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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 7660 -- Looks like a reference, but probably isn't: '2' on line 7669 -- Looks like a reference, but probably isn't: '3' on line 7678 -- Looks like a reference, but probably isn't: '4' on line 7748 -- Looks like a reference, but probably isn't: '5' on line 7747 -- Looks like a reference, but probably isn't: '6' on line 7741 -- Looks like a reference, but probably isn't: '7' on line 7750 -- 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: 4 errors (**), 0 flaws (~~), 2 warnings (==), 17 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT J. Lazzaro 3 July 26, 2010 J. Wawrzynek 4 Expires: January 26, 2011 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 January 26, 2011. 33 Copyright Notice 35 Copyright (c) 2010 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 Provisions 39 Relating to IETF Documents (http://trustee.ietf.org/license-info) 40 in effect on the date of publication of this document. Please 41 review these documents carefully, as they describe your rights and 42 restrictions with respect to this document. Code Components 43 extracted from this document must include Simplified BSD License 44 text as described in Section 4.e of the Trust Legal Provisions and 45 are provided without warranty as described in the Simplified BSD 46 License. 48 Abstract 50 This memo describes a Real-time Transport Protocol (RTP) payload 51 format for the MIDI (Musical Instrument Digital Interface) command 52 language. The format encodes all commands that may legally appear on 53 a MIDI 1.0 DIN cable. The format is suitable for interactive 54 applications (such as network musical performance) and content- 55 delivery applications (such as file streaming). The format may be 56 used over unicast and multicast UDP and TCP, and it defines tools for 57 graceful recovery from packet loss. Stream behavior, including the 58 MIDI rendering method, may be customized during session setup. The 59 format also serves as a mode for the mpeg4-generic format, to support 60 the MPEG 4 Audio Object Types for General MIDI, Downloadable Sounds 61 Level 2, and Structured Audio. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 67 1.2. Bitfield Conventions . . . . . . . . . . . . . . . . . . . 6 68 2. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . . . 7 69 2.1. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 7 70 2.2. MIDI Payload . . . . . . . . . . . . . . . . . . . . . . . 12 71 3. MIDI Command Section . . . . . . . . . . . . . . . . . . . . . . 14 72 3.1. Timestamps . . . . . . . . . . . . . . . . . . . . . . . . 15 73 3.2. Command Coding . . . . . . . . . . . . . . . . . . . . . . 17 74 4. The Recovery Journal System . . . . . . . . . . . . . . . . . . . 24 75 5. Recovery Journal Format . . . . . . . . . . . . . . . . . . . . . 26 76 6. Session Description Protocol . . . . . . . . . . . . . . . . . . 30 77 6.1. Session Descriptions for Native Streams . . . . . . . . . 31 78 6.2. Session Descriptions for mpeg4-generic Streams . . . . . . 33 79 6.3. Parameters . . . . . . . . . . . . . . . . . . . . . . . . 35 80 7. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . . . 37 81 8. Congestion Control . . . . . . . . . . . . . . . . . . . . . . . 38 82 9. Security Considerations . . . . . . . . . . . . . . . . . . . . . 39 83 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 40 84 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 40 85 11.1. rtp-midi Media Type Registration . . . . . . . . . . . . 41 86 11.1.1. Repository Request for "audio/rtp-midi" . . . . . 43 87 11.2. mpeg4-generic Media Type Registration . . . . . . . . . . 45 88 11.2.1. Repository Request for Mode rtp-midi for 89 mpeg4-generic . . . . . . . . . . . . . . . . . . 48 90 11.3. asc Media Type Registration . . . . . . . . . . . . . . . 49 91 A. The Recovery Journal Channel Chapters . . . . . . . . . . . . . . 52 92 A.1. Recovery Journal Definitions . . . . . . . . . . . . . . . 52 93 A.2. Chapter P: MIDI Program Change . . . . . . . . . . . . . . 57 94 A.3. Chapter C: MIDI Control Change . . . . . . . . . . . . . . 58 95 A.3.1. Log Inclusion Rules . . . . . . . . . . . . . . . . 58 96 A.3.2. Controller Log Format . . . . . . . . . . . . . . . 60 97 A.3.3. Log List Coding Rules . . . . . . . . . . . . . . . 62 98 A.3.4. The Parameter System . . . . . . . . . . . . . . . 65 99 A.4. Chapter M: MIDI Parameter System . . . . . . . . . . . . . 67 100 A.4.1. Log Inclusion Rules . . . . . . . . . . . . . . . . 68 101 A.4.2. Log Coding Rules . . . . . . . . . . . . . . . . . 70 102 A.4.2.1. The Value Tool . . . . . . . . . . . . . . . 71 103 A.4.2.2. The Count Tool . . . . . . . . . . . . . . . 75 104 A.5. Chapter W: MIDI Pitch Wheel . . . . . . . . . . . . . . . 76 105 A.6. Chapter N: MIDI NoteOff and NoteOn . . . . . . . . . . . . 77 106 A.6.1. Header Structure . . . . . . . . . . . . . . . . . 78 107 A.6.2. Note Structures . . . . . . . . . . . . . . . . . . 79 108 A.7. Chapter E: MIDI Note Command Extras . . . . . . . . . . . 81 109 A.7.1. Note Log Format . . . . . . . . . . . . . . . . . . 82 110 A.7.2. Log Inclusion Rules . . . . . . . . . . . . . . . . 82 111 A.8. Chapter T: MIDI Channel Aftertouch . . . . . . . . . . . . 83 112 A.9. Chapter A: MIDI Poly Aftertouch . . . . . . . . . . . . . 84 113 B. The Recovery Journal System Chapters . . . . . . . . . . . . . . 86 114 B.1. System Chapter D: Simple System Commands . . . . . . . . . 