stream is to code Access Units 1382 (AUs). We define the mpeg4-generic RTP MIDI AU as the MIDI payload 1383 shown in Figure 1 of Section 2.1 of this memo: a MIDI command section 1384 optionally followed by a journal section. 1386 Exactly one RTP MIDI AU MUST be mapped to one mpeg4-generic RTP MIDI 1387 packet. The mpeg4-generic options for placing several AUs in an RTP 1388 packet MUST NOT be used with RTP MIDI. The mpeg4-generic options for 1389 fragmenting and interleaving AUs MUST NOT be used with RTP MIDI. The 1390 mpeg4-generic RTP packet payload (Figure 1 in [RFC3640]) MUST contain 1391 empty AU Header and Auxiliary sections. These rules yield mpeg4-generic 1392 packets that are structurally identical to native RTP MIDI packets, an 1393 essential property for the correct operation of the payload format. 1395 The session description that follows defines a unicast UDP RTP session 1396 (via a media ("m=") line) whose sole payload type (96) is mapped to a 1397 minimal mpeg4-generic RTP MIDI stream. This example uses the General 1398 MIDI Audio Object Type under Synthesis Profile @ Level 2. 1400 v=0 1401 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 1402 s=Example 1403 t=0 0 1404 m=audio 5004 RTP/AVP 96 1405 c=IN IP6 2001:DB80::7F2E:172A:1E24 1406 a=rtpmap:96 mpeg4-generic/44100 1407 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 1408 config=7A0A0000001A4D546864000000060000000100604D54726B0000 1409 000600FF2F000 1411 (The a=fmtp line has been wrapped to fit the page to accommodate memo 1412 formatting restrictions; it comprises a single line in SDP.) 1414 The fmtp attribute line codes the four parameters (streamtype, mode, 1415 profile-level-id, and config) that are required in all mpeg4-generic 1416 session descriptions [RFC3640]. For RTP MIDI streams, the streamtype 1417 parameter MUST be set to 5, the "mode" parameter MUST be set to "rtp- 1418 midi", and the "profile-level-id" parameter MUST be set to the MPEG-4 1419 Profile Level for the stream. For the Synthesis Profile, legal profile- 1420 level-id values are 11, 12, and 13, coding low (11), medium (12), or 1421 high (13) decoder computational complexity, as defined by MPEG 1422 conformance tests. 1424 In a minimal RTP MIDI session description, the config value MUST be a 1425 hexadecimal encoding [RFC3640] of the AudioSpecificConfig data block 1426 [MPEGAUDIO] for the stream. AudioSpecificConfig encodes the Audio 1427 Object Type for the stream and also encodes initialization data (SAOL 1428 programs, DLS 2 wave tables, etc.). Standard MIDI Files encoded in 1429 AudioSpecificConfig in a minimal session description MUST be ignored by 1430 the receiver. 1432 Receivers determine the rendering algorithm for the session by 1433 interpreting the first 5 bits of AudioSpecificConfig as an unsigned 1434 integer that codes the Audio Object Type. In our example above, the 1435 leading config string nibbles "7A" yield the Audio Object Type 15 1436 (General MIDI). In Appendix E.4, we derive the config string value in 1437 the session description shown above; the starting point of the 1438 derivation is the MPEG bitstreams defined in [MPEGSA] and [MPEGAUDIO]. 1440 We consider the stream to be "minimal" because the session description 1441 does not customize the stream through the use of parameters, other than 1442 the 4 required mpeg4-generic parameters described above. In Section 1443 6.1, we describe the behavior of a minimal native stream, as a numbered 1444 list of characteristics. Items 1-4 on that list also describe the 1445 minimal mpeg4-generic stream, but items 5 and 6 require restatements, as 1446 listed below: 1448 5. If more than one minimal mpeg4-generic stream appears in 1449 a session, each stream uses an independent instance of the 1450 Audio Object Type coded in the config parameter value. 1452 6. A minimal mpeg4-generic stream encodes the AudioSpecificConfig 1453 as an inline hexadecimal constant. If a session description 1454 is sent over UDP, it may be impossible to transport large 1455 AudioSpecificConfig blocks within the Maximum Transmission Size 1456 (MTU) of the underlying network (for Ethernet, the MTU is 1500 1457 octets). In some cases, the AudioSpecificConfig block may 1458 exceed the maximum size of the UDP packet itself. 1460 The comments in Section 6.1 on SIP and RTSP stream directional defaults, 1461 sendrecv MIDI channel usage, and MIDI 1.0 DIN multicast networks also 1462 apply to mpeg4-generic RTP MIDI sessions. 1464 In sendrecv sessions, each party's session description MUST use 1465 identical values for the mpeg4-generic parameters (including the 1466 required streamtype, mode, profile-level-id, and config parameters). As 1467 a consequence, each party uses an identically configured MPEG 4 Audio 1468 Object Type to render MIDI commands into audio. The preamble to 1469 Appendix C discusses a way to create "virtual sendrecv" sessions that do 1470 not have this restriction. 1472 6.3. Parameters 1474 This section introduces parameters for session configuration for RTP 1475 MIDI streams. In session descriptions, parameters modify the semantics 1476 of a payload type. Parameters are specified on an fmtp attribute line. 1477 See the session description example in Section 6.2 for an example of a 1478 fmtp attribute line. 1480 The parameters add features to the minimal streams described in Sections 1481 6.1-2, and support several types of services: 1483 o Stream subsetting. By default, all MIDI commands that 1484 are legal to appear on a MIDI 1.0 DIN cable may appear 1485 in an RTP MIDI stream. The cm_unused parameter overrides 1486 this default by prohibiting certain commands from appearing 1487 in the stream. The cm_used parameter is used in conjunction 1488 with cm_unused, to simplify the specification of complex 1489 exclusion rules. We describe cm_unused and cm_used in 1490 Appendix C.1. 1492 o Journal customization. The j_sec and j_update parameters 1493 configure the use of the journal section. The ch_default, 1494 ch_never, and ch_anchor parameters configure the semantics 1495 of the recovery journal chapters. These parameters are 1496 described in Appendix C.2 and override the default stream 1497 behaviors 1 and 2, listed in Section 6.1 and referenced in 1498 Section 6.2. 1500 o MIDI command timestamp semantics. The tsmode, octpos, 1501 mperiod, and linerate parameters customize the semantics 1502 of timestamps in the MIDI command section. These parameters 1503 let RTP MIDI accurately encode the implicit time coding of 1504 MIDI 1.0 DIN cables. These parameters are described in 1505 Appendix C.3 and override default stream behavior 3, 1506 listed in Section 6.1 and referenced in Section 6.2 1508 o Media time. The rtp_ptime and rtp_maxptime parameters define 1509 the temporal duration ("media time") of an RTP MIDI packet. 1510 The guardtime parameter sets the minimum sending rate of stream 1511 packets. These parameters are described in Appendix C.4 1512 and override default stream behavior 4, listed in Section 6.1 1513 and referenced in Section 6.2. 1515 o Stream description. The musicport parameter labels the 1516 MIDI name space of RTP streams in a multimedia session. 1517 Musicport is described in Appendix C.5. The musicport 1518 parameter overrides default stream behavior 5, in Sections 1519 6.1 and 6.2. 1521 o MIDI rendering. Several parameters specify the MIDI 1522 rendering method of a stream. These parameters are described 1523 in Appendix C.6 and override default stream behavior 6, in 1524 Sections 6.1 and 6.2. 1526 In Appendix C.7, we specify interoperability guidelines for two RTP MIDI 1527 application areas: content-streaming using RTSP (Appendix C.7.1) and 1528 network musical performance using SIP (Appendix C.7.2). 1530 7. Extensibility 1532 The payload format defined in this memo exclusively encodes all commands 1533 that may legally appear on a MIDI 1.0 DIN cable. 1535 Many worthy uses of MIDI over RTP do not fall within the narrow scope of 1536 the payload format. For example, the payload format does not support 1537 the direct transport of Standard MIDI File (SMF) meta-event and metric 1538 timing data. As a second example, the payload format does not define 1539 transport tools for user-defined commands (apart from tools to support 1540 System Exclusive commands [MIDI]). 1542 The payload format does not provide an extension mechanism to support 1543 new features of this nature, by design. Instead, we encourage the 1544 development of new payload formats for specialized musical applications. 1545 The IETF session management tools [RFC3264] [RFC2326] support codec 1546 negotiation, to facilitate the use of new payload formats in a backward- 1547 compatible way. 1549 However, the payload format does provide several extensibility tools, 1550 which we list below: 1552 o Journalling. As described in Appendix C.2, new token 1553 values for the j_sec and j_update parameters may 1554 be defined in IETF standards-track documents. This 1555 mechanism supports the design of new journal formats 1556 and the definition of new journal sending policies. 1558 o Rendering. The payload format may be extended to support 1559 new MIDI renderers (Appendix C.6.2). Certain general aspects 1560 of the RTP MIDI rendering process may also be extended, via 1561 the definition of new token values for the render (Appendix C.6) 1562 and smf_info (Appendix C.6.4.1) parameters. 1564 o Undefined commands. [MIDI] reserves 4 MIDI System commands 1565 for future use (0xF4, 0xF5, 0xF9, 0xFD). If updates 1566 to [MIDI] define the reserved commands, IETF standards-track 1567 documents may be defined to provide resiliency support for 1568 the commands. Opaque LEGAL fields appear in System Chapter 1569 D for this purpose (Appendix B.1.1). 1571 A final form of extensibility involves the inclusion of the payload 1572 format in framework documents. Framework documents describe how to 1573 combine protocols to form a platform for interoperable applications. 1574 For example, a stage and studio framework might define how to use SIP 1575 [RFC3261], RTSP [RFC2326], SDP [RFC4566], and RTP [RFC3550] to support 1576 media networking for professional audio equipment and electronic musical 1577 instruments. 1579 8. Congestion Control 1581 The RTP congestion control requirements defined in [RFC3550] apply to 1582 RTP MIDI sessions, and implementors should carefully read the congestion 1583 control section in [RFC3550]. As noted in [RFC3550], all transport 1584 protocols used on the Internet need to address congestion control in 1585 some way, and RTP is not an exception. 1587 In addition, the congestion control requirements defined in [RFC3551] 1588 applies to RTP MIDI sessions run under applicable profiles. The basic 1589 congestion control requirement defined in [RFC3551] is that RTP sessions 1590 that use UDP transport should monitor packet loss (via RTCP or other 1591 means) to ensure that the RTP stream competes fairly with TCP flows that 1592 share the network. 1594 Finally, RTP MIDI has congestion control issues that are unique for an 1595 audio RTP payload format. In applications such as network musical 1596 performance [NMP], the packet rate is linked to the gestural rate of a 1597 human performer. Senders MUST monitor the MIDI command source for 1598 patterns that result in excessive packet rates and take actions during 1599 RTP transcoding to reduce the RTP packet rate. [RFC4696] offers 1600 implementation guidance on this issue. 1602 9. Security Considerations 1604 Implementors should carefully read the Security Considerations sections 1605 of the RTP [RFC3550], AVP [RFC3551], and other RTP profile documents, as 1606 the issues discussed in these sections directly apply to RTP MIDI 1607 streams. Implementors should also review the Secure Real-time Transport 1608 Protocol (SRTP, [RFC3711]), an RTP profile that addresses the security 1609 issues discussed in [RFC3550] and [RFC3551]. 1611 Here, we discuss security issues that are unique to the RTP MIDI payload 1612 format. 1614 When using RTP MIDI, authentication of incoming RTP and RTCP packets is 1615 RECOMMENDED. Per-packet authentication may be provided by SRTP or by 1616 other means. Without the use of authentication, attackers could forge 1617 MIDI commands into an ongoing stream, damaging speakers and eardrums. 1618 An attacker could also craft RTP and RTCP packets to exploit known bugs 1619 in the client and take effective control of a client machine. 1621 Session management tools (such as SIP [RFC3261]) SHOULD use 1622 authentication during the transport of all session descriptions 1623 containing RTP MIDI media streams. For SIP, the Security Considerations 1624 section in [RFC3261] provides an overview of possible authentication 1625 mechanisms. RTP MIDI session descriptions should use authentication 1626 because the session descriptions may code initialization data using the 1627 parameters described in Appendix C. If an attacker inserts bogus 1628 initialization data into a session description, he can corrupt the 1629 session or forge an client attack. 1631 Session descriptions may also code renderer initialization data by 1632 reference, via the url (Appendix C.6.3) and smf_url (Appendix C.6.4.2) 1633 parameters. If the coded URL is spoofed, both session and client are 1634 open to attack, even if the session description itself is authenticated. 1635 Therefore, URLs specified in url and smf_url parameters SHOULD use 1636 [RFC2818]. 1638 Section 2.1 allows streams sent by a party in two RTP sessions to have 1639 the same SSRC value and the same RTP timestamp initialization value, 1640 under certain circumstances. Normally, these values are randomly chosen 1641 for each stream in a session, to make plaintext guessing harder to do if 1642 the payloads are encrypted. Thus, Section 2.1 weakens this aspect of 1643 RTP security. 1645 10. Acknowledgements 1647 We thank the networking, media compression, and computer music community 1648 members who have commented or contributed to the effort, including Kurt 1649 B, Cynthia Bruyns, Steve Casner, Paul Davis, Robin Davies, Joanne Dow, 1650 Tobias Erichsen, Nicolas Falquet, Dominique Fober, Philippe Gentric, 1651 Michael Godfrey, Chris Grigg, Todd Hager, Alfred Hoenes, Michel Jullian, 1652 Phil Kerr, Young-Kwon Lim, Jessica Little, Jan van der Meer, Colin 1653 Perkins, Charlie Richmond, Herbie Robinson, Larry Rowe, Eric Scheirer, 1654 Dave Singer, Martijn Sipkema, William Stewart, Kent Terry, Magnus 1655 Westerlund, Tom White, Jim Wright, Doug Wyatt, and Giorgio Zoia. We 1656 also thank the members of the San Francisco Bay Area music and audio 1657 community for creating the context for the work, including Don Buchla, 1658 Chris Chafe, Richard Duda, Dan Ellis, Adrian Freed, Ben Gold, Jaron 1659 Lanier, Roger Linn, Richard Lyon, Dana Massie, Max Mathews, Keith 1660 McMillen, Carver Mead, Nelson Morgan, Tom Oberheim, Malcolm Slaney, Dave 1661 Smith, Julius Smith, David Wessel, and Matt Wright. 1663 11. IANA Considerations 1665 This section makes a series of requests to IANA. The IANA has completed 1666 registration/assignments of the below requests. 1668 The sub-sections that follow hold the actual, detailed requests. All 1669 registrations in this section are in the IETF tree and follow the rules 1670 of [RFC4288] and [RFC4855], as appropriate. 1672 In Section 11.1, we request the registration of a new media type: 1673 "audio/rtp-midi". Paired with this request is a request for a 1674 repository for new values for several parameters associated with 1675 "audio/rtp-midi". We request this repository in Section 11.1.1. 1677 In Section 11.2, we request the registration of a new value ("rtp- 1678 midi") for the "mode" parameter of the "mpeg4-generic" media type. The 1679 "mpeg4-generic" media type is defined in [RFC3640], and [RFC3640] 1680 defines a repository for the "mode" parameter. However, we believe we 1681 are the first to request the registration of a "mode" value, so we 1682 believe the registry for "mode" has not yet been created by IANA. 1684 Paired with our "mode" parameter value request for "mpeg4-generic" is a 1685 request for a repository for new values for several parameters we have 1686 defined for use with the "rtp-midi" mode value. We request this 1687 repository in Section 11.2.1. 1689 In Section 11.3, we request the registration of a new media type: 1690 "audio/asc". No repository request is associated with this request. 1692 11.1. rtp-midi Media Type Registration 1694 This section requests the registration of the "rtp-midi" subtype for the 1695 "audio" media type. We request the registration of the parameters 1696 listed in the "optional parameters" section below (both the "non- 1697 extensible parameters" and the "extensible parameters" lists). We also 1698 request the creation of repositories for the "extensible parameters"; 1699 the details of this request appear in Section 11.1.1, below. 1701 Media type name: 1703 audio 1705 Subtype name: 1707 rtp-midi 1709 Required parameters: 1711 rate: The RTP timestamp clock rate. See Sections 2.1 and 6.1 1712 for usage details. 1714 Optional parameters: 1716 Non-extensible parameters: 1718 ch_anchor: See Appendix C.2.3 for usage details. 1719 ch_default: See Appendix C.2.3 for usage details. 1720 ch_never: See Appendix C.2.3 for usage details. 1721 cm_unused: See Appendix C.1 for usage details. 1722 cm_used: See Appendix C.1 for usage details. 1723 chanmask: See Appendix C.6.4.3 for usage details. 1724 cid: See Appendix C.6.3 for usage details. 1725 guardtime: See Appendix C.4.2 for usage details. 1726 inline: See Appendix C.6.3 for usage details. 1727 linerate: See Appendix C.3 for usage details. 1728 mperiod: See Appendix C.3 for usage details. 1729 multimode: See Appendix C.6.1 for usage details. 1730 musicport: See Appendix C.5 for usage details. 1731 octpos: See Appendix C.3 for usage details. 1732 rinit: See Appendix C.6.3 for usage details. 1733 rtp_maxptime: See Appendix C.4.1 for usage details. 1734 rtp_ptime: See Appendix C.4.1 for usage details. 1736 smf_cid: See Appendix C.6.4.2 for usage details. 1737 smf_inline: See Appendix C.6.4.2 for usage details. 1738 smf_url: See Appendix C.6.4.2 for usage details. 1739 tsmode: See Appendix C.3 for usage details. 1740 url: See Appendix C.6.3 for usage details. 1742 Extensible parameters: 1744 j_sec: See Appendix C.2.1 for usage details. See 1745 Section 11.1.1 for repository details. 1746 j_update: See Appendix C.2.2 for usage details. See 1747 Section 11.1.1 for repository details. 1748 render: See Appendix C.6 for usage details. See 1749 Section 11.1.1 for repository details. 1750 subrender: See Appendix C.6.2 for usage details. See 1751 Section 11.1.1 for repository details. 1752 smf_info: See Appendix C.6.4.1 for usage details. See 1753 Section 11.1.1 for repository details. 1755 Encoding considerations: 1757 The format for this type is framed and binary. 1759 Restrictions on usage: 1761 This type is only defined for real-time transfers of MIDI 1762 streams via RTP. Stored-file semantics for rtp-midi may 1763 be defined in the future. 1765 Security considerations: 1767 See Section 9 of this memo. 1769 Interoperability considerations: 1771 None. 1773 Published specification: 1775 This memo and [MIDI] serve as the normative specification. In 1776 addition, references [NMP], [GRAME], and [RFC4696] provide 1777 non-normative implementation guidance. 1779 Applications that use this media type: 1781 Audio content-creation hardware, such as MIDI controller piano 1782 keyboards and MIDI audio synthesizers. Audio content-creation 1783 software, such as music sequencers, digital audio workstations, 1784 and soft synthesizers. Computer operating systems, for network 1785 support of MIDI Application Programmer Interfaces. Content 1786 distribution servers and terminals may use this media type for 1787 low bit-rate music coding. 1789 Additional information: 1791 None. 1793 Person & email address to contact for further information: 1795 John Lazzaro 1797 Intended usage: 1799 COMMON. 1801 Author: 1803 John Lazzaro 1805 Change controller: 1807 IETF Audio/Video Transport Working Group delegated 1808 from the IESG. 1810 11.1.1. Repository Request for "audio/rtp-midi" 1812 For the "rtp-midi" subtype, we request the creation of repositories for 1813 extensions to the following parameters (which are those listed as 1814 "extensible parameters" in Section 11.1). 1816 j_sec: 1818 Registrations for this repository may only occur 1819 via an IETF standards-track document. Appendix C.2.1 1820 of this memo describes appropriate registrations for this 1821 repository. 1823 Initial values for this repository appear below: 1825 "none": Defined in Appendix C.2.1 of this memo. 1826 "recj": Defined in Appendix C.2.1 of this memo. 1828 j_update: 1830 Registrations for this repository may only occur 1831 via an IETF standards-track document. Appendix C.2.2 1832 of this memo describes appropriate registrations for this 1833 repository. 1835 Initial values for this repository appear below: 1837 "anchor": Defined in Appendix C.2.2 of this memo. 1838 "open-loop": Defined in Appendix C.2.2 of this memo. 1839 "closed-loop": Defined in Appendix C.2.2 of this memo. 1841 render: 1843 Registrations for this repository MUST include a 1844 specification of the usage of the proposed value. 1845 See text in the preamble of Appendix C.6 for details 1846 (the paragraph that begins "Other render token ..."). 1848 Initial values for this repository appear below: 1850 "unknown": Defined in Appendix C.6 of this memo. 1851 "synthetic": Defined in Appendix C.6 of this memo. 1852 "api": Defined in Appendix C.6 of this memo. 1853 "null": Defined in Appendix C.6 of this memo. 1855 subrender: 1857 Registrations for this repository MUST include a 1858 specification of the usage of the proposed value. 1859 See text Appendix C.6.2 for details (the paragraph 1860 that begins "Other subrender token ..."). 1862 Initial values for this repository appear below: 1864 "default": Defined in Appendix C.6.2 of this memo. 1866 smf_info: 1868 Registrations for this repository MUST include a 1869 specification of the usage of the proposed value. 1870 See text in Appendix C.6.4.1 for details (the 1871 paragraph that begins "Other smf_info token ..."). 1873 Initial values for this repository appear below: 1875 "ignore": Defined in Appendix C.6.4.1 of this memo. 1876 "sdp_start": Defined in Appendix C.6.4.1 of this memo. 1877 "identity": Defined in Appendix C.6.4.1 of this memo. 1879 11.2. mpeg4-generic Media Type Registration 1881 This section requests the registration of the "rtp-midi" value for the 1882 "mode" parameter of the "mpeg4-generic" media type. The "mpeg4- 1883 generic" media type is defined in [RFC3640], and [RFC3640] defines a 1884 repository for the "mode" parameter. We are registering mode rtp- midi 1885 to support the MPEG Audio codecs [MPEGSA] that use MIDI. 1887 In conjunction with this registration request, we request the 1888 registration of the parameters listed in the "optional parameters" 1889 section below (both the "non-extensible parameters" and the "extensible 1890 parameters" lists). We also request the creation of repositories for 1891 the "extensible parameters"; the details of this request appear in 1892 Appendix 11.2.1, below. 1894 Media type name: 1896 audio 1898 Subtype name: 1900 mpeg4-generic 1902 Required parameters: 1904 The "mode" parameter is required by [RFC3640]. [RFC3640] requests 1905 a repository for "mode", so that new values for mode 1906 may be added. We request that the value "rtp-midi" be 1907 added to the "mode" repository. 1909 In mode rtp-midi, the mpeg4-generic parameter rate is 1910 a required parameter. Rate specifies the RTP timestamp 1911 clock rate. See Sections 2.1 and 6.2 for usage details 1912 of rate in mode rtp-midi. 1914 Optional parameters: 1916 We request registration of the following parameters 1917 for use in mode rtp-midi for mpeg4-generic. 1919 Non-extensible parameters: 1921 ch_anchor: See Appendix C.2.3 for usage details. 1922 ch_default: See Appendix C.2.3 for usage details. 1923 ch_never: See Appendix C.2.3 for usage details. 1924 cm_unused: See Appendix C.1 for usage details. 1925 cm_used: See Appendix C.1 for usage details. 1926 chanmask: See Appendix C.6.4.3 for usage details. 1927 cid: See Appendix C.6.3 for usage details. 1928 guardtime: See Appendix C.4.2 for usage details. 1929 inline: See Appendix C.6.3 for usage details. 1930 linerate: See Appendix C.3 for usage details. 1931 mperiod: See Appendix C.3 for usage details. 1932 multimode: See Appendix C.6.1 for usage details. 1933 musicport: See Appendix C.5 for usage details. 1934 octpos: See Appendix C.3 for usage details. 1935 rinit: See Appendix C.6.3 for usage details. 1936 rtp_maxptime: See Appendix C.4.1 for usage details. 1937 rtp_ptime: See Appendix C.4.1 for usage details. 1938 smf_cid: See Appendix C.6.4.2 for usage details. 1939 smf_inline: See Appendix C.6.4.2 for usage details. 1940 smf_url: See Appendix C.6.4.2 for usage details. 1941 tsmode: See Appendix C.3 for usage details. 1942 url: See Appendix C.6.3 for usage details. 1944 Extensible parameters: 1946 j_sec: See Appendix C.2.1 for usage details. See 1947 Section 11.2.1 for repository details. 1948 j_update: See Appendix C.2.2 for usage details. See 1949 Section 11.2.1 for repository details. 1950 render: See Appendix C.6 for usage details. See 1951 Section 11.2.1 for repository details. 1952 subrender: See Appendix C.6.2 for usage details. See 1953 Section 11.2.1 for repository details. 1954 smf_info: See Appendix C.6.4.1 for usage details. See 1955 Section 11.2.1 for repository details. 1957 Encoding considerations: 1959 The format for this type is framed and binary. 1961 Restrictions on usage: 1963 Only defined for real-time transfers of audio/mpeg4-generic 1964 RTP streams with mode=rtp-midi. 1966 Security considerations: 1968 See Section 9 of this memo. 1970 Interoperability considerations: 1972 Except for the marker bit (Section 2.1), the packet formats 1973 for audio/rtp-midi and audio/mpeg4-generic (mode rtp-midi) 1974 are identical. The formats differ in use: audio/mpeg4-generic 1975 is for MPEG work, and audio/rtp-midi is for all other work. 1977 Published specification: 1979 This memo, [MIDI], and [MPEGSA] are the normative references. 1980 In addition, references [NMP], [GRAME], and [RFC4696] provide 1981 non-normative implementation guidance. 1983 Applications that use this media type: 1985 MPEG 4 servers and terminals that support [MPEGSA]. 1987 Additional information: 1989 None. 1991 Person & email address to contact for further information: 1993 John Lazzaro 1995 Intended usage: 1997 COMMON. 1999 Author: 2001 John Lazzaro 2003 Change controller: 2005 IETF Audio/Video Transport Working Group delegated 2006 from the IESG. 2008 11.2.1. Repository Request for Mode rtp-midi for mpeg4-generic 2010 For mode rtp-midi of the mpeg4-generic subtype, we request the creation 2011 of repositories for extensions to the following parameters (which are 2012 those listed as "extensible parameters" in Section 11.2). 2014 j_sec: 2016 Registrations for this repository may only occur 2017 via an IETF standards-track document. Appendix C.2.1 2018 of this memo describes appropriate registrations for this 2019 repository. 2021 Initial values for this repository appear below: 2023 "none": Defined in Appendix C.2.1 of this memo. 2024 "recj": Defined in Appendix C.2.1 of this memo. 2026 j_update: 2028 Registrations for this repository may only occur 2029 via an IETF standards-track document. Appendix C.2.2 2030 of this memo describes appropriate registrations for this 2031 repository. 2033 Initial values for this repository appear below: 2035 "anchor": Defined in Appendix C.2.2 of this memo. 2036 "open-loop": Defined in Appendix C.2.2 of this memo. 2037 "closed-loop": Defined in Appendix C.2.2 of this memo. 2039 render: 2041 Registrations for this repository MUST include a 2042 specification of the usage of the proposed value. 2043 See text in the preamble of Appendix C.6 for details 2044 (the paragraph that begins "Other render token ..."). 2046 Initial values for this repository appear below: 2048 "unknown": Defined in Appendix C.6 of this memo. 2049 "synthetic": Defined in Appendix C.6 of this memo. 2050 "null": Defined in Appendix C.6 of this memo. 2052 subrender: 2054 Registrations for this repository MUST include a 2055 specification of the usage of the proposed value. 2056 See text in Appendix C.6.2 for details (the paragraph 2057 that begins "Other subrender token ..." and 2058 subsequent paragraphs). Note that the text in 2059 Appendix C.6.2 contains restrictions on subrender 2060 registrations for mpeg4-generic ("Registrations 2061 for mpeg4-generic subrender values ..."). 2063 Initial values for this repository appear below: 2065 "default": Defined in Appendix C.6.2 of this memo. 2067 smf_info: 2069 Registrations for this repository MUST include a 2070 specification of the usage of the proposed value. 2071 See text in Appendix C.6.4.1 for details (the 2072 paragraph that begins "Other smf_info token ..."). 2074 Initial values for this repository appear below: 2076 "ignore": Defined in Appendix C.6.4.1 of this memo. 2077 "sdp_start": Defined in Appendix C.6.4.1 of this memo. 2078 "identity": Defined in Appendix C.6.4.1 of this memo. 2080 11.3. asc Media Type Registration 2082 This section registers "asc" as a subtype for the "audio" media type. 2083 We register this subtype to support the remote transfer of the "config" 2084 parameter of the mpeg4-generic media type [RFC3640] when it is used with 2085 mpeg4-generic mode rtp-midi (registered in Appendix 11.2 above). We 2086 explain the mechanics of using "audio/asc" to set the config parameter 2087 in Section 6.2 and Appendix C.6.5 of this document. 2089 Note that this registration is a new subtype registration and is not an 2090 addition to a repository defined by MPEG-related memos (such as 2091 [RFC3640]). Also note that this request for "audio/asc" does not 2092 register parameters, and does not request the creation of a repository. 2094 Media type name: 2096 audio 2098 Subtype name: 2100 asc 2102 Required parameters: 2104 None. 2106 Optional parameters: 2108 None. 2110 Encoding considerations: 2112 The native form of the data object is binary data, 2113 zero-padded to an octet boundary. 2115 Restrictions on usage: 2117 This type is only defined for data object (stored file) 2118 transfer. The most common transports for the type are 2119 HTTP and SMTP. 2121 Security considerations: 2123 See Section 9 of this memo. 2125 Interoperability considerations: 2127 None. 2129 Published specification: 2131 The audio/asc data object is the AudioSpecificConfig 2132 binary data structure, which is normatively defined in [MPEGAUDIO]. 2134 Applications that use this media type: 2136 MPEG 4 Audio servers and terminals that support 2137 audio/mpeg4-generic RTP streams for mode rtp-midi. 2139 Additional information: 2141 None. 2143 Person & email address to contact for further information: 2145 John Lazzaro 2147 Intended usage: 2149 COMMON. 2151 Author: 2153 John Lazzaro 2155 Change controller: 2157 IETF Audio/Video Transport Working Group delegated 2158 from the IESG. 2160 A. The Recovery Journal Channel Chapters 2162 A.1. Recovery Journal Definitions 2164 This appendix defines the terminology and the coding idioms that are 2165 used in the recovery journal bitfield descriptions in Section 5 (journal 2166 header structure), Appendices A.2 to A.9 (channel journal chapters) and 2167 Appendices B.1 to B.5 (system journal chapters). 2169 We assume that the recovery journal resides in the journal section of an 2170 RTP packet with sequence number I ("packet I") and that the Checkpoint 2171 Packet Seqnum field in the top-level recovery journal header refers to a 2172 previous packet with sequence number C (an exception is the self- 2173 referential C = I case). Unless stated otherwise, algorithms are 2174 assumed to use modulo 2^16 arithmetic for calculations on 16-bit 2175 sequence numbers and modulo 2^32 arithmetic for calculations on 32-bit 2176 extended sequence numbers. 2178 Several bitfield coding idioms appear throughout the recovery journal 2179 system, with consistent semantics. Most recovery journal elements begin 2180 with an "S" (Single-packet loss) bit. S bits are designed to help 2181 receivers efficiently parse through the recovery journal hierarchy in 2182 the common case of the loss of a single packet. 2184 As a rule, S bits MUST be set to 1. However, an exception applies if a 2185 recovery journal element in packet I encodes data about a command stored 2186 in the MIDI command section of packet I - 1. In this case, the S bit of 2187 the recovery journal element MUST be set to 0. If a recovery journal 2188 element has its S bit set to 0, all higher-level recovery journal 2189 elements that contain it MUST also have S bits that are set to 0, 2190 including the top-level recovery journal header. 2192 Other consistent bitfield coding idioms are described below: 2194 o R flag bit. R flag bits are reserved for future use. Senders 2195 MUST set R bits to 0. Receivers MUST ignore R bit values. 2197 o LENGTH field. All fields named LENGTH (as distinct from LEN) 2198 code the number of octets in the structure that contains it, 2199 including the header it resides in and all hierarchical levels 2200 below it. If a structure contains a LENGTH field, a receiver 2201 MUST use the LENGTH field value to advance past the structure 2202 during parsing, rather than use knowledge about the internal 2203 format of the structure. 2205 We now define normative terms used to describe recovery journal 2206 semantics. 2208 o Checkpoint history. The checkpoint history of a recovery journal 2209 is the concatenation of the MIDI command sections of packets C 2210 through I - 1. The final command in the MIDI command section for 2211 packet I - 1 is considered the most recent command; the first 2212 command in the MIDI command section for packet C is the oldest 2213 command. If command X is less recent than command Y, X is 2214 considered to be "before Y". A checkpoint history with no 2215 commands is considered to be empty. The checkpoint history 2216 never contains the MIDI command section of packet I (the 2217 packet containing the recovery journal), so if C == I, the 2218 checkpoint history is empty by definition. 2220 o Session history. The session history of a recovery journal is 2221 the concatenation of MIDI command sections from the first 2222 packet of the session up to packet I - 1. The definitions of 2223 command recency and history emptiness follow those in the 2224 checkpoint history. The session history never contains the 2225 MIDI command section of packet I, and so the session history of 2226 the first packet in the session is empty by definition. 2228 o Finished/unfinished commands. If all octets of a MIDI command 2229 appear in the session history, the command is defined as being 2230 finished. If some but not all octets of a command appear 2231 in the session history, the command is defined as being unfinished. 2232 Unfinished commands occur if segments of a SysEx command appear 2233 in several RTP packets. For example, if a SysEx command is coded 2234 as 3 segments, with segment 1 in packet K, segment 2 in packet 2235 K + 1, and segment 3 in packet K + 2, the session histories for 2236 packets K + 1 and K + 2 contain unfinished versions of the command. 2237 A session history contains a finished version of a cancelled SysEx 2238 command if the history contains the cancel sublist for the command. 2240 o Reset State commands. Reset State (RS) commands reset 2241 renderers to an initialized "powerup" condition. The 2242 RS commands are: System Reset (0xFF), General MIDI System Enable 2243 (0xF0 0x7E 0xcc 0x09 0x01 0xF7), General MIDI 2 System Enable 2244 (0xF0 0x7E 0xcc 0x09 0x03 0xF7), General MIDI System Disable 2245 (0xF0 0x7E 0xcc 0x09 0x00 0xF7), Turn DLS On (0xF0 0x7E 0xcc 0x0A 2246 0x01 0xF7), and Turn DLS Off (0xF0 0x7E 0xcc 0x0A 0x02 0xF7). 2247 Registrations of subrender parameter token values (Appendix C.6.2) 2248 and IETF standards-track documents MAY specify additional 2249 RS commands. 2251 o Active commands. Active command are MIDI commands that do not 2252 appear before a Reset State command in the session history. 2254 o N-active commands. N-active commands are MIDI commands that do 2255 not appear before one of the following commands in the session 2256 history: MIDI Control Change numbers 123-127 (numbers with All 2257 Notes Off semantics) or 120 (All Sound Off), and any Reset 2258 State command. 2260 o C-active commands. C-active commands are MIDI commands that do 2261 not appear before one of the following commands in the session 2262 history: MIDI Control Change number 121 (Reset All Controllers) 2263 and any Reset State command. 2265 o Oldest-first ordering rule. Several recovery journal chapters 2266 contain a list of elements, where each element is associated 2267 with a MIDI command that appears in the session history. In 2268 most cases, the chapter definition requires that list elements 2269 be ordered in accordance with the "oldest-first ordering rule". 