86 115 B.1.1. Undefined System Commands . . . . . . . . . . 87 116 B.2. System Chapter V: Active Sense Command . . . . . . . . . . 90 117 B.3. System Chapter Q: Sequencer State Commands . . . . . . . . 91 118 B.3.1. Non-compliant Sequencers . . . . . . . . . . . 93 119 B.4. System Chapter F: MIDI Time Code Tape Position . . . . . . 94 120 B.4.1. Partial Frames . . . . . . . . . . . . . . . . . . 96 121 B.5. System Chapter X: System Exclusive . . . . . . . . . . . . 98 122 B.5.1. Chapter Format . . . . . . . . . . . . . . . . 98 123 B.5.2. Log Inclusion Semantics . . . . . . . . . . . 101 124 B.5.3. TCOUNT and COUNT Fields . . . . . . . . . . . 103 125 C. Session Configuration Tools . . . . . . . . . . . . . . . . . . . 105 126 C.1. Configuration Tools: Stream Subsetting . . . . . . . . . . 106 127 C.2. Configuration Tools: The Journalling System . . . . . . . 110 128 C.2.1. The j_sec Parameter . . . . . . . . . . . . . . . . 111 129 C.2.2. The j_update Parameter . . . . . . . . . . . . . . 112 130 C.2.2.1. The anchor Sending Policy . . . . . . . . . 113 131 C.2.2.2. The closed-loop Sending Policy . . . . . . . 113 132 C.2.2.3. The open-loop Sending Policy . . . . . . . . 117 133 C.2.3. Recovery Journal Chapter Inclusion Parameters . . . 119 134 C.3. Configuration Tools: Timestamp Semantics . . . . . . . . . 124 135 C.3.1. The comex Algorithm . . . . . . . . . . . . . . . . 124 136 C.3.2. The async Algorithm . . . . . . . . . . . . . . . . 125 137 C.3.3. The buffer Algorithm . . . . . . . . . . . . . . . 126 138 C.4. Configuration Tools: Packet Timing Tools . . . . . . . . . 128 139 C.4.1. Packet Duration Tools . . . . . . . . . . . . . . . 128 140 C.4.2. The guardtime Parameter . . . . . . . . . . . . . . 129 141 C.5. Configuration Tools: Stream Description . . . . . . . . . 131 142 C.6. Configuration Tools: MIDI Rendering . . . . . . . . . . . 137 143 C.6.1. The multimode Parameter . . . . . . . . . . . . . . 138 144 C.6.2. Renderer Specification . . . . . . . . . . . . . . 138 145 C.6.3. Renderer Initialization . . . . . . . . . . . . . . 141 146 C.6.4. MIDI Channel Mapping . . . . . . . . . . . . . . . 143 147 C.6.4.1. The smf_info Parameter . . . . . . . . . . . 143 148 C.6.4.2. The smf_inline, smf_url, and smf_cid 149 Parameters . . . . . . . . . . . . . . . . . 145 150 C.6.4.3. The chanmask Parameter . . . . . . . . . . . 146 151 C.6.5. The audio/asc Media Type . . . . . . . . . . . . . 147 152 C.7. Interoperability . . . . . . . . . . . . . . . . . . . . . 149 153 C.7.1. MIDI Content Streaming Applications . . . . . . . 149 154 C.7.2. MIDI Network Musical Performance Applications . . . 152 155 D. Parameter Syntax Definitions . . . . . . . . . . . . . . . . . . 161 156 E. A MIDI Overview for Networking Specialists . . . . . . . . . . . 168 157 E.1. Commands Types . . . . . . . . . . . . . . . . . . . . . . 170 158 E.2. Running Status . . . . . . . . . . . . . . . . . . . . . . 170 159 E.3. Command Timing . . . . . . . . . . . . . . . . . . . . . . 171 160 E.4. AudioSpecificConfig Templates for MMA Renderers . . . . . 171 161 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 162 Normative References . . . . . . . . . . . . . . . . . . . . . 176 163 Informative References . . . . . . . . . . . . . . . . . . . . 177 164 Change Log for . . . . . . . . . 180 165 1. Introduction 167 The Internet Engineering Task Force (IETF) has developed a set of 168 focused tools for multimedia networking ([RFC3550] [RFC4566] [RFC3261] 169 [RFC2326]). These tools can be combined in different ways to support a 170 variety of real-time applications over Internet Protocol (IP) networks. 172 For example, a telephony application might use the Session Initiation 173 Protocol (SIP, [RFC3261]) to set up a phone call. Call setup would 174 include negotiations to agree on a common audio codec [RFC3264]. 175 Negotiations would use the Session Description Protocol (SDP, [RFC4566]) 176 to describe candidate codecs. 178 After a call is set up, audio data would flow between the parties using 179 the Real Time Protocol (RTP, [RFC3550]) under any applicable profile 180 (for example, the Audio/Visual Profile (AVP, [RFC3551])). The tools 181 used in this telephony example (SIP, SDP, RTP) might be combined in a 182 different way to support a content streaming application, perhaps in 183 conjunction with other tools, such as the Real Time Streaming Protocol 184 (RTSP, [RFC2326]). 186 The MIDI (Musical Instrument Digital Interface) command language [MIDI] 187 is widely used in musical applications that are analogous to the 188 examples described above. On stage and in the recording studio, MIDI is 189 used for the interactive remote control of musical instruments, an 190 application similar in spirit to telephony. On web pages, Standard MIDI 191 Files (SMFs, [MIDI]) rendered using the General MIDI standard [MIDI] 192 provide a low-bandwidth substitute for audio streaming. 194 This memo is motivated by a simple premise: if MIDI performances could 195 be sent as RTP streams that are managed by IETF session tools, a 196 hybridization of the MIDI and IETF application domains may occur. 198 For example, interoperable MIDI networking may foster network music 199 performance applications, in which a group of musicians, located at 200 different physical locations, interact over a network to perform as they 201 would if they were located in the same room [NMP]. As a second example, 202 the streaming community may begin to use MIDI for low- bitrate audio 203 coding, perhaps in conjunction with normative sound synthesis methods 204 [MPEGSA]. 