2270 Below, we normatively define this rule: 2272 Elements associated with the most recent command in the session 2273 history coded in the list MUST appear at the end of the list. 2275 Elements associated with the oldest command in the session 2276 history coded in the list MUST appear at the start of the list. 2278 All other list elements MUST be arranged with respect to these 2279 boundary elements, to produce a list ordering that strictly 2280 reflects the relative session history recency of the commands 2281 coded by the elements in the list. 2283 o Parameter system. A MIDI feature that provides two sets of 2284 16,384 parameters to expand the 0-127 controller number space. 2285 The Registered Parameter Names (RPN) system and the Non-Registered 2286 Parameter Names (NRPN) system each provides 16,384 parameters. 2288 o Parameter system transaction. The value of RPNs and NRPNs are 2289 changed by a series of Control Change commands that form a 2290 parameter system transaction. A canonical transaction begins 2291 with two Control Change commands to set the parameter number 2292 (controller numbers 99 and 98 for NRPNs, controller numbers 101 2293 and 100 for RPNs). The transaction continues with an arbitrary 2294 number of Data Entry (controller numbers 6 and 38), Data Increment 2295 (controller number 96), and Data Decrement (controller number 2296 97) Control Change commands to set the parameter value. The 2297 transaction ends with a second pair of (99, 98) or (101, 100) 2298 Control Change commands that specify the null parameter (MSB 2299 value 0x7F, LSB value 0x7F). 2301 Several variants of the canonical transaction sequence are 2302 possible. Most commonly, the terminal pair of (99, 98) or 2303 (101, 100) Control Change commands may specify a parameter 2304 other than the null parameter. In this case, the command 2305 pair terminates the first transaction and starts a second 2306 transaction. The command pair is considered to be a part 2307 of both transactions. This variant is legal and recommended 2308 in [MIDI]. We refer to this variant as a "type 1 variant". 2310 Less commonly, the MSB (99 or 101) or LSB (98 or 100) command 2311 of a (99, 98) or (101, 100) Control Change pair may be omitted. 2313 If the MSB command is omitted, the transaction uses the MSB value 2314 of the most recent C-active Control Change command for controller 2315 number 99 or 101 that appears in the session history. We refer to 2316 this variant as a "type 2 variant". 2318 If the LSB command is omitted, the LSB value 0x00 is assumed. We 2319 refer to this variant as a "type 3 variant". The type 2 and type 3 2320 variants are defined as legal, but are not recommended, in [MIDI]. 2322 System real-time commands may appear at any point during 2323 a transaction (even between octets of individual commands 2324 in the transaction). More generally, [MIDI] does not forbid 2325 the appearance of unrelated MIDI commands during an open 2326 transaction. As a rule, these commands are considered to 2327 be "outside" the transaction and do not affect the status 2328 of the transaction in any way. Exceptions to this rule are 2329 commands whose semantics act to terminate transactions: 2330 Reset State commands, and Control Change (0xB) for controller 2331 number 121 (Reset All Controllers) [RP015]. 2333 o Initiated parameter system transaction. A canonical parameter 2334 system transaction whose (99, 98) or (101, 100) initial Control 2335 Change command pair appears in the session history is considered 2336 to be an initiated parameter system transaction. This definition 2337 also holds for type 1 variants. For type 2 variants (dropped MSB), 2338 a transaction whose initial LSB Control Change command appears in 2339 the session history is an initiated transaction. For type 3 2340 variants (dropped LSB), a transaction is considered to be 2341 initiated if at least one transaction command follows the initial 2342 MSB (99 or 101) Control Change command in the session history. 2343 The completion of a transaction does not nullify its "initiated" 2344 status. 2346 o Session history reference counts. Several recovery journal 2347 chapters include a reference count field, which codes the 2348 total number of commands of a type that appear in the session 2349 history. Examples include the Reset and Tune Request command 2350 logs (Chapter D, Appendix B.1) and the Active Sense command 2351 (Chapter V, Appendix B.2). Upon the detection of a loss event, 2352 reference count fields let a receiver deduce if any instances of 2353 the command have been lost, by comparing the journal reference 2354 count with its own reference count. Thus, a reference count 2355 field makes sense, even for command types in which knowing the 2356 NUMBER of lost commands is irrelevant (as is true with all of 2357 the example commands mentioned above). 2359 The chapter definitions in Appendices A.2 to A.9 and B.1 to B.5 reflect 2360 the default recovery journal behavior. The ch_default, ch_never, and 2361 ch_anchor parameters modify these definitions, as described in Appendix 2362 C.2.3. 2364 The chapter definitions specify if data MUST be present in the journal. 2365 Senders MAY also include non-required data in the journal. This 2366 optional data MUST comply with the normative chapter definition. For 2367 example, if a chapter definition states that a field codes data from the 2368 most recent active command in the session history, the sender MUST NOT 2369 code inactive commands or older commands in the field. 2371 Finally, we note that a channel journal only encodes information about 2372 MIDI commands appearing on the MIDI channel the journal protects. All 2373 references to MIDI commands in Appendices A.2 to A.9 should be read as 2374 "MIDI commands appearing on this channel." 2375 A.2. Chapter P: MIDI Program Change 2377 A channel journal MUST contain Chapter P if an active Program Change 2378 (0xC) command appears in the checkpoint history. Figure A.2.1 shows the 2379 format for Chapter P. 2381 0 1 2 2382 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 2383 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2384 |S| PROGRAM |B| BANK-MSB |X| BANK-LSB | 2385 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2387 Figure A.2.1 -- Chapter P format 2389 The chapter has a fixed size of 24 bits. The PROGRAM field indicates 2390 the data value of the most recent active Program Change command in the 2391 session history. By default, the B, BANK-MSB, X, and BANK-LSB fields 2392 MUST be set to 0. Below, we define exceptions to this default 2393 condition. 2395 If an active Control Change (0xB) command for controller number 0 (Bank 2396 Select MSB) appears before the Program Change command in the session 2397 history, the B bit MUST be set to 1, and the BANK-MSB field MUST code 2398 the data value of the Control Change command. 2400 If B is set to 1, the BANK-LSB field MUST code the data value of the 2401 most recent Control Change command for controller number 32 (Bank Select 2402 LSB) that preceded the Program Change command coded in the PROGRAM field 2403 and followed the Control Change command coded in the BANK-MSB field. If 2404 no such Control Change command exists, the BANK-LSB field MUST be set to 2405 0. 2407 If B is set to 1, and if a Control Change command for controller number 2408 121 (Reset All Controllers) appears in the MIDI stream between the 2409 Control Change command coded by the BANK-MSB field and the Program 2410 Change command coded by the PROGRAM field, the X bit MUST be set to 1. 2412 Note that [RP015] specifies that Reset All Controllers does not reset 2413 the values of controller numbers 0 (Bank Select MSB) and 32 (Bank Select 2414 LSB). Thus, the X bit does not effect how receivers will use the BANK- 2415 LSB and BANK-MSB values when recovering from a lost Program Change 2416 command. The X bit serves to aid recovery in MIDI applications where 2417 controller numbers 0 and 32 are used in a non-standard way. 2419 A.3. Chapter C: MIDI Control Change 2421 Figure A.3.1 shows the format for Chapter C. 2423 0 1 2 3 2424 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 8 0 1 2425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2426 |S| LEN |S| NUMBER |A| VALUE/ALT |S| NUMBER | 2427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2428 |A| VALUE/ALT | .... | 2429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2431 Figure A.3.1 -- Chapter C format 2433 The chapter consists of a 1-octet header, followed by a variable length 2434 list of 2-octet controller logs. The list MUST contain at least one 2435 controller log. The 7-bit LEN field codes the number of controller logs 2436 in the list, minus one. We define the semantics of the controller log 2437 fields in Appendix A.3.2. 2439 A channel journal MUST contain Chapter C if the rules defined in this 2440 appendix require that one or more controller logs appear in the list. 2442 A.3.1. Log Inclusion Rules 2444 A controller log encodes information about a particular Control Change 2445 command in the session history. 2447 In the default use of the payload format, list logs MUST encode 2448 information about the most recent active command in the session history 2449 for a controller number. Logs encoding earlier commands MUST NOT appear 2450 in the list. 2452 Also, as a rule, the list MUST contain a log for the most recent active 2453 command for a controller number that appears in the checkpoint history. 2454 Below, we define exceptions to this rule: 2456 o MIDI streams may transmit 14-bit controller values using paired 2457 Most Significant Byte (MSB, controller numbers 0-31, 99, 101) and 2458 Least Significant Byte (LSB, controller numbers 32-63, 98, 100) 2459 Control Change commands [MIDI]. 2461 If the most recent active Control Change command in the session 2462 history for a 14-bit controller pair uses the MSB number, Chapter 2463 C MAY omit the controller log for the most recent active Control 2464 Change command for the associated LSB number, as the command 2465 ordering makes this LSB value irrelevant. However, this exception 2466 MUST NOT be applied if the sender is not certain that the MIDI 2467 source uses 14-bit semantics for the controller number pair. Note 2468 that some MIDI sources ignore 14-bit controller semantics and use 2469 the LSB controller numbers as independent 7-bit controllers. 2471 o If active Control Change commands for controller numbers 0 (Bank 2472 Select MSB) or 32 (Bank Select LSB) appear in the checkpoint 2473 history, and if the command instances are also coded in the 2474 BANK-MSB and BANK-LSB fields of the Chapter P (Appendix A.2), 2475 Chapter C MAY omit the controller logs for the commands. 2477 o Several controller number pairs are defined to be mutually 2478 exclusive. Controller numbers 124 (Omni Off) and 125 (Omni On) 2479 form a mutually exclusive pair, as do controller numbers 126 2480 (Mono) and 127 (Poly). 2482 If active Control Change commands for one or both members of 2483 a mutually exclusive pair appear in the checkpoint history, a 2484 log for the controller number of the most recent command for the 2485 pair in the checkpoint history MUST appear in the controller list. 2486 However, the list MAY omit the controller log for the most recent 2487 active command for the other number in the pair. 2489 If active Control Change commands for one or both members of a 2490 mutually exclusive pair appear in the session history, and if a 2491 log for the controller number of the most recent command for the 2492 pair does not appear in the controller list, a log for the most 2493 recent command for the other number of the pair MUST NOT appear 2494 in the controller list. 2496 o If an active Control Change command for controller number 121 2497 (Reset All Controllers) appears in the session history, the 2498 controller list MAY omit logs for Control Change commands that 2499 precede the Reset All Controllers command in the session history, 2500 under certain conditions. 2502 Namely, a log MAY be omitted if the sender is certain that a 2503 command stream follows the Reset All Controllers semantics 2504 defined in [RP015], and if the log codes a controller number 2505 for which [RP015] specifies a reset value. 2507 For example, [RP015] specifies that controller number 1 2508 (Modulation Wheel) is reset to the value 0, and thus 2509 a controller log for Modulation Wheel MAY be omitted 2510 from the controller log list. In contrast, [RP015] specifies 2511 that controller number 7 (Channel Volume) is not reset, 2512 and thus a controller log for Channel Volume MUST NOT 2513 be omitted from the controller log list. 2515 o Appendix A.3.4 defines exception rules for the MIDI Parameter 2516 System controller numbers 6, 38, and 96-101. 2518 A.3.2. Controller Log Format 2520 Figure A.3.2 shows the controller log structure of Chapter C. 2522 0 1 2523 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2525 |S| NUMBER |A| VALUE/ALT | 2526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2528 Figure A.3.2 -- Chapter C controller log 2530 The 7-bit NUMBER field identifies the controller number of the coded 2531 command. The 7-bit VALUE/ALT field codes recovery information for the 2532 command. The A bit sets the format of the VALUE/ALT field. 2534 A log encodes recovery information using one of the following tools: the 2535 value tool, the toggle tool, or the count tool. 2537 A log uses the value tool if the A bit is set to 0. The value tool 2538 codes the 7-bit data value of a command in the VALUE/ALT field. The 2539 value tool works best for controllers that code a continuous quantity, 2540 such as number 1 (Modulation Wheel). 2542 The A bit is set to 1 to code the toggle or count tool. These tools 2543 work best for controllers that code discrete actions. Figure A.3.3 2544 shows the controller log for these tools. 2546 0 1 2547 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2549 |S| NUMBER |1|T| ALT | 2550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2552 Figure A.3.3 -- Controller log for ALT tools 2554 A log uses the toggle tool if the T bit is set to 0. A log uses the 2555 count tool if the T bit is set to 1. Both methods use the 6-bit ALT 2556 field as an unsigned integer. 2558 The toggle tool works best for controllers that act as on/off switches, 2559 such as 64 (Damper Pedal (Sustain)). These controllers code the "off" 2560 state with control values 0-63 and the "on" state with 64-127. 2562 For the toggle tool, the ALT field codes the total number of toggles 2563 (off->on and on->off) due to Control Change commands in the session 2564 history, up to and including a toggle caused by the command coded by the 2565 log. The toggle count includes toggles caused by Control Change 2566 commands for controller number 121 (Reset All Controllers). 2568 Toggle counting is performed modulo 64. The toggle count is reset at 2569 the start of a session, and whenever a Reset State command (Appendix 2570 A.1) appears in the session history. When these reset events occur, the 2571 toggle count for a controller is set to 0 (for controllers whose default 2572 value is 0-63) or 1 (for controllers whose default value is 64-127). 2574 The Damper Pedal (Sustain) controller illustrates the benefits of the 2575 toggle tool over the value tool for switch controllers. As often used 2576 in piano applications, the "on" state of the controller lets notes 2577 resonate, while the "off" state immediately damps notes to silence. The 2578 loss of the "off" command in an "on->off->on" sequence results in 2579 ringing notes that should have been damped silent. The toggle tool lets 2580 receivers detect this lost "off" command, but the value tool does not. 2582 The count tool is conceptually similar to the toggle tool. For the 2583 count tool, the ALT field codes the total number of Control Change 2584 commands in the session history, up to and including the command coded 2585 by the log. Command counting is performed modulo 64. The command count 2586 is set to 0 at the start of the session and is reset to 0 whenever a 2587 Reset State command (Appendix A.1) appears in the session history. 2589 Because the count tool ignores the data value, it is a good match for 2590 controllers whose controller value is ignored, such as number 123 (All 2591 Notes Off). More generally, the count tool may be used to code a 2592 (modulo 64) identification number for a command. 2594 A.3.3. Log List Coding Rules 2596 In this section, we describe the organization of controller logs in the 2597 Chapter C log list. 2599 A log encodes information about a particular Control Change command in 2600 the session history. In most cases, a command SHOULD be coded by a 2601 single tool (and, thus, a single log). If a number is coded with a 2602 single tool and this tool is the count tool, recovery Control Change 2603 commands generated by a receiver SHOULD use the default control value 2604 for the controller. 2606 However, a command MAY be coded by several tool types (and, thus, 2607 several logs, each using a different tool). This technique may improve 2608 recovery performance for controllers with complex semantics, such as 2609 controller number 84 (Portamento Control) or controller number 121 2610 (Reset All Controllers) when used with a non-zero data octet (with the 2611 semantics described in [DLS2]). 2613 If a command is encoded by multiple tools, the logs MUST be placed in 2614 the list in the following order: count tool log (if any), followed by 2615 value tool log (if any), followed by toggle tool log (if any). 2617 The Chapter C log list MUST obey the oldest-first ordering rule (defined 2618 in Appendix A.1). Note that this ordering preserves the information 2619 necessary for the recovery of 14-bit controller values, without 2620 precluding the use of MSB and LSB controller pairs as independent 7-bit 2621 controllers. 2623 In the default use of the payload format, all logs that appear in the 2624 list for a controller number encode information about one Control Change 2625 command -- namely, the most recent active Control Change command in the 2626 session history for the number. 2628 This coding scheme provides good recovery performance for the standard 2629 uses of Control Change commands defined in [MIDI]. However, not all 2630 MIDI applications restrict the use of Control Change commands to those 2631 defined in [MIDI]. 2633 For example, consider the common MIDI encoding of rotary encoders 2634 ("infinite" rotation knobs). The mixing console MIDI convention defined 2635 in [LCP] codes the position of rotary encoders as a series of Control 2636 Change commands. Each command encodes a relative change of knob 2637 position from the last update (expressed as a clockwise or counter- 2638 clockwise knob turning angle). 2640 As the knob position is encoded incrementally over a series of Control 2641 Change commands, the best recovery performance is obtained if the log 2642 list encodes all Control Change commands for encoder controller numbers 2643 that appear in the checkpoint history, not only the most recent command. 2645 To support application areas that use Control Change commands in this 2646 way, Chapter C may be configured to encode information about several 2647 Control Change commands for a controller number. We use the term 2648 "enhanced" to describe this encoding method, which we describe below. 2650 In Appendix C.2.3, we show how to configure a stream to use enhanced 2651 Chapter C encoding for specific controller numbers. In Section 5 in the 2652 main text, we show how the H bits in the recovery journal header (Figure 2653 8) and in the channel journal header (Figure 9) indicate the use of 2654 enhanced Chapter C encoding. 2656 Here, we define how to encode a Chapter C log list that uses the 2657 enhanced encoding method. 2659 Senders that use the enhanced encoding method for a controller number 2660 MUST obey the rules below. These rules let a receiver determine which 2661 logs in the list correspond to lost commands. Note that these rules 2662 override the exceptions listed in Appendix A.3.1. 2664 o If N commands for a controller number are encoded in the list, 2665 the commands MUST be the N most recent commands for the controller 2666 number in the session history. For example, for N = 2, the sender 2667 MUST encode the most recent command and the second most recent 2668 command, not the most recent command and the third most recent 2669 command. 2671 o If a controller number uses enhanced encoding, the encoding 2672 of the least-recent command for the controller number in the 2673 log list MUST include a count tool log. In addition, if 2674 commands are encoded for the controller number whose logs 2675 have S bits set to 0, the encoding of the least-recent 2676 command with S = 0 logs MUST include a count tool log. 2678 The count tool is OPTIONAL for the other commands for the 2679 controller number encoded in the list, as a receiver is 2680 able to efficiently deduce the count tool value for these 2681 commands, for both single-packet and multi-packet loss events. 2683 o The use of the value and toggle tools MUST be identical for all 2684 commands for a controller number encoded in the list. For 2685 example, a value tool log either MUST appear for all commands 2686 for the controller number coded in the list, or alternatively, 2687 value tool logs for the controller number MUST NOT appear in 2688 the list. Likewise, a toggle tool log either MUST appear for 2689 all commands for the controller number coded in the list, or 2690 alternatively, toggle tool logs for the controller number MUST 2691 NOT appear in the list. 2693 o If a command is encoded by multiple tools, the logs MUST be 2694 placed in the list in the following order: count tool log 2695 (if any), followed by value tool log (if any), followed by 2696 toggle tool log (if any). 2698 These rules permit a receiver recovering from a packet loss to use the 2699 count tool log to match the commands encoded in the list with its own 2700 history of the stream, as we describe below. Note that the text below 2701 describes a non-normative algorithm; receivers are free to use any 2702 algorithm to match its history with the log list. 2704 In a typical implementation of the enhanced encoding method, a receiver 2705 computes and stores count, value, and toggle tool data field values for 2706 the most recent Control Change command it has received for a controller 2707 number. 2709 After a loss event, a receiver parses the Chapter C list and processes 2710 list logs for a controller number that uses enhanced encoding as 2711 follows. 2713 The receiver compares the count tool ALT field for the least-recent 2714 command for the controller number in the list against its stored count 2715 data for the controller number, to determine if recovery is necessary 2716 for the command coded in the list. The value and toggle tool logs (if 2717 any) that directly follow the count tool log are associated with this 2718 least-recent command. 2720 To check more-recent commands for the controller, the receiver detects 2721 additional value and/or toggle tool logs for the controller number in 2722 the list and infers count tool data for the command coded by these logs. 2723 This inferred data is used to determine if recovery is necessary for the 2724 command coded by the value and/or toggle tool logs. 2726 In this way, a receiver is able to execute only lost commands, without 2727 executing a command twice. While recovering from a single packet loss, 2728 a receiver may skip through S = 1 logs in the list, as the first S = 0 2729 log for an enhanced controller number is always a count tool log. 2731 Note that the requirements in Appendix C.2.2.2 for protective sender and 2732 receiver actions during session startup for multicast operation are of 2733 particular importance for enhanced encoding, as receivers need to 2734 initialize its count tool data structures with recovery journal data in 2735 order to match commands correctly after a loss event. 2737 Finally, we note in passing that in some applications of rotary 2738 encoders, a good user experience may be possible without the use of 2739 enhanced encoding. These applications are distinguished by visual 2740 feedback of encoding position that is driven by the post-recovery rotary 2741 encoding stream, and relatively low packet loss. In these domains, 2742 recovery performance may be acceptable for rotary encoders if the log 2743 list encodes only the most recent command, if both count and value logs 2744 appear for the command. 2746 A.3.4. The Parameter System 2748 Readers may wish to review the Appendix A.1 definitions of "parameter 2749 system", "parameter system transaction", and "initiated parameter system 2750 transaction" before reading this section. 2752 Parameter system transactions update a MIDI Registered Parameter Number 2753 (RPN) or Non-Registered Parameter Number (NRPN) value. A parameter 2754 system transaction is a sequence of Control Change commands that may use 2755 the following controllers numbers: 2757 o Data Entry MSB (6) 2758 o Data Entry LSB (38) 2759 o Data Increment (96) 2760 o Data Decrement (97) 2761 o Non-Registered Parameter Number (NRPN) LSB (98) 2762 o Non-Registered Parameter Number (NRPN) MSB (99) 2763 o Registered Parameter Number (RPN) LSB (100) 2764 o Registered Parameter Number (RPN) MSB (101) 2766 Control Change commands that are a part of a parameter system 2767 transaction MUST NOT be coded in Chapter C controller logs. Instead, 2768 these commands are coded in Chapter M, the MIDI Parameter chapter 2769 defined in Appendix A.4. 2771 However, Control Change commands that use the listed controllers as 2772 general-purpose controllers (i.e., outside of a parameter system 2773 transaction) MUST NOT be coded in Chapter M. 2775 Instead, the controllers are coded in Chapter C controller logs. The 2776 controller logs follow the coding rules stated in Appendix A.3.2 and 2777 A.3.3. The rules for coding paired LSB and MSB controllers, as defined 2778 in Appendix A.3.1, apply to the pairs (6, 38), (99, 98), and (101, 100) 2779 when coded in Chapter C. 2781 If active Control Change commands for controller numbers 6, 38, or 2782 96-101 appear in the checkpoint history, and these commands are used as 2783 general-purpose controllers, the most recent general-purpose command 2784 instance for these controller numbers MUST appear as entries in the 2785 Chapter C controller list. 2787 MIDI syntax permits a source to use controllers 6, 38, 96, and 97 as 2788 parameter-system controllers and general-purpose controllers in the same 2789 stream. An RTP MIDI sender MUST deduce the role of each Control Change 2790 command for these controller numbers by noting the placement of the 2791 command in the stream and MUST use this information to code the command 2792 in Chapter C or Chapter M, as appropriate. 2794 Specifically, active Control Change commands for controllers 6, 38, 96, 2795 and 97 act in a general-purpose way when 2797 o no active Control Change commands that set an RPN or 2798 NRPN parameter number appear in the session history, or 2800 o the most recent active Control Change commands in the session 2801 history that set an RPN or NRPN parameter number code the null 2802 parameter (MSB value 0x7F, LSB value 0x7F), or 2804 o a Control Change command for controller number 121 (Reset 2805 All Controllers) appears more recently in the session history 2806 than all active Control Change commands that set an RPN or 2807 NRPN parameter number (see [RP015] for details). 2809 Finally, we note that a MIDI source that follows the recommendations of 2810 [MIDI] exclusively uses numbers 98-101 as parameter system controllers. 2811 Alternatively, a MIDI source may exclusively use 98-101 as general- 2812 purpose controllers and lose the ability to perform parameter system 2813 transactions in a stream. 2815 In the language of [MIDI], the general-purpose use of controllers 98-101 2816 constitutes a non-standard controller assignment. As most real-world 2817 MIDI sources use the standard controller assignment for controller 2818 numbers 98-101, an RTP MIDI sender SHOULD assume these controllers act 2819 as parameter system controllers, unless it knows that a MIDI source uses 2820 controller numbers 98-101 in a general-purpose way. 2822 A.4. Chapter M: MIDI Parameter System 2824 Readers may wish to review the Appendix A.1 definitions for "C-active", 2825 "parameter system", "parameter system transaction", and "initiated 2826 parameter system transaction" before reading this appendix. 2828 Chapter M protects parameter system transactions for Registered 2829 Parameter Number (RPN) and Non-Registered Parameter Number (NRPN) 2830 values. Figure A.4.1 shows the format for Chapter M. 2832 0 1 2 3 2833 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2834 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2835 |S|P|E|U|W|Z| LENGTH |Q| PENDING | Log list ... | 2836 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2838 Figure A.4.1 -- Top-level Chapter M format 2840 Chapter M begins with a 2-octet header. If the P header bit is set to 2841 1, a 1-octet field follows the header, coding the 7-bit PENDING value 2842 and its associated Q bit. 2844 The 10-bit LENGTH field codes the size of Chapter M and conforms to 2845 semantics described in Appendix A.1. 2847 Chapter M ends with a list of zero or more variable-length parameter 2848 logs. Appendix A.4.2 defines the bitfield format of a parameter log. 2849 Appendix A.4.1 defines the inclusion semantics of the log list. 2851 A channel journal MUST contain Chapter M if the rules defined in 2852 Appendix A.4.1 require that one or more parameter logs appear in the 2853 list. 2855 A channel journal also MUST contain Chapter M if the most recent C- 2856 active Control Change command involved in a parameter system transaction 2857 in the checkpoint history is 2859 o an RPN MSB (101) or NRPN MSB (99) controller, or 2861 o an RPN LSB (100) or NRPN LSB (98) controller that completes the 2862 coding of the null parameter (MSB value 0x7F, LSB value 0x7F). 2864 This rule provides loss protection for partially transmitted parameter 2865 numbers and for the null parameter numbers. 2867 If the most recent C-active Control Change command involved in a 2868 parameter system transaction in the session history is for the RPN MSB 2869 or NRPN MSB controller, the P header bit MUST be set to 1, and the 2870 PENDING field (and its associated Q bit) MUST follow the Chapter M 2871 header. Otherwise, the P header bit MUST be set to 0, and the PENDING 2872 field and Q bit MUST NOT appear in Chapter M. 2874 If PENDING codes an NRPN MSB, the Q bit MUST be set to 1. If PENDING 2875 codes an RPN MSB, the Q bit MUST be set to 0. 2877 The E header bit codes the current transaction state of the MIDI stream. 2878 If E = 1, an initiated transaction is in progress. Below, we define the 2879 rules for setting the E header bit: 2881 o If no C-active parameter system transaction Control Change 2882 commands appear in the session history, the E bit MUST be 2883 set to 0. 2885 o If the P header bit is set to 1, the E bit MUST be set to 0. 2887 o If the most recent C-active parameter system transaction 2888 Control Change command in the session history is for the 2889 NRPN LSB or RPN LSB controller number, and if this command 2890 acts to complete the coding of the null parameter (MSB 2891 value 0x7F, LSB value 0x7F), the E bit MUST be set to 0. 2893 o Otherwise, an initiated transaction is in progress, and the 2894 E bit MUST be set to 1. 2896 The U, W, and Z header bits code properties that are shared by all 2897 parameter logs in the list. If these properties are set, parameter logs 2898 may be coded with improved efficiency (we explain how in A.4.1). 2900 By default, the U, W, and Z bits MUST be set to 0. If all parameter 2901 logs in the list code RPN parameters, the U bit MAY be set to 1. If all 2902 parameter logs in the list code NRPN parameters, the W bit MAY be set to 2903 1. If the parameter numbers of all RPN and NRPN logs in the list lie in 2904 the range 0-127 (and thus have an MSB value of 0), the Z bit MAY be set 2905 to 1. 2907 Note that C-active semantics appear in the preceding paragraphs because 2908 [RP015] specifies that pending Parameter System transactions are closed 2909 by a Control Change command for controller number 121 (Reset All 2910 Controllers). 2912 A.4.1. Log Inclusion Rules 2914 Parameter logs code recovery information for a specific RPN or NRPN 2915 parameter. 2917 A parameter log MUST appear in the list if an active Control Change 2918 command that forms a part of an initiated transaction for the parameter 2919 appears in the checkpoint history. 2921 An exception to this rule applies if the checkpoint history only 2922 contains transaction Control Change commands for controller numbers 2923 98-101 that act to terminate the transaction. In this case, a log for 2924 the parameter MAY be omitted from the list. 2926 A log MAY appear in the list if an active Control Change command that 2927 forms a part of an initiated transaction for the parameter appears in 2928 the session history. Otherwise, a log for the parameter MUST NOT appear 2929 in the list. 2931 Multiple logs for the same RPN or NRPN parameter MUST NOT appear in the 2932 log list. 2934 The parameter log list MUST obey the oldest-first ordering rule (defined 2935 in Appendix A.1), with the phrase "parameter transaction" replacing the 2936 word "command" in the rule definition. 2938 Parameter logs associated with the RPN or NRPN null parameter (LSB = 2939 0x7F, MSB = 0x7F) MUST NOT appear in the log list. Chapter M uses the E 2940 header bit (Figure A.4.1) and the log list ordering rules to code null 2941 parameter semantics. 2943 Note that "active" semantics (rather than "C-active" semantics) appear 2944 in the preceding paragraphs because [RP015] specifies that pending 2945 Parameter System transactions are not reset by a Control Change command 2946 for controller number 121 (Reset All Controllers). However, the rule 2947 that follows uses C-active semantics, because it concerns the protection 2948 of the transaction system itself, and [RP015] specifies that Reset All 2949 Controllers acts to close a transaction in progress. 2951 In most cases, parameter logs for RPN and NRPN parameters that are 2952 assigned to the ch_never parameter (Appendix C.2.3) MAY be omitted from 2953 the list. An exception applies if 2955 o the log codes the most recent initiated transaction 2956 in the session history, and 2958 o a C-active command that forms a part of the transaction 2959 appears in the checkpoint history, and 2961 o the E header bit for the top-level Chapter M header (Figure 2962 A.4.1) is set to 1. 2964 In this case, a log for the parameter MUST appear in the list. This log 2965 informs receivers recovering from a loss that a transaction is in 2966 progress, so that the receiver is able to correctly interpret RPN or 2967 NRPN Control Change commands that follow the loss event. 2969 A.4.2. Log Coding Rules 2971 Figure A.4.2 shows the parameter log structure of Chapter M. 2973 0 1 2 3 2974 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 8 0 1 2975 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2976 |S| PNUM-LSB |Q| PNUM-MSB |J|K|L|M|N|T|V|R| Fields ... | 2977 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2979 Figure A.4.2 -- Parameter log format 2981 The log begins with a header, whose default size (as shown in Figure 2982 A.4.2) is 3 octets. If the Q header bit is set to 0, the log encodes an 2983 RPN parameter. If Q = 1, the log encodes an NRPN parameter. The 7-bit 2984 PNUM-MSB and PNUM-LSB fields code the parameter number and reflect the 2985 Control Change command data values for controllers 99 and 98 (for NRPNs) 2986 or 101 and 100 (for RPNs). 2988 The J, K, L, M, and N header bits form a Table of Contents (TOC) for the 2989 log and signal the presence of fixed-sized fields that follow the 2990 header. A header bit that is set to 1 codes the presence of a field in 2991 the log. The ordering of fields in the log follows the ordering of the 2992 header bits in the TOC. Appendices A.4.2.1-2 define the fields 2993 associated with each TOC header bit. 2995 The T and V header bits code information about the parameter log but are 2996 not part of the TOC. A set T or V bit does not signal the presence of 2997 any parameter log field. 2999 If the rules in Appendix A.4.1 state that a log for a given parameter 3000 MUST appear in Chapter M, the log MUST code sufficient information to 3001 protect the parameter from the loss of active parameter transaction 3002 Control Change commands in the checkpoint history. 3004 This rule does not apply if the parameter coded by the log is assigned 3005 to the ch_never parameter (Appendix C.2.3). In this case, senders MAY 3006 choose to set the J, K, L, M, and N TOC bits to 0, coding a parameter 3007 log with no fields. 3009 Note that logs to protect parameters that are assigned to ch_never are 3010 REQUIRED under certain conditions (see Appendix A.4.1). The purpose of 3011 the log is to inform receivers recovering from a loss that a transaction 3012 is in progress, so that the receiver is able to correctly interpret RPN 3013 or NRPN Control Change commands that follow the loss event. 3015 Parameter logs provide two tools for parameter protection: the value 3016 tool and the count tool. Depending on the semantics of the parameter, 3017 senders may use either tool, both tools, or neither tool to protect a 3018 given parameter. 