206 To enable MIDI applications to use RTP, this memo defines an RTP payload 207 format and its media type. Sections 2-5 and Appendices A-B define the 208 RTP payload format. Section 6 and Appendices C-D define the media types 209 identifying the payload format, the parameters needed for configuration, 210 and how the parameters are utilized in SDP. 212 Appendix C also includes interoperability guidelines for the example 213 applications described above: network musical performance using SIP 214 (Appendix C.7.2) and content-streaming using RTSP (Appendix C.7.1). 216 Another potential application area for RTP MIDI is MIDI networking for 217 professional audio equipment and electronic musical instruments. We do 218 not offer interoperability guidelines for this application in this memo. 219 However, RTP MIDI has been designed with stage and studio applications 220 in mind, and we expect that efforts to define a stage and studio 221 framework will rely on RTP MIDI for MIDI transport services. 223 Some applications may require MIDI media delivery at a certain service 224 quality level (latency, jitter, packet loss, etc). RTP itself does not 225 provide service guarantees. However, applications may use lower-layer 226 network protocols to configure the quality of the transport services 227 that RTP uses. These protocols may act to reserve network resources for 228 RTP flows [RFC2205] or may simply direct RTP traffic onto a dedicated 229 "media network" in a local installation. Note that RTP and the MIDI 230 payload format do provide tools that applications may use to achieve the 231 best possible real-time performance at a given service level. 233 This memo normatively defines the syntax and semantics of the MIDI 234 payload format. However, this memo does not define algorithms for 235 sending and receiving packets. An ancillary document [RFC4696] provides 236 informative guidance on algorithms. Supplemental information may be 237 found in related conference publications [NMP] [GRAME]. 239 Throughout this memo, the phrase "native stream" refers to a stream that 240 uses the rtp-midi media type. The phrase "mpeg4-generic stream" refers 241 to a stream that uses the mpeg4-generic media type (in mode rtp-midi) to 242 operate in an MPEG 4 environment [RFC3640]. Section 6 describes this 243 distinction in detail. 245 1.1. Terminology 247 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 248 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 249 document are to be interpreted as described in BCP 14, RFC 2119 250 [RFC2119]. 252 1.2. Bitfield Conventions 254 In this document, the packet bitfields that share a common name often 255 have identical semantics. As most of these bitfields appear in 256 Appendices A-B, we define the common bitfield names in Appendix A.1. 258 However, a few of these common names also appear in the main text of 259 this document. For convenience, we list these definitions below: 261 o R flag bit. R flag bits are reserved for future use. Senders 262 MUST set R bits to 0. Receivers MUST ignore R bit values. 264 o LENGTH field. All fields named LENGTH (as distinct from LEN) 265 code the number of octets in the structure that contains it, 266 including the header it resides in and all hierarchical levels 267 below it. If a structure contains a LENGTH field, a receiver 268 MUST use the LENGTH field value to advance past the structure 269 during parsing, rather than use knowledge about the internal 270 format of the structure. 272 2. Packet Format 274 In this section, we introduce the format of RTP MIDI packets. The 275 description includes some background information on RTP, for the benefit 276 of MIDI implementors new to IETF tools. Implementors should consult 277 [RFC3550] for an authoritative description of RTP. 279 This memo assumes that the reader is familiar with MIDI syntax and 280 semantics. Appendix E provides a MIDI overview, at a level of detail 281 sufficient to understand most of this memo. Implementors should consult 282 [MIDI] for an authoritative description of MIDI. 284 The MIDI payload format maps a MIDI command stream (16 voice channels + 285 systems) onto an RTP stream. An RTP media stream is a sequence of 286 logical packets that share a common format. Each packet consists of two 287 parts: the RTP header and the MIDI payload. Figure 1 shows this format 288 (vertical space delineates the header and payload). 290 We describe RTP packets as "logical" packets to highlight the fact that 291 RTP itself is not a network-layer protocol. Instead, RTP packets are 292 mapped onto network protocols (such as unicast UDP, multicast UDP, or 293 TCP) by an application [ALF]. The interleaved mode of the Real Time 294 Streaming Protocol (RTSP, [RFC2326]) is an example of an RTP mapping to 295 TCP transport, as is [RFC4571]. 297 2.1. RTP Header 299 [RFC3550] provides a complete description of the RTP header fields. In 300 this section, we clarify the role of a few RTP header fields for MIDI 301 applications. All fields are coded in network byte order (big- endian). 303 0 1 2 3 304 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 1 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 | V |P|X| CC |M| PT | Sequence number | 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 | Timestamp | 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 | SSRC | 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 314 | MIDI command section ... | 315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 316 | Journal section ... | 317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 319 Figure 1 -- Packet format 321 The behavior of the 1-bit M field depends on the media type of the 322 stream. For native streams, the M bit MUST be set to 1 if the MIDI 323 command section has a non-zero LEN field, and MUST be set to 0 324 otherwise. For mpeg4-generic streams, the M bit MUST be set to 1 for 325 all packets (to conform to [RFC3640]). 327 In an RTP MIDI stream, the 16-bit sequence number field is initialized 328 to a randomly chosen value and is incremented by one (modulo 2^16) for 329 each packet sent in the stream. A related quantity, the 32-bit extended 330 packet sequence number, may be computed by tracking rollovers of the 331 16-bit sequence number. Note that different receivers of the same 332 stream may compute different extended packet sequence numbers, depending 333 on when the receiver joined the session. 335 The 32-bit timestamp field sets the base timestamp value for the packet. 336 The payload codes MIDI command timing relative to this value. The 337 timestamp units are set by the clock rate parameter. For example, if 338 the clock rate has a value of 44100 Hz, two packets whose base timestamp 339 values differ by 2 seconds have RTP timestamp fields that differ by 340 88200. 342 Note that the clock rate parameter is not encoded within each RTP MIDI 343 packet. A receiver of an RTP MIDI stream becomes aware of the clock 344 rate as part of the session setup process. For example, if a session 345 management tool uses the Session Description Protocol (SDP, [RFC4566]) 346 to describe a media session, the clock rate parameter is set using the 347 rtpmap attribute. We show examples of session setup in Section 6. 349 For RTP MIDI streams destined to be rendered into audio, the clock rate 350 SHOULD be an audio sample rate of 32 KHz or higher. This recommendation 351 is due to the sensitivity of human musical perception to small timing 352 errors in musical note sequences, and due to the timbral changes that 353 occur when two near-simultaneous MIDI NoteOns are rendered with a 354 different timing than that desired by the content author due to clock 355 rate quantization. RTP MIDI streams that are not destined for audio 356 rendering (such as MIDI streams that control stage lighting) MAY use a 357 lower clock rate but SHOULD use a clock rate high enough to avoid timing 358 artifacts in the application. 360 For RTP MIDI streams destined to be rendered into audio, the clock rate 361 SHOULD be chosen from rates in common use in professional audio 362 applications or in consumer audio distribution. At the time of this 363 writing, these rates include 32 KHz, 44.1 KHz, 48 KHz, 64 KHz, 88.2 KHz, 364 96 KHz, 176.4 KHz, and 192 KHz. If the RTP MIDI session is a part of a 365 synchronized media session that includes another (non-MIDI) RTP audio 366 stream with a clock rate of 32 KHz or higher, the RTP MIDI stream SHOULD 367 use a clock rate that matches the clock rate of the other audio stream. 368 However, if the RTP MIDI stream is destined to be rendered into audio, 369 the RTP MIDI stream SHOULD NOT use a clock rate lower than 32 KHz, even 370 if this second stream has a clock rate less than 32 KHz. 372 Timestamps of consecutive packets do not necessarily increment at a 373 fixed rate, because RTP MIDI packets are not necessarily sent at a fixed 374 rate. The degree of packet transmission regularity reflects the 375 underlying application dynamics. Interactive applications may vary the 376 packet sending rate to track the gestural rate of a human performer, 377 whereas content-streaming applications may send packets at a fixed rate. 379 Therefore, the timestamps for two sequential RTP packets may be 380 identical, or the second packet may have a timestamp arbitrarily larger 381 than the first packet (modulo 2^32). Section 3 places additional 382 restrictions on the RTP timestamps for two sequential RTP packets, as 383 does the guardtime parameter (Appendix C.4.2). 385 We use the term "media time" to denote the temporal duration of the 386 media coded by an RTP packet. The media time coded by a packet is 387 computed by subtracting the last command timestamp in the MIDI command 388 section from the RTP timestamp (modulo 2^32). If the MIDI list of the 389 MIDI command section of a packet is empty, the media time coded by the 390 packet is 0 ms. Appendix C.4.1 discusses media time issues in detail. 392 We now define RTP session semantics, in the context of sessions 393 specified using the session description protocol [RFC4566]. A session 394 description media line ("m=") specifies an RTP session. An RTP session 395 has an independent space of 2^32 synchronization sources. 396 Synchronization source identifiers are coded in the SSRC header field of 397 RTP session packets. The payload types that may appear in the PT header 398 field of RTP session packets are listed at the end of the media line. 400 Several RTP MIDI streams may appear in an RTP session. Each stream is 401 distinguished by a unique SSRC value and has a unique sequence number 402 and RTP timestamp space. Multiple streams in the RTP session may be 403 sent by a single party. Multiple parties may send streams in the RTP 404 session. An RTP MIDI stream encodes data for a single MIDI command name 405 space (16 voice channels + Systems). 