3020 The value tool codes information a receiver may use to determine the 3021 current value of an RPN or NRPN parameter. If a parameter log uses the 3022 value tool, the V header bit MUST be set to 1, and the semantics defined 3023 in Appendices A.4.2.1 for setting the J, K, L, and M TOC bits MUST be 3024 followed. If a parameter log does not use the value tool, the V bit 3025 MUST be set to 0, and the J, K, L, and M TOC bits MUST also be set to 0. 3027 The count tool codes the number of transactions for an RPN or NRPN 3028 parameter. If a parameter log uses the count tool, the T header bit 3029 MUST be set to 1, and the semantics defined in Appendices A.4.2.2 for 3030 setting the N TOC bit MUST be followed. If a parameter log does not use 3031 the count tool, the T bit and the N TOC bit MUST be set to 0. 3033 Note that V and T are set if the sender uses value (V) or count (T) tool 3034 for the log on an ongoing basis. Thus, V may be set even if J = K = L = 3035 M = 0, and T may be set even if N = 0. 3037 In many cases, all parameters coded in the log list are of one type (RPN 3038 and NRPN), and all parameter numbers lie in the range 0-127. As 3039 described in Appendix A.4.1, senders MAY signal this condition by 3040 setting the top-level Chapter M header bit Z to 1 (to code the 3041 restricted range) and by setting the U or W bit to 1 (to code the 3042 parameter type). 3044 If the top-level Chapter M header codes Z = 1 and either U = 1 or W = 1, 3045 all logs in the parameter log list MUST use a modified header format. 3046 This modification deletes bits 8-15 of the bitfield shown in Figure 3047 A.4.2, to yield a 2-octet header. The values of the deleted PNUM-MSB 3048 and Q fields may be inferred from the U, W, and Z bit values. 3050 A.4.2.1. The Value Tool 3052 The value tool uses several fields to track the value of an RPN or NRPN 3053 parameter. 3055 The J TOC bit codes the presence of the octet shown in Figure A.4.3 in 3056 the field list. 3058 0 3059 0 1 2 3 4 5 6 7 3060 +-+-+-+-+-+-+-+-+ 3061 |X| ENTRY-MSB | 3062 +-+-+-+-+-+-+-+-+ 3064 Figure A.4.3 -- ENTRY-MSB field 3066 The 7-bit ENTRY-MSB field codes the data value of the most recent active 3067 Control Change command for controller number 6 (Data Entry MSB) in the 3068 session history that appears in a transaction for the log parameter. 3070 The X bit MUST be set to 1 if the command coded by ENTRY-MSB precedes 3071 the most recent Control Change command for controller 121 (Reset All 3072 Controllers) in the session history. Otherwise, the X bit MUST be set 3073 to 0. 3075 A parameter log that uses the value tool MUST include the ENTRY-MSB 3076 field if an active Control Change command for controller number 6 3077 appears in the checkpoint history. 3079 Note that [RP015] specifies that Control Change commands for controller 3080 121 (Reset All Controllers) do not reset RPN and NRPN values, and thus 3081 the X bit would not play a recovery role for MIDI systems that comply 3082 with [RP015]. 3084 However, certain renderers (such as DLS 2 [DLS2]) specify that certain 3085 RPN values are reset for some uses of Reset All Controllers. The X bit 3086 (and other bitfield features of this nature in this appendix) plays a 3087 role in recovery for renderers of this type. 3089 The K TOC bit codes the presence of the octet shown in Figure A.4.4 in 3090 the field list. 3092 0 3093 0 1 2 3 4 5 6 7 3094 +-+-+-+-+-+-+-+-+ 3095 |X| ENTRY-LSB | 3096 +-+-+-+-+-+-+-+-+ 3098 Figure A.4.4 -- ENTRY-LSB field 3100 The 7-bit ENTRY-LSB field codes the data value of the most recent active 3101 Control Change command for controller number 38 (Data Entry LSB) in the 3102 session history that appears in a transaction for the log parameter. 3104 The X bit MUST be set to 1 if the command coded by ENTRY-LSB precedes 3105 the most recent Control Change command for controller 121 (Reset All 3106 Controllers) in the session history. Otherwise, the X bit MUST be set 3107 to 0. 3109 As a rule, a parameter log that uses the value tool MUST include the 3110 ENTRY-LSB field if an active Control Change command for controller 3111 number 38 appears in the checkpoint history. However, the ENTRY-LSB 3112 field MUST NOT appear in a parameter log if the Control Change command 3113 associated with the ENTRY-LSB precedes a Control Change command for 3114 controller number 6 (Data Entry MSB) that appears in a transaction for 3115 the log parameter in the session history. 3117 The L TOC bit codes the presence of the octets shown in Figure A.4.5 in 3118 the field list. 3120 0 1 3121 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3122 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3123 |G|X| A-BUTTON | 3124 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3126 Figure A.4.5 -- A-BUTTON field 3128 The 14-bit A-BUTTON field codes a count of the number of active Control 3129 Change commands for controller numbers 96 and 97 (Data Increment and 3130 Data Decrement) in the session history that appear in a transaction for 3131 the log parameter. 3133 The M TOC bit codes the presence of the octets shown in Figure A.4.6 in 3134 the field list. 3136 0 1 3137 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3138 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3139 |G|R| C-BUTTON | 3140 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3142 Figure A.4.6 -- C-BUTTON field 3144 The 14-bit C-BUTTON field has semantics identical to A-BUTTON, except 3145 that Data Increment and Data Decrement Control Change commands that 3146 precede the most recent Control Change command for controller 121 (Reset 3147 All Controllers) in the session history are not counted. 3149 For both A-BUTTON and C-BUTTON, Data Increment and Data Decrement 3150 Control Change commands are not counted if they precede Control Changes 3151 commands for controller numbers 6 (Data Entry MSB) or 38 (Data Entry 3152 LSB) that appear in a transaction for the log parameter in the session 3153 history. 3155 The A-BUTTON and C-BUTTON fields are interpreted as unsigned integers, 3156 and the G bit associated with the field codes the sign of the integer (G 3157 = 0 for positive or zero, G = 1 for negative). 3159 To compute and code the count value, initialize the count value to 0, 3160 add 1 for each qualifying Data Increment command, and subtract 1 for 3161 each qualifying Data Decrement command. After each add or subtract, 3162 limit the count magnitude to 16383. The G bit codes the sign of the 3163 count, and the A-BUTTON or C-BUTTON field codes the count magnitude. 3165 For the A-BUTTON field, if the most recent qualified Data Increment or 3166 Data Decrement command precedes the most recent Control Change command 3167 for controller 121 (Reset All Controllers) in the session history, the X 3168 bit associated with A-BUTTON field MUST be set to 1. Otherwise, the X 3169 bit MUST be set to 0. 3171 A parameter log that uses the value tool MUST include the A-BUTTON and 3172 C-BUTTON fields if an active Control Change command for controller 3173 numbers 96 or 97 appears in the checkpoint history. However, to improve 3174 coding efficiency, this rule has several exceptions: 3176 o If the log includes the A-BUTTON field, and if the X bit of 3177 the A-BUTTON field is set to 1, the C-BUTTON field (and its 3178 associated R and G bits) MAY be omitted from the log. 3180 o If the log includes the A-BUTTON field, and if the A-BUTTON 3181 and C-BUTTON fields (and their associated G bits) code identical 3182 values, the C-BUTTON field (and its associated R and G bits) 3183 MAY be omitted from the log. 3185 A.4.2.2. The Count Tool 3187 The count tool tracks the number of transactions for an RPN or NRPN 3188 parameter. The N TOC bit codes the presence of the octet shown in 3189 Figure A.4.7 in the field list. 3191 0 3192 0 1 2 3 4 5 6 7 3193 +-+-+-+-+-+-+-+-+ 3194 |X| COUNT | 3195 +-+-+-+-+-+-+-+-+ 3197 Figure A.4.7 -- COUNT field 3199 The 7-bit COUNT codes the number of initiated transactions for the log 3200 parameter that appear in the session history. Initiated transactions 3201 are counted if they contain one or more active Control Change commands, 3202 including commands for controllers 98-101 that initiate the parameter 3203 transaction. 3205 If the most recent counted transaction precedes the most recent Control 3206 Change command for controller 121 (Reset All Controllers) in the session 3207 history, the X bit associated with the COUNT field MUST be set to 1. 3208 Otherwise, the X bit MUST be set to 0. 3210 Transaction counting is performed modulo 128. The transaction count is 3211 set to 0 at the start of a session and is reset to 0 whenever a Reset 3212 State command (Appendix A.1) appears in the session history. 3214 A parameter log that uses the count tool MUST include the COUNT field if 3215 an active command that increments the transaction count (modulo 128) 3216 appears in the checkpoint history. 3218 A.5. Chapter W: MIDI Pitch Wheel 3220 A channel journal MUST contain Chapter W if a C-active MIDI Pitch Wheel 3221 (0xE) command appears in the checkpoint history. Figure A.5.1 shows the 3222 format for Chapter W. 3224 0 1 3225 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3226 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3227 |S| FIRST |R| SECOND | 3228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3230 Figure A.5.1 -- Chapter W format 3232 The chapter has a fixed size of 16 bits. The FIRST and SECOND fields 3233 are the 7-bit values of the first and second data octets of the most 3234 recent active Pitch Wheel command in the session history. 3236 Note that Chapter W encodes C-active commands and thus does not encode 3237 active commands that are not C-active (see the second-to-last paragraph 3238 of Appendix A.1 for an explanation of chapter inclusion text in this 3239 regard). 3241 Chapter W does not encode "active but not C-active" commands because 3242 [RP015] declares that Control Change commands for controller number 121 3243 (Reset All Controllers) act to reset the Pitch Wheel value to 0. If 3244 Chapter W encoded "active but not C-active" commands, a repair operation 3245 following a Reset All Controllers command could incorrectly repair the 3246 stream with a stale Pitch Wheel value. 3248 A.6. Chapter N: MIDI NoteOff and NoteOn 3250 In this appendix, we consider NoteOn commands with zero velocity to be 3251 NoteOff commands. Readers may wish to review the Appendix A.1 3252 definition of "N-active commands" before reading this appendix. 3254 Chapter N completely protects note commands in streams that alternate 3255 between NoteOn and NoteOff commands for a particular note number. 3256 However, in rare applications, multiple overlapping NoteOn commands may 3257 appear for a note number. Chapter E, described in Appendix A.7, 3258 augments Chapter N to completely protect these streams. 3260 A channel journal MUST contain Chapter N if an N-active MIDI NoteOn 3261 (0x9) or NoteOff (0x8) command appears in the checkpoint history. 3262 Figure A.6.1 shows the format for Chapter N. 3264 0 1 2 3 3265 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 8 0 1 3266 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3267 |B| LEN | LOW | HIGH |S| NOTENUM |Y| VELOCITY | 3268 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3269 |S| NOTENUM |Y| VELOCITY | .... | 3270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3271 | OFFBITS | OFFBITS | .... | OFFBITS | 3272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3274 Figure A.6.1 -- Chapter N format 3276 Chapter N consists of a 2-octet header, followed by at least one of the 3277 following data structures: 3279 o A list of note logs to code NoteOn commands. 3280 o A NoteOff bitfield structure to code NoteOff commands. 3282 We define the header bitfield semantics in Appendix A.6.1. We define 3283 the note log semantics and the NoteOff bitfield semantics in Appendix 3284 A.6.2. 3286 If one or more N-active NoteOn or NoteOff commands in the checkpoint 3287 history reference a note number, the note number MUST be coded in either 3288 the note log list or the NoteOff bitfield structure. 3290 The note log list MUST contain an entry for all note numbers whose most 3291 recent checkpoint history appearance is in an N-active NoteOn command. 3292 The NoteOff bitfield structure MUST contain a set bit for all note 3293 numbers whose most recent checkpoint history appearance is in an N- 3294 active NoteOff command. 3296 A note number MUST NOT be coded in both structures. 3298 All note logs and NoteOff bitfield set bits MUST code the most recent N- 3299 active NoteOn or NoteOff reference to a note number in the session 3300 history. 3302 The note log list MUST obey the oldest-first ordering rule (defined in 3303 Appendix A.1). 3305 A.6.1. Header Structure 3307 The header for Chapter N, shown in Figure A.6.2, codes the size of the 3308 note list and bitfield structures. 3310 0 1 3311 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3313 |B| LEN | LOW | HIGH | 3314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3316 Figure A.6.2 -- Chapter N header 3318 The LEN field, a 7-bit integer value, codes the number of 2-octet note 3319 logs in the note list. Zero is a valid value for LEN and codes an empty 3320 note list. 3322 The 4-bit LOW and HIGH fields code the number of OFFBITS octets that 3323 follow the note log list. LOW and HIGH are unsigned integer values. If 3324 LOW <= HIGH, there are (HIGH - LOW + 1) OFFBITS octets in the chapter. 3325 The value pairs (LOW = 15, HIGH = 0) and (LOW = 15, HIGH = 1) code an 3326 empty NoteOff bitfield structure (i.e., no OFFBITS octets). Other (LOW 3327 > HIGH) value pairs MUST NOT appear in the header. 3329 The B bit provides S-bit functionality (Appendix A.1) for the NoteOff 3330 bitfield structure. By default, the B bit MUST be set to 1. However, 3331 if the MIDI command section of the previous packet (packet I - 1, with I 3332 as defined in Appendix A.1) includes a NoteOff command for the channel, 3333 the B bit MUST be set to 0. If the B bit is set to 0, the higher-level 3334 recovery journal elements that contain Chapter N MUST have S bits that 3335 are set to 0, including the top-level journal header. 3337 The LEN value of 127 codes a note list length of 127 or 128 note logs, 3338 depending on the values of LOW and HIGH. If LEN = 127, LOW = 15, and 3339 HIGH = 0, the note list holds 128 note logs, and the NoteOff bitfield 3340 structure is empty. For other values of LOW and HIGH, LEN = 127 codes 3341 that the note list contains 127 note logs. In this case, the chapter 3342 has (HIGH - LOW + 1) NoteOff OFFBITS octets if LOW <= HIGH and has no 3343 OFFBITS octets if LOW = 15 and HIGH = 1. 3345 A.6.2. Note Structures 3347 Figure A.6.3 shows the 2-octet note log structure. 3349 0 1 3350 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3351 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3352 |S| NOTENUM |Y| VELOCITY | 3353 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3355 Figure A.6.3 -- Chapter N note log 3357 The 7-bit NOTENUM field codes the note number for the log. A note 3358 number MUST NOT be represented by multiple note logs in the note list. 3360 The 7-bit VELOCITY field codes the velocity value for the most recent N- 3361 active NoteOn command for the note number in the session history. 3362 Multiple overlapping NoteOns for a given note number may be coded using 3363 Chapter E, as discussed in Appendix A.7. 3365 VELOCITY is never zero; NoteOn commands with zero velocity are coded as 3366 NoteOff commands in the NoteOff bitfield structure. 3368 The note log does not code the execution time of the NoteOn command. 3369 However, the Y bit codes a hint from the sender about the NoteOn 3370 execution time. The Y bit codes a recommendation to play (Y = 1) or 3371 skip (Y = 0) the NoteOn command recovered from the note log. See 3372 Section 4.2 of [RFC4696] for non-normative guidance on the use of the Y 3373 bit. 3375 Figure A.6.1 shows the NoteOff bitfield structure, as the list of 3376 OFFBITS octets at the end of the chapter. A NoteOff OFFBITS octet codes 3377 NoteOff information for eight consecutive MIDI note numbers, with the 3378 most-significant bit representing the lowest note number. The most- 3379 significant bit of the first OFFBITS octet codes the note number 8*LOW; 3380 the most-significant bit of the last OFFBITS octet codes the note number 3381 8*HIGH. 3383 A set bit codes a NoteOff command for the note number. In the most 3384 efficient coding for the NoteOff bitfield structure, the first and last 3385 octets of the structure contain at least one set bit. Note that Chapter 3386 N does not code NoteOff velocity data. 3388 Note that in the general case, the recovery journal does not code the 3389 relative placement of a NoteOff command and a Change Control command for 3390 controller 64 (Damper Pedal (Sustain)). In many cases, a receiver 3391 processing a loss event may deduce this relative placement from the 3392 history of the stream and thus determine if a NoteOff note is sustained 3393 by the pedal. If such a determination is not possible, receivers SHOULD 3394 err on the side of silencing pedal sustains, as erroneously sustained 3395 notes may produce unpleasant (albeit transient) artifacts. 3397 A.7. Chapter E: MIDI Note Command Extras 3399 Readers may wish to review the Appendix A.1 definition of "N-active 3400 commands" before reading this appendix. In this appendix, a NoteOn 3401 command with a velocity of 0 is considered to be a NoteOff command with 3402 a release velocity value of 64. 3404 Chapter E encodes recovery information about MIDI NoteOn (0x9) and 3405 NoteOff (0x8) command features that rarely appear in MIDI streams. 3406 Receivers use Chapter E to reduce transient artifacts for streams where 3407 several NoteOn commands appear for a note number without an intervening 3408 NoteOff. Receivers also use Chapter E to reduce transient artifacts for 3409 streams that use NoteOff release velocity. Chapter E supplements the 3410 note information coded in Chapter N (Appendix A.6). 3412 Figure A.7.1 shows the format for Chapter E. 3414 0 1 2 3 3415 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 8 0 1 3416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3417 |S| LEN |S| NOTENUM |V| COUNT/VEL |S| NOTENUM | 3418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3419 |V| COUNT/VEL | .... | 3420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3422 Figure A.7.1 -- Chapter E format 3424 The chapter consists of a 1-octet header, followed by a variable-length 3425 list of 2-octet note logs. Appendix A.7.1 defines the bitfield format 3426 for a note log. 3428 The log list MUST contain at least one note log. The 7-bit LEN header 3429 field codes the number of note logs in the list, minus one. A channel 3430 journal MUST contain Chapter E if the rules defined in this appendix 3431 require that one or more note logs appear in the list. The note log 3432 list MUST obey the oldest-first ordering rule (defined in Appendix A.1). 3434 A.7.1. Note Log Format 3436 Figure A.7.2 reproduces the note log structure of Chapter E. 3438 0 1 3439 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3441 |S| NOTENUM |V| COUNT/VEL | 3442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3444 Figure A.7.2 -- Chapter E note log 3446 A note log codes information about the MIDI note number coded by the 3447 7-bit NOTENUM field. The nature of the information depends on the value 3448 of the V flag bit. 3450 If the V bit is set to 1, the COUNT/VEL field codes the release velocity 3451 value for the most recent N-active NoteOff command for the note number 3452 that appears in the session history. 3454 If the V bit is set to 0, the COUNT/VEL field codes a reference count of 3455 the number of NoteOn and NoteOff commands for the note number that 3456 appear in the session history. 3458 The reference count is set to 0 at the start of the session. NoteOn 3459 commands increment the count by 1. NoteOff commands decrement the count 3460 by 1. However, a decrement that generates a negative count value is not 3461 performed. 3463 If the reference count is in the range 0-126, the 7-bit COUNT/VEL field 3464 codes an unsigned integer representation of the count. If the count is 3465 greater than or equal to 127, COUNT/VEL is set to 127. 3467 By default, the count is reset to 0 whenever a Reset State command 3468 (Appendix A.1) appears in the session history, and whenever MIDI Control 3469 Change commands for controller numbers 123-127 (numbers with All Notes 3470 Off semantics) or 120 (All Sound Off) appear in the session history. 3472 A.7.2. Log Inclusion Rules 3474 If the most recent N-active NoteOn or NoteOff command for a note number 3475 in the checkpoint history is a NoteOff command with a release velocity 3476 value other than 64, a note log whose V bit is set to 1 MUST appear in 3477 Chapter E for the note number. 3479 If the most recent N-active NoteOn or NoteOff command for a note number 3480 in the checkpoint history is a NoteOff command, and if the reference 3481 count for the note number is greater than 0, a note log whose V bit is 3482 set to 0 MUST appear in Chapter E for the note number. 3484 If the most recent N-active NoteOn or NoteOff command for a note number 3485 in the checkpoint history is a NoteOn command, and if the reference 3486 count for the note number is greater than 1, a note log whose V bit is 3487 set to 0 MUST appear in Chapter E for the note number. 3489 At most, two note logs MAY appear in Chapter E for a note number: one 3490 log whose V bit is set to 0, and one log whose V bit is set to 1. 3492 Chapter E codes a maximum of 128 note logs. If the log inclusion rules 3493 yield more than 128 REQUIRED logs, note logs whose V bit is set to 1 3494 MUST be dropped from Chapter E in order to reach the 128-log limit. 3495 Note logs whose V bit is set to 0 MUST NOT be dropped. 3497 Most MIDI streams do not use NoteOn and NoteOff commands in ways that 3498 would trigger the log inclusion rules. For these streams, Chapter E 3499 would never be REQUIRED to appear in a channel journal. 3501 The ch_never parameter (Appendix C.2.3) may be used to configure the log 3502 inclusion rules for Chapter E. 3504 A.8. Chapter T: MIDI Channel Aftertouch 3506 A channel journal MUST contain Chapter T if an N-active and C-active 3507 MIDI Channel Aftertouch (0xD) command appears in the checkpoint history. 3508 Figure A.8.1 shows the format for Chapter T. 3510 0 3511 0 1 2 3 4 5 6 7 3512 +-+-+-+-+-+-+-+-+ 3513 |S| PRESSURE | 3514 +-+-+-+-+-+-+-+-+ 3516 Figure A.8.1 -- Chapter T format 3518 The chapter has a fixed size of 8 bits. The 7-bit PRESSURE field holds 3519 the pressure value of the most recent N-active and C-active Channel 3520 Aftertouch command in the session history. 3522 Chapter T only encodes commands that are C-active and N-active. We 3523 define a C-active restriction because [RP015] declares that a Control 3524 Change command for controller 121 (Reset All Controllers) acts to reset 3525 the channel pressure to 0 (see the discussion at the end of Appendix A.5 3526 for a more complete rationale). 3528 We define an N-active restriction on the assumption that aftertouch 3529 commands are linked to note activity, and thus Channel Aftertouch 3530 commands that are not N-active are stale and should not be used to 3531 repair a stream. 3533 A.9. Chapter A: MIDI Poly Aftertouch 3535 A channel journal MUST contain Chapter A if a C-active Poly Aftertouch 3536 (0xA) command appears in the checkpoint history. Figure A.9.1 shows the 3537 format for Chapter A. 3539 0 1 2 3 3540 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 8 0 1 3541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3542 |S| LEN |S| NOTENUM |X| PRESSURE |S| NOTENUM | 3543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3544 |X| PRESSURE | .... | 3545 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3547 Figure A.9.1 -- Chapter A format 3549 The chapter consists of a 1-octet header, followed by a variable-length 3550 list of 2-octet note logs. A note log MUST appear for a note number if 3551 a C-active Poly Aftertouch command for the note number appears in the 3552 checkpoint history. A note number MUST NOT be represented by multiple 3553 note logs in the note list. The note log list MUST obey the oldest- 3554 first ordering rule (defined in Appendix A.1). 3556 The 7-bit LEN field codes the number of note logs in the list, minus 3557 one. Figure A.9.2 reproduces the note log structure of Chapter A. 3559 0 1 3560 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3562 |S| NOTENUM |X| PRESSURE | 3563 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3565 Figure A.9.2 -- Chapter A note log 3567 The 7-bit PRESSURE field codes the pressure value of the most recent C- 3568 active Poly Aftertouch command in the session history for the MIDI note 3569 number coded in the 7-bit NOTENUM field. 3571 As a rule, the X bit MUST be set to 0. However, the X bit MUST be set 3572 to 1 if the command coded by the log appears before one of the following 3573 commands in the session history: MIDI Control Change numbers 123-127 3574 (numbers with All Notes Off semantics) or 120 (All Sound Off). 3576 We define C-active restrictions for Chapter A because [RP015] declares 3577 that a Control Change command for controller 121 (Reset All Controllers) 3578 acts to reset the polyphonic pressure to 0 (see the discussion at the 3579 end of Appendix A.5 for a more complete rationale). 3581 B. The Recovery Journal System Chapters 3583 B.1. System Chapter D: Simple System Commands 3585 The system journal MUST contain Chapter D if an active MIDI Reset 3586 (0xFF), MIDI Tune Request (0xF6), MIDI Song Select (0xF3), undefined 3587 MIDI System Common (0xF4 and 0xF5), or undefined MIDI System Real-time 3588 (0xF9 and 0xFD) command appears in the checkpoint history. 3590 Figure B.1.1 shows the variable-length format for Chapter D. 3592 0 1 2 3 3593 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 3594 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3595 |S|B|G|H|J|K|Y|Z| Command logs ... | 3596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3598 Figure B.1.1 -- System Chapter D format 3600 The chapter consists of a 1-octet header, followed by one or more 3601 command logs. Header flag bits indicate the presence of command logs 3602 for the Reset (B = 1), Tune Request (G = 1), Song Select (H = 1), 3603 undefined System Common 0xF4 (J = 1), undefined System Common 0xF5 (K = 3604 1), undefined System Real-time 0xF9 (Y = 1), or undefined System Real- 3605 time 0xFD (Z = 1) commands. 3607 Command logs appear in a list following the header, in the order that 3608 the flag bits appear in the header. 3610 Figure B.1.2 shows the 1-octet command log format for the Reset and Tune 3611 Request commands. 3613 0 3614 0 1 2 3 4 5 6 7 3615 +-+-+-+-+-+-+-+-+ 3616 |S| COUNT | 3617 +-+-+-+-+-+-+-+-+ 3619 Figure B.1.2 -- Command log for Reset and Tune Request 3621 Chapter D MUST contain the Reset command log if an active Reset command 3622 appears in the checkpoint history. The 7-bit COUNT field codes the 3623 total number of Reset commands (modulo 128) present in the session 3624 history. 3626 Chapter D MUST contain the Tune Request command log if an active Tune 3627 Request command appears in the checkpoint history. The 7-bit COUNT 3628 field codes the total number of Tune Request commands (modulo 128) 3629 present in the session history. 3631 For these commands, the COUNT field acts as a reference count. See the 3632 definition of "session history reference counts" in Appendix A.1 for 3633 more information. 3635 Figure B.1.3 shows the 1-octet command log format for the Song Select 3636 command. 3638 0 3639 0 1 2 3 4 5 6 7 3640 +-+-+-+-+-+-+-+-+ 3641 |S| VALUE | 3642 +-+-+-+-+-+-+-+-+ 3644 Figure B.1.3 -- Song Select command log format 3646 Chapter D MUST contain the Song Select command log if an active Song 3647 Select command appears in the checkpoint history. The 7-bit VALUE field 3648 codes the song number of the most recent active Song Select command in 3649 the session history. 3651 B.1.1. Undefined System Commands 3653 In this section, we define the Chapter D command logs for the undefined 3654 System commands. [MIDI] reserves the undefined System commands 0xF4, 3655 0xF5, 0xF9, and 0xFD for future use. At the time of this writing, any 3656 MIDI command stream that uses these commands is non-compliant with 3657 [MIDI]. However, future versions of [MIDI] may define these commands, 3658 and a few products do use these commands in a non-compliant manner. 3660 Figure B.1.4 shows the variable-length command log format for the 3661 undefined System Common commands (0xF4 and 0xF5). 3663 0 1 2 3 3664 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 3665 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3666 |S|C|V|L|DSZ| LENGTH | COUNT | VALUE ... | 3667 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3668 | LEGAL ... | 3669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3671 Figure B.1.4 -- Undefined System Common command log format 3673 The command log codes a single command type (0xF4 or 0xF5, not both). 3674 Chapter D MUST contain a command log if an active 0xF4 command appears 3675 in the checkpoint history and MUST contain an independent command log if 3676 an active 0xF5 command appears in the checkpoint history. 3678 A Chapter D Undefined System Common command log consists of a two-octet 3679 header followed by a variable number of data fields. Header flag bits 3680 indicate the presence of the COUNT field (C = 1), the VALUE field (V = 3681 1), and the LEGAL field (L = 1). The 10-bit LENGTH field codes the size 3682 of the command log and conforms to semantics described in Appendix A.1. 3684 The 2-bit DSZ field codes the number of data octets in the command 3685 instance that appears most recently in the session history. If DSZ = 3686 0-2, the command has 0-2 data octets. If DSZ = 3, the command has 3 or 3687 more command data octets. 3689 We now define the default rules for the use of the COUNT, VALUE, and 3690 LEGAL fields. The session configuration tools defined in Appendix C.2.3 3691 may be used to override this behavior. 3693 By default, if the DSZ field is set to 0, the command log MUST include 3694 the COUNT field. The 8-bit COUNT field codes the total number of 3695 commands of the type coded by the log (0xF4 or 0xF5) present in the 3696 session history, modulo 256. 3698 By default, if the DSZ field is set to 1-3, the command log MUST include 3699 the VALUE field. The variable-length VALUE field codes a verbatim copy 3700 the data octets for the most recent use of the command type coded by the 3701 log (0xF4 or 0xF5) in the session history. The most-significant bit of 3702 the final data octet MUST be set to 1, and the most-significant bit of 3703 all other data octets MUST be set to 0. 3705 The LEGAL field is reserved for future use. If an update to [MIDI] 3706 defines the 0xF4 or 0xF5 command, an IETF standards-track document may 3707 define the LEGAL field. Until such a document appears, senders MUST NOT 3708 use the LEGAL field, and receivers MUST use the LENGTH field to skip 3709 over the LEGAL field. The LEGAL field would be defined by the IETF if 3710 the semantics of the new 0xF4 or 0xF5 command could not be protected 3711 from packet loss via the use of the COUNT and VALUE fields. 3713 Figure B.1.5 shows the variable-length command log format for the 3714 undefined System Real-time commands (0xF9 and 0xFD). 3716 0 1 2 3 3717 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 3718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3719 |S|C|L| LENGTH | COUNT | LEGAL ... | 3720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3722 Figure B.1.5 -- Undefined System Real-time command log format 3724 The command log codes a single command type (0xF9 or 0xFD, not both). 3725 Chapter D MUST contain a command log if an active 0xF9 command appears 3726 in the checkpoint history and MUST contain an independent command log if 3727 an active 0xFD command appears in the checkpoint history. 3729 A Chapter D Undefined System Real-time command log consists of a one- 3730 octet header followed by a variable number of data fields. Header flag 3731 bits indicate the presence of the COUNT field (C = 1) and the LEGAL 3732 field (L = 1). The 5-bit LENGTH field codes the size of the command log 3733 and conforms to semantics described in Appendix A.1. 3735 We now define the default rules for the use of the COUNT and LEGAL 3736 fields. The session configuration tools defined in Appendix C.2.3 may 3737 be used to override this behavior. 3739 The 8-bit COUNT field codes the total number of commands of the type 3740 coded by the log present in the session history, modulo 256. By 3741 default, the COUNT field MUST be present in the command log. 3743 The LEGAL field is reserved for future use. If an update to [MIDI] 3744 defines the 0xF9 or 0xFD command, an IETF standards-track document may 3745 define the LEGAL field to protect the command. Until such a document 3746 appears, senders MUST NOT use the LEGAL field, and receivers MUST use 3747 the LENGTH field to skip over the LEGAL field. The LEGAL field would be 3748 defined by the IETF if the semantics of the new 0xF9 or 0xFD command 3749 could not be protected from packet loss via the use of the COUNT field. 3751 Finally, we note that some non-standard uses of the undefined System 3752 Real-time commands act to implement non-compliant variants of the MIDI 3753 sequencer system. In Appendix B.3.1, we describe resiliency tools for 3754 the MIDI sequencer system that provide some protection in this case. 3756 B.2. System Chapter V: Active Sense Command 3758 The system journal MUST contain Chapter V if an active MIDI Active Sense 3759 (0xFE) command appears in the checkpoint history. Figure B.2.1 shows 3760 the format for Chapter V. 3762 0 3763 0 1 2 3 4 5 6 7 3764 +-+-+-+-+-+-+-+-+ 3765 |S| COUNT | 3766 +-+-+-+-+-+-+-+-+ 3768 Figure B.2.1 -- System Chapter V format 3770 The 7-bit COUNT field codes the total number of Active Sense commands 3771 (modulo 128) present in the session history. The COUNT field acts as a 3772 reference count. See the definition of "session history reference 3773 counts" in Appendix A.1 for more information. 3775 B.3. System Chapter Q: Sequencer State Commands 3777 This appendix describes Chapter Q, the system chapter for the MIDI 3778 sequencer commands. 3780 The system journal MUST contain Chapter Q if an active MIDI Song 3781 Position Pointer (0xF2), MIDI Clock (0xF8), MIDI Start (0xFA), MIDI 3782 Continue (0xFB), or MIDI Stop (0xFC) command appears in the checkpoint 3783 history, and if the rules defined in this appendix require a change in 3784 the Chapter Q bitfield contents because of the command appearance. 3786 Figure B.3.1 shows the variable-length format for Chapter Q. 3788 0 1 2 3 3789 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 3790 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3791 |S|N|D|C|T| TOP | CLOCK | TIMETOOLS ... | 3792 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3793 | ... | 3794 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3796 Figure B.3.1 -- System Chapter Q format 3798 Chapter Q consists of a 1-octet header followed by several optional 3799 fields, in the order shown in Figure B.3.1. 3801 Header flag bits signal the presence of the 16-bit CLOCK field (C = 1) 3802 and the 24-bit TIMETOOLS field (T = 1). The 3-bit TOP header field is 3803 interpreted as an unsigned integer, as are CLOCK and TIMETOOLS. We 3804 describe the TIMETOOLS field in Appendix B.3.1. 3806 Chapter Q encodes the most recent state of the sequencer system. 3807 Receivers use the chapter to re-synchronize the sequencer after a packet 3808 loss episode. Chapter fields encode the on/off state of the sequencer, 3809 the current position in the song, and the downbeat. 3811 The N header bit encodes the relative occurrence of the Start, Stop, and 3812 Continue commands in the session history. If an active Start or 3813 Continue command appears most recently, the N bit MUST be set to 1. If 3814 an active Stop appears most recently, or if no active Start, Stop, or 3815 Continue commands appear in the session history, the N bit MUST be set 3816 to 0. 3818 The C header flag, the TOP header field, and the CLOCK field act to code 3819 the current position in the sequence: 3821 o If C = 1, the 3-bit TOP header field and the 16-bit 3822 CLOCK field are combined to form the 19-bit unsigned quantity 3823 65536*TOP + CLOCK. This value encodes the song position 3824 in units of MIDI Clocks (24 clocks per quarter note), 3825 modulo 524288. Note that the maximum song position value 3826 that may be coded by the Song Position Pointer command is 3827 98303 clocks (which may be coded with 17 bits), and that 3828 MIDI-coded songs are generally constructed to avoid durations 3829 longer than this value. However, the 19-bit size may be useful 3830 for real-time applications, such as a drum machine MIDI output 3831 that is sending clock commands for long periods of time. 3833 o If C = 0, the song position is the start of the song. 3834 The C = 0 position is identical to the position coded 3835 by C = 1, TOP = 0, and CLOCK = 0, for the case where 3836 the song position is less than 524288 MIDI clocks. 3837 In certain situations (defined later in this section), 3838 normative text may require the C = 0 or the C = 1, 3839 TOP = 0, CLOCK = 0 encoding of the start of the song. 3841 The C, TOP, and CLOCK fields MUST be set to code the current song 3842 position, for both N = 0 and N = 1 conditions. If C = 0, the TOP field 3843 MUST be set to 0. See [MIDI] for a precise definition of a song 3844 position. 3846 The D header bit encodes information about the downbeat and acts to 3847 qualify the song position coded by the C, TOP, and CLOCK fields. 3849 If the D bit is set to 1, the song position represents the most recent 3850 position in the sequence that has played. If D = 1, the next Clock 3851 command (if N = 1) or the next (Continue, Clock) pair (if N = 0) acts to 3852 increment the song position by one clock, and to play the updated 3853 position. 3855 If the D bit is set to 0, the song position represents a position in the 3856 sequence that has not yet been played. If D = 0, the next Clock command 3857 (if N = 1) or the next (Continue, Clock) pair (if N = 0) acts to play 3858 the point in the song coded by the song position. The song position is 3859 not incremented. 3861 An example of a stream that uses D = 0 coding is one whose most recent 3862 sequence command is a Start or Song Position Pointer command (both N = 1 3863 conditions). However, it is also possible to construct examples where D 3864 = 0 and N = 0. A Start command immediately followed by a Stop command 3865 is coded in Chapter Q by setting C = 0, D = 0, N = 0, TOP = 0. 3867 If N = 1 (coding Start or Continue), D = 0 (coding that the downbeat has 3868 yet to be played), and the song position is at the start of the song, 3869 the C = 0 song position encoding MUST be used if a Start command occurs 3870 more recently than a Continue command in the session history, and the C 3871 = 1, TOP = 0, CLOCK = 0 song position encoding MUST be used if a 3872 Continue command occurs more recently than a Start command in the 3873 session history. 3875 B.3.1. Non-compliant Sequencers 3877 The Chapter Q description in this appendix assumes that the sequencer 3878 system counts off time with Clock commands, as mandated in [MIDI]. 3879 However, a few non-compliant products do not use Clock commands to count 3880 off time, but instead use non-standard methods. 3882 Chapter Q uses the TIMETOOLS field to provide resiliency support for 3883 these non-standard products. By default, the TIMETOOLS field MUST NOT 3884 appear in Chapter Q, and the T header bit MUST be set to 0. The session 3885 configuration tools described in Appendix C.2.3 may be used to select 3886 TIMETOOLS coding. 3888 Figure B.3.2 shows the format of the 24-bit TIMETOOLS field. 3890 0 1 2 3891 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 3892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3893 | TIME | 3894 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3896 Figure B.3.2 -- TIMETOOLS format 3898 The TIME field is a 24-bit unsigned integer quantity, with units of 3899 milliseconds. TIME codes an additive correction term for the song 3900 position coded by the TOP, CLOCK, and C fields. TIME is coded in 3901 network byte order (big-endian). 3903 A receiver computes the correct song position by converting TIME into 3904 units of MIDI clocks and adding it to 65536*TOP + CLOCK (assuming C = 3905 1). Alternatively, a receiver may convert 65536*TOP + CLOCK into 3906 milliseconds (assuming C = 1) and add it to TIME. The downbeat (D 3907 header bit) semantics defined in Appendix B.3 apply to the corrected 3908 song position. 3910 B.4. System Chapter F: MIDI Time Code Tape Position 3912 This appendix describes Chapter F, the system chapter for the MIDI Time 3913 Code (MTC) commands. Readers may wish to review the Appendix A.1 3914 definition of "finished/unfinished commands" before reading this 3915 appendix. 3917 The system journal MUST contain Chapter F if an active System Common 3918 Quarter Frame command (0xF1) or an active finished System Exclusive 3919 (Universal Real Time) MTC Full Frame command (F0 7F cc 01 01 hr mn sc fr 3920 F7) appears in the checkpoint history. Otherwise, the system journal 3921 MUST NOT contain Chapter F. 3923 Figure B.4.1 shows the variable-length format for Chapter F. 3925 0 1 2 3 3926 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 3927 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3928 |S|C|P|Q|D|POINT| COMPLETE ... | 3929 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3930 | ... | PARTIAL ... | 3931 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3932 | ... | 3933 +-+-+-+-+-+-+-+-+ 3935 Figure B.4.1 -- System Chapter F format 3937 Chapter F holds information about recent MTC tape positions coded in the 3938 session history. Receivers use Chapter F to re-synchronize the MTC 3939 system after a packet loss episode. 3941 Chapter F consists of a 1-octet header followed by several optional 3942 fields, in the order shown in Figure B.4.1. The C and P header bits 3943 form a Table of Contents (TOC) and signal the presence of the 32-bit 3944 COMPLETE field (C = 1) and the 32-bit PARTIAL field (P = 1). 3946 The Q header bit codes information about the COMPLETE field format. If 3947 Chapter F does not contain a COMPLETE field, Q MUST be set to 0. 3949 The D header bit codes the tape movement direction. If the tape is 3950 moving forward, or if the tape direction is indeterminate, the D bit 3951 MUST be set to 0. If the tape is moving in the reverse direction, the D 3952 bit MUST be set to 1. In most cases, the ordering of commands in the 3953 session history clearly defines the tape direction. However, a few 3954 command sequences have an indeterminate direction (such as a session 3955 history consisting of one Full Frame command). 3957 The 3-bit POINT header field is interpreted as an unsigned integer. 3958 Appendix B.4.1 defines how the POINT field codes information about the 3959 contents of the PARTIAL field. If Chapter F does not contain a PARTIAL 3960 field, POINT MUST be set to 7 (if D = 0) or 0 (if D = 1). 3962 Chapter F MUST include the COMPLETE field if an active finished Full 3963 Frame command appears in the checkpoint history, or if an active Quarter 3964 Frame command that completes the encoding of a frame value appears in 3965 the checkpoint history. 3967 The COMPLETE field encodes the most recent active complete MTC frame 3968 value that appears in the session history. This frame value may take 3969 the form of a series of 8 active Quarter Frame commands (0xF1 0x0n 3970 through 0xF1 0x7n for forward tape movement, 0xF1 0x7n through 0xF1 0x0n 3971 for reverse tape movement) or may take the form of an active finished 3972 Full Frame command. 3974 If the COMPLETE field encodes a Quarter Frame command series, the Q 3975 header bit MUST be set to 1, and the COMPLETE field MUST have the format 3976 shown in Figure B.4.2. The 4-bit fields MT0 through MT7 code the data 3977 (lower) nibble for the Quarter Frame commands for Message Type 0 through 3978 Message Type 7 [MIDI]. These nibbles encode a complete frame value, in 3979 addition to fields reserved for future use by [MIDI]. 3981 0 1 2 3 3982 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 3983 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3984 | MT0 | MT1 | MT2 | MT3 | MT4 | MT5 | MT6 | MT7 | 3985 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3987 Figure B.4.2 -- COMPLETE field format, Q = 1 3989 In this usage, the frame value encoded in the COMPLETE field MUST be 3990 offset by 2 frames (relative to the frame value encoded in the Quarter 3991 Frame commands) if the frame value codes a 0xF1 0x0n through 0xF1 0x7n 3992 command sequence. This offset compensates for the two-frame latency of 3993 the Quarter Frame encoding for forward tape movement. No offset is 3994 applied if the frame value codes a 0xF1 0x7n through 0xF1 0x0n Quarter 3995 Frame command sequence. 3997 The most recent active complete MTC frame value may alternatively be 3998 encoded by an active finished Full Frame command. In this case, the Q 3999 header bit MUST be set to 0, and the COMPLETE field MUST have format 4000 shown in Figure B.4.3. The HR, MN, SC, and FR fields correspond to the 4001 hr, mn, sc, and fr data octets of the Full Frame command. 4003 0 1 2 3 4004 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 4005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4006 | HR | MN | SC | FR | 4007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4009 Figure B.4.3 -- COMPLETE field format, Q = 0 4011 B.4.1. Partial Frames 4013 The most recent active session history command that encodes MTC frame 4014 value data may be a Quarter Frame command other than a forward-moving 4015 0xF1 0x7n command (which completes a frame value for forward tape 4016 movement) or a reverse-moving 0xF1 0x1n command (which completes a frame 4017 value for reverse tape movement). 4019 We consider this type of Quarter Frame command to be associated with a 4020 partial frame value. The Quarter Frame sequence that defines a partial 4021 frame value MUST either start at Message Type 0 and increment 4022 contiguously to an intermediate Message Type less than 7, or start at 4023 Message Type 7 and decrement contiguously to an intermediate Message 4024 type greater than 0. A Quarter Frame command sequence that does not 4025 follow this pattern is not associated with a partial frame value. 4027 Chapter F MUST include a PARTIAL field if the most recent active command 4028 in the checkpoint history that encodes MTC frame value data is a Quarter 4029 Frame command that is associated with a partial frame value. Otherwise, 4030 Chapter F MUST NOT include a PARTIAL field. 4032 The partial frame value consists of the data (lower) nibbles of the 4033 Quarter Frame command sequence. The PARTIAL field codes the partial 4034 frame value, using the format shown in Figure B.4.2. Message Type 4035 fields that are not associated with a Quarter Frame command MUST be set 4036 to 0. 4038 The POINT header field identifies the Message Type fields in the PARTIAL 4039 field that code valid data. If P = 1, the POINT field MUST encode the 4040 unsigned integer value formed by the lower 3 bits of the upper nibble of 4041 the data value of the most recent active Quarter Frame command in the 4042 session history. If D = 0 and P = 1, POINT MUST take on a value in the 4043 range 0-6. If D = 1 and P = 1, POINT MUST take on a value in the range 4044 1-7. 4046 If D = 0, MT fields (Figure B.4.2) in the inclusive range from 0 up to 4047 and including the POINT value encode the partial frame value. If D = 1, 4048 MT fields in the inclusive range from 7 down to and including the POINT 4049 value encode the partial frame value. Note that, unlike the COMPLETE 4050 field encoding, senders MUST NOT add a 2-frame offset to the partial 4051 frame value encoded in PARTIAL. 4053 For the default semantics, if a recovery journal contains Chapter F, and 4054 if the session history codes a legal [MIDI] series of Quarter Frame and 4055 Full Frame commands, the chapter always contains a COMPLETE or a PARTIAL 4056 field (and may contain both fields). Thus, a one-octet Chapter F (C = P 4057 = 0) always codes the presence of an illegal command sequence in the 4058 session history (under some conditions, the C = 1, P = 0 condition may 4059 also code the presence of an illegal command sequence). The illegal 4060 command sequence conditions are transient in nature and usually indicate 4061 that a Quarter Frame command sequence began with an intermediate Message 4062 Type. 4064 B.5. System Chapter X: System Exclusive 4066 This appendix describes Chapter X, the system chapter for MIDI System 4067 Exclusive (SysEx) commands (0xF0). Readers may wish to review the 4068 Appendix A.1 definition of "finished/unfinished commands" before reading 4069 this appendix. 4071 Chapter X consists of a list of one or more command logs. Each log in 4072 the list codes information about a specific finished or unfinished SysEx 4073 command that appears in the session history. The system journal MUST 4074 contain Chapter X if the rules defined in Appendix B.5.2 require that 4075 one or more logs appear in the list. 4077 The log list is not preceded by a header. Instead, each log implicitly 4078 encodes its own length. Given the length of the N'th list log, the 4079 presence of the (N+1)'th list log may be inferred from the LENGTH field 4080 of the system journal header (Figure 10 in Section 5 of the main text). 4081 The log list MUST obey the oldest-first ordering rule (defined in 4082 Appendix A.1). 4084 B.5.1. Chapter Format 4086 Figure B.5.1 shows the bitfield format for the Chapter X command logs. 4088 0 1 2 3 4089 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 4090 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4091 |S|T|C|F|D|L|STA| TCOUNT | COUNT | FIRST ... | 4092 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4093 | DATA ... | 4094 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4096 Figure B.5.1 -- Chapter X command log format 4098 A Chapter X command log consists of a 1-octet header, followed by the 4099 optional TCOUNT, COUNT, FIRST, and DATA fields. 4101 The T, C, F, and D header bits act as a Table of Contents (TOC) for the 4102 log. If T is set to 1, the 1-octet TCOUNT field appears in the log. If 4103 C is set to 1, the 1-octet COUNT field appears in the log. If F is set 4104 to 1, the variable-length FIRST field appears in the log. If D is set 4105 to 1, the variable-length DATA field appears in the log. 4107 The L header bit sets the coding tool for the log. We define the log 4108 coding tools in Appendix B.5.2. 4110 The STA field codes the status of the command coded by the log. The 4111 2-bit STA value is interpreted as an unsigned integer. If STA is 0, the 4112 log codes an unfinished command. Non-zero STA values code different 4113 classes of finished commands. An STA value of 1 codes a cancelled 4114 command, an STA value of 2 codes a command that uses the "dropped F7" 4115 construction, and an STA value of 3 codes all other finished commands. 4116 Section 3.2 in the main text describes cancelled and "dropped F7" 4117 commands. 4119 The S bit (Appendix A.1) of the first log in the list acts as the S bit 4120 for Chapter X. For the other logs in the list, the S bit refers to the 4121 log itself. The value of the "phantom" S bit associated with the first 4122 log is defined by the following rules: 4124 o If the list codes one log, the phantom S-bit value is 4125 the same as the Chapter X S-bit value. 4127 o If the list codes multiple logs, the phantom S-bit value is 4128 the logical OR of the S-bit value of the first and second 4129 command logs in the list. 4131 In all other respects, the S bit follows the semantics defined in 4132 Appendix A.1. 4134 The FIRST field (present if F = 1) encodes a variable-length unsigned 4135 integer value that sets the coverage of the DATA field. 4137 The FIRST field (present if F = 1) encodes a variable-length unsigned 4138 integer value that specifies which SysEx data bytes are encoded in the 4139 DATA field of the log. The FIRST field consists of an octet whose most- 4140 significant bit is set to 0, optionally preceded by one or more octets 4141 whose most-significant bit is set to 1. The algorithm shown in Figure 4142 B.5.2 decodes this format into an unsigned integer, to yield the value 4143 dec(FIRST). FIRST uses a variable-length encoding because dec(FIRST) 4144 references a data octet in a SysEx command, and a SysEx command may 4145 contain an arbitrary number of data octets. 4147 One-Octet FIRST value: 4149 Encoded form: 0ddddddd 4150 Decoded form: 00000000 00000000 00000000 0ddddddd 4152 Two-Octet FIRST value: 4154 Encoded form: 1ccccccc 0ddddddd 4155 Decoded form: 00000000 00000000 00cccccc cddddddd 4157 Three-Octet FIRST value: 4159 Encoded form: 1bbbbbbb 1ccccccc 0ddddddd 4160 Decoded form: 00000000 000bbbbb bbcccccc cddddddd 4162 Four-Octet FIRST value: 4164 Encoded form: 1aaaaaaa 1bbbbbbb 1ccccccc 0ddddddd 4165 Decoded form: 0000aaaa aaabbbbb bbcccccc cddddddd 4167 Figure B.5.2 -- Decoding FIRST field formats 4169 The DATA field (present if D = 1) encodes a modified version of the data 4170 octets of the SysEx command coded by the log. Status octets MUST NOT be 4171 coded in the DATA field. 4173 If F = 0, the DATA field begins with the first data octet of the SysEx 4174 command and includes all subsequent data octets for the command that 4175 appear in the session history. If F = 1, the DATA field begins with the 4176 (dec(FIRST) + 1)'th data octet of the SysEx command and includes all 4177 subsequent data octets for the command that appear in the session 4178 history. Note that the word "command" in the descriptions above refers 4179 to the original SysEx command as it appears in the source MIDI data 4180 stream, not to a particular MIDI list SysEx command segment. 4182 The length of the DATA field is coded implicitly, using the most- 4183 significant bit of each octet. The most-significant bit of the final 4184 octet of the DATA field MUST be set to 1. The most-significant bit of 4185 all other DATA octets MUST be set to 0. This coding method relies on 4186 the fact that the most-significant bit of a MIDI data octet is 0 by 4187 definition. Apart from this length-coding modification, the DATA field 4188 encodes a verbatim copy of all data octets it encodes. 4190 B.5.2. Log Inclusion Semantics 4192 Chapter X offers two tools to protect SysEx commands: the "recency" tool 4193 and the "list" tool. The tool definitions use the concept of the "SysEx 4194 type" of a command, which we now define. 4196 Each SysEx command instance in a session, excepting MTC Full Frame 4197 commands, is said to have a "SysEx type". Types are used in equality 4198 comparisons: two SysEx commands in a session are said to have "the same 4199 SysEx type" or "different SysEx types". 4201 If efficiency is not a concern, a sender may follow a simple typing 4202 rule: every SysEx command in the session history has a different SysEx 4203 type, and thus no two commands in the session have the same type. 4205 To improve efficiency, senders MAY implement exceptions to this rule. 4206 These exceptions declare that certain sets of SysEx command instances 4207 have the same SysEx type. Any command not covered by an exception 4208 follows the simple rule. We list exceptions below: 4210 o All commands with identical data octet fields (same number of 4211 data octets, same value for each data octet) have the same type. 4212 This rule MUST be applied to all SysEx commands in the session, 4213 or not at all. Note that the implementation of this exception 4214 requires no sender knowledge of the format and semantics of 4215 the SysEx commands in the stream, merely the ability to count 4216 and compare octets. 4218 o Two instances of the same command whose semantics set or report 4219 the value of the same "parameter" have the same type. The 4220 implementation of this exception requires specific knowledge of 4221 the format and semantics of SysEx commands. In practice, a 4222 sender implementation chooses to support this exception for 4223 certain classes of commands (such as the Universal System 4224 Exclusive commands defined in [MIDI]). If a sender supports 4225 this exception for a particular command in a class (for 4226 example, the Universal Real Time System Exclusive message 4227 for Master Volume, F0 F7 cc 04 01 vv vv F7, defined in [MIDI]), 4228 it MUST support the exception to all instances of this 4229 particular command in the session. 4231 We now use this definition of "SysEx type" to define the "recency" tool 4232 and the "list" tool for Chapter X. 4234 By default, the Chapter X log list MUST code sufficient information to 4235 protect the rendered MIDI performance from indefinite artifacts caused 4236 by the loss of all finished or unfinished active SysEx commands that 4237 appear in the checkpoint history (excluding finished MTC Full Frame 4238 commands, which are coded in Chapter F (Appendix B.4)). 4240 To protect a command of a specific SysEx type with the recency tool, 4241 senders MUST code a log in the log list for the most recent finished 4242 active instance of the SysEx type that appears in the checkpoint 4243 history. Additionally, if an unfinished active instance of the SysEx 4244 type appears in the checkpoint history, senders MUST code a log in the 4245 log list for the unfinished command instance. The L header bit of both 4246 command logs MUST be set to 0. 4248 To protect a command of a specific SysEx type with the list tool, 4249 senders MUST code a log in the Chapter X log list for each finished or 4250 unfinished active instance of the SysEx type that appears in the 4251 checkpoint history. The L header bit of list tool command logs MUST be 4252 set to 1. 4254 As a rule, a log REQUIRED by the list or recency tool MUST include a 4255 DATA field that codes all data octets that appear in the checkpoint 4256 history for the SysEx command instance associated with the log. The 4257 FIRST field MAY be used to configure a DATA field that minimally meets 4258 this requirement. 4260 An exception to this rule applies to cancelled commands (defined in 4261 Section 3.2). REQUIRED command logs associated with cancelled commands 4262 MAY be coded with no DATA field. However, if DATA appears in the log, 4263 DATA MUST code all data octets that appear in the checkpoint history for 4264 the command associated with the log. 4266 As defined by the preceding text in this section, by default all 4267 finished or unfinished active SysEx commands that appear in the 4268 checkpoint history (excluding finished MTC Full Frame commands) MUST be 4269 protected by the list tool or the recency tool. 4271 For some MIDI source streams, this default yields a Chapter X whose size 4272 is too large. For example, imagine that a sender begins to transcode a 4273 SysEx command with 10,000 data octets onto a UDP RTP stream "on the 4274 fly", by sending SysEx command segments as soon as data octets are 4275 delivered by the MIDI source. After 1000 octets have been sent, the 4276 expansion of Chapter X yields an RTP packet that is too large to fit in 4277 the Maximum Transmission Unit (MTU) for the stream. 4279 In this situation, if a sender uses the closed-loop sending policy for 4280 SysEx commands, the RTP packet size may always be capped by stalling the 4281 stream. In a stream stall, once the packet reaches a maximum size, the 4282 sender refrains from sending new packets with non-empty MIDI Command 4283 Sections until receiver feedback permits the trimming of Chapter X. If 4284 the stream permits arbitrary commands to appear between SysEx segments 4285 (selectable during configuration using the tools defined in Appendix 4286 C.1), the sender may stall the SysEx segment stream but continue to code 4287 other commands in the MIDI list. 4289 Stalls are a workable but sub-optimal solution to Chapter X size issues. 4290 As an alternative to stalls, senders SHOULD take preemptive action 4291 during session configuration to reduce the anticipated size of Chapter 4292 X, using the methods described below: 4294 o Partitioned transport. Appendix C.5 provides tools 4295 for sending a MIDI name space over several RTP streams. 4296 Senders may use these tools to map a MIDI source 4297 into a low-latency UDP RTP stream (for channel commands 4298 and short SysEx commands) and a reliable [RFC4571] TCP stream 4299 (for bulk-data SysEx commands). The cm_unused and 4300 cm_used parameters (Appendix C.1) may be used to 4301 communicate the nature of the SysEx command partition. 4302 As TCP is reliable, the RTP MIDI TCP stream would not 4303 use the recovery journal. To minimize transmission 4304 latency for short SysEx commands, senders may begin 4305 segmental transmission for all SysEx commands over the 4306 UDP stream and then cancel the UDP transmission of long 4307 commands (using tools described in Section 3.2) and 4308 resend the commands over the TCP stream. 4310 o Selective protection. Journal protection may not be 4311 necessary for all SysEx commands in a stream. The 4312 ch_never parameter (Appendix C.2) may be used to 4313 communicate which SysEx commands are excluded from 4314 Chapter X. 4316 B.5.3. TCOUNT and COUNT Fields 4318 If the T header bit is set to 1, the 8-bit TCOUNT field appears in the 4319 command log. If the C header bit is set to 1, the 8-bit COUNT field 4320 appears in the command log. TCOUNT and COUNT are interpreted as 4321 unsigned integers. 4323 The TCOUNT field codes the total number of SysEx commands of the SysEx 4324 type coded by the log that appear in the session history, at the moment 4325 after the (finished or unfinished) command coded by the log enters the 4326 session history. 4328 The COUNT field codes the total number of SysEx commands that appear in 4329 the session history, excluding commands that are excluded from Chapter X 4330 via the ch_never parameter (Appendix C.2), at the moment after the 4331 (finished or unfinished) command coded by the log enters the session 4332 history. 4334 Command counting for TCOUNT and COUNT uses modulo-256 arithmetic. MTC 4335 Full Frame command instances (Appendix B.4) are included in command 4336 counting if the TCOUNT and COUNT definitions warrant their inclusion, as 4337 are cancelled commands (Section 3.2). 4339 Senders use the TCOUNT and COUNT fields to track the identity and (for 4340 TCOUNT) the sequence position of a command instance. Senders MUST use 4341 the TCOUNT or COUNT fields if identity or sequence information is 4342 necessary to protect the command type coded by the log. 4344 If a sender uses the COUNT field in a session, the final command log in 4345 every Chapter X in the stream MUST code the COUNT field. This rule lets 4346 receivers resynchronize the COUNT value after a packet loss. 4348 C. Session Configuration Tools 4350 In Sections 6.1-2 of the main text, we show session descriptions for 4351 minimal native and mpeg4-generic RTP MIDI streams. Minimal streams lack 4352 the flexibility to support some applications. In this appendix, we 4353 describe how to customize stream behavior through the use of the payload 4354 format parameters. 4356 The appendix begins with 6 sections, each devoted to parameters that 4357 affect a particular aspect of stream behavior: 4359 o Appendix C.1 describes the stream subsetting system 4360 (cm_unused and cm_used). 4362 o Appendix C.2 describes the journalling system (ch_anchor, 4363 ch_default, ch_never, j_sec, j_update). 4365 o Appendix C.3 describes MIDI command timestamp semantics 4366 (linerate, mperiod, octpos, tsmode). 4368 o Appendix C.4 describes the temporal duration ("media time") 4369 of an RTP MIDI packet (guardtime, rtp_maxptime, rtp_ptime). 4371 o Appendix C.5 concerns stream description (musicport). 4373 o Appendix C.6 describes MIDI rendering (chanmask, cid, 4374 inline, multimode, render, rinit, subrender, smf_cid, 4375 smf_info, smf_inline, smf_url, url). 4377 The parameters listed above may optionally appear in session 4378 descriptions of RTP MIDI streams. If these parameters are used in an 4379 SDP session description, the parameters appear on an fmtp attribute 4380 line. This attribute line applies to the payload type associated with 4381 the fmtp line. 4383 The parameters listed above add extra functionality ("features") to 4384 minimal RTP MIDI streams. In Appendix C.7, we show how to use these 4385 features to support two classes of applications: content-streaming using 4386 RTSP (Appendix C.7.1) and network musical performance using SIP 4387 (Appendix C.7.2). 4389 The participants in a multimedia session MUST share a common view of all 4390 of the RTP MIDI streams that appear in an RTP session, as defined by a 4391 single media (m=) line. In some RTP MIDI applications, the "common 4392 view" restriction makes it difficult to use sendrecv streams (all 4393 parties send and receive), as each party has its own requirements. For 4394 example, a two-party network musical performance application may wish to 4395 customize the renderer on each host to match the CPU performance of the 4396 host [NMP]. 4398 We solve this problem by using two RTP MIDI streams -- one sendonly, one 4399 recvonly -- in lieu of one sendrecv stream. The data flows in the two 4400 streams travel in opposite directions, to control receivers configured 4401 to use different renderers. In the third example in Appendix C.5, we 4402 show how the musicport parameter may be used to define virtual sendrecv 4403 streams. 4405 As a general rule, the RTP MIDI protocol does not handle parameter 4406 changes during a session well, because the parameters describe 4407 heavyweight or stateful configuration that is not easily changed once a 4408 session has begun. Thus, parties SHOULD NOT expect that parameter 4409 change requests during a session will be accepted by other parties. 4410 However, implementors SHOULD support in-session parameter changes that 4411 are easy to handle (for example, the guardtime parameter defined in 4412 Appendix C.4) and SHOULD be capable of accepting requests for changes of 4413 those parameters, as received by its session management protocol (for 4414 example, re-offers in SIP [RFC3264]). 4416 Appendix D defines the Augmented Backus-Naur Form (ABNF, [RFC5234]) 4417 syntax for the payload parameters. Section 11 provides information to 4418 the Internet Assigned Numbers Authority (IANA) on the media types and 4419 parameters defined in this document. 4421 Appendix C.6.5 defines the media type "audio/asc", a stored object for 4422 initializing mpeg4-generic renderers. As described in Appendix C.6, the 4423 audio/asc media type is assigned to the "rinit" parameter to specify an 4424 initialization data object for the default mpeg4-generic renderer. Note 4425 that RTP stream semantics are not defined for "audio/asc". Therefore, 4426 the "asc" subtype MUST NOT appear on the rtpmap line of a session 4427 description. 4429 C.1. Configuration Tools: Stream Subsetting 4431 As defined in Section 3.2 in the main text, the MIDI list of an RTP MIDI 4432 packet may encode any MIDI command that may legally appear on a MIDI 1.0 4433 DIN cable. 4435 In this appendix, we define two parameters (cm_unused and cm_used) that 4436 modify this default condition, by excluding certain types of MIDI 4437 commands from the MIDI list of all packets in a stream. For example, if 4438 a multimedia session partitions a MIDI name space into two RTP MIDI 4439 streams, the parameters may be used to define which commands appear in 4440 each stream. 4442 In this appendix, we define a simple language for specifying MIDI 4443 command types. If a command type is assigned to cm_unused, the commands 4444 coded by the string MUST NOT appear in the MIDI list. If a command type 4445 is assigned to cm_used, the commands coded by the string MAY appear in 4446 the MIDI list. 4448 The parameter list may code multiple assignments to cm_used and 4449 cm_unused. Assignments have a cumulative effect and are applied in the 4450 order of appearance in the parameter list. A later assignment of a 4451 command type to the same parameter expands the scope of the earlier 4452 assignment. A later assignment of a command type to the opposite 4453 parameter cancels (partially or completely) the effect of an earlier 4454 assignment. 4456 To initialize the stream subsetting system, "implicit" assignments to 4457 cm_unused and cm_used are processed before processing the actual 4458 assignments that appear in the parameter list. The System Common 4459 undefined commands (0xF4, 0xF5) and the System Real-Time Undefined 4460 commands (0xF9, 0xFD) are implicitly assigned to cm_unused. All other 4461 command types are implicitly assigned to cm_used. 4463 Note that the implicit assignments code the default behavior of an RTP 4464 MIDI stream as defined in Section 3.2 in the main text (namely, that all 4465 commands that may legally appear on a MIDI 1.0 DIN cable may appear in 4466 the stream). Also note that assignments of the System Common undefined 4467 commands (0xF4, 0xF5) apply to the use of these commands in the MIDI 4468 source command stream, not the special use of 0xF4 and 0xF5 in SysEx 4469 segment encoding defined in Section 3.2 in the main text. 4471 As a rule, parameter assignments obey the following syntax (see Appendix 4472 D for ABNF): 4474 = [channel list][field list] 4476 The command-type list is mandatory; the channel and field lists are 4477 optional. 4479 The command-type list specifies the MIDI command types for which the 4480 parameter applies. The command-type list is a concatenated sequence of 4481 one or more of the letters (ABCFGHJKMNPQTVWXYZ). The letters code the 4482 following command types: 4484 o A: Poly Aftertouch (0xA) 4485 o B: System Reset (0xFF) 4486 o C: Control Change (0xB) 4487 o F: System Time Code (0xF1) 4488 o G: System Tune Request (0xF6) 4489 o H: System Song Select (0xF3) 4490 o J: System Common Undefined (0xF4) 4491 o K: System Common Undefined (0xF5) 4492 o N: NoteOff (0x8), NoteOn (0x9) 4493 o P: Program Change (0xC) 4494 o Q: System Sequencer (0xF2, 0xF8, 0xFA, 0xFB, 0xFC) 4495 o T: Channel Aftertouch (0xD) 4496 o V: System Active Sense (0xFE) 4497 o W: Pitch Wheel (0xE) 4498 o X: SysEx (0xF0, 0xF7) 4499 o Y: System Real-Time Undefined (0xF9) 4500 o Z: System Real-Time Undefined (0xFD) 4502 In addition to the letters above, the letter M may also appear in the 4503 command-type list. The letter M refers to the MIDI parameter system 4504 (see definition in Appendix A.1 and in [MIDI]). An assignment of M to 4505 cm_unused codes that no RPN or NRPN transactions may appear in the MIDI 4506 list. 4508 Note that if cm_unused is assigned the letter M, Control Change (0xB) 4509 commands for the controller numbers in the standard controller 4510 assignment might still appear in the MIDI list. For an explanation, see 4511 Appendix A.3.4 for a discussion of the "general-purpose" use of 4512 parameter system controller numbers. 4514 In the text below, rules that apply to "MIDI voice channel commands" 4515 also apply to the letter M. 4517 The letters in the command-type list MUST be uppercase and MUST appear 4518 in alphabetical order. Letters other than (ABCFGHJKMNPQTVWXYZ) that 4519 appear in the list MUST be ignored. 4521 For MIDI voice channel commands, the channel list specifies the MIDI 4522 channels for which the parameter applies. If no channel list is 4523 provided, the parameter applies to all MIDI channels (0-15). The 4524 channel list takes the form of a list of channel numbers (0 through 15) 4525 and dash-separated channel number ranges (i.e., 0-5, 8-12, etc.). Dots 4526 (i.e., "." characters) separate elements in the channel list. 4528 Recall that System commands do not have a MIDI channel associated with 4529 them. Thus, for most command-type letters that code System commands (B, 4530 F, G, H, J, K, Q, V, Y, and Z), the channel list is ignored. 4532 For the command-type letter X, the appearance of certain numbers in the 4533 channel list codes special semantics. 4535 o The digit 0 codes that SysEx "cancel" sublists (Section 4536 3.2 in the main text) MUST NOT appear in the MIDI list. 4538 o The digit 1 codes that cancel sublists MAY appear in the 4539 MIDI list (the default condition). 4541 o The digit 2 codes that commands other than System 4542 Real-time MIDI commands MUST NOT appear between SysEx 4543 command segments in the MIDI list (the default condition). 4545 o The digit 3 codes that any MIDI command type may 4546 appear between SysEx command segments in the MIDI list, 4547 with the exception of the segmented encoding of a second 4548 SysEx command (verbatim SysEx commands are OK). 4550 For command-type X, the channel list MUST NOT contain both digits 0 and 4551 1, and it MUST NOT contain both digits 2 and 3. For command-type X, 4552 channel list numbers other than the numbers defined above are ignored. 4553 If X does not have a channel list, the semantics marked "the default 4554 condition" in the list above apply. 4556 The syntax for field lists in a parameter assignment follows the syntax 4557 for channel lists. If no field list is provided, the parameter applies 4558 to all controller or note numbers. 4560 For command-type C (Control Change), the field list codes the controller 4561 numbers (0-255) for which the parameter applies. 4563 For command-type M (Parameter System), the field list codes the 4564 Registered Parameter Numbers (RPNs) and Non-Registered Parameter Numbers 4565 (NRPNs) for which the parameter applies. The number range 0-16383 4566 specifies RPNs, the number range 16384-32767 specifies NRPNs (16384 4567 corresponds to NRPN 0, 32767 corresponds to NRPN 16383). 4569 For command-types N (NoteOn and NoteOff) and A (Poly Aftertouch), the 4570 field list codes the note numbers for which the parameter applies. 4572 For command-types J and K (System Common Undefined), the field list 4573 consists of a single digit, which specifies the number of data octets 4574 that follow the command octet. 4576 For command-type X (SysEx), the field list codes the number of data 4577 octets that may appear in a SysEx command. Thus, the field list 0-255 4578 specifies SysEx commands with 255 or fewer data octets, the field list 4579 256-4294967295 specifies SysEx commands with more than 255 data octets 4580 but excludes commands with 255 or fewer data octets, and the field list 4581 0 excludes all commands. 