407 Streams in an RTP session may use different payload types, or they may 408 use the same payload type. However, each party may send, at most, one 409 RTP MIDI stream for each payload type mapped to an RTP MIDI payload 410 format in an RTP session. Recall that dynamic binding of payload type 411 numbers in [RFC4566] lets a party map many payload type numbers to the 412 RTP MIDI payload format; thus a party may send many RTP MIDI streams in 413 a single RTP session. Pairs of streams (unicast or multicast) that 414 communicate between two parties in an RTP session and that share a 415 payload type have the same association as a MIDI cable pair that cross- 416 connects two devices in a MIDI 1.0 DIN network. 418 The RTP session architecture described above is efficient in its use of 419 network ports, as one RTP session (using a port pair per party) supports 420 the transport of many MIDI name spaces (16 MIDI channels + systems). We 421 define tools for grouping and labelling MIDI name spaces across streams 422 and sessions in Appendix C.5 of this memo. 424 The RTP header timestamps for each stream in an RTP session have 425 separately and randomly chosen initialization values. Receivers use the 426 timing fields encoded in the RTP control protocol (RTCP, [RFC3550]) 427 sender reports to synchronize the streams sent by a party. The SSRC 428 values for each stream in an RTP session are also separately and 429 randomly chosen, as described in [RFC3550]. Receivers use the CNAME 430 field encoded in RTCP sender reports to verify that streams were sent by 431 the same party, and to detect SSRC collisions, as described in 432 [RFC3550]. 434 In some applications, a receiver renders MIDI commands into audio (or 435 into control actions, such as the rewind of a tape deck or the dimming 436 of stage lights). In other applications, a receiver presents a MIDI 437 stream to software programs via an Application Programmer Interface 438 (API). Appendix C.6 defines session configuration tools to specify what 439 receivers should do with a MIDI command stream. 441 If a multimedia session uses different RTP MIDI streams to send 442 different classes of media, the streams MUST be sent over different RTP 443 sessions. For example, if a multimedia session uses one MIDI stream for 444 audio and a second MIDI stream to control a lighting system, the audio 445 and lighting streams MUST be sent over different RTP sessions, each with 446 its own media line. 448 Session description tools defined in Appendix C.5 let a sending party 449 split a single MIDI name space (16 voice channels + systems) over 450 several RTP MIDI streams. Split transport of a MIDI command stream is a 451 delicate task, because correct command stream reconstruction by a 452 receiver depends on exact timing synchronization across the streams. 454 To support split name spaces, we define the following requirements: 456 o A party MUST NOT send several RTP MIDI streams that share a MIDI 457 name space in the same RTP session. Instead, each stream MUST 458 be sent from a different RTP session. 460 o If several RTP MIDI streams sent by a party share a MIDI name 461 space, all streams MUST use the same SSRC value and MUST use the 462 same randomly chosen RTP timestamp initialization value. 464 These rules let a receiver identify streams that share a MIDI name space 465 (by matching SSRC values) and also let a receiver accurately reconstruct 466 the source MIDI command stream (by using RTP timestamps to interleave 467 commands from the two streams). Care MUST be taken by senders to ensure 468 that SSRC changes due to collisions are reflected in both streams. 469 Receivers MUST regularly examine the RTCP CNAME fields associated with 470 the linked streams, to ensure that the assumed link is legitimate and 471 not the result of an SSRC collision by another sender. 473 Except for the special cases described above, a party may send many RTP 474 MIDI streams in the same session. However, it is sometimes advantageous 475 for two RTP MIDI streams to be sent over different RTP sessions. For 476 example, two streams may need different values for RTP session-level 477 attributes (such as the sendonly and recvonly attributes). As a second 478 example, two RTP sessions may be needed to send two unicast streams in a 479 multimedia session that originate on different computers (with different 480 IP numbers). Two RTP sessions are needed in this case because transport 481 addresses are specified on the RTP-session or multimedia-session level, 482 not on a payload type level. 484 On a final note, in some uses of MIDI, parties send bidirectional 485 traffic to conduct transactions (such as file exchange). These commands 486 were designed to work over MIDI 1.0 DIN cable networks may be configured 487 in a multicast topology, which use pure "party-line" signalling. Thus, 488 if a multimedia session ensures a multicast connection between all 489 parties, bidirectional MIDI commands will work without additional 490 support from the RTP MIDI payload format. 492 2.2. MIDI Payload 494 The payload (Figure 1) MUST begin with the MIDI command section. The 495 MIDI command section codes a (possibly empty) list of timestamped MIDI 496 commands, and provides the essential service of the payload format. 498 The payload MAY also contain a journal section. The journal section 499 provides resiliency by coding the recent history of the stream. A flag 500 in the MIDI command section codes the presence of a journal section in 501 the payload. 