4583 A secondary parameter assignment syntax customizes command-type X (see 4584 Appendix D for complete ABNF): 4586 = "__" *( "_" ) "__" 4588 The assignment defines the class of SysEx commands that obeys the 4589 semantics of the assigned parameter. The command class is specified by 4590 listing the permitted values of the first N data octets that follow the 4591 SysEx 0xF0 command octet. Any SysEx command whose first N data octets 4592 match the list is a member of the class. 4594 Each defines a data octet of the command, as a dot-separated 4595 (".") list of one or more hexadecimal constants (such as "7F") or dash- 4596 separated hexadecimal ranges (such as "01-1F"). Underscores ("_") 4597 separate each . Double-underscores ("__") delineate the data 4598 octet list. 4600 Using this syntax, each assignment specifies a single SysEx command 4601 class. Session descriptions may use several assignments to cm_used and 4602 cm_unused to specify complex behaviors. 4604 The example session description below illustrates the use of the stream 4605 subsetting parameters: 4607 v=0 4608 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 4609 s=Example 4610 t=0 0 4611 m=audio 5004 RTP/AVP 96 4612 c=IN IP6 2001:DB80::7F2E:172A:1E24 4613 a=rtpmap:96 rtp-midi/44100 4614 a=fmtp:96 cm_unused=ACGHJKNMPTVWXYZ; cm_used=__7F_00-7F_01_01__ 4616 The session description configures the stream for use in clock 4617 applications. All voice channels are unused, as are all System Commands 4618 except those used for MIDI Time Code (command-type F, and the Full Frame 4619 SysEx command that is matched by the string assigned to cm_used), the 4620 System Sequencer commands (command-type Q), and System Reset (command- 4621 type B). 4623 C.2. Configuration Tools: The Journalling System 4625 In this appendix, we define the payload format parameters that configure 4626 stream journalling and the recovery journal system. 4628 The j_sec parameter (Appendix C.2.1) sets the journalling method for the 4629 stream. The j_update parameter (Appendix C.2.2) sets the recovery 4630 journal sending policy for the stream. Appendix C.2.2 also defines the 4631 sending policies of the recovery journal system. 4633 Appendix C.2.3 defines several parameters that modify the recovery 4634 journal semantics. These parameters change the default recovery journal 4635 semantics as defined in Section 5 and Appendices A-B. 4637 The journalling method for a stream is set at the start of a session and 4638 MUST NOT be changed thereafter. This requirement forbids changes to the 4639 j_sec parameter once a session has begun. 4641 A related requirement, defined in the appendix sections below, forbids 4642 the acceptance of parameter values that would violate the recovery 4643 journal mandate. In many cases, a change in one of the parameters 4644 defined in this appendix during an ongoing session would result in a 4645 violation of the recovery journal mandate for an implementation; in this 4646 case, the parameter change MUST NOT be accepted. 4648 C.2.1. The j_sec Parameter 4650 Section 2.2 defines the default journalling method for a stream. 4651 Streams that use unreliable transport (such as UDP) default to using the 4652 recovery journal. Streams that use reliable transport (such as TCP) 4653 default to not using a journal. 4655 The parameter j_sec may be used to override this default. This memo 4656 defines two symbolic values for j_sec: "none", to indicate that all 4657 stream payloads MUST NOT contain a journal section, and "recj", to 4658 indicate that all stream payloads MUST contain a journal section that 4659 uses the recovery journal format. 4661 For example, the j_sec parameter might be set to "none" for a UDP stream 4662 that travels between two hosts on a local network that is known to 4663 provide reliable datagram delivery. 4665 The session description below configures a UDP stream that does not use 4666 the recovery journal: 4668 v=0 4669 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 4670 s=Example 4671 t=0 0 4672 m=audio 5004 RTP/AVP 96 4673 c=IN IP4 192.0.2.94 4674 a=rtpmap:96 rtp-midi/44100 4675 a=fmtp:96 j_sec=none 4677 Other IETF standards-track documents may define alternative journal 4678 formats. These documents MUST define new symbolic values for the j_sec 4679 parameter to signal the use of the format. 4681 Parties MUST NOT accept a j_sec value that violates the recovery journal 4682 mandate (see Section 4 for details). If a session description uses a 4683 j_sec value unknown to the recipient, the recipient MUST NOT accept the 4684 description. 4686 Special j_sec issues arise when sessions are managed by session 4687 management tools (like RTSP, [RFC2326]) that use SDP for "declarative 4688 usage" purposes (see the preamble of Section 6 for details). For these 4689 session management tools, SDP does not code transport details (such as 4690 UDP or TCP) for the session. Instead, server and client negotiate 4691 transport details via other means (for RTSP, the SETUP method). 4693 In this scenario, the use of the j_sec parameter may be ill-advised, as 4694 the creator of the session description may not yet know the transport 4695 type for the session. In this case, the session description SHOULD 4696 configure the journalling system using the parameters defined in the 4697 remainder of Appendix C.2, but it SHOULD NOT use j_sec to set the 4698 journalling status. Recall that if j_sec does not appear in the session 4699 description, the default method for choosing the journalling method is 4700 in effect (no journal for reliable transport, recovery journal for 4701 unreliable transport). 4703 However, in declarative usage situations where the creator of the 4704 session description knows that journalling is always required or never 4705 required, the session description SHOULD use the j_sec parameter. 4707 C.2.2. The j_update Parameter 4709 In Section 4, we use the term "sending policy" to describe the method a 4710 sender uses to choose the checkpoint packet identity for each recovery 4711 journal in a stream. In the sub-sections that follow, we normatively 4712 define three sending policies: anchor, closed-loop, and open-loop. 4714 As stated in Section 4, the default sending policy for a stream is the 4715 closed-loop policy. The j_update parameter may be used to override this 4716 default. 4718 We define three symbolic values for j_update: "anchor", to indicate that 4719 the stream uses the anchor sending policy, "open-loop", to indicate that 4720 the stream uses the open-loop sending policy, and "closed-loop", to 4721 indicate that the stream uses the closed-loop sending policy. See 4722 Appendix C.2.3 for examples session descriptions that use the j_update 4723 parameter. 4725 Parties MUST NOT accept a j_update value that violates the recovery 4726 journal mandate (Section 4). 4728 Other IETF standards-track documents may define additional sending 4729 policies for the recovery journal system. These documents MUST define 4730 new symbolic values for the j_update parameter to signal the use of the 4731 new policy. If a session description uses a j_update value unknown to 4732 the recipient, the recipient MUST NOT accept the description. 4734 C.2.2.1. The anchor Sending Policy 4736 In the anchor policy, the sender uses the first packet in the stream as 4737 the checkpoint packet for all packets in the stream. The anchor policy 4738 satisfies the recovery journal mandate (Section 4), as the checkpoint 4739 history always covers the entire stream. 4741 The anchor policy does not require the use of the RTP control protocol 4742 (RTCP, [RFC3550]) or other feedback from receiver to sender. Senders do 4743 not need to take special actions to ensure that received streams start 4744 up free of artifacts, as the recovery journal always covers the entire 4745 history of the stream. Receivers are relieved of the responsibility of 4746 tracking the changing identity of the checkpoint packet, because the 4747 checkpoint packet never changes. 4749 The main drawback of the anchor policy is bandwidth efficiency. Because 4750 the checkpoint history covers the entire stream, the size of the 4751 recovery journals produced by this policy usually exceeds the journal 4752 size of alternative policies. For single-channel MIDI data streams, the 4753 bandwidth overhead of the anchor policy is often acceptable (see 4754 Appendix A.4 of [NMP]). For dense streams, the closed-loop or open-loop 4755 policies may be more appropriate. 4757 C.2.2.2. The closed-loop Sending Policy 4759 The closed-loop policy is the default policy of the recovery journal 4760 system. For each packet in the stream, the policy lets senders choose 4761 the smallest possible checkpoint history that satisfies the recovery 4762 journal mandate. As smaller checkpoint histories generally yield 4763 smaller recovery journals, the closed-loop policy reduces the bandwidth 4764 of a stream, relative to the anchor policy. 4766 The closed-loop policy relies on feedback from receiver to sender. The 4767 policy assumes that a receiver periodically informs the sender of the 4768 highest sequence number it has seen so far in the stream, coded in the 4769 32-bit extension format defined in [RFC3550]. For RTCP, receivers 4770 transmit this information in the Extended Highest Sequence Number 4771 Received (EHSNR) field of Receiver Reports. RTCP Sender or Receiver 4772 Reports MUST be sent by any participant in a session with closed loop 4773 sending policy, unless another feedback mechanism has been agreed upon. 4775 The sender may safely use receiver sequence number feedback to guide 4776 checkpoint history management, because Section 4 requires that receivers 4777 repair indefinite artifacts whenever a packet loss event occur. 4779 We now normatively define the closed-loop policy. At the moment a 4780 sender prepares an RTP packet for transmission, the sender is aware of R 4781 >= 0 receivers for the stream. Senders may become aware of a receiver 4782 via RTCP traffic from the receiver, via RTP packets from a paired stream 4783 sent by the receiver to the sender, via messages from a session 4784 management tool, or by other means. As receivers join and leave a 4785 session, the value of R changes. 4787 Each known receiver k (1 <= k <= R) is associated with a 32-bit extended 4788 packet sequence number M(k), where the extension reflects the sequence 4789 number rollover count of the sender. 4791 If the sender has received at least one feedback report from receiver k, 4792 M(k) is the most recent report of the highest RTP packet sequence number 4793 seen by the receiver, normalized to reflect the rollover count of the 4794 sender. 4796 If the sender has not received a feedback report from the receiver, M(k) 4797 is the extended sequence number of the last packet the sender 4798 transmitted before it became aware of the receiver. If the sender 4799 became aware of this receiver before it sent the first packet in the 4800 stream, M(k) is the extended sequence number of the first packet in the 4801 stream. 4803 Given this definition of M(), we now state the closed-loop policy. When 4804 preparing a new packet for transmission, a sender MUST choose a 4805 checkpoint packet with extended sequence number N, such that M(k) >= (N 4806 - 1) for all k, 1 <= k <= R, where R >= 1. The policy does not restrict 4807 sender behavior in the R == 0 (no known receivers) case. 4809 Under the closed-loop policy as defined above, a sender may transmit 4810 packets whose checkpoint history is shorter than the session history (as 4811 defined in Appendix A.1). In this event, a new receiver that joins the 4812 stream may experience indefinite artifacts. 4814 For example, if a Control Change (0xB) command for Channel Volume 4815 (controller number 7) was sent early in a stream, and later a new 4816 receiver joins the session, the closed-loop policy may permit all 4817 packets sent to the new receiver to use a checkpoint history that does 4818 not include the Channel Volume Control Change command. As a result, the 4819 new receiver experiences an indefinite artifact, and plays all notes on 4820 a channel too loudly or too softly. 4822 To address this issue, the closed-loop policy states that whenever a 4823 sender becomes aware of a new receiver, the sender MUST determine if the 4824 receiver would be subject to indefinite artifacts under the closed-loop 4825 policy. If so, the sender MUST ensure that the receiver starts the 4826 session free of indefinite artifacts. For example, to solve the Channel 4827 Volume issue described above, the sender may code the current state of 4828 the Channel Volume controller numbers in the recovery journal Chapter C, 4829 until it receives the first RTCP RR report that signals that a packet 4830 containing this Chapter C has been received. 4832 In satisfying this requirement, senders MAY infer the initial MIDI state 4833 of the receiver from the session description. For example, the stream 4834 example in Section 6.2 has the initial state defined in [MIDI] for 4835 General MIDI. 4837 In a unicast RTP session, a receiver may safely assume that the sender 4838 is aware of its presence as a receiver from the first packet sent in the 4839 RTP stream. However, in other types of RTP sessions (multicast, 4840 conference focus, RTP translator/mixer), a receiver is often not able to 4841 determine if the sender is initially aware of its presence as a 4842 receiver. 4844 To address this issue, the closed-loop policy states that if a receiver 4845 participates in a session where it may have access to a stream whose 4846 sender is not aware of the receiver, the receiver MUST take actions to 4847 ensure that its rendered MIDI performance does not contain indefinite 4848 artifacts. These protections will be necessarily incomplete. For 4849 example, a receiver may monitor the Checkpoint Packet Seqnum for 4850 uncovered loss events, and "err on the side of caution" with respect to 4851 handling stuck notes due to lost MIDI NoteOff commands, but the receiver 4852 is not able to compensate for the lack of Channel Volume initialization 4853 data in the recovery journal. 4855 The receiver MUST NOT discontinue these protective actions until it is 4856 certain that the sender is aware of its presence. If a receiver is not 4857 able to ascertain sender awareness, the receiver MUST continue these 4858 protective actions for the duration of the session. 4860 Note that in a multicast session where all parties are expected to send 4861 and receive, the reception of RTCP receiver reports from the sender 4862 about the RTP stream a receiver is multicasting back is evidence of the 4863 sender's awareness that the RTP stream multicast by the sender is being 4864 monitored by the receiver. Receivers may also obtain sender awareness 4865 evidence from session management tools, or by other means. In practice, 4866 ongoing observation of the Checkpoint Packet Seqnum to determine if the 4867 sender is taking actions to prevent loss events for a receiver is a good 4868 indication of sender awareness, as is the sudden appearance of recovery 4869 journal chapters with numerous Control Change controller data that was 4870 not foreshadowed by recent commands coded in the MIDI list shortly after 4871 sending an RTCP RR. 4873 The final set of normative closed-loop policy requirements concerns how 4874 senders and receivers handle unplanned disruptions of RTCP feedback from 4875 a receiver to a sender. By "unplanned", we refer to disruptions that 4876 are not due to the signalled termination of an RTP stream, via an RTCP 4877 BYE or via session management tools. 4879 As defined earlier in this section, the closed-loop policy states that a 4880 sender MUST choose a checkpoint packet with extended sequence number N, 4881 such that M(k) >= (N - 1) for all k, 1 <= k <= R, where R >= 1. If the 4882 sender has received at least one feedback report from receiver k, M(k) 4883 is the most recent report of the highest RTP packet sequence number seen 4884 by the receiver, normalized to reflect the rollover count of the sender. 4886 If this receiver k stops sending feedback to the sender, the M(k) value 4887 used by the sender reflects the last feedback report from the receiver. 4888 As time progresses without feedback from receiver k, this fixed M(k) 4889 value forces the sender to increase the size of the checkpoint history, 4890 and thus increases the bandwidth of the stream. 4892 At some point, the sender may need to take action in order to limit the 4893 bandwidth of the stream. In most envisioned uses of RTP MIDI, long 4894 before this point is reached, the SSRC time-out mechanism defined in 4895 [RFC3550] will remove the uncooperative receiver from the session (note 4896 that the closed-loop policy does not suggest or require any special 4897 sender behavior upon an SSRC time-out, other than the sender actions 4898 related to changing R, described earlier in this section). 4900 However, in rare situations, the bandwidth of the stream (due to a lack 4901 of feedback reports from the sender) may become too large to continue 4902 sending the stream to the receiver before the SSRC time-out occurs for 4903 the receiver. In this case, the closed-loop policy states that the 4904 sender should invoke the SSRC time-out for the receiver early. 4906 We now discuss receiver responsibilities in the case of unplanned 4907 disruptions of RTCP feedback from receiver to sender. 4909 In the unicast case, if a sender invokes the SSRC time-out mechanism for 4910 a receiver, the receiver stops receiving packets from the sender. The 4911 sender behavior imposed by the guardtime parameter (Appendix C.4.2) lets 4912 the receiver conclude that an SSRC time-out has occurred in a reasonable 4913 time period. 4915 In this case of a time-out, a receiver MUST keep sending RTCP feedback, 4916 in order to re-establish the RTP flow from the sender. Unless the 4917 receiver expects a prompt recovery of the RTP flow, the receiver MUST 4918 take actions to ensure that the rendered MIDI performance does not 4919 exhibit "very long transient artifacts" (for example, by silencing 4920 NoteOns to prevent stuck notes) while awaiting reconnection of the flow. 4922 In the multicast case, if a sender invokes the SSRC time-out mechanism 4923 for a receiver, the receiver may continue to receive packets, but the 4924 sender will no longer be using the M(k) feedback from the receiver to 4925 choose each checkpoint packet. If the receiver does not have additional 4926 information that precludes an SSRC time-out (such as RTCP Receiver 4927 Reports from the sender about an RTP stream the receiver is multicasting 4928 back to the sender), the receiver MUST monitor the Checkpoint Packet 4929 Seqnum to detect an SSRC time-out. If an SSRC time-out is detected, the 4930 receiver MUST follow the instructions for SSRC time-outs described for 4931 the unicast case above. 4933 Finally, we note that the closed-loop policy is suitable for use in 4934 RTP/RTCP sessions that use multicast transport. However, aspects of the 4935 closed-loop policy do not scale well to sessions with large numbers of 4936 participants. The sender state scales linearly with the number of 4937 receivers, as the sender needs to track the identity and M(k) value for 4938 each receiver k. The average recovery journal size is not independent 4939 of the number of receivers, as the RTCP reporting interval backoff slows 4940 down the rate of a full update of M(k) values. The backoff algorithm 4941 may also increase the amount of ancillary state used by implementations 4942 of the normative sender and receiver behaviors defined in Section 4. 4944 C.2.2.3. The open-loop Sending Policy 4946 The open-loop policy is suitable for sessions that are not able to 4947 implement the receiver-to-sender feedback required by the closed-loop 4948 policy, and that are also not able to use the anchor policy because of 4949 bandwidth constraints. 4951 The open-loop policy does not place constraints on how a sender chooses 4952 the checkpoint packet for each packet in the stream. In the absence of 4953 such constraints, a receiver may find that the recovery journal in the 4954 packet that ends a loss event has a checkpoint history that does not 4955 cover the entire loss event. We refer to loss events of this type as 4956 uncovered loss events. 4958 To ensure that uncovered loss events do not compromise the recovery 4959 journal mandate, the open-loop policy assigns specific recovery tasks to 4960 senders, receivers, and the creators of session descriptions. The 4961 underlying premise of the open-loop policy is that the indefinite 4962 artifacts produced during uncovered loss events fall into two classes. 4964 One class of artifacts is recoverable indefinite artifacts. Receivers 4965 are able to repair recoverable artifacts that occur during an uncovered 4966 loss event without intervention from the sender, at the potential cost 4967 of unpleasant transient artifacts. 4969 For example, after an uncovered loss event, receivers are able to repair 4970 indefinite artifacts due to NoteOff (0x8) commands that may have 4971 occurred during the loss event, by executing NoteOff commands for all 4972 active NoteOns commands. This action causes a transient artifact (a 4973 sudden silent period in the performance), but ensures that no stuck 4974 notes sound indefinitely. We refer to MIDI commands that are amenable 4975 to repair in this fashion as recoverable MIDI commands. 4977 A second class of artifacts is unrecoverable indefinite artifacts. If 4978 this class of artifact occurs during an uncovered loss event, the 4979 receiver is not able to repair the stream. 4981 For example, after an uncovered loss event, receivers are not able to 4982 repair indefinite artifacts due to Control Change (0xB) Channel Volume 4983 (controller number 7) commands that have occurred during the loss event. 4984 A repair is impossible because the receiver has no way of determining 4985 the data value of a lost Channel Volume command. We refer to MIDI 4986 commands that are fragile in this way as unrecoverable MIDI commands. 4988 The open-loop policy does not specify how to partition the MIDI command 4989 set into recoverable and unrecoverable commands. Instead, it assumes 4990 that the creators of the session descriptions are able to come to 4991 agreement on a suitable recoverable/unrecoverable MIDI command partition 4992 for an application. 4994 Given these definitions, we now state the normative requirements for the 4995 open-loop policy. 4997 In the open-loop policy, the creators of the session description MUST 4998 use the ch_anchor parameter (defined in Appendix C.2.3) to protect all 4999 unrecoverable MIDI command types from indefinite artifacts, or 5000 alternatively MUST use the cm_unused parameter (defined in Appendix C.1) 5001 to exclude the command types from the stream. These options act to 5002 shield command types from artifacts during an uncovered loss event. 5004 In the open-loop policy, receivers MUST examine the Checkpoint Packet 5005 Seqnum field of the recovery journal header after every loss event, to 5006 check if the loss event is an uncovered loss event. Section 5 shows how 5007 to perform this check. If an uncovered loss event has occurred, a 5008 receiver MUST perform indefinite artifact recovery for all MIDI command 5009 types that are not shielded by ch_anchor and cm_unused parameter 5010 assignments in the session description. 5012 The open-loop policy does not place specific constraints on the sender. 5013 However, the open-loop policy works best if the sender manages the size 5014 of the checkpoint history to ensure that uncovered losses occur 5015 infrequently, by taking into account the delay and loss characteristics 5016 of the network. Also, as each checkpoint packet change incurs the risk 5017 of an uncovered loss, senders should only move the checkpoint if it 5018 reduces the size of the journal. 5020 C.2.3. Recovery Journal Chapter Inclusion Parameters 5022 The recovery journal chapter definitions (Appendices A-B) specify under 5023 what conditions a chapter MUST appear in the recovery journal. In most 5024 cases, the definition states that if a certain command appears in the 5025 checkpoint history, a certain chapter type MUST appear in the recovery 5026 journal to protect the command. 5028 In this section, we describe the chapter inclusion parameters. These 5029 parameters modify the conditions under which a chapter appears in the 5030 journal. These parameters are essential to the use of the open-loop 5031 policy (Appendix C.2.2.3) and may also be used to simplify 5032 implementations of the closed-loop (Appendix C.2.2.2) and anchor 5033 (Appendix C.2.2.1) policies. 5035 Each parameter represents a type of chapter inclusion semantics. An 5036 assignment to a parameter declares which chapters (or chapter subsets) 5037 obey the inclusion semantics. We describe the assignment syntax for 5038 these parameters later in this section. 5040 A party MUST NOT accept chapter inclusion parameter values that violate 5041 the recovery journal mandate (Section 4). All assignments of the 5042 subsetting parameters (cm_used and cm_unused) MUST precede the first 5043 assignment of a chapter inclusion parameter in the parameter list. 5045 Below, we normatively define the semantics of the chapter inclusion 5046 parameters. For clarity, we define the action of parameters on complete 5047 chapters. If a parameter is assigned a subset of a chapter, the 5048 definition applies only to the chapter subset. 5050 o ch_never. A chapter assigned to the ch_never parameter MUST 5051 NOT appear in the recovery journal (Appendix A.4.1-2 defines 5052 exceptions to this rule for Chapter M). To signal the exclusion 5053 of a chapter from the journal, an assignment to ch_never MUST 5054 be made, even if the commands coded by the chapter are assigned 5055 to cm_unused. This rule simplifies the handling of commands 5056 types that may be coded in several chapters. 5058 o ch_default. A chapter assigned to the ch_default parameter 5059 MUST follow the default semantics for the chapter, as defined 5060 in Appendices A-B. 5062 o ch_anchor. A chapter assigned to the ch_anchor MUST obey a 5063 modified version of the default chapter semantics. In the 5064 modified semantics, all references to the checkpoint history 5065 are replaced with references to the session history, and all 5066 references to the checkpoint packet are replaced with 5067 references to the first packet sent in the stream. 5069 Parameter assignments obey the following syntax (see Appendix D for 5070 ABNF): 5072 = [channel list][field list] 5074 The chapter list is mandatory; the channel and field lists are optional. 5075 Multiple assignments to parameters have a cumulative effect and are 5076 applied in the order of parameter appearance in a media description. 5078 To determine the semantics of a list of chapter inclusion parameter 5079 assignments, we begin by assuming an implicit assignment of all channel 5080 and system chapters to the ch_default parameter, with the default values 5081 for the channel list and field list for each chapter that are defined 5082 below. 5084 We then interpret the semantics of the actual parameter assignments, 5085 using the rules below. 5087 A later assignment of a chapter to the same parameter expands the scope 5088 of the earlier assignment. In most cases, a later assignment of a 5089 chapter to a different parameter cancels (partially or completely) the 5090 effect of an earlier assignment. 5092 The chapter list specifies the channel or system chapters for which the 5093 parameter applies. The chapter list is a concatenated sequence of one 5094 or more of the letters corresponding to the chapter types 5095 (ACDEFMNPQTVWX). In addition, the list may contain one or more of the 5096 letters for the sub-chapter types (BGHJKYZ) of System Chapter D. 5098 The letters in a chapter list MUST be uppercase and MUST appear in 5099 alphabetical order. Letters other than (ABCDEFGHJKMNPQTVWXYZ) that 5100 appear in the chapter list MUST be ignored. 5102 The channel list specifies the channel journals for which this parameter 5103 applies; if no channel list is provided, the parameter applies to all 5104 channel journals. The channel list takes the form of a list of channel 5105 numbers (0 through 15) and dash-separated channel number ranges (i.e., 5106 0-5, 8-12, etc.). Dots (i.e., "." characters) separate elements in the 5107 channel list. 5109 Several of the systems chapters may be configured to have special 5110 semantics. Configuration occurs by specifying a channel list for the 5111 systems channel, using the coding described below (note that MIDI 5112 Systems commands do not have a "channel", and thus the original purpose 5113 of the channel list does not apply to systems chapters). The expression 5114 "the digit N" in the text below refers to the inclusion of N as a 5115 "channel" in the channel list for a systems chapter. 5117 For the J and K Chapter D sub-chapters (undefined System Common), the 5118 digit 0 codes that the parameter applies to the LEGAL field of the 5119 associated command log (Figure B.1.4 of Appendix B.1), the digit 1 codes 5120 that the parameter applies to the VALUE field of the command log, and 5121 the digit 2 codes that the parameter applies to the COUNT field of the 5122 command log. 5124 For the Y and Z Chapter D sub-chapters (undefined System Real-time), the 5125 digit 0 codes that the parameter applies to the LEGAL field of the 5126 associated command log (Figure B.1.5 of Appendix B.1) and the digit 1 5127 codes that the parameter applies to the COUNT field of the command log. 5129 For Chapter Q (Sequencer State Commands), the digit 0 codes that the 5130 parameter applies to the default Chapter Q definition, which forbids the 5131 TIME field. The digit 1 codes that the parameter applies to the 5132 optional Chapter Q definition, which supports the TIME field. 5134 The syntax for field lists follows the syntax for channel lists. If no 5135 field list is provided, the parameter applies to all controller or note 5136 numbers. For Chapter C, if no field list is provided, the controller 5137 numbers do not use enhanced Chapter C encoding (Appendix A.3.3). 5139 For Chapter C, the field list may take on values in the range 0 to 255. 5140 A field value X in the range 0-127 refers to a controller number X, and 5141 indicates that the controller number does not use enhanced Chapter C 5142 encoding. A field value X in the range 128-255 refers to a controller 5143 number "X minus 128" and indicates the controller number does use the 5144 enhanced Chapter C encoding. 5146 Assignments made to configure the Chapter C encoding method for a 5147 controller number MUST be made to the ch_default or ch_anchor 5148 parameters, as assignments to ch_never act to exclude the number from 5149 the recovery journal (and thus the indicated encoding method is 5150 irrelevant). 5152 A Chapter C field list MUST NOT encode conflicting information about the 5153 enhanced encoding status of a particular controller number. For 5154 example, values 0 and 128 MUST NOT both be coded by a field list. 5156 For Chapter M, the field list codes the Registered Parameter Numbers 5157 (RPNs) and Non-Registered Parameter Numbers (NRPNs) for which the 5158 parameter applies. The number range 0-16383 specifies RPNs, the number 5159 range 16384-32767 specifies NRPNs (16384 corresponds to NRPN 0, 32767 5160 corresponds to NRPN 16383). 5162 For Chapters N and A, the field list codes the note numbers for which 5163 the parameter applies. The note number range specified for Chapter N 5164 also applies to Chapter E. 5166 For Chapter E, the digit 0 codes that the parameter applies to Chapter E 5167 note logs whose V bit is set to 0, and the digit 1 codes that the 5168 parameter applies to note logs whose V bit is set to 1. 5170 For Chapter X, the field list codes the number of data octets that may 5171 appear in a SysEx command that is coded in the chapter. Thus, the field 5172 list 0-255 specifies SysEx commands with 255 or fewer data octets, the 5173 field list 256-4294967295 specifies SysEx commands with more than 255 5174 data octets but excludes commands with 255 or fewer data octets, and the 5175 field list 0 excludes all commands. 5177 A secondary parameter assignment syntax customizes Chapter X (see 5178 Appendix D for complete ABNF): 5180 = "__" *( "_" ) "__" 5182 The assignment defines a class of SysEx commands whose Chapter X coding 5183 obeys the semantics of the assigned parameter. The command class is 5184 specified by listing the permitted values of the first N data octets 5185 that follow the SysEx 0xF0 command octet. Any SysEx command whose first 5186 N data octets match the list is a member of the class. 5188 Each defines a data octet of the command, as a dot-separated 5189 (".") list of one or more hexadecimal constants (such as "7F") or dash- 5190 separated hexadecimal ranges (such as "01-1F"). Underscores ("_") 5191 separate each . Double-underscores ("__") delineate the data 5192 octet list. 5194 Using this syntax, each assignment specifies a single SysEx command 5195 class. Session descriptions may use several assignments to the same (or 5196 different) parameters to specify complex Chapter X behaviors. The 5197 ordering behavior of multiple assignments follows the guidelines for 5198 chapter parameter assignments described earlier in this section. 5200 The example session description below illustrates the use of the chapter 5201 inclusion parameters: 5203 v=0 5204 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5205 s=Example 5206 t=0 0 5207 m=audio 5004 RTP/AVP 96 5208 c=IN IP6 2001:DB80::7F2E:172A:1E24 5209 a=rtpmap:96 rtp-midi/44100 5210 a=fmtp:96 j_update=open-loop; cm_unused=ABCFGHJKMQTVWXYZ; 5211 cm_used=__7E_00-7F_09_01.02.03__; 5212 cm_used=__7F_00-7F_04_01.02__; cm_used=C7.64; 5213 ch_never=ABCDEFGHJKMQTVWXYZ; ch_never=4.11-13N; 5214 ch_anchor=P; ch_anchor=C7.64; 5215 ch_anchor=__7E_00-7F_09_01.02.03__; 5216 ch_anchor=__7F_00-7F_04_01.02__ 5218 (The a=fmtp line has been wrapped to fit the page to accommodate 5219 memo formatting restrictions; it comprises a single line in SDP.) 5221 The j_update parameter codes that the stream uses the open-loop policy. 5222 Most MIDI command-types are assigned to cm_unused and thus do not appear 5223 in the stream. As a consequence, the assignments to the first ch_never 5224 parameter reflect that most chapters are not in use. 5226 Chapter N for several MIDI channels is assigned to ch_never. Chapter N 5227 for MIDI channels other than 4, 11, 12, and 13 may appear in the 5228 recovery journal, using the (default) ch_default semantics. In 5229 practice, this assignment pattern would reflect knowledge about a 5230 resilient rendering method in use for the excluded channels. 5232 The MIDI Program Change command and several MIDI Control Change 5233 controller numbers are assigned to ch_anchor. Note that the ordering of 5234 the ch_anchor chapter C assignment after the ch_never command acts to 5235 override the ch_never assignment for the listed controller numbers (7 5236 and 64). 5238 The assignment of command-type X to cm_unused excludes most SysEx 5239 commands from the stream. Exceptions are made for General MIDI System 5240 On/Off commands and for the Master Volume and Balance commands, via the 5241 use of the secondary assignment syntax. The cm_used assignment codes 5242 the exception, and the ch_anchor assignment codes how these commands are 5243 protected in Chapter X. 5245 C.3. Configuration Tools: Timestamp Semantics 5247 The MIDI command section of the payload format consists of a list of 5248 commands, each with an associated timestamp. The semantics of command 5249 timestamps may be set during session configuration, using the parameters 5250 we describe in this section 5252 The parameter "tsmode" specifies the timestamp semantics for a stream. 5253 The parameter takes on one of three token values: "comex", "async", or 5254 "buffer". 5256 The default "comex" value specifies that timestamps code the execution 5257 time for a command (Appendix C.3.1) and supports the accurate 5258 transcoding of Standard MIDI Files (SMFs, [MIDI]). The "comex" value is 5259 also RECOMMENDED for new MIDI user-interface controller designs. The 5260 "async" value specifies an asynchronous timestamp sampling algorithm for 5261 time-of-arrival sources (Appendix C.3.2). The "buffer" value specifies 5262 a synchronous timestamp sampling algorithm (Appendix C.3.3) for time-of- 5263 arrival sources. 5265 Ancillary parameters MAY follow tsmode in a media description. We 5266 define these parameters in Appendices C.3.2-3 below. 5268 C.3.1. The comex Algorithm 5270 The default "comex" (COMmand EXecution) tsmode value specifies the 5271 execution time for the command. With comex, the difference between two 5272 timestamps indicates the time delay between the execution of the 5273 commands. This difference may be zero, coding simultaneous execution. 5275 The comex interpretation of timestamps works well for transcoding a 5276 Standard MIDI File (SMF, [MIDI]) into an RTP MIDI stream, as SMFs code a 5277 timestamp for each MIDI command stored in the file. To transcode an SMF 5278 that uses metric time markers, use the SMF tempo map (encoded in the SMF 5279 as meta-events) to convert metric SMF timestamp units into seconds-based 5280 RTP timestamp units. 