503 Section 3 defines the MIDI command section. Sections 4-5 and Appendices 504 A-B define the recovery journal, the default format for the journal 505 section. Here, we describe how these payload sections operate in a 506 stream in an RTP session. 508 The journalling method for a stream is set at the start of a session and 509 MUST NOT be changed thereafter. A stream may be set to use the recovery 510 journal, to use an alternative journal format (none are defined in this 511 memo), or not to use a journal. 513 The default journalling method of a stream is inferred from its 514 transport type. Streams that use unreliable transport (such as UDP) 515 default to using the recovery journal. Streams that use reliable 516 transport (such as TCP) default to not using a journal. Appendix C.2.1 517 defines session configuration tools for overriding these defaults. For 518 all types of transport, a sender MUST transmit an RTP packet stream with 519 consecutive sequence numbers (modulo 2^16). 521 If a stream uses the recovery journal, every payload in the stream MUST 522 include a journal section. If a stream does not use journalling, a 523 journal section MUST NOT appear in a stream payload. If a stream uses 524 an alternative journal format, the specification for the journal format 525 defines an inclusion policy. 527 If a stream is sent over UDP transport, the Maximum Transmission Unit 528 (MTU) of the underlying network limits the practical size of the payload 529 section (for example, an Ethernet MTU is 1500 octets), for applications 530 where predictable and minimal packet transmission latency is critical. 531 A sender SHOULD NOT create RTP MIDI UDP packets whose size exceeds the 532 MTU of the underlying network. Instead, the sender SHOULD take steps to 533 keep the maximum packet size under the MTU limit. 535 These steps may take many forms. The default closed-loop recovery 536 journal sending policy (defined in Appendix C.2.2.2) uses RTP control 537 protocol (RTCP, [RFC3550]) feedback to manage the RTP MIDI packet size. 538 In addition, Section 3.2 and Appendix B.5.2 provide specific tools for 539 managing the size of packets that code MIDI System Exclusive (0xF0) 540 commands. Appendix C.5 defines session configuration tools that may be 541 used to split a dense MIDI name space into several UDP streams (each 542 sent in a different RTP session, per Section 2.1) so that the payload 543 fits comfortably into an MTU. Another option is to use TCP. Section 544 4.3 of [RFC4696] provides non-normative advice for packet size 545 management. 547 3. MIDI Command Section 549 Figure 2 shows the format of the MIDI command section. 551 0 1 2 3 552 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 1 553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 554 |B|J|Z|P|LEN... | MIDI list ... | 555 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 557 Figure 2 -- MIDI command section 559 The MIDI command section begins with a variable-length header. 561 The header field LEN codes the number of octets in the MIDI list that 562 follow the header. If the header flag B is 0, the header is one octet 563 long, and LEN is a 4-bit field, supporting a maximum MIDI list length of 564 15 octets. 566 If B is 1, the header is two octets long, and LEN is a 12-bit field, 567 supporting a maximum MIDI list length of 4095 octets. LEN is coded in 568 network byte order (big-endian): the 4 bits of LEN that appear in the 569 first header octet code the most significant 4 bits of the 12-bit LEN 570 value. 572 A LEN value of 0 is legal, and it codes an empty MIDI list. 574 If the J header bit is set to 1, a journal section MUST appear after the 575 MIDI command section in the payload. If the J header bit is set to 0, 576 the payload MUST NOT contain a journal section. 578 We define the semantics of the P header bit in Section 3.2. 580 If the LEN header field is nonzero, the MIDI list has the structure 581 shown in Figure 3. 583 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 584 | Delta Time 0 (1-4 octets long, or 0 octets if Z = 1) | 585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 586 | MIDI Command 0 (1 or more octets long) | 587 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 588 | Delta Time 1 (1-4 octets long) | 589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 590 | MIDI Command 1 (1 or more octets long) | 591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 592 | ... | 593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 594 | Delta Time N (1-4 octets long) | 595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 596 | MIDI Command N (0 or more octets long) | 597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 599 Figure 3 -- MIDI list structure 601 If the header flag Z is 1, the MIDI list begins with a complete MIDI 602 command (coded in the MIDI Command 0 field, in Figure 3) preceded by a 603 delta time (coded in the Delta Time 0 field). If Z is 0, the Delta Time 604 0 field is not present in the MIDI list, and the command coded in the 605 MIDI Command 0 field has an implicit delta time of 0. 607 The MIDI list structure may also optionally encode a list of N 608 additional complete MIDI commands, each coded in a MIDI Command K field. 609 Each additional command MUST be preceded by a Delta Time K field, which 610 codes the command's delta time. We discuss exceptions to the "command 611 fields code complete MIDI commands" rule in Section 3.2. 