5282 New MIDI controller designs (piano keyboard, drum pads, etc.) that 5283 support RTP MIDI and that have direct access to sensor data SHOULD use 5284 comex interpretation for timestamps, so that simultaneous gestural 5285 events may be accurately coded by RTP MIDI. 5287 Comex is a poor choice for transcoding MIDI 1.0 DIN cables [MIDI], for a 5288 reason that we will now explain. A MIDI DIN cable is an asynchronous 5289 serial protocol (320 microseconds per MIDI byte). MIDI commands on a 5290 DIN cable are not tagged with timestamps. Instead, MIDI DIN receivers 5291 infer command timing from the time of arrival of the bytes. Thus, two 5292 two-byte MIDI commands that occur at a source simultaneously are encoded 5293 on a MIDI 1.0 DIN cable with a 640 microsecond time offset. A MIDI DIN 5294 receiver is unable to tell if this time offset existed in the source 5295 performance or is an artifact of the serial speed of the cable. 5296 However, the RTP MIDI comex interpretation of timestamps declares that a 5297 timestamp offset between two commands reflects the timing of the source 5298 performance. 5300 This semantic mismatch is the reason that comex is a poor choice for 5301 transcoding MIDI DIN cables. Note that the choice of the RTP timestamp 5302 rate (Section 6.1-2 in the main text) cannot fix this inaccuracy issue. 5303 In the sections that follow, we describe two alternative timestamp 5304 interpretations ("async" and "buffer") that are a better match to MIDI 5305 1.0 DIN cable timing, and to other MIDI time-of-arrival sources. 5307 The "octpos", "linerate", and "mperiod" ancillary parameters (defined 5308 below) SHOULD NOT be used with comex. 5310 C.3.2. The async Algorithm 5312 The "async" tsmode value specifies the asynchronous sampling of a MIDI 5313 time-of-arrival source. In asynchronous sampling, the moment an octet 5314 is received from a source, it is labelled with a wall-clock time value. 5315 The time value has RTP timestamp units. 5317 The "octpos" ancillary parameter defines how RTP command timestamps are 5318 derived from octet time values. If octpos has the token value "first", 5319 a timestamp codes the time value of the first octet of the command. If 5320 octpos has the token value "last", a timestamp codes the time value of 5321 the last octet of the command. If the octpos parameter does not appear 5322 in the media description, the sender does not know which octet of the 5323 command the timestamp references (for example, the sender may be relying 5324 on an operating system service that does not specify this information). 5326 The octpos semantics refer to the first or last octet of a command as it 5327 appears on a time-of-arrival MIDI source, not as it appears in an RTP 5328 MIDI packet. This distinction is significant because the RTP coding may 5329 contain octets that are not present in the source. For example, the 5330 status octet of the first MIDI command in a packet may have been added 5331 to the MIDI stream during transcoding, to comply with the RTP MIDI 5332 running status requirements (Section 3.2). 5334 The "linerate" ancillary parameter defines the timespan of one MIDI 5335 octet on the transmission medium of the MIDI source to be sampled (such 5336 as a MIDI 1.0 DIN cable). The parameter has units of nanoseconds, and 5337 takes on integral values. For MIDI 1.0 DIN cables, the correct linerate 5338 value is 320000 (this value is also the default value for the 5339 parameter). 5341 We now show a session description example for the async algorithm. 5342 Consider a sender that is transcoding a MIDI 1.0 DIN cable source into 5343 RTP. The sender runs on a computing platform that assigns time values 5344 to every incoming octet of the source, and the sender uses the time 5345 values to label the first octet of each command in the RTP packet. This 5346 session description describes the transcoding: 5348 v=0 5349 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5350 s=Example 5351 t=0 0 5352 m=audio 5004 RTP/AVP 96 5353 c=IN IP4 192.0.2.94 5354 a=rtpmap:96 rtp-midi/44100 5355 a=sendonly 5356 a=fmtp:96 tsmode=async; linerate=320000; octpos=first 5358 C.3.3. The buffer Algorithm 5360 The "buffer" tsmode value specifies the synchronous sampling of a MIDI 5361 time-of-arrival source. 5363 In synchronous sampling, octets received from a source are placed in a 5364 holding buffer upon arrival. At periodic intervals, the RTP sender 5365 examines the buffer. The sender removes complete commands from the 5366 buffer and codes those commands in an RTP packet. The command timestamp 5367 codes the moment of buffer examination, expressed in RTP timestamp 5368 units. Note that several commands may have the same timestamp value. 5370 The "mperiod" ancillary parameter defines the nominal periodic sampling 5371 interval. The parameter takes on positive integral values and has RTP 5372 timestamp units. 5374 The "octpos" ancillary parameter, defined in Appendix C.3.1 for 5375 asynchronous sampling, plays a different role in synchronous sampling. 5376 In synchronous sampling, the parameter specifies the timestamp semantics 5377 of a command whose octets span several sampling periods. 5379 If octpos has the token value "first", the timestamp reflects the 5380 arrival period of the first octet of the command. If octpos has the 5381 token value "last", the timestamp reflects the arrival period of the 5382 last octet of the command. The octpos semantics refer to the first or 5383 last octet of the command as it appears on a time-of-arrival source, not 5384 as it appears in the RTP packet. 5386 If the octpos parameter does not appear in the media description, the 5387 timestamp MAY reflect the arrival period of any octet of the command; 5388 senders use this option to signal a lack of knowledge about the timing 5389 details of the buffering process at sub-command granularity. 5391 We now show a session description example for the buffer algorithm. 5392 Consider a sender that is transcoding a MIDI 1.0 DIN cable source into 5393 RTP. The sender runs on a computing platform that places source data 5394 into a buffer upon receipt. The sender polls the buffer 1000 times a 5395 second, extracts all complete commands from the buffer, and places the 5396 commands in an RTP packet. This session description describes the 5397 transcoding: 5399 v=0 5400 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5401 s=Example 5402 t=0 0 5403 m=audio 5004 RTP/AVP 96 5404 c=IN IP6 2001:DB80::7F2E:172A:1E24 5405 a=rtpmap:96 rtp-midi/44100 5406 a=sendonly 5407 a=fmtp:96 tsmode=buffer; linerate=320000; octpos=last; mperiod=44 5409 The mperiod value of 44 is derived by dividing the clock rate specified 5410 by the rtpmap attribute (44100 Hz) by the 1000 Hz buffer sampling rate 5411 and rounding to the nearest integer. Command timestamps might not 5412 increment by exact multiples of 44, as the actual sampling period might 5413 not precisely match the nominal mperiod value. 5415 C.4. Configuration Tools: Packet Timing Tools 5417 In this appendix, we describe session configuration tools for 5418 customizing the temporal behavior of MIDI stream packets. 5420 C.4.1. Packet Duration Tools 5422 Senders control the granularity of a stream by setting the temporal 5423 duration ("media time") of the packets in the stream. Short media times 5424 (20 ms or less) often imply an interactive session. Longer media times 5425 (100 ms or more) usually indicate a content streaming session. The RTP 5426 AVP profile [RFC3551] recommends audio packet media times in a range 5427 from 0 to 200 ms. 5429 By default, an RTP receiver dynamically senses the media time of packets 5430 in a stream and chooses the length of its playout buffer to match the 5431 stream. A receiver typically sizes its playout buffer to fit several 5432 audio packets and adjusts the buffer length to reflect the network 5433 jitter and the sender timing fidelity. 5435 Alternatively, the packet media time may be statically set during 5436 session configuration. Session descriptions MAY use the RTP MIDI 5437 parameter "rtp_ptime" to set the recommended media time for a packet. 5438 Session descriptions MAY also use the RTP MIDI parameter "rtp_maxptime" 5439 to set the maximum media time for a packet permitted in a stream. Both 5440 parameters MAY be used together to configure a stream. 5442 The values assigned to the rtp_ptime and rtp_maxptime parameters have 5443 the units of the RTP timestamp for the stream, as set by the rtpmap 5444 attribute (see Section 6.1). Thus, if rtpmap sets the clock rate of a 5445 stream to 44100 Hz, a maximum packet media time of 10 ms is coded by 5446 setting rtp_maxptime=441. As stated in the Appendix C preamble, the 5447 senders and receivers of a stream MUST agree on common values for 5448 rtp_ptime and rtp_maxptime if the parameters appear in the media 5449 description for the stream. 5451 0 ms is a reasonable media time value for MIDI packets and is often used 5452 in low-latency interactive applications. In a packet with a 0 ms media 5453 time, all commands execute at the instant they are coded by the packet 5454 timestamp. The session description below configures all packets in the 5455 stream to have 0 ms media time: 5457 v=0 5458 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5459 s=Example 5460 t=0 0 5461 m=audio 5004 RTP/AVP 96 5462 c=IN IP4 192.0.2.94 5463 a=rtpmap:96 rtp-midi/44100 5464 a=fmtp:96 rtp_ptime=0; rtp_maxptime=0 5466 The session attributes ptime and maxptime [RFC4566] MUST NOT be used to 5467 configure an RTP MIDI stream. Sessions MUST use rtp_ptime in lieu of 5468 ptime and MUST use rtp_maxptime in lieu of maxptime. RTP MIDI defines 5469 its own parameters for media time configuration because 0 ms values for 5470 ptime and maxptime are forbidden by [RFC3264] but are essential for 5471 certain applications of RTP MIDI. 5473 See the Appendix C.7 examples for additional discussion about using 5474 rtp_ptime and rtp_maxptime for session configuration. 5476 C.4.2. The guardtime Parameter 5478 RTP permits a sender to stop sending audio packets for an arbitrary 5479 period of time during a session. When sending resumes, the RTP sequence 5480 number series continues unbroken, and the RTP timestamp value reflects 5481 the media time silence gap. 5483 This RTP feature has its roots in telephony, but it is also well matched 5484 to interactive MIDI sessions, as players may fall silent for several 5485 seconds during (or between) songs. 5487 Certain MIDI applications benefit from a slight enhancement to this RTP 5488 feature. In interactive applications, receivers may use on-line network 5489 models to guide heuristics for handling lost and late RTP packets. 5490 These models may work poorly if a sender ceases packet transmission for 5491 long periods of time. 5493 Session descriptions may use the parameter "guardtime" to set a minimum 5494 sending rate for a media session. The value assigned to guardtime codes 5495 the maximum separation time between two sequential packets, as expressed 5496 in RTP timestamp units. 5498 Typical guardtime values are 500-2000 ms. This value range is not a 5499 normative bound, and parties SHOULD be prepared to process values 5500 outside this range. 5502 The congestion control requirements for sender implementations 5503 (described in Section 8 and [RFC3550]) take precedence over the 5504 guardtime parameter. Thus, if the guardtime parameter requests a 5505 minimum sending rate, but sending at this rate would violate the 5506 congestion control requirements, senders MUST ignore the guardtime 5507 parameter value. In this case, senders SHOULD use the lowest minimum 5508 sending rate that satisfies the congestion control requirements. 5510 Below, we show a session description that uses the guardtime parameter. 5512 v=0 5513 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5514 s=Example 5515 t=0 0 5516 m=audio 5004 RTP/AVP 96 5517 c=IN IP6 2001:DB80::7F2E:172A:1E24 5518 a=rtpmap:96 rtp-midi/44100 5519 a=fmtp:96 guardtime=44100; rtp_ptime=0; rtp_maxptime=0 5520 C.5. Configuration Tools: Stream Description 5522 As we discussed in Section 2.1, a party may send several RTP MIDI 5523 streams in the same RTP session, and several RTP sessions that carry 5524 MIDI may appear in a multimedia session. 5526 By default, the MIDI name space (16 channels + systems) of each RTP 5527 stream sent by a party in a multimedia session is independent. By 5528 independent, we mean three distinct things: 5530 o If a party sends two RTP MIDI streams (A and B), MIDI voice 5531 channel 0 in stream A is a different "channel 0" than MIDI 5532 voice channel 0 in stream B. 5534 o MIDI voice channel 0 in stream B is not considered to be 5535 "channel 16" of a 32-channel MIDI voice channel space whose 5536 "channel 0" is channel 0 of stream A. 5538 o Streams sent by different parties over different RTP sessions, 5539 or over the same RTP session but with different payload type 5540 numbers, do not share the association that is shared by a MIDI 5541 cable pair that cross-connects two devices in a MIDI 1.0 DIN 5542 network. By default, this association is only held by streams 5543 sent by different parties in the same RTP session that use the 5544 same payload type number. 5546 In this appendix, we show how to express that specific RTP MIDI streams 5547 in a multimedia session are not independent but instead are related in 5548 one of the three ways defined above. We use two tools to express these 5549 relations: 5551 o The musicport parameter. This parameter is assigned a 5552 non-negative integer value between 0 and 4294967295. It 5553 appears in the fmtp lines of payload types. 5555 o The FID grouping attribute [RFC3388] signals that several RTP 5556 sessions in a multimedia session are using the musicport 5557 parameter to express an inter-session relationship. 5559 If a multimedia session has several payload types whose musicport 5560 parameters are assigned the same integer value, streams using these 5561 payload types share an "identity relationship" (including streams that 5562 use the same payload type). Streams in an identity relationship share 5563 two properties: 5565 o Identity relationship streams sent by the same party 5566 target the same MIDI name space. Thus, if streams A 5567 and B share an identity relationship, voice channel 0 5568 in stream A is the same "channel 0" as voice channel 5569 0 in stream B. 5571 o Pairs of identity relationship streams that are sent by 5572 different parties share the association that is shared 5573 by a MIDI cable pair that cross-connects two devices in 5574 a MIDI 1.0 DIN network. 5576 A party MUST NOT send two RTP MIDI streams that share an identity 5577 relationship in the same RTP session. Instead, each stream MUST be in a 5578 separate RTP session. As explained in Section 2.1, this restriction is 5579 necessary to support the RTP MIDI method for the synchronization of 5580 streams that share a MIDI name space. 5582 If a multimedia session has several payload types whose musicport 5583 parameters are assigned sequential values (i.e., i, i+1, ... i+k), the 5584 streams using the payload types share an "ordered relationship". For 5585 example, if payload type A assigns 2 to musicport and payload type B 5586 assigns 3 to musicport, A and B are in an ordered relationship. 5588 Streams in an ordered relationship that are sent by the same party are 5589 considered by renderers to form a single larger MIDI space. For 5590 example, if stream A has a musicport value of 2 and stream B has a 5591 musicport value of 3, MIDI voice channel 0 in stream B is considered to 5592 be voice channel 16 in the larger MIDI space formed by the relationship. 5593 Note that it is possible for streams to participate in both an identity 5594 relationship and an ordered relationship. 5596 We now state several rules for using musicport: 5598 o If streams from several RTP sessions in a multimedia 5599 session use the musicport parameter, the RTP sessions 5600 MUST be grouped using the FID grouping attribute 5601 defined in [RFC3388]. 5603 o An ordered or identity relationship MUST NOT 5604 contain both native RTP MIDI streams and 5605 mpeg4-generic RTP MIDI streams. An exception applies 5606 if a relationship consists of sendonly and recvonly 5607 (but not sendrecv) streams. In this case, the sendonly 5608 streams MUST NOT contain both types of streams, and the 5609 recvonly streams MUST NOT contain both types of streams. 5611 o It is possible to construct identity relationships 5612 that violate the recovery journal mandate (for example, 5613 sending NoteOns for a voice channel on stream A and 5614 NoteOffs for the same voice channel on stream B). 5615 Parties MUST NOT generate (or accept) session 5616 descriptions that exhibit this flaw. 5618 o Other payload formats MAY define musicport media type 5619 parameters. Formats would define these parameters so that 5620 their sessions could be bundled into RTP MIDI name spaces. 5621 The parameter definitions MUST be compatible with the 5622 musicport semantics defined in this appendix. 5624 As a rule, at most one payload type in a relationship may specify a MIDI 5625 renderer. An exception to the rule applies to relationships that 5626 contain sendonly and recvonly streams but no sendrecv streams. In this 5627 case, one sendonly session and one recvonly session may each define a 5628 renderer. 5630 Renderer specification in a relationship may be done using the tools 5631 described in Appendix C.6. These tools work for both native streams and 5632 mpeg4-generic streams. An mpeg4-generic stream that uses the Appendix 5633 C.6 tools MUST set all "config" parameters to the empty string (""). 5635 Alternatively, for mpeg4-generic streams, renderer specification may be 5636 done by setting one "config" parameter in the relationship to the 5637 renderer configuration string, and all other config parameters to the 5638 empty string (""). 5640 We now define sender and receiver rules that apply when a party sends 5641 several streams that target the same MIDI name space. 5643 Senders MAY use the subsetting parameters (Appendix C.1) to predefine 5644 the partitioning of commands between streams, or they MAY use a dynamic 5645 partitioning strategy. 5647 Receivers that merge identity relationship streams into a single MIDI 5648 command stream MUST maintain the structural integrity of the MIDI 5649 commands coded in each stream during the merging process, in the same 5650 way that software that merges traditional MIDI 1.0 DIN cable flows is 5651 responsible for creating a merged command flow compatible with [MIDI]. 5653 Senders MUST partition the name space so that the rendered MIDI 5654 performance does not contain indefinite artifacts (as defined in Section 5655 4). This responsibility holds even if all streams are sent over 5656 reliable transport, as different stream latencies may yield indefinite 5657 artifacts. For example, stuck notes may occur in a performance split 5658 over two TCP streams, if NoteOn commands are sent on one stream and 5659 NoteOff commands are sent on the other. 5661 Senders MUST NOT split a Registered Parameter Name (RPN) or Non- 5662 Registered Parameter Name (NRPN) transaction appearing on a MIDI channel 5663 across multiple identity relationship sessions. Receivers MUST assume 5664 that the RPN/NRPN transactions that appear on different identity 5665 relationship sessions are independent and MUST preserve transactional 5666 integrity during the MIDI merge. 5668 A simple way to safely partition voice channel commands is to place all 5669 MIDI commands for a particular voice channel into the same session. 5670 Safe partitioning of MIDI Systems commands may be more complicated for 5671 sessions that extensively use System Exclusive. 5673 We now show several session description examples that use the musicport 5674 parameter. 5676 Our first session description example shows two RTP MIDI streams that 5677 drive the same General MIDI decoder. The sender partitions MIDI 5678 commands between the streams dynamically. The musicport values indicate 5679 that the streams share an identity relationship. 5681 v=0 5682 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5683 s=Example 5684 t=0 0 5685 a=group:FID 1 2 5686 c=IN IP4 192.0.2.94 5687 m=audio 5004 RTP/AVP 96 5688 a=rtpmap:96 mpeg4-generic/44100 5689 a=mid:1 5690 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5691 config=7A0A0000001A4D546864000000060000000100604D54726B0 5692 000000600FF2F000; musicport=12 5693 m=audio 5006 RTP/AVP 96 5694 a=rtpmap:96 mpeg4-generic/44100 5695 a=mid:2 5696 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 5697 musicport=12 5699 (The a=fmtp lines have been wrapped to fit the page to accommodate 5700 memo formatting restrictions; they comprise single lines in SDP.) 5702 Recall that Section 2.1 defines rules for streams that target the same 5703 MIDI name space. Those rules, implemented in the example above, require 5704 that each stream resides in a separate RTP session, and that the 5705 grouping mechanisms defined in [RFC3388] signal an inter-session 5706 relationship. The "group" and "mid" attribute lines implement this 5707 grouping mechanism. 5709 A variant on this example, whose session description is not shown, would 5710 use two streams in an identity relationship driving the same MIDI 5711 renderer, each with a different transport type. One stream would use 5712 UDP and would be dedicated to real-time messages. A second stream would 5713 use TCP [RFC4571] and would be used for SysEx bulk data messages. 5715 In the next example, two mpeg4-generic streams form an ordered 5716 relationship to drive a Structured Audio decoder with 32 MIDI voice 5717 channels. Both streams reside in the same RTP session. 5719 v=0 5720 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5721 s=Example 5722 t=0 0 5723 m=audio 5006 RTP/AVP 96 97 5724 c=IN IP6 2001:DB80::7F2E:172A:1E24 5725 a=rtpmap:96 mpeg4-generic/44100 5726 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=13; 5727 musicport=5 5728 a=rtpmap:97 mpeg4-generic/44100 5729 a=fmtp:97 streamtype=5; mode=rtp-midi; config=""; profile-level-id=13; 5730 musicport=6; render=synthetic; rinit="audio/asc"; 5731 url="http://example.com/cardinal.asc"; 5732 cid="azsldkaslkdjqpwojdkmsldkfpe" 5734 (The a=fmtp lines have been wrapped to fit the page to accommodate 5735 memo formatting restrictions; they comprise single lines in SDP.) 5737 The sequential musicport values for the two sessions establish the 5738 ordered relationship. The musicport=5 session maps to Structured Audio 5739 extended channels range 0-15, the musicport=6 session maps to Structured 5740 Audio extended channels range 16-31. 5742 Both config strings are empty. The configuration data is specified by 5743 parameters that appear in the fmtp line of the second media description. 5744 We define this configuration method in Appendix C.6. 5746 The next example shows two RTP MIDI streams (one recvonly, one sendonly) 5747 that form a "virtual sendrecv" session. Each stream resides in a 5748 different RTP session (a requirement because sendonly and recvonly are 5749 RTP session attributes). 5751 v=0 5752 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5753 s=Example 5754 t=0 0 5755 a=group:FID 1 2 5756 c=IN IP4 192.0.2.94 5757 m=audio 5004 RTP/AVP 96 5758 a=sendonly 5759 a=rtpmap:96 mpeg4-generic/44100 5760 a=mid:1 5761 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5762 config=7A0A0000001A4D546864000000060000000100604D54726B0 5763 000000600FF2F000; musicport=12 5764 m=audio 5006 RTP/AVP 96 5765 a=recvonly 5766 a=rtpmap:96 mpeg4-generic/44100 5767 a=mid:2 5768 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5769 config=7A0A0000001A4D546864000000060000000100604D54726B0 5770 000000600FF2F000; musicport=12 5772 (The a=fmtp lines have been wrapped to fit the page to accommodate 5773 memo formatting restrictions; they comprise single lines in SDP.) 5775 To signal the "virtual sendrecv" semantics, the two streams assign 5776 musicport to the same value (12). As defined earlier in this section, 5777 pairs of identity relationship streams that are sent by different 5778 parties share the association that is shared by a MIDI cable pair that 5779 cross-connects two devices in a MIDI 1.0 network. We use the term 5780 "virtual sendrecv" because streams sent by different parties in a true 5781 sendrecv session also have this property. 5783 As discussed in the preamble to Appendix C, the primary advantage of the 5784 virtual sendrecv configuration is that each party can customize the 5785 property of the stream it receives. In the example above, each stream 5786 defines its own "config" string that could customize the rendering 5787 algorithm for each party (in fact, the particular strings shown in this 5788 example are identical, because General MIDI is not a configurable MPEG 4 5789 renderer). 5791 C.6. Configuration Tools: MIDI Rendering 5793 This appendix defines the session configuration tools for rendering. 5795 The "render" parameter specifies a rendering method for a stream. The 5796 parameter is assigned a token value that signals the top-level rendering 5797 class. This memo defines four token values for render: "unknown", 5798 "synthetic", "api", and "null": 5800 o An "unknown" renderer is a renderer whose nature is unspecified. 5801 It is the default renderer for native RTP MIDI streams. 5803 o A "synthetic" renderer transforms the MIDI stream into audio 5804 output (or sometimes into stage lighting changes or other 5805 actions). It is the default renderer for mpeg4-generic 5806 RTP MIDI streams. 5808 o An "api" renderer presents the command stream to applications 5809 via an Application Programmer Interface (API). 5811 o The "null" renderer discards the MIDI stream. 5813 The "null" render value plays special roles during Offer/Answer 5814 negotiations [RFC3264]. A party uses the "null" value in an answer to 5815 reject an offered renderer. Note that rejecting a renderer is 5816 independent from rejecting a payload type (coded by removing the payload 5817 type from a media line) and rejecting a media stream (coded by zeroing 5818 the port of a media line that uses the renderer). 5820 Other render token values MAY be registered with IANA. The token value 5821 MUST adhere to the ABNF for render tokens defined in Appendix D. 5822 Registrations MUST include a complete specification of parameter value 5823 usage, similar in depth to the specifications that appear throughout 5824 Appendix C.6 for "synthetic" and "api" render values. If a party is 5825 offered a session description that uses a render token value that is not 5826 known to the party, the party MUST NOT accept the renderer. Options 5827 include rejecting the renderer (using the "null" value), the payload 5828 type, the media stream, or the session description. 5830 Other parameters MAY follow a render parameter in a parameter list. The 5831 additional parameters act to define the exact nature of the renderer. 5832 For example, the "subrender" parameter (defined in Appendix C.6.2) 5833 specifies the exact nature of the renderer. 5835 Special rules apply to using the render parameter in an mpeg4-generic 5836 stream. We define these rules in Appendix C.6.5. 5838 C.6.1. The multimode Parameter 5840 A media description MAY contain several render parameters. By default, 5841 if a parameter list includes several render parameters, a receiver MUST 5842 choose exactly one renderer from the list to render the stream. The 5843 "multimode" parameter may be used to override this default. We define 5844 two token values for multimode: "one" and "all": 5846 o The default "one" value requests rendering by exactly one of 5847 the listed renderers. 5849 o The "all" value requests the synchronized rendering of the RTP 5850 MIDI stream by all listed renderers, if possible. 5852 If the multimode parameter appears in a parameter list, it MUST appear 5853 before the first render parameter assignment. 5855 Render parameters appear in the parameter list in order of decreasing 5856 priority. A receiver MAY use the priority ordering to decide which 5857 renderer(s) to retain in a session. 5859 If the "offer" in an Offer/Answer-style negotiation [RFC3264] contains a 5860 parameter list with one or more render parameters, the "answer" MUST set 5861 the render parameters of all unchosen renderers to "null". 5863 C.6.2. Renderer Specification 5865 The render parameter (Appendix C.6 preamble) specifies, in a broad 5866 sense, what a renderer does with a MIDI stream. In this appendix, we 5867 describe the "subrender" parameter. The token value assigned to 5868 subrender defines the exact nature of the renderer. Thus, "render" and 5869 "subrender" combine to define a renderer, in the same way as MIME types 5870 and MIME subtypes combine to define a type of media [RFC2045]. 5872 If the subrender parameter is used for a renderer definition, it MUST 5873 appear immediately after the render parameter in the parameter list. At 5874 most one subrender parameter may appear in a renderer definition. 5876 This document defines one value for subrender: the value "default". The 5877 "default" token specifies the use of the default renderer for the stream 5878 type (native or mpeg4-generic). The default renderer for native RTP 5879 MIDI streams is a renderer whose nature is unspecified (see point 6 in 5880 Section 6.1 for details). The default renderer for mpeg4-generic RTP 5881 MIDI streams is an MPEG 4 Audio Object Type whose ID number is 13, 14, 5882 or 15 (see Section 6.2 for details). 5884 If a renderer definition does not use the subrender parameter, the value 5885 "default" is assumed for subrender. 5887 Other subrender token values may be registered with IANA. We now 5888 discuss guidelines for registering subrender values. 5890 A subrender value is registered for a specific stream type (native or 5891 mpeg4-generic) and a specific render value (excluding "null" and 5892 "unknown"). Registrations for mpeg4-generic subrender values are 5893 restricted to new MPEG 4 Audio Object Types that accept MIDI input. The 5894 syntax of the token MUST adhere to the token definition in Appendix D. 5896 For "render=synthetic" renderers, a subrender value registration 5897 specifies an exact method for transforming the MIDI stream into audio 5898 (or sometimes into video or control actions, such as stage lighting). 5899 For standardized renderers, this specification is usually a pointer to a 5900 standards document, perhaps supplemented by RTP-MIDI-specific 5901 information. For commercial products and open-source projects, this 5902 specification usually takes the form of instructions for interfacing the 5903 RTP MIDI stream with the product or project software. A 5904 "render=synthetic" registration MAY specify additional Reset State 5905 commands for the renderer (Appendix A.1). 5907 A "render=api" subrender value registration specifies how an RTP MIDI 5908 stream interfaces with an API (Application Programmers Interface). This 5909 specification is usually a pointer to programmer's documentation for the 5910 API, perhaps supplemented by RTP-MIDI-specific information. 5912 A subrender registration MAY specify an initialization file (referred to 5913 in this document as an initialization data object) for the stream. The 5914 initialization data object MAY be encoded in the parameter list 5915 (verbatim or by reference) using the coding tools defined in Appendix 5916 C.6.3. An initialization data object MUST have a registered [RFC4288] 5917 media type and subtype [RFC2045]. 5919 For "render=synthetic" renderers, the data object usually encodes 5920 initialization data for the renderer (sample files, synthesis patch 5921 parameters, reverberation room impulse responses, etc.). 5923 For "render=api" renderers, the data object usually encodes data about 5924 the stream used by the API (for example, for an RTP MIDI stream 5925 generated by a piano keyboard controller, the manufacturer and model 5926 number of the keyboard, for use in GUI presentation). 5928 Usually, only one initialization object is encoded for a renderer. If a 5929 renderer uses multiple data objects, the correct receiver interpretation 5930 of multiple data objects MUST be defined in the subrender registration. 5932 A subrender value registration may also specify additional parameters, 5933 to appear in the parameter list immediately after subrender. These 5934 parameter names MUST begin with the subrender value, followed by an 5935 underscore ("_"), to avoid name space collisions with future RTP MIDI 5936 parameter names (for example, a parameter "foo_bar" defined for 5937 subrender value "foo"). 5939 We now specify guidelines for interpreting the subrender parameter 5940 during session configuration. 5942 If a party is offered a session description that uses a renderer whose 5943 subrender value is not known to the party, the party MUST NOT accept the 5944 renderer. Options include rejecting the renderer (using the "null" 5945 value), the payload type, the media stream, or the session description. 5947 Receivers MUST be aware of the Reset State commands (Appendix A.1) for 5948 the renderer specified by the subrender parameter and MUST insure that 5949 the renderer does not experience indefinite artifacts due to the 5950 presence (or the loss) of a Reset State command. 5952 C.6.3. Renderer Initialization 5954 If the renderer for a stream uses an initialization data object, an 5955 "rinit" parameter MUST appear in the parameter list immediately after 5956 the "subrender" parameter. If the renderer parameter list does not 5957 include a subrender parameter (recall the semantics for "default" in 5958 Appendix C.6.2), the "rinit" parameter MUST appear immediately after the 5959 "render" parameter. 5961 The value assigned to the rinit parameter MUST be the media type/subtype 5962 [RFC2045] for the initialization data object. If an initialization 5963 object type is registered with several media types, including audio, the 5964 assignment to rinit MUST use the audio media type. 5966 RTP MIDI supports several parameters for encoding initialization data 5967 objects for renderers in the parameter list: "inline", "url", and "cid". 5969 If the "inline", "url", and/or "cid" parameters are used by a renderer, 5970 these parameters MUST immediately follow the "rinit" parameter. 5972 If a "url" parameter appears for a renderer, an "inline" parameter MUST 5973 NOT appear. If an "inline" parameter appears for a renderer, a "url" 5974 parameter MUST NOT appear. However, neither "url" or "inline" is 5975 required to appear. If neither "url" or "inline" parameters follow 5976 "rinit", the "cid" parameter MUST follow "rinit". 5978 The "inline" parameter supports the inline encoding of the data object. 5979 The parameter is assigned a double-quoted Base64 [RFC2045] encoding of 5980 the binary data object, with no line breaks. Appendix E.4 shows an 5981 example that constructs an inline parameter value. 5983 The "url" parameter is assigned a double-quoted string representation of 5984 a Uniform Resource Locator (URL) for the data object. The string MUST 5985 specify either a HyperText Transport Protocol URI (HTTP, [RFC2616]) or 5986 an HTTP over TLS URI (HTTPS, [RFC2818]). The media type/subtype for the 5987 data object SHOULD be specified in the appropriate HTTP or HTTPS 5988 transport header. 5990 The "url" parameter is assigned a double-quoted string representation of 5991 a Uniform Resource Locator (URL) for the data object. The string MUST 5992 specify a HyperText Transport Protocol URL (HTTP, [RFC2616]). HTTP MAY 5993 be used over TCP or MAY be used over a secure network transport, such as 5994 the method described in [RFC2818]. The media type/subtype for the data 5995 object SHOULD be specified in the appropriate HTTP transport header. 5997 The "cid" parameter supports data object caching. The parameter is 5998 assigned a double-quoted string value that encodes a globally unique 5999 identifier for the data object. 6001 A cid parameter MAY immediately follow an inline parameter, in which 6002 case the cid identifier value MUST be associated with the inline data 6003 object. 6005 If a url parameter is present, and if the data object for the URL is 6006 expected to be unchanged for the life of the URL, a cid parameter MAY 6007 immediately follow the url parameter. The cid identifier value MUST be 6008 associated with the data object for the URL. A cid parameter assigned 6009 to the same identifier value SHOULD be specified following the data 6010 object type/subtype in the appropriate HTTP transport header. 6012 If a url parameter is present, and if the data object for the URL is 6013 expected to change during the life of the URL, a cid parameter MUST NOT 6014 follow the url parameter. A receiver interprets the presence of a cid 6015 parameter as an indication that it is safe to use a cached copy of the 6016 url data object; the absence of a cid parameter is an indication that it 6017 is not safe to use a cached copy, as it may change. 6019 Finally, the cid parameter MAY be used without the inline and url 6020 parameters. In this case, the identifier references a local or 6021 distributed catalog of data objects. 6023 In most cases, only one data object is coded in the parameter list for 6024 each renderer. For example, the default renderer for mpeg4-generic 6025 streams uses a single data object (see Appendix C.6.5 for example 6026 usage). 