613 The final MIDI command field (i.e., the MIDI Command N field, shown in 614 Figure 3) in the MIDI list MAY be empty. Moreover, a MIDI list MAY 615 consist a single delta time (encoded in the Delta Time 0 field) without 616 an associated command (which would have been encoded in the MIDI Command 617 0 field). These rules enable MIDI coding features that are explained in 618 Section 3.1. We delay the explanations because an understanding of RTP 619 MIDI timestamps is necessary to describe the features. 621 3.1. Timestamps 623 In this section, we describe how RTP MIDI encodes a timestamp for each 624 MIDI list command. Command timestamps have the same units as RTP packet 625 header timestamps (described in Section 2.1 and [RFC3550]). Recall that 626 RTP timestamps have units of seconds, whose scaling is set during 627 session configuration (see Section 6.1 and [RFC4566]). 629 As shown in Figure 3, the MIDI list encodes time using a compact delta- 630 time format. The RTP MIDI delta time syntax is a modified form of the 631 MIDI File delta time syntax [MIDI]. RTP MIDI delta times use 1-4 octet 632 fields to encode 32-bit unsigned integers. Figure 4 shows the encoded 633 and decoded forms of delta times. Note that delta time values may be 634 legally encoded in multiple formats; for example, there are four legal 635 ways to encode the zero delta time (0x00, 0x8000, 0x808000, 0x80808000). 637 RTP MIDI uses delta times to encode a timestamp for each MIDI command. 638 The timestamp for MIDI Command K is the summation (modulo 2^32) of the 639 RTP timestamp and decoded delta times 0 through K. This cumulative 640 coding technique, borrowed from MIDI File delta time coding, is 641 efficient because it reduces the number of multi-octet delta times. 643 All command timestamps in a packet MUST be less than or equal to the RTP 644 timestamp of the next packet in the stream (modulo 2^32). 646 This restriction ensures that a particular RTP MIDI packet in a stream 647 is uniquely responsible for encoding time starting at the moment after 648 the RTP timestamp encoded in the RTP packet header, and ending at the 649 moment before the final command timestamp encoded in the MIDI list. The 650 "moment before" and "moment after" qualifiers acknowledge the "less than 651 or equal" semantics (as opposed to "strictly less than") in the sentence 652 above this paragraph. 654 Note that it is possible to "pad" the end of an RTP MIDI packet with 655 time that is guaranteed to be void of MIDI commands, by setting the 656 "Delta Time N" field of the MIDI list to the end of the void time, and 657 by omitting its corresponding "MIDI Command N" field (a syntactic 658 construction the preamble of Section 3 expressly made legal). 660 In addition, it is possible to code an RTP MIDI packet to express that a 661 period of time in the stream is void of MIDI commands. The RTP 662 timestamp in the header would code the start of the void time. The MIDI 663 list of this packet would consist of a "Delta Time 0" field that coded 664 the end of the void time. No other fields would be present in the MIDI 665 list (a syntactic construction the preamble of Section 3 also expressly 666 made legal). 668 By default, a command timestamp indicates the execution time for the 669 command. The difference between two timestamps indicates the time delay 670 between the execution of the commands. This difference may be zero, 671 coding simultaneous execution. In this memo, we refer to this 672 interpretation of timestamps as "comex" (COMmand EXecution) semantics. 673 We formally define comex semantics in Appendix C.3. 675 The comex interpretation of timestamps works well for transcoding a 676 Standard MIDI File (SMF) into an RTP MIDI stream, as SMFs code a 677 timestamp for each MIDI command stored in the file. To transcode an SMF 678 that uses metric time markers, use the SMF tempo map (encoded in the SMF 679 as meta-events) to convert metric SMF timestamp units into seconds-based 680 RTP timestamp units. 682 The comex interpretation also works well for MIDI hardware controllers 683 that are coding raw sensor data directly onto an RTP MIDI stream. Note 684 that this controller design is preferable to a design that converts raw 685 sensor data into a MIDI 1.0 cable command stream and then transcodes the 686 stream onto an RTP MIDI stream. 688 The comex interpretation of timestamps is usually not the best timestamp 689 interpretation for transcoding a MIDI source that uses implicit command 690 timing (such as MIDI 1.0 DIN cables) into an RTP MIDI stream. Appendix 691 C.3 defines alternatives to comex semantics and describes session 692 configuration tools for selecting the timestamp interpretation semantics 693 for a stream. 695 One-Octet Delta Time: 697 Encoded form: 0ddddddd 698 Decoded form: 00000000 00000000 00000000 0ddddddd 700 Two-Octet Delta Time: 702 Encoded form: 1ccccccc 0ddddddd 703 Decoded form: 00000000 00000000 00cccccc cddddddd 705 Three-Octet Delta Time: 707 Encoded form: 1bbbbbbb 1ccccccc 0ddddddd 708 Decoded form: 00000000 000bbbbb bbcccccc cddddddd 710 Four-Octet Delta Time: 712 Encoded form: 1aaaaaaa 1bbbbbbb 1ccccccc 0ddddddd 713 Decoded form: 0000aaaa aaabbbbb bbcccccc cddddddd 715 Figure 4 -- Decoding delta time formats 717 3.2. Command Coding 719 Each non-empty MIDI Command field in the MIDI list codes one of the MIDI 720 command types that may legally appear on a MIDI 1.0 DIN cable. Standard 721 MIDI File meta-events do not fit this definition and MUST NOT appear in 722 the MIDI list. As a rule, each MIDI Command field codes a complete 723 command, in the binary command format defined in [MIDI]. In the 724 remainder of this section, we describe exceptions to this rule. 726 The first MIDI channel command in the MIDI list MUST include a status 727 octet. Running status coding, as defined in [MIDI], MAY be used for all 728 subsequent MIDI channel commands in the list. As in [MIDI], System 729 Common and System Exclusive messages (0xF0 ... 