6028 However, a subrender registration MAY permit the use of multiple data 6029 objects for a renderer. If multiple data objects are encoded for a 6030 renderer, each object encoding begins with an "rinit" parameter, 6031 followed by "inline", "url", and/or "cid" parameters. 6033 Initialization data objects MAY encapsulate a Standard MIDI File (SMF). 6034 By default, the SMFs that are encapsulated in a data object MUST be 6035 ignored by an RTP MIDI receiver. We define parameters to override this 6036 default in Appendix C.6.4. 6038 To end this section, we offer guidelines for registering media types for 6039 initialization data objects. These guidelines are in addition to the 6040 information in [RFC4288]. 6042 Some initialization data objects are also capable of encoding MIDI note 6043 information and thus complete audio performances. These objects SHOULD 6044 be registered using the "audio" media type, so that the objects may also 6045 be used for store-and-forward rendering, and "application" media type, 6046 to support editing tools. Initialization objects without note storage, 6047 or initialization objects for non-audio renderers, SHOULD be registered 6048 only for an "application" media type. 6050 C.6.4. MIDI Channel Mapping 6052 In this appendix, we specify how to map MIDI name spaces (16 voice 6053 channels + systems) onto a renderer. 6055 In the general case: 6057 o A session may define an ordered relationship (Appendix C.5) 6058 that presents more than one MIDI name space to a renderer. 6060 o A renderer may accept an arbitrary number of MIDI name spaces, 6061 or it may expect a specific number of MIDI name spaces. 6063 A session description SHOULD provide a compatible MIDI name space to 6064 each renderer in the session. If a receiver detects that a session 6065 description has too many or too few MIDI name spaces for a renderer, 6066 MIDI data from extra stream name spaces MUST be discarded, and extra 6067 renderer name spaces MUST NOT be driven with MIDI data (except as 6068 described in Appendix C.6.4.1, below). 6070 If a parameter list defines several renderers and assigns the "all" 6071 token value to the multimode parameter, the same name space is presented 6072 to each renderer. However, the "chanmask" parameter may be used to mask 6073 out selected voice channels to each renderer. We define "chanmask" and 6074 other MIDI management parameters in the sub-sections below. 6076 C.6.4.1. The smf_info Parameter 6078 The smf_info parameter defines the use of the SMFs encapsulated in 6079 renderer data objects (if any). The smf_info parameter also defines the 6080 use of SMFs coded in the smf_inline, smf_url, and smf_cid parameters 6081 (defined in Appendix C.6.4.2). 6083 The smf_info parameter describes the "render" parameter that most 6084 recently precedes it in the parameter list. The smf_info parameter MUST 6085 NOT appear in parameter lists that do not use the "render" parameter, 6086 and MUST NOT appear before the first use of "render" in the parameter 6087 list. 6089 We define three token values for smf_info: "ignore", "sdp_start", and 6090 "identity": 6092 o The "ignore" value indicates that the SMFs MUST be discarded. 6093 This behavior is the default SMF rendering behavior. 6095 o The "sdp_start" value codes that SMFs MUST be rendered, 6096 and that the rendering MUST begin upon the acceptance of 6097 the session description. If a receiver is offered a session 6098 description with a renderer that uses an smf_info parameter 6099 set to sdp_start, and if the receiver does not support 6100 rendering SMFs, the receiver MUST NOT accept the renderer 6101 associated with the smf_info parameter. Options include 6102 rejecting the renderer (by setting the "render" parameter 6103 to "null"), the payload type, the media stream, or the 6104 entire session description. 6106 o The "identity" value indicates that the SMFs code the identity 6107 of the renderer. The value is meant for use with the 6108 "unknown" renderer (see Appendix C.6 preamble). The MIDI commands 6109 coded in the SMF are informational in nature and MUST NOT be 6110 presented to a renderer for audio presentation. In 6111 typical use, the SMF would use SysEx Identity Reply 6112 commands (F0 7E nn 06 02, as defined in [MIDI]) to identify 6113 devices, and use device-specific SysEx commands to describe 6114 current state of the devices (patch memory contents, etc.). 6116 Other smf_info token values MAY be registered with IANA. The token 6117 value MUST adhere to the ABNF for render tokens defined in Appendix D. 6118 Registrations MUST include a complete specification of parameter usage, 6119 similar in depth to the specifications that appear in this appendix for 6120 "sdp_start" and "identity". 6122 If a party is offered a session description that uses an smf_info 6123 parameter value that is not known to the party, the party MUST NOT 6124 accept the renderer associated with the smf_info parameter. Options 6125 include rejecting the renderer, the payload type, the media stream, or 6126 the entire session description. 6128 We now define the rendering semantics for the "sdp_start" token value in 6129 detail. 6131 The SMFs and RTP MIDI streams in a session description share the same 6132 MIDI name space(s). In the simple case of a single RTP MIDI stream and 6133 a single SMF, the SMF MIDI commands and RTP MIDI commands are merged 6134 into a single name space and presented to the renderer. The indefinite 6135 artifact responsibilities for merged MIDI streams defined in Appendix 6136 C.5 also apply to merging RTP and SMF MIDI data. 6138 If a payload type codes multiple SMFs, the SMF name spaces are presented 6139 as an ordered entity to the renderer. To determine the ordering of SMFs 6140 for a renderer (which SMF is "first", which is "second", etc.), use the 6141 following rules: 6143 o If the renderer uses a single data object, the order of 6144 appearance of the SMFs in the object's internal structure 6145 defines the order of the SMFs (the earliest SMF in the object 6146 is "first", the next SMF in the object is "second", etc.). 6148 o If multiple data objects are encoded for a renderer, the 6149 appearance of each data object in the parameter list 6150 sets the relative order of the SMFs encoded in each 6151 data object (SMFs encoded in parameters that appear 6152 earlier in the list are ordered before SMFs encoded 6153 in parameters that appear later in the list). 6155 o If SMFs are encoded in data objects parameters and in 6156 the parameters defined in C.6.4.2, the relative order 6157 of the data object parameters and C.6.4.2 parameters 6158 in the parameter list sets the relative order of SMFs 6159 (SMFs encoded in parameters that appear earlier in the 6160 list are ordered before SMFs in parameters that appear 6161 later in the list). 6163 Given this ordering of SMFs, we now define the mapping of SMFs to 6164 renderer name spaces. The SMF that appears first for a renderer maps to 6165 the first renderer name space. The SMF that appears second for a 6166 renderer maps to the second renderer name space, etc. If the associated 6167 RTP MIDI streams also form an ordered relationship, the first SMF is 6168 merged with the first name space of the relationship, the second SMF is 6169 merged to the second name space of the relationship, etc. 6171 Unless the streams and the SMFs both use MIDI Time Code, the time offset 6172 between SMF and stream data is unspecified. This restriction limits the 6173 use of SMFs to applications where synchronization is not critical, such 6174 as the transport of System Exclusive commands for renderer 6175 initialization, or human-SMF interactivity. 6177 Finally, we note that each SMF in the sdp_start discussion above encodes 6178 exactly one MIDI name space (16 voice channels + systems). Thus, the 6179 use of the Device Name SMF meta event to specify several MIDI name 6180 spaces in an SMF is not supported for sdp_start. 6182 C.6.4.2. The smf_inline, smf_url, and smf_cid Parameters 6184 In some applications, the renderer data object may not encapsulate SMFs, 6185 but an application may wish to use SMFs in the manner defined in 6186 Appendix C.6.4.1. 6188 The "smf_inline", "smf_url", and "smf_cid" parameters address this 6189 situation. These parameters use the syntax and semantics of the inline, 6190 url, and cid parameters defined in Appendix C.6.3, except that the 6191 encoded data object is an SMF. 6193 The "smf_inline", "smf_url", and "smf_cid" parameters belong to the 6194 "render" parameter that most recently precedes it in the session 6195 description. The "smf_inline", "smf_url", and "smf_cid" parameters MUST 6196 NOT appear in parameter lists that do not use the "render" parameter and 6197 MUST NOT appear before the first use of "render" in the parameter list. 6198 If several "smf_inline", "smf_url", or "smf_cid" parameters appear for a 6199 renderer, the order of the parameters defines the SMF name space 6200 ordering. 6202 C.6.4.3. The chanmask Parameter 6204 The chanmask parameter instructs the renderer to ignore all MIDI voice 6205 commands for certain channel numbers. The parameter value is a 6206 concatenated string of "1" and "0" digits. Each string position maps to 6207 a MIDI voice channel number (system channels may not be masked). A "1" 6208 instructs the renderer to process the voice channel; a "0" instructs the 6209 renderer to ignore the voice channel. 6211 The string length of the chanmask parameter value MUST be 16 (for a 6212 single stream or an identity relationship) or a multiple of 16 (for an 6213 ordered relationship). 6215 The chanmask parameter describes the "render" parameter that most 6216 recently precedes it in the session description; chanmask MUST NOT 6217 appear in parameter lists that do not use the "render" parameter and 6218 MUST NOT appear before the first use of "render" in the parameter list. 6220 The chanmask parameter describes the final MIDI name spaces presented to 6221 the renderer. The SMF and stream components of the MIDI name spaces may 6222 not be independently masked. 6224 If a receiver is offered a session description with a renderer that uses 6225 the chanmask parameter, and if the receiver does not implement the 6226 semantics of the chanmask parameter, the receiver MUST NOT accept the 6227 renderer unless the chanmask parameter value contains only "1"s. 6229 C.6.5. The audio/asc Media Type 6231 In Appendix 11.3, we register the audio/asc media type. The data object 6232 for audio/asc is a binary encoding of the AudioSpecificConfig data block 6233 used to initialize mpeg4-generic streams (Section 6.2 and [MPEGAUDIO]). 6235 An mpeg4-generic parameter list MAY use the render, subrender, and rinit 6236 parameters with the audio/asc media type for renderer configuration. 6237 Several restrictions apply to the use of these parameters in 6238 mpeg4-generic parameter lists: 6240 o An mpeg4-generic media description that uses the render parameter 6241 MUST assign the empty string ("") to the mpeg4-generic "config" 6242 parameter. The use of the streamtype, mode, and profile-level-id 6243 parameters MUST follow the normative text in Section 6.2. 6245 o Sessions that use identity or ordered relationships MUST follow 6246 the mpeg4-generic configuration restrictions in Appendix C.5. 6248 o The render parameter MUST be assigned the value "synthetic", 6249 "unknown", "null", or a render value that has been added to 6250 the IANA repository for use with mpeg4-generic RTP MIDI 6251 streams. The "api" token value for render MUST NOT be used. 6253 o If a subrender parameter is present, it MUST immediately follow 6254 the render parameter, and it MUST be assigned the token value 6255 "default" or assigned a subrender value added to the IANA 6256 repository for use with mpeg4-generic RTP MIDI streams. A 6257 subrender parameter assignment may be left out of the renderer 6258 configuration, in which case the implied value of subrender 6259 is the default value of "default". 6261 o If the render parameter is assigned the value "synthetic" 6262 and the subrender parameter has the value "default" (assigned 6263 or implied), the rinit parameter MUST be assigned the value 6264 "audio/asc", and an AudioSpecificConfig data object MUST be encoded 6265 using the mechanisms defined in C.6.2-3. The AudioSpecificConfig 6266 data MUST encode one of the MPEG 4 Audio Object Types defined for 6267 use with mpeg4-generic in Section 6.2. If the subrender value is 6268 other than "default", refer to the subrender registration 6269 for information on the use of "audio/asc" with the renderer. 6271 o If the render parameter is assigned the value "null" or 6272 "unknown", the data object MAY be omitted. 6274 Several general restrictions apply to the use of the audio/asc media 6275 type in RTP MIDI: 6277 o A native stream MUST NOT assign "audio/asc" to rinit. The 6278 audio/asc media type is not intended to be a general-purpose 6279 container for rendering systems outside of MPEG usage. 6281 o The audio/asc media type defines a stored object type; it does 6282 not define semantics for RTP streams. Thus, audio/asc MUST NOT 6283 appear on an rtpmap line of a session description. 6285 Below, we show session description examples for audio/asc. The session 6286 description below uses the inline parameter to code the 6287 AudioSpecificConfig block for a mpeg4-generic General MIDI stream. We 6288 derive the value assigned to the inline parameter in Appendix E.4. The 6289 subrender token value of "default" is implied by the absence of the 6290 subrender parameter in the parameter list. 6292 v=0 6293 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 6294 s=Example 6295 t=0 0 6296 m=audio 5004 RTP/AVP 96 6297 c=IN IP4 192.0.2.94 6298 a=rtpmap:96 mpeg4-generic/44100 6299 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6300 render=synthetic; rinit="audio/asc"; 6301 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6303 (The a=fmtp line has been wrapped to fit the page to accommodate 6304 memo formatting restrictions; it comprises a single line in SDP.) 6306 The session description below uses the url parameter to code the 6307 AudioSpecificConfig block for the same General MIDI stream: 6309 v=0 6310 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 6311 s=Example 6312 t=0 0 6313 m=audio 5004 RTP/AVP 96 6314 c=IN IP4 192.0.2.94 6315 a=rtpmap:96 mpeg4-generic/44100 6316 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6317 render=synthetic; rinit="audio/asc"; url="http://example.net/oski.asc"; 6318 cid="xjflsoeiurvpa09itnvlduihgnvet98pa3w9utnuighbuk" 6320 (The a=fmtp line has been wrapped to fit the page to accommodate 6321 memo formatting restrictions; it comprises a single line in SDP.) 6323 C.7. Interoperability 6325 In this appendix, we define interoperability guidelines for two 6326 application areas: 6328 o MIDI content-streaming applications. RTP MIDI is added to 6329 RTSP-based content-streaming servers, so that viewers may 6330 experience MIDI performances (produced by a specified client- 6331 side renderer) in synchronization with other streams (video, 6332 audio). 6334 o Long-distance network musical performance applications. RTP 6335 MIDI is added to SIP-based voice chat or videoconferencing 6336 programs, as an alternative, or as an addition, to audio and/or 6337 video RTP streams. 6339 For each application, we define a core set of functionality that all 6340 implementations MUST implement. 6342 The applications we address in this section are not an exhaustive list 6343 of potential RTP MIDI uses. We expect framework documents for other 6344 applications to be developed, within the IETF or within other 6345 organizations. We discuss other potential application areas for RTP 6346 MIDI in Section 1 of the main text of this memo. 6348 C.7.1. MIDI Content Streaming Applications 6350 In content-streaming applications, a user invokes an RTSP client to 6351 initiate a request to an RTSP server to view a multimedia session. For 6352 example, clicking on a web page link for an Internet Radio channel 6353 launches an RTSP client that uses the link's RTSP URL to contact the 6354 RTSP server hosting the radio channel. 6356 The content may be pre-recorded (for example, on-demand replay of 6357 yesterday's football game) or "live" (for example, football game 6358 coverage as it occurs), but in either case the user is usually an 6359 "audience member" as opposed to a "participant" (as the user would be in 6360 telephony). 6362 Note that these examples describe the distribution of audio content to 6363 an audience member. The interoperability guidelines in this appendix 6364 address RTP MIDI applications of this nature, not applications such as 6365 the transmission of raw MIDI command streams for use in a professional 6366 environment (recording studio, performance stage, etc.). 6368 In an RTSP session, a client accesses a session description that is 6369 "declared" by the server, either via the RTSP DESCRIBE method, or via 6370 other means, such as HTTP or email. The session description defines the 6371 session from the perspective of the client. For example, if a media 6372 line in the session description contains a non-zero port number, it 6373 encodes the server's preference for the client's port numbers for RTP 6374 and RTCP reception. Once media flow begins, the server sends an RTP 6375 MIDI stream to the client, which renders it for presentation, perhaps in 6376 synchrony with video or other audio streams. 6378 We now define the interoperability text for content-streaming RTSP 6379 applications. 6381 In most cases, server interoperability responsibilities are described in 6382 terms of limits on the "reference" session description a server provides 6383 for a performance if it has no information about the capabilities of the 6384 client. The reference session is a "lowest common denominator" session 6385 that maximizes the odds that a client will be able to view the session. 6386 If a server is aware of the capabilities of the client, the server is 6387 free to provide a session description customized for the client in the 6388 DESCRIBE reply. 6390 Clients MUST support unicast UDP RTP MIDI streams that use the recovery 6391 journal with the closed-loop or the anchor sending policies. Clients 6392 MUST be able to interpret stream subsetting and chapter inclusion 6393 parameters in the session description that qualify the sending policies. 6394 Client support of enhanced Chapter C encoding is OPTIONAL. 6396 The reference session description offered by a server MUST send all RTP 6397 MIDI UDP streams as unicast streams that use the recovery journal and 6398 the closed-loop or anchor sending policies. Servers SHOULD use the 6399 stream subsetting and chapter inclusion parameters in the reference 6400 session description, to simplify the rendering task of the client. 6401 Server support of enhanced Chapter C encoding is OPTIONAL. 6403 Clients and servers MUST support the use of RTSP interleaved mode (a 6404 method for interleaving RTP onto the RTSP TCP transport). 6406 Clients MUST be able to interpret the timestamp semantics signalled by 6407 the "comex" value of the tsmode parameter (i.e., the timestamp semantics 6408 of Standard MIDI Files [MIDI]). Servers MUST use the "comex" value for 6409 the "tsmode" parameter in the reference session description. 6411 Clients MUST be able to process an RTP MIDI stream whose packets encode 6412 an arbitrary temporal duration ("media time"). Thus, in practice, 6413 clients MUST implement a MIDI playout buffer. Clients MUST NOT depend 6414 on the presence of rtp_ptime, rtp_maxtime, and guardtime parameters in 6415 the session description in order to process packets, but they SHOULD be 6416 able to use these parameters to improve packet processing. 6418 Servers SHOULD strive to send RTP MIDI streams in the same way media 6419 servers send conventional audio streams: a sequence of packets that 6420 either all code the same temporal duration (non-normative example: 50 ms 6421 packets) or that code one of an integral number of temporal durations 6422 (non-normative example: 50 ms, 100 ms, 250 ms, or 500 ms packets). 6423 Servers SHOULD encode information about the packetization method in the 6424 rtp_ptime and rtp_maxtime parameters in the session description. 6426 Clients MUST be able to examine the render and subrender parameter, to 6427 determine if a multimedia session uses a renderer it supports. Clients 6428 MUST be able to interpret the default "one" value of the "multimode" 6429 parameter, to identify supported renderers from a list of renderer 6430 descriptions. Clients MUST be able to interpret the musicport 6431 parameter, to the degree that it is relevant to the renderers it 6432 supports. Clients MUST be able to interpret the chanmask parameter. 6434 Clients supporting renderers whose data object (as encoded by a 6435 parameter value for "inline") could exceed 300 octets in size MUST 6436 support the url and cid parameters and thus must implement the HTTP 6437 protocol in addition to RTSP. HTTP over TLS [RFC2818] support for data 6438 objects is OPTIONAL. 6440 Servers MUST specify complete rendering systems for RTP MIDI streams. 6441 Note that a minimal RTP MIDI native stream does not meet this 6442 requirement (Section 6.1), as the rendering method for such streams is 6443 "not specified". 6445 At the time of this memo, the only way for servers to specify a complete 6446 rendering system is to specify an mpeg4-generic RTP MIDI stream in mode 6447 rtp-midi (Section 6.2 and C.6.5). As a consequence, the only rendering 6448 systems that may be presently used are General MIDI [MIDI], DLS 2 6449 [DLS2], or Structured Audio [MPEGSA]. Note that the maximum inline 6450 value for General MIDI is well under 300 octets (and thus clients need 6451 not support the "url" parameter), and that the maximum inline values for 6452 DLS 2 and Structured Audio may be much larger than 300 octets (and thus 6453 clients MUST support the url parameter). 6455 We anticipate that the owners of rendering systems (both standardized 6456 and proprietary) will register subrender parameters for their renderers. 6457 Once registration occurs, native RTP MIDI sessions may use render and 6458 subrender (Appendix C.6.2) to specify complete rendering systems for 6459 RTSP content-streaming multimedia sessions. 6461 Servers MUST NOT use the sdp_start value for the smf_info parameter in 6462 the reference session description, as this use would require that 6463 clients be able to parse and render Standard MIDI Files. 6465 Clients MUST support mpeg4-generic mode rtp-midi General MIDI (GM) 6466 sessions, at a polyphony limited by the hardware capabilities of the 6467 client. This requirement provides a "lowest common denominator" 6468 rendering system for content providers to target. Note that this 6469 requirement does not force implementors of a non-GM renderer (such as 6470 DLS 2 or Structured Audio) to add a second rendering engine. Instead, a 6471 client may satisfy the requirement by including a set of voice patches 6472 that implement the GM instrument set, and using this emulation for 6473 mpeg4-generic GM sessions. 6475 It is RECOMMENDED that servers use General MIDI as the renderer for the 6476 reference session description, because clients are REQUIRED to support 6477 it. We do not require General MIDI as the reference renderer, because 6478 for normative applications it is an inappropriate choice. Servers using 6479 General MIDI as a "lowest common denominator" renderer SHOULD use 6480 Universal Real-Time SysEx MIP messages [SPMIDI] to communicate the 6481 priority of voices to polyphony-limited clients. 6483 C.7.2. MIDI Network Musical Performance Applications 6485 In Internet telephony and videoconferencing applications, parties 6486 interact over an IP network as they would face-to-face. Good user 6487 experiences require low end-to-end audio latency and tight audiovisual 6488 synchronization (for "lip-sync"). The Session Initiation Protocol (SIP, 6489 [RFC3261]) is used for session management. 6491 In this appendix section, we define interoperability guidelines for 6492 using RTP MIDI streams in interactive SIP applications. Our primary 6493 interest is supporting Network Musical Performances (NMP), where 6494 musicians in different locations interact over the network as if they 6495 were in the same room. See [NMP] for background information on NMP, and 6496 see [RFC4696] for a discussion of low-latency RTP MIDI implementation 6497 techniques for NMP. 6499 Note that the goal of NMP applications is telepresence: the parties 6500 should hear audio that is close to what they would hear if they were in 6501 the same room. The interoperability guidelines in this appendix address 6502 RTP MIDI applications of this nature, not applications such as the 6503 transmission of raw MIDI command streams for use in a professional 6504 environment (recording studio, performance stage, etc.). 6506 We focus on session management for two-party unicast sessions that 6507 specify a renderer for RTP MIDI streams. Within this limited scope, the 6508 guidelines defined here are sufficient to let applications interoperate. 6509 We define the REQUIRED capabilities of RTP MIDI senders and receivers in 6510 NMP sessions and define how session descriptions exchanged are used to 6511 set up network musical performance sessions. 6513 SIP lets parties negotiate details of the session, using the 6514 Offer/Answer protocol [RFC3264]. However, RTP MIDI has so many 6515 parameters that "blind" negotiations between two parties using different 6516 applications might not yield a common session configuration. 6518 Thus, we now define a set of capabilities that NMP parties MUST support. 6519 Session description offers whose options lie outside the envelope of 6520 REQUIRED party behavior risk negotiation failure. We also define 6521 session description idioms that the RTP MIDI part of an offer MUST 6522 follow, in order to structure the offer for simpler analysis. 6524 We use the term "offerer" for the party making a SIP offer, and 6525 "answerer" for the party answering the offer. Finally, we note that 6526 unless it is qualified by the adjective "sender" or "receiver", a 6527 statement that a party MUST support X implies that it MUST support X for 6528 both sending and receiving. 6530 If an offerer wishes to define a "sendrecv" RTP MIDI stream, it may use 6531 a true sendrecv session or the "virtual sendrecv" construction described 6532 in the preamble to Appendix C and in Appendix C.5. A true sendrecv 6533 session indicates that the offerer wishes to participate in a session 6534 where both parties use identically configured renderers. A virtual 6535 sendrecv session indicates that the offerer is willing to participate in 6536 a session where the two parties may be using different renderer 6537 configurations. Thus, parties MUST be prepared to see both real and 6538 virtual sendrecv sessions in an offer. 6540 Parties MUST support unicast UDP transport of RTP MIDI streams. These 6541 streams MUST use the recovery journal with the closed-loop or anchor 6542 sending policies. These streams MUST use the stream subsetting and 6543 chapter inclusion parameters to declare the types of MIDI commands that 6544 will be sent on the stream (for sendonly streams) or will be processed 6545 (for recvonly streams), including the size limits on System Exclusive 6546 commands. Support of enhanced Chapter C encoding is OPTIONAL. 6548 Note that both TCP and multicast UDP support are OPTIONAL. We make TCP 6549 OPTIONAL because we expect NMP renderers to rely on data objects 6550 (signalled by "rinit" and associated parameters) for initialization at 6551 the start of the session, and only to use System Exclusive commands for 6552 interactive control during the session. These interactive commands are 6553 small enough to be protected via the recovery journal mechanism of RTP 6554 MIDI UDP streams. 6556 We now discuss timestamps, packet timing, and packet sending algorithms. 6558 Recall that the tsmode parameter controls the semantics of command 6559 timestamps in the MIDI list of RTP packets. 6561 Parties MUST support clock rates of 44.1 kHz, 48 kHz, 88.2 kHz, and 96 6562 kHz. Parties MUST support streams using the "comex", "async", and 6563 "buffer" tsmode values. Recvonly offers MUST offer the default "comex". 6565 Parties MUST support a wide range of packet temporal durations: from 6566 rtp_ptime and rtp_maxptime values of 0, to rtp_ptime and rtp_maxptime 6567 values that code 100 ms. Thus, receivers MUST be able to implement a 6568 playout buffer. 6570 Offers and answers MUST present rtp_ptime, rtp_maxptime, and guardtime 6571 values that support the latency that users would expect in the 6572 application, subject to bandwidth constraints. As senders MUST abide by 6573 values set for these parameters in a session description, a receiver 6574 SHOULD use these values to size its playout buffer to produce the lowest 6575 reliable latency for a session. Implementers should refer to [RFC4696] 6576 for information on packet sending algorithms for latency-sensitive 6577 applications. Parties MUST be able to implement the semantics of the 6578 guardtime parameter, for times from 5 ms to 5000 ms. 6580 We now discuss the use of the render parameter. 6582 Sessions MUST specify complete rendering systems for all RTP MIDI 6583 streams. Note that a minimal RTP MIDI native stream does not meet this 6584 requirement (Section 6.1), as the rendering method for such streams is 6585 "not specified". 6587 At the time this writing, the only way for parties to specify a complete 6588 rendering system is to specify an mpeg4-generic RTP MIDI stream in mode 6589 rtp-midi (Section 6.2 and C.6.5). We anticipate that the owners of 6590 rendering systems (both standardized and proprietary) will register 6591 subrender values for their renderers. Once IANA registration occurs, 6592 native RTP MIDI sessions may use render and subrender (Appendix C.6.2) 6593 to specify complete rendering systems for SIP network musical 6594 performance multimedia sessions. 6596 All parties MUST support General MIDI (GM) sessions, at a polyphony 6597 limited by the hardware capabilities of the party. This requirement 6598 provides a "lowest common denominator" rendering system, without which 6599 practical interoperability will be quite difficult. When using GM, 6600 parties SHOULD use Universal Real-Time SysEx MIP messages [SPMIDI] to 6601 communicate the priority of voices to polyphony-limited clients. 6603 Note that this requirement does not force implementors of a non-GM 6604 renderer (for mpeg4-generic sessions, DLS 2, or Structured Audio) to add 6605 a second rendering engine. Instead, a client may satisfy the 6606 requirement by including a set of voice patches that implement the GM 6607 instrument set, and using this emulation for mpeg4-generic GM sessions. 6608 We require GM support so that an offerer that wishes to maximize 6609 interoperability may do so by offering GM if its preferred renderer is 6610 not accepted by the answerer. 6612 Offerers MUST NOT present several renderers as options in a session 6613 description by listing several payload types on a media line, as Section 6614 2.1 uses this construct to let a party send several RTP MIDI streams in 6615 the same RTP session. 6617 Instead, an offerer wishing to present rendering options SHOULD offer a 6618 single payload type that offers several renderers. In this construct, 6619 the parameter list codes a list of render parameters (each followed by 6620 its support parameters). As discussed in Appendix C.6.1, the order of 6621 renderers in the list declares the offerer's preference. The "unknown" 6622 and "null" values MUST NOT appear in the offer. The answer MUST set all 6623 render values except the desired renderer to "null". Thus, "unknown" 6624 MUST NOT appear in the answer. 6626 We use SHOULD instead of MUST in the first sentence in the paragraph 6627 above, because this technique does not work in all situations (example: 6628 an offerer wishes to offer both mpeg4-generic renderers and native RTP 6629 MIDI renderers as options). In this case, the offerer MUST present a 6630 series of session descriptions, each offering a single renderer, until 6631 the answerer accepts a session description. 6633 Parties MUST support the musicport, chanmask, subrender, rinit, and 6634 inline parameters. Parties supporting renderers whose data object (as 6635 encoded by a parameter value for "inline") could exceed 300 octets in 6636 size MUST support the url and cid parameters and thus must implement the 6637 HTTP protocol. HTTP over TLS [RFC2818] support for data objects is 6638 OPTIONAL. Note that in mpeg4-generic, General MIDI data objects cannot 6639 exceed 300 octets, but DLS 2 and Structured Audio data objects may. 6640 Support for the other rendering parameters (smf_cif, smf_info, 6641 smf_inline, smf_url) is OPTIONAL. 6643 Thus far in this document, our discussion has assumed that the only MIDI 6644 flows that drive a renderer are the network flows described in the 6645 session description. In NMP applications, this assumption would require 6646 two rendering engines: one for local use by a party, a second for the 6647 remote party. 6649 In practice, applications may wish to have both parties share a single 6650 rendering engine. In this case, the session description MUST use a 6651 virtual sendrecv session and MUST use the stream subsetting and chapter 6652 inclusion parameters to allocate which MIDI channels are intended for 6653 use by a party. If two parties are sharing a MIDI channel, the 6654 application MUST ensure that appropriate MIDI merging occurs at the 6655 input to the renderer. 6657 We now discuss the use of (non-MIDI) audio streams in the session. 6659 Audio streams may be used for two purposes: as a "talkback" channel for 6660 parties to converse, or as a way to conduct a performance that includes 6661 MIDI and audio channels. In the latter case, offers MUST use sample 6662 rates and the packet temporal durations for the audio and MIDI streams 6663 that support low-latency synchronized rendering. 6665 We now show an example of an offer/answer exchange in a network musical 6666 performance application (next page). 6668 Below, we show an offer that complies with the interoperability text in 6669 this appendix section. 6671 v=0 6672 o=first 2520644554 2838152170 IN IP4 first.example.net 6673 s=Example 6674 t=0 0 6675 a=group:FID 1 2 6676 c=IN IP4 192.0.2.94 6677 m=audio 16112 RTP/AVP 96 6678 a=recvonly 6679 a=mid:1 6680 a=rtpmap:96 mpeg4-generic/44100 6681 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6682 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=2NPTW; 6683 cm_used=2C0.1.7.10.11.64.121.123; cm_used=2M0.1.2; 6684 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6685 ch_default=2NPTW; ch_default=2C0.1.7.10.11.64.121.123; 6686 ch_default=2M0.1.2; cm_default=X0-16; 6687 rtp_ptime=0; rtp_maxptime=0; guardtime=44100; 6688 musicport=1; render=synthetic; rinit="audio/asc"; 6689 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6690 m=audio 16114 RTP/AVP 96 6691 a=sendonly 6692 a=mid:2 6693 a=rtpmap:96 mpeg4-generic/44100 6694 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6695 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=1NPTW; 6696 cm_used=1C0.1.7.10.11.64.121.123; cm_used=1M0.1.2; 6697 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6698 ch_default=1NPTW; ch_default=1C0.1.7.10.11.64.121.123; 6699 ch_default=1M0.1.2; cm_default=X0-16; 6700 rtp_ptime=0; rtp_maxptime=0; guardtime=44100; 6701 musicport=1; render=synthetic; rinit="audio/asc"; 6702 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6704 (The a=fmtp lines have been wrapped to fit the page to accommodate 6705 memo formatting restrictions; it comprises a single line in SDP.) 6707 The owner line (o=) identifies the session owner as "first". 6709 The session description defines two MIDI streams: a recvonly stream on 6710 which "first" receives a performance, and a sendonly stream that "first" 6711 uses to send a performance. The recvonly port number encodes the ports 6712 on which "first" wishes to receive RTP (16112) and RTCP (16113) media at 6713 IP4 address 192.0.2.94. The sendonly port number encodes the port on 6714 which "first" wishes to receive RTCP for the stream (16115). 6716 The musicport parameters code that the two streams share and identity 6717 relationship and thus form a virtual sendrecv stream. 6719 Both streams are mpeg4-generic RTP MIDI streams that specify a General 6720 MIDI renderer. The stream subsetting parameters code that the recvonly 6721 stream uses MIDI channel 1 exclusively for voice commands, and that the 6722 sendonly stream uses MIDI channel 2 exclusively for voice commands. 6723 This mapping permits the application software to share a single renderer 6724 for local and remote performers. 6726 We now show the answer to the offer. 6728 v=0 6729 o=second 2520644554 2838152170 IN IP4 second.example.net 6730 s=Example 6731 t=0 0 6732 a=group:FID 1 2 6733 c=IN IP4 192.0.2.105 6734 m=audio 5004 RTP/AVP 96 6735 a=sendonly 6736 a=mid:1 6737 a=rtpmap:96 mpeg4-generic/44100 6738 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6739 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=2NPTW; 6740 cm_used=2C0.1.7.10.11.64.121.123; cm_used=2M0.1.2; 6741 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6742 ch_default=2NPTW; ch_default=2C0.1.7.10.11.64.121.123; 6743 ch_default=2M0.1.2; cm_default=X0-16; 6744 rtp_ptime=0; rtp_maxptime=882; guardtime=44100; 6745 musicport=1; render=synthetic; rinit="audio/asc"; 6746 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6747 m=audio 5006 RTP/AVP 96 6748 a=recvonly 6749 a=mid:2 6750 a=rtpmap:96 mpeg4-generic/44100 6751 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6752 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=1NPTW; 6753 cm_used=1C0.1.7.10.11.64.121.123; cm_used=1M0.1.2; 6754 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6755 ch_default=1NPTW; ch_default=1C0.1.7.10.11.64.121.123; 6756 ch_default=1M0.1.2; cm_default=X0-16; 6757 rtp_ptime=0; rtp_maxptime=0; guardtime=88200; 6758 musicport=1; render=synthetic; rinit="audio/asc"; 6759 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6761 (The a=fmtp lines have been wrapped to fit the page to accommodate 6762 memo formatting restrictions; they comprise single lines in SDP.) 6764 The owner line (o=) identifies the session owner as "second". 6766 The port numbers for both media streams are non-zero; thus, "second" has 6767 accepted the session description. The stream marked "sendonly" in the 6768 offer is marked "recvonly" in the answer, and vice versa, coding the 6769 different view of the session held by "session". The IP4 number 6770 (192.0.2.105) and the RTP (5004 and 5006) and RTCP (5005 and 5007) have 6771 been changed by "second" to match its transport wishes. 6773 In addition, "second" has made several parameter changes: rtp_maxptime 6774 for the sendonly stream has been changed to code 2 ms (441 in clock 6775 units), and the guardtime for the recvonly stream has been doubled. As 6776 these parameter modifications request capabilities that are REQUIRED to 6777 be implemented by interoperable parties, "second" can make these changes 6778 with confidence that "first" can abide by them. 6780 D. Parameter Syntax Definitions 6782 In this appendix, we define the syntax for the RTP MIDI media type 6783 parameters in Augmented Backus-Naur Form (ABNF, [RFC5234]). When using 6784 these parameters with SDP, all parameters MUST appear on a single fmtp 6785 attribute line of an RTP MIDI media description. For mpeg4-generic RTP 6786 MIDI streams, this line MUST also include any mpeg4-generic parameters 6787 (usage described in Section 6.2). An fmtp attribute line may be defined 6788 (after [RFC3640]) as: 6790 ; 6791 ; SDP fmtp line definition 6792 ; 6794 fmtp = "a=fmtp:" token SP param-assign 0*(";" SP param-assign) CRLF 6796 where codes the RTP payload type. Note that white space MUST 6797 NOT appear between the "a=fmtp:" and the RTP payload type. 6799 We now define the syntax of the parameters defined in Appendix C. The 6800 definition takes the form of the incremental assembly of the token. See [RFC3640] for the syntax of the mpeg4-generic 6802 parameters discussed in Section 6.2. 6804 ; 6805 ; 6806 ; top-level definition for all parameters 6807 ; 6808 ; 6810 ; 6811 ; Parameters defined in Appendix C.1 6813 param-assign = ("cm_unused=" (([channel-list] command-type 6814 [f-list]) / sysex-data)) 6816 param-assign =/ ("cm_used=" (([channel-list] command-type 6817 [f-list]) / sysex-data)) 6819 ; 6820 ; Parameters defined in Appendix C.2 6822 param-assign =/ ("j_sec=" ("none" / "recj" / ietf-extension)) 6824 param-assign =/ ("j_update=" ("anchor" / "closed-loop" / 6825 "open-loop" / ietf-extension)) 6827 param-assign =/ ("ch_default=" (([channel-list] chapter-list 6828 [f-list]) / sysex-data)) 6830 param-assign =/ ("ch_never=" (([channel-list] chapter-list 6831 [f-list]) / sysex-data)) 6833 param-assign =/ ("ch_anchor=" (([channel-list] chapter-list 6834 [f-list]) / sysex-data)) 6836 ; 6837 ; Parameters defined in Appendix C.3 6839 param-assign =/ ("tsmode=" ("comex" / "async" / "buffer")) 6841 param-assign =/ ("linerate=" nonzero-four-octet) 6843 param-assign =/ ("octpos=" ("first" / "last")) 6845 param-assign =/ ("mperiod=" nonzero-four-octet) 6847 ; 6848 ; Parameter defined in Appendix C.4 6850 param-assign =/ ("guardtime=" nonzero-four-octet) 6852 param-assign =/ ("rtp_ptime=" four-octet) 6854 param-assign =/ ("rtp_maxptime=" four-octet) 6856 ; 6857 ; Parameters defined in Appendix C.5 6859 param-assign =/ ("musicport=" four-octet) 6861 ; 6862 ; Parameters defined in Appendix C.6 6864 param-assign =/ ("chanmask=" 1*( 16(BIT) )) 6866 param-assign =/ ("cid=" DQUOTE cid-block DQUOTE) 6868 param-assign =/ ("inline=" DQUOTE base-64-block DQUOTE) 6870 param-assign =/ ("multimode=" ("all" / "one")) 6872 param-assign =/ ("render=" ("synthetic" / "api" / "null" / 6873 "unknown" / extension)) 6875 param-assign =/ ("rinit=" mime-type "/" mime-subtype) 6877 param-assign =/ ("smf_cid=" DQUOTE cid-block DQUOTE) 6879 param-assign =/ ("smf_info=" ("ignore" / "identity" / 6880 "sdp_start" / extension)) 6882 param-assign =/ ("smf_inline=" DQUOTE base-64-block DQUOTE) 6884 param-assign =/ ("smf_url=" DQUOTE uri-element DQUOTE) 6886 param-assign =/ ("subrender=" ("default" / extension)) 6888 param-assign =/ ("url=" DQUOTE uri-element DQUOTE) 6890 ; 6891 ; list definitions for the cm_ command-type 6892 ; 6894 command-type = [A] [B] [C] [F] [G] [H] [J] [K] [M] 6895 [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 6897 ; 6898 ; list definitions for the ch_ chapter-list 6899 ; 6901 chapter-list = [A] [B] [C] [D] [E] [F] [G] [H] [J] [K] 6902 [M] [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 6904 ; 6905 ; list definitions for the channel-list (used in ch_* / cm_* params) 6906 ; 6908 channel-list = midi-chan-element *("." midi-chan-element) 6910 midi-chan-element = midi-chan / midi-chan-range 6912 midi-chan-range = midi-chan "-" midi-chan 6913 ; 6914 ; decimal value of left midi-chan 6915 ; MUST be strictly less than 6916 ; decimal value of right midi-chan 6918 midi-chan = DIGIT / ("1" %x30-35) ; "0" .. "15" 6919 ; 6920 ; list definitions for the ch_ field list (f-list) 6921 ; 6923 f-list = midi-field-element *("." midi-field-element) 6925 midi-field-element = midi-field / midi-field-range 6927 midi-field-range = midi-field "-" midi-field 6928 ; 6929 ; decimal value of left midi-field 6930 ; MUST be strictly less than 6931 ; decimal value of right midi-field 6933 midi-field = four-octet 6934 ; 6935 ; large range accommodates Chapter M 6936 ; RPN (0-16383) and NRPN (16384-32767) 6937 ; parameters, and Chapter X octet sizes. 6939 ; 6940 ; definitions for ch_ sysex-data 6941 ; 6943 sysex-data = "__" h-list *("_" h-list) "__" 6945 h-list = hex-field-element *("." hex-field-element) 6947 hex-field-element = hex-octet / hex-field-range 6949 hex-field-range = hex-octet "-" hex-octet 6950 ; 6951 ; hexadecimal value of left hex-octet 6952 ; MUST be strictly less than hexadecimal 6953 ; value of right hex-octet 6955 hex-octet = %x30-37 U-HEXDIG 6956 ; 6957 ; rewritten special case of hex-octet in [RFC2045] 6958 ; (page 23). 6959 ; note that a-f are not permitted, only A-F. 6960 ; hex-octet values MUST NOT exceed 0x7F. 6962 ; 6963 ; definitions for rinit parameter 6964 ; 6966 mime-type = "audio" / "application" 6967 mime-subtype = token 6968 ; 6969 ; See Appendix C.6.2 for registration 6970 ; requirements for rinit type/subtypes. 6972 ; 6973 ; definitions for base64 encoding 6974 ; copied from [RFC4566] 6975 ; changes from [RFC4566] to improve automatic syntax checking 6976 ; 6978 base-64-block = *base64-unit [base64-pad] 6980 base64-unit = 4(base64-char) 6982 base64-pad = (2(base64-char) "==") / (3(base64-char) "=") 6984 base64-char = %x41-5A / %x61-7A / %x30-39 / "+" / "/" 6985 ; A-Z, a-z, 0-9, "+" and "/" 6987 ; 6988 ; generic rules 6989 ; 6991 ietf-extension = token 6992 ; 6993 ; may only be defined in standards-track RFCs 6995 extension = token 6996 ; 6997 ; may be defined 6998 ; by filing a registration with IANA 7000 nonzero-four-octet = (NZ-DIGIT 0*8(DIGIT)) 7001 / (%x30-33 9(DIGIT)) 7002 / ("4" %x30-31 8(DIGIT)) 7003 / ("42" %x30-38 7(DIGIT)) 7004 / ("429" %x30-33 6(DIGIT)) 7005 / ("4294" %x30-38 5(DIGIT)) 7006 / ("42949" %x30-35 4(DIGIT)) 7007 / ("429496" %x30-36 3(DIGIT)) 7008 / ("4294967" %x30-31 2(DIGIT)) 7009 / ("42949672" %x30-38 (DIGIT)) 7010 / ("429496729" %x30-34) 7011 ; 7012 ; unsigned encoding of non-zero 32-bit value: 7013 ; 1 .. 4294967295 7015 four-octet = "0" / nonzero-four-octet 7016 ; 7017 ; unsigned encoding of 32-bit value: 7018 ; 0 .. 4294967295 7020 uri-element = URI-reference 7021 ; as defined in [RFC3986] 7023 token = 1*token-char 7024 ; copied from [RFC4566] 7026 token-char = %x21 / %x23-27 / %x2A-2B / %x2D-2E / 7027 %x30-39 / %x41-5A / %x5E-7E 7028 ; copied from [RFC4566] 7030 cid-block = 1*cid-char 7032 cid-char = token-char 7033 cid-char =/ "@" 7034 cid-char =/ "," 7035 cid-char =/ ";" 7036 cid-char =/ ":" 7037 cid-char =/ "\" 7038 cid-char =/ "/" 7039 cid-char =/ "[" 7040 cid-char =/ "]" 7041 cid-char =/ "?" 7042 cid-char =/ "=" 7043 ; 7044 ; - add back in the tspecials [RFC2045], except 7045 ; for DQUOTE and the non-email safe ( ) < > 7046 ; - note that the definitions above ensure that 7047 ; cid-block is always enclosed with DQUOTEs 7049 A = %x41 ; uppercase only letters used above 7050 B = %x42 7051 C = %x43 7052 D = %x44 7053 E = %x45 7054 F = %x46 7055 G = %x47 7056 H = %x48 7057 J = %x4A 7058 K = %x4B 7059 M = %x4D 7060 N = %x4E 7061 P = %x50 7062 Q = %x51 7063 T = %x54 7064 V = %x56 7065 W = %x57 7066 X = %x58 7067 Y = %x59 7068 Z = %x5A 7070 NZ-DIGIT = %x31-39 ; non-zero decimal digit 7072 U-HEXDIG = DIGIT / A / B / C / D / E / F 7073 ; variant of HEXDIG [RFC5234] : 7074 ; hexadecimal digit using uppercase A-F only 7076 ; the rules below are from the Core Rules from [RFC5234] 7078 BIT = "0" / "1" 7080 DQUOTE = %x22 ; " (Double Quote) 7082 DIGIT = %x30-39 ; 0-9 7084 ; external references 7085 ; URI-reference: from [RFC3986] 7087 ; 7088 ; End of ABNF 7090 The mpeg4-generic RTP payload [RFC3640] defines a "mode" parameter that 7091 signals the type of MPEG stream in use. We add a new mode value, "rtp- 7092 midi", using the ABNF rule below: 7094 ; 7095 ; mpeg4-generic mode parameter extension 7096 ; 7098 mode =/ "rtp-midi" 7099 ; as described in Section 6.2 of this memo 7101 E. A MIDI Overview for Networking Specialists 7103 This appendix presents an overview of the MIDI standard, for the benefit 7104 of networking specialists new to musical applications. Implementors 7105 should consult [MIDI] for a normative description of MIDI. 7107 Musicians make music by performing a controlled sequence of physical 7108 movements. For example, a pianist plays by coordinating a series of key 7109 presses, key releases, and pedal actions. MIDI represents a musical 7110 performance by encoding these physical gestures as a sequence of MIDI 7111 commands. This high-level musical representation is compact but 7112 fragile: one lost command may be catastrophic to the performance. 7114 MIDI commands have much in common with the machine instructions of a 7115 microprocessor. MIDI commands are defined as binary elements. 7116 Bitfields within a MIDI command have a regular structure and a 7117 specialized purpose. For example, the upper nibble of the first command 7118 octet (the opcode field) codes the command type. MIDI commands may 7119 consist of an arbitrary number of complete octets, but most MIDI 7120 commands are 1, 2, or 3 octets in length. 7122 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7123 | Channel Voice Messages | Bitfield Pattern | 7124 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7125 | NoteOff (end a note) | 1000cccc 0nnnnnnn 0vvvvvvv | 7126 |-------------------------------------------------------------| 7127 | NoteOn (start a note) | 1001cccc 0nnnnnnn 0vvvvvvv | 7128 |-------------------------------------------------------------| 7129 | PTouch (Polyphonic Aftertouch) | 1010cccc 0nnnnnnn 0aaaaaaa | 7130 |-------------------------------------------------------------| 7131 | CControl (Controller Change) | 1011cccc 0xxxxxxx 0yyyyyyy | 7132 |-------------------------------------------------------------| 7133 | PChange (Program Change) | 1100cccc 0ppppppp | 7134 |-------------------------------------------------------------| 7135 | CTouch (Channel Aftertouch) | 1101cccc 0aaaaaaa | 7136 |-------------------------------------------------------------| 7137 | PWheel (Pitch Wheel) | 1110cccc 0xxxxxxx 0yyyyyyy | 7138 ------------------------------------------------------------- 7140 Figure E.1 -- MIDI Channel Messages 7142 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7143 | System Common Messages | Bitfield Pattern | 7144 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7145 | System Exclusive | 11110000, followed by a | 7146 | | list of 0xxxxxx octets, | 7147 | | followed by 11110111 | 7148 |-------------------------------------------------------------| 7149 | MIDI Time Code Quarter Frame | 11110001 0xxxxxxx | 7150 |-------------------------------------------------------------| 7151 | Song Position Pointer | 11110010 0xxxxxxx 0yyyyyyy | 7152 |-------------------------------------------------------------| 7153 | Song Select | 11110011 0xxxxxxx | 7154 |-------------------------------------------------------------| 7155 | Undefined | 11110100 | 7156 |-------------------------------------------------------------| 7157 | Undefined | 11110101 | 7158 |-------------------------------------------------------------| 7159 | Tune Request | 11110110 | 7160 |-------------------------------------------------------------| 7161 | System Exclusive End Marker | 11110111 | 7162 ------------------------------------------------------------- 7164 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7165 | System Realtime Messages | Bitfield Pattern | 7166 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7167 | Clock | 11111000 | 7168 |-------------------------------------------------------------| 7169 | Undefined | 11111001 | 7170 |-------------------------------------------------------------| 7171 | Start | 11111010 | 7172 |-------------------------------------------------------------| 7173 | Continue | 11111011 | 7174 |-------------------------------------------------------------| 7175 | Stop | 11111100 | 7176 |-------------------------------------------------------------| 7177 | Undefined | 11111101 | 7178 |-------------------------------------------------------------| 7179 | Active Sense | 11111110 | 7180 |-------------------------------------------------------------| 7181 | System Reset | 11111111 | 7182 ------------------------------------------------------------- 7184 Figure E.2 -- MIDI System Messages 7186 Figure E.1 and E.2 show the MIDI command family. There are three major 7187 classes of commands: voice commands (opcode field values in the range 7188 0x8 through 0xE), system common commands (opcode field 0xF, commands 7189 0xF0 through 0xF7), and system real-time commands (opcode field 0xF, 7190 commands 0xF8 through 0xFF). Voice commands code the musical gestures 7191 for each timbre in a composition. Systems commands perform functions 7192 that usually affect all voice channels, such as System Reset (0xFF). 7194 E.1. Commands Types 7196 Voice commands execute on one of 16 MIDI channels, as coded by its 4-bit 7197 channel field (field cccc in Figure E.1). In most applications, notes 7198 for different timbres are assigned to different channels. To support 7199 applications that require more than 16 channels, MIDI systems use 7200 several MIDI command streams in parallel, to yield 32, 48, or 64 MIDI 7201 channels. 7203 As an example of a voice command, consider a NoteOn command (opcode 7204 0x9), with binary encoding 1001cccc 0nnnnnnn 0aaaaaaa. This command 7205 signals the start of a musical note on MIDI channel cccc. The note has 7206 a pitch coded by the note number nnnnnnn, and an onset amplitude coded 7207 by note velocity aaaaaaa. 7209 Other voice commands signal the end of notes (NoteOff, opcode 0x8), map 7210 a specific timbre to a MIDI channel (PChange, opcode 0xC), or set the 7211 value of parameters that modulate the timbral quality (all other voice 7212 commands). The exact meaning of most voice channel commands depends on 7213 the rendering algorithms the MIDI receiver uses to generate sound. In 7214 most applications, a MIDI sender has a model (in some sense) of the 7215 rendering method used by the receiver. 7217 System commands perform a variety of global tasks in the stream, 7218 including "sequencer" playback control of pre-recorded MIDI commands 7219 (the Song Position Pointer, Song Select, Clock, Start, Continue, and 7220 Stop messages), SMPTE time code (the MIDI Time Code Quarter Frame 7221 command), and the communication of device-specific data (the System 7222 Exclusive messages). 7224 E.2. Running Status 7226 All MIDI command bitfields share a special structure: the leading bit of 7227 the first octet is set to 1, and the leading bit of all subsequent 7228 octets is set to 0. This structure supports a data compression system, 7229 called running status [MIDI], that improves the coding efficiency of 7230 MIDI. 7232 In running status coding, the first octet of a MIDI voice command may be 7233 dropped if it is identical to the first octet of the previous MIDI voice 7234 command. This rule, in combination with a convention to consider NoteOn 7235 commands with a null third octet as NoteOff commands, supports the 7236 coding of note sequences using two octets per command. 7238 Running status coding is only used for voice commands. The presence of 7239 a system common message in the stream cancels running status mode for 7240 the next voice command. However, system real-time messages do not 7241 cancel running status mode. 7243 E.3. Command Timing 7245 The bitfield formats in Figures E.1 and E.2 do not encode the execution 7246 time for a command. Timing information is not a part of the MIDI 7247 command syntax itself; different applications of the MIDI command 7248 language use different methods to encode timing. 7250 For example, the MIDI command set acts as the transport layer for MIDI 7251 1.0 DIN cables [MIDI]. MIDI cables are short asynchronous serial lines 7252 that facilitate the remote operation of musical instruments and audio 7253 equipment. Timestamps are not sent over a MIDI 1.0 DIN cable. Instead, 7254 the standard uses an implicit "time of arrival" code. Receivers execute 7255 MIDI commands at the moment of arrival. 7257 In contrast, Standard MIDI Files (SMFs, [MIDI]), a file format for 7258 representing complete musical performances, add an explicit timestamp to 7259 each MIDI command, using a delta encoding scheme that is optimized for 7260 statistics of musical performance. SMF timestamps usually code timing 7261 using the metric notation of a musical score. SMF meta-events are used 7262 to add a tempo map to the file, so that score beats may be accurately 7263 converted into units of seconds during rendering. 7265 E.4. AudioSpecificConfig Templates for MMA Renderers 7267 In Section 6.2 and Appendix C.6.5, we describe how session descriptions 7268 include an AudioSpecificConfig data block to specify a MIDI rendering 7269 algorithm for mpeg4-generic RTP MIDI streams. 7271 The bitfield format of AudioSpecificConfig is defined in [MPEGAUDIO]. 7272 StructuredAudioSpecificConfig, a key data structure coded in 7273 AudioSpecificConfig, is defined in [MPEGSA]. 7275 For implementors wishing to specify Structured Audio renderers, a full 7276 understanding of [MPEGSA] and [MPEGAUDIO] is essential. However, many 7277 implementors will limit their rendering options to the two MIDI 7278 Manufacturers Association renderers that may be specified in 7279 AudioSpecificConfig: General MIDI (GM, [MIDI]) and Downloadable Sounds 2 7280 (DLS 2, [DLS2]). 7282 To aid these implementors, we reproduce the AudioSpecificConfig bitfield 7283 formats for a GM renderer and a DLS 2 renderer below. We have checked 7284 these bitfields carefully and believe they are correct. However, we 7285 stress that the material below is informative, and that [MPEGAUDIO] and 7286 [MPEGSA] are the normative definitions for AudioSpecificConfig. 7288 As described in Section 6.2, a minimal mpeg4-generic session description 7289 encodes the AudioSpecificConfig binary bitfield as a hexadecimal string 7290 (whose format is defined in [RFC3640]) that is assigned to the "config" 7291 parameter. As described in Appendix C.6.3, a session description that 7292 uses the render parameter encodes the AudioSpecificConfig binary 7293 bitfield as a Base64-encoded string assigned to the "inline" parameter, 7294 or in the body of an HTTP URL assigned to the "url" parameter. 7296 Below, we show a simplified binary AudioSpecificConfig bitfield format, 7297 suitable for sending and receiving GM and DLS 2 data: 7299 0 1 2 3 7300 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 7301 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7302 | AOTYPE |FREQIDX|CHANNEL|SACNK| FILE_BLK 1 (required) ... | 7303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7304 |1|SACNK| FILE_BLK 2 (optional) ... | 7305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7306 | ... |1|SACNK| FILE_BLK N (optional) ... | 7307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7308 |0|0| (first "0" bit terminates FILE_BLK list) 7309 +-+-+ 7311 Figure E.3 -- Simplified AudioSpecificConfig 7313 The 5-bit AOTYPE field specifies the Audio Object Type as an unsigned 7314 integer. The legal values for use with mpeg4-generic RTP MIDI streams 7315 are "15" (General MIDI), "14" (DLS 2), and "13" (Structured Audio). 7316 Thus, receivers that do not support all three mpeg4-generic renderers 7317 may parse the first 5 bits of an AudioSpecificConfig coded in a session 7318 description and reject sessions that specify unsupported renderers. 7320 The 4-bit FREQIDX field specifies the sampling rate of the renderer. We 7321 show the mapping of FREQIDX values to sampling rates in Figure E.4. 7322 Senders MUST specify a sampling frequency that matches the RTP clock 7323 rate, if possible; if not, senders MUST specify the escape value. 7324 Receivers MUST consult the RTP clock parameter for the true sampling 7325 rate if the escape value is specified. 7327 FREQIDX Sampling Frequency 7329 0x0 96000 7330 0x1 88200 7331 0x2 64000 7332 0x3 48000 7333 0x4 44100 7334 0x5 32000 7335 0x6 24000 7336 0x7 22050 7337 0x8 16000 7338 0x9 12000 7339 0xa 11025 7340 0xb 8000 7341 0xc reserved 7342 0xd reserved 7343 0xe reserved 7344 0xf escape value 7346 Figure E.4 -- FreqIdx encoding 7348 The 4-bit CHANNEL field specifies the number of audio channels for the 7349 renderer. The values 0x1 to 0x5 specify 1 to 5 audio channels; the 7350 value 0x6 specifies 5+1 surround sound, and the value 0x7 specifies 7+1 7351 surround sound. If the rtpmap line in the session description specifies 7352 one of these formats, CHANNEL MUST be set to the corresponding value. 7353 Otherwise, CHANNEL MUST be set to 0x0. 7355 The CHANNEL field is followed by a list of one or more binary file data 7356 blocks. The 3-bit SACNK field (the chunk_type field in class 7357 StructuredAudioSpecificConfig, defined in [MPEGSA]) specifies the type 7358 of each data block. 7360 For General MIDI, only Standard MIDI Files may appear in the list (SACNK 7361 field value 2). For DLS 2, only Standard MIDI Files and DLS 2 RIFF 7362 files (SACNK field value 4) may appear. For both of these file types, 7363 the FILE_BLK field has the format shown in Figure E.5: a 32-bit unsigned 7364 integer value (FILE_LEN) coding the number of bytes in the SMF or RIFF 7365 file, followed by FILE_LEN bytes coding the file data. 7367 0 1 2 3 7368 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 7369 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7370 | FILE_LEN (32-bit, a byte count SMF file or RIFF file) | 7371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7372 | FILE_DATA (file contents, a list of FILE_LEN bytes) ... | 7373 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7375 Figure E.5 -- The FILE_BLK field format 7377 Note that several files may follow the CHANNEL field. The "1" constant 7378 fields in Figure E.3 code the presence of another file; the "0" constant 7379 field codes the end of the list. The final "0" bit in Figure E.3 codes 7380 the absence of special coding tools (see [MPEGAUDIO] for details). 7381 Senders not using these tools MUST append this "0" bit; receivers that 7382 do not understand these coding tools MUST ignore all data following a 7383 "1" in this position. 7385 The StructuredAudioSpecificConfig bitfield structure requires the 7386 presence of one FILE_BLK. For mpeg4-generic RTP MIDI use of DLS 2, 7387 FILE_BLKs MUST code RIFF files or SMF files. For mpeg4-generic RTP MIDI 7388 use of General MIDI, FILE_BLKs MUST code SMF files. By default, this 7389 SMF will be ignored (Appendix C.6.4.1). In this default case, a GM 7390 StructuredAudioSpecificConfig bitfield SHOULD code a FILE_BLK whose 7391 FILE_LEN is 0, and whose FILE_DATA is empty. 7393 To complete this appendix, we derive the StructuredAudioSpecificConfig 7394 that we use in the General MIDI session examples in this memo. 7395 Referring to Figure E.3, we note that for GM, AOTYPE = 15. Our examples 7396 use a 44,100 Hz sample rate (FREQIDX = 4) and are in mono (CHANNEL = 1). 7397 For GM, a single SMF is encoded (SACNK = 2), using the SMF shown in 7398 Figure E.6 (a 26 byte file). 7400 -------------------------------------------- 7401 | MIDI File =
| 7402 -------------------------------------------- 7404
= 7405 4D 54 68 64 00 00 00 06 00 00 00 01 00 60 7407 = 7408 4D 54 72 6B 00 00 00 04 00 FF 2F 00 7410 Figure E.6 -- SMF file encoded in the example 7412 Placing these constants in binary format into the data structure shown 7413 in Figure E.3 yields the constant shown in Figure E.7. 7415 0 1 2 3 7416 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 7417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7418 |0 1 1 1 1|0 1 0 0|0 0 0 1|0 1 0|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0| 7419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7420 |0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 0|0 1 0 0|1 1 0 1|0 1 0 1|0 1 0 0| 7421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7422 |0 1 1 0|1 0 0 0|0 1 1 0|0 1 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0| 7423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7424 |0 0 0 0|0 0 0 0|0 0 0 0|0 1 1 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0| 7425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7426 |0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 1|0 0 0 0|0 0 0 0|0 1 1 0|0 0 0 0| 7427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7428 |0 1 0 0|1 1 0 1|0 1 0 1|0 1 0 0|0 1 1 1|0 0 1 0|0 1 1 0|1 0 1 1| 7429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7430 |0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 1 1 0| 7431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7432 |0 0 0 0|0 0 0 0|1 1 1 1|1 1 1 1|0 0 1 0|1 1 1 1|0 0 0 0|0 0 0 0| 7433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7434 |0|0| 7435 +-+-+ 7437 Figure E.7 -- AudioSpecificConfig used in GM examples 7439 Expressing this bitfield as an ASCII hexadecimal string yields: 7441 7A0A0000001A4D546864000000060000000100604D54726B0000000600FF2F000 7443 This string is assigned to the "config" parameter in the minimal 7444 mpeg4-generic General MIDI examples in this memo (such as the example in 7445 Section 6.2). Expressing this string in Base64 [RFC2045] yields: 7447 egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA 7449 This string is assigned to the "inline" parameter in the General MIDI 7450 example shown in Appendix C.6.5. 7452 References 7454 Normative References 7456 [MIDI] MIDI Manufacturers Association. "The Complete MIDI 1.0 7457 Detailed Specification", 1996. 7459 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 7460 Jacobson, "RTP: A Transport Protocol for Real-Time 7461 Applications", STD 64, RFC 3550, July 2003. 7463 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 7464 Video Conferences with Minimal Control", STD 65, RFC 7465 3551, July 2003. 7467 [RFC3640] van der Meer, J., Mackie, D., Swaminathan, V., Singer, 7468 D., and P. Gentric, "RTP Payload Format for Transport of 7469 MPEG-4 Elementary Streams", RFC 3640, November 2003. 7471 [MPEGSA] International Standards Organization. "ISO/IEC 14496 7472 MPEG-4", Part 3 (Audio), Subpart 5 (Structured Audio), 7473 2001. 7475 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 7476 Description Protocol", RFC 4566, July 2006. 7478 [MPEGAUDIO] International Standards Organization. "ISO 14496 MPEG- 7479 4", Part 3 (Audio), 2001. 7481 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 7482 Extensions (MIME) Part One: Format of Internet Message 7483 Bodies", RFC 2045, November 1996. 7485 [DLS2] MIDI Manufacturers Association. "The MIDI Downloadable 7486 Sounds Specification", v98.2, 1998. 7488 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 7489 Specifications: ABNF", RFC 5234, January 2008. 7491 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 7492 Requirement Levels", BCP 14, RFC 2119, March 1997. 7494 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 7495 Norrman, "The Secure Real-time Transport Protocol 7496 (SRTP)", RFC 3711, March 2004. 7498 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 7499 with Session Description Protocol (SDP)", RFC 3264, June 7500 2002. 7502 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 7503 Resource Identifier (URI): Generic Syntax", STD 66, RFC 7504 3986, January 2005. 7506 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 7507 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 7508 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 7510 [RFC3388] Camarillo, G., Eriksson, G., Holler, J., and H. 7511 Schulzrinne, "Grouping of Media Lines in the Session 7512 Description Protocol (SDP)", RFC 3388, December 2002. 7514 [RP015] MIDI Manufacturers Association. "Recommended Practice 7515 015 (RP-015): Response to Reset All Controllers", 11/98. 7517 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 7518 Registration Procedures", BCP 13, RFC 4288, December 7519 2005. 7521 [RFC4855] Casner, S., "MIME Type Registration of RTP 7522 Payload Formats", RFC 4855, February 2007. 7524 Informative References 7526 [NMP] Lazzaro, J. and J. Wawrzynek. "A Case for Network 7527 Musical Performance", 11th International Workshop on 7528 Network and Operating Systems Support for Digital Audio 7529 and Video (NOSSDAV 2001) June 25-26, 2001, Port 7530 Jefferson, New York. 7532 [GRAME] Fober, D., Orlarey, Y. and S. Letz. "Real Time Musical 7533 Events Streaming over Internet", Proceedings of the 7534 International Conference on WEB Delivering of Music 2001, 7535 pages 147-154. 7537 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 7538 A., Peterson, J., Sparks, R., Handley, M., and E. 7539 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 7540 June 2002. 7542 [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time 7543 Streaming Protocol (RTSP)", RFC 2326, April 1998. 7545 [ALF] Clark, D. D. and D. L. Tennenhouse. "Architectural 7546 considerations for a new generation of protocols", 7547 SIGCOMM Symposium on Communications Architectures and 7548 Protocols , (Philadelphia, Pennsylvania), pp. 200--208, 7549 ACM, Sept. 1990. 7551 [RFC4696] Lazzaro, J. and J. Wawrzynek, "An Implementation Guide 7552 for RTP MIDI", RFC 4696, November 2006. 7554 [RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S., and S. 7555 Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 7556 Functional Specification", RFC 2205, September 1997. 7558 [RFC4571] Lazzaro, J. "Framing Real-time Transport Protocol (RTP) 7559 and RTP Control Protocol (RTCP) Packets over Connection- 7560 Oriented Transport", RFC 4571, July 2006. 7562 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 7564 [SPMIDI] MIDI Manufacturers Association. "Scalable Polyphony 7565 MIDI, Specification and Device Profiles", Document 7566 Version 1.0a, 2002. 7568 [LCP] Apple Computer. "Logic 7 Dedicated Control Surface 7569 Support", Appendix B. Product manual available from 7570 www.apple.com. 7572 Authors' Addresses 7574 John Lazzaro (corresponding author) 7575 UC Berkeley 7576 CS Division 7577 315 Soda Hall 7578 Berkeley CA 94720-1776 7579 EMail: lazzaro@cs.berkeley.edu 7581 John Wawrzynek 7582 UC Berkeley 7583 CS Division 7584 631 Soda Hall 7585 Berkeley CA 94720-1776 7586 EMail: johnw@cs.berkeley.edu 7588 Full Copyright Statement 7590 Copyright (c) 2009 IETF Trust and the persons identified as the document 7591 authors. All rights reserved. 7593 This document is subject to BCP 78 and the IETF Trust's Legal Provisions 7594 Relating to IETF Documents (http://trustee.ietf.org/license-info) in 7595 effect on the date of publication of this document. Please review these 7596 documents carefully, as they describe your rights and restrictions with 7597 respect to this document. 7599 Acknowledgement 7601 Funding for the RFC Editor function is currently provided by the 7602 Internet Society. 7604 Change Log for 7606 This I-D is a modified version of RFC 4695. For every error found to 7607 date in RFC 4695, the I-D has been modified to fix the error. 7609 Below, we list the errors found in RFC 4695 that are most likely to 7610 confuse implementors. The fixes to Appendix D ABNF errors listed 7611 below are presented without comments; see Appendix D to see the 7612 commented rule in context. The list below includes the fixes for all 7613 normative errors; most fixes for other types of errors are not listed. 7614 However, the I-D itself contains fixes for all known errors. 7616 -- 7618 03.txt & 04.txt & 05.txt changes: 7620 No errata has been reported for RFC 4695 in the past year. 7621 Apart from updates in the document name and expiration dates, 7622 03.txt, 04.txt and 05.txt contains no changes from 02.txt 7624 -- 7626 02.txt changes: 7628 No errata has been reported for RFC 4695 in the past six months. 7629 Apart from updates in the document name and expiration dates, 7630 02.txt contains no changes from 01.txt 7632 -- 7634 01.txt changes: 7636 A typo was fixed in the Appendix D ABNF. P and Q are now 7637 correctly defined as: 7639 P = %x50 7640 Q = %x51 7642 Thanks to Alfred Hoenes for these changes. 7644 -- 7646 00.txt changes: 7648 Thanks to Alfred Hoenes for these changes. 7650 [1] In Appendix C.1 and Appendix C.2.3 of RFC 4695, an ABNF rule 7651 related to System Chapter X is incorrectly defined as: 7653 = "__" ["_" ] "__" 7655 The correct version of this rule is: 7657 = "__" *( "_" ) "__" 7659 [2] In Appendix C.6.3 of RFC 4695, the URIs permitted to be assigned 7660 to the "url" parameter are not stated clearly. URIs assigned to "url" 7661 MUST specify either HTTP or HTTP over TLS transport protocols. 7663 In Appendix C.7.1 and C.7.2 of RFC 4695, the transport 7664 interoperability requirements for the "url" parameter are not stated 7665 clearly. For both C.7.1 and C.7.2, HTTP is REQUIRED and HTTP over TLS 7666 is OPTIONAL. 7668 [3] Both fmtp lines in both session description examples in Appendix 7669 C.7.2 of RFC 4695 contain instances of the same syntax error (a 7670 missing ";" at a line wrap after "cm_used=2M0.1.2"). 7672 [4] In Appendix D of RFC 4695, all uses of "*ietf-extension" in rules 7673 are in error, and should be replaced with "ietf-extension". Likewise, 7674 all uses of "*extension" are in error, and should be replaced with 7675 "extension". This bug incorrectly lets the null token be assigned to 7676 the j_sec, j_update, render, smf_info, and subrender parameters. 7678 [5] In Appendix D of RFC 4695, the definitions of the 7679 and incorrectly allow lowercase letters to appear in 7680 these strings. The correct definitions of these rules appear below: 7682 command-type = [A] [B] [C] [F] [G] [H] [J] [K] [M] 7683 [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 7685 chapter-list = [A] [B] [C] [D] [E] [F] [G] [H] [J] [K] 7686 [M] [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 7688 A = %x41 7689 B = %x42 7690 C = %x43 7691 D = %x44 7692 E = %x45 7693 F = %x46 7694 G = %x47 7695 H = %x48 7696 J = %x4A 7697 K = %x4B 7698 M = %x4D 7699 N = %x4E 7700 P = %x50 ; correct as shown, these values were 7701 Q = %x51 ; incorrect in the -00.txt I-D version 7702 T = %x54 7703 V = %x56 7704 W = %x57 7705 X = %x58 7706 Y = %x59 7707 Z = %x5A 7709 [5] In Appendix D of RFC 4695, the definitions of the , 7710 , and are incorrect. The correct 7711 definitions of these rules appear below: 7713 nonzero-four-octet = (NZ-DIGIT 0*8(DIGIT)) 7714 / (%x30-33 9(DIGIT)) 7715 / ("4" %x30-31 8(DIGIT)) 7716 / ("42" %x30-38 7(DIGIT)) 7717 / ("429" %x30-33 6(DIGIT)) 7718 / ("4294" %x30-38 5(DIGIT)) 7719 / ("42949" %x30-35 4(DIGIT)) 7720 / ("429496" %x30-36 3(DIGIT)) 7721 / ("4294967" %x30-31 2(DIGIT)) 7722 / ("42949672" %x30-38 (DIGIT)) 7723 / ("429496729" %x30-34) 7725 four-octet = "0" / nonzero-four-octet 7726 midi-chan = DIGIT / ("1" %x30-35) 7728 DIGIT = %x30-39 7729 NZ-DIGIT = %x31-39 7731 [6] In Appendix D of RFC4695, the rule is 7732 incorrect. The correct definition of this rule appears below. 7734 hex-octet = %x30-37 U-HEXDIG 7735 U-HEXDIG = DIGIT / A / B / C / D / E / F 7737 ; DIGIT as defined in [5] above 7738 ; A, B, C, D, E, F as defined in [4] above 7740 [7] In Appendix D of RFC4695, the rules and 7741 are defined unclearly. The rewritten rules 7742 appear below: 7744 base64-unit = 4(base64-char) 7745 base64-pad = (2(base64-char) "==") / (3(base64-char) "=") 7747 ---