0xF7) cancel the running 730 status state, but System Real-time messages (0xF8 ... 0xFF) do not 731 affect the running status state. All System commands in the MIDI list 732 MUST include a status octet. 734 As we note above, the first channel command in the MIDI list MUST 735 include a status octet. However, the corresponding command in the 736 original MIDI source data stream might not have a status octet (in this 737 case, the source would be coding the command using running status). If 738 the status octet of the first channel command in the MIDI list does not 739 appear in the source data stream, the P (phantom) header bit MUST be set 740 to 1. In all other cases, the P bit MUST be set to 0. 742 Note that the P bit describes the MIDI source data stream, not the MIDI 743 list encoding; regardless of the state of the P bit, the MIDI list MUST 744 include the status octet. 746 As receivers MUST be able to decode running status, sender implementors 747 should feel free to use running status to improve bandwidth efficiency. 748 However, senders SHOULD NOT introduce timing jitter into an existing 749 MIDI command stream through an inappropriate use or removal of running 750 status coding. This warning primarily applies to senders whose RTP MIDI 751 streams may be transcoded onto a MIDI 1.0 DIN cable [MIDI] by the 752 receiver: both the timestamps and the command coding (running status or 753 not) must comply with the physical restrictions of implicit time coding 754 over a slow serial line. 756 On a MIDI 1.0 DIN cable [MIDI], a System Real-time command may be 757 embedded inside of another "host" MIDI command. This syntactic 758 construction is not supported in the payload format: a MIDI Command 759 field in the MIDI list codes exactly one MIDI command (partially or 760 completely). 762 To encode an embedded System Real-time command, senders MUST extract the 763 command from its host and code it in the MIDI list as a separate 764 command. The host command and System Real-time command SHOULD appear in 765 the same MIDI list. The delta time of the System Real-time command 766 SHOULD result in a command timestamp that encodes the System Real-time 767 command placement in its original embedded position. 769 Two methods are provided for encoding MIDI System Exclusive (SysEx) 770 commands in the MIDI list. A SysEx command may be encoded in a MIDI 771 Command field verbatim: a 0xF0 octet, followed by an arbitrary number of 772 data octets, followed by a 0xF7 octet. 774 Alternatively, a SysEx command may be encoded as multiple segments. The 775 command is divided into two or more SysEx command segments; each segment 776 is encoded in its own MIDI Command field in the MIDI list. 778 The payload format supports segmentation in order to encode SysEx 779 commands that encode information in the temporal pattern of data octets. 780 By encoding these commands as a series of segments, each data octet may 781 be associated with a distinct delta time. Segmentation also supports 782 the coding of large SysEx commands across several packets. 784 To segment a SysEx command, first partition its data octet list into two 785 or more sublists. The last sublist MAY be empty (i.e., contain no 786 octets); all other sublists MUST contain at least one data octet. To 787 complete the segmentation, add the status octets defined in Figure 5 to 788 the head and tail of the first, last, and any "middle" sublists. Figure 789 6 shows example segmentations of a SysEx command. 791 A sender MAY cancel a segmented SysEx command transmission that is in 792 progress, by sending the "cancel" sublist shown in Figure 5. A "cancel" 793 sublist MAY follow a "first" or "middle" sublist in the transmission, 794 but MUST NOT follow a "last" sublist. The cancel MUST be empty (thus, 795 0xF7 0xF4 is the only legal cancel sublist). 797 The cancellation feature is needed because Appendix C.1 defines 798 configuration tools that let session parties exclude certain SysEx 799 commands in the stream. Senders that transcode a MIDI source onto an 800 RTP MIDI stream under these constraints have the responsibility of 801 excluding undesired commands from the RTP MIDI stream. 803 The cancellation feature lets a sender start the transmission of a 804 command before the MIDI source has sent the entire command. If a sender 805 determines that the command whose transmission is in progress should not 806 appear on the RTP stream, it cancels the command. Without a method for 807 cancelling a SysEx command transmission, senders would be forced to use 808 a high-latency store-and-forward approach to transcoding SysEx commands 809 onto RTP MIDI packets, in order to validate each SysEx command before 810 transmission. 812 The recommended receiver reaction to a cancellation depends on the 813 capabilities of the receiver. For example, a sound synthesizer that is 814 directly parsing RTP MIDI packets and rendering them to audio will be 815 aware of the fact that SysEx commands may be cancelled in RTP MIDI. 816 These receivers SHOULD detect a SysEx cancellation in the MIDI list and 817 act as if they had never received the SysEx command. 819 As a second example, a synthesizer may be receiving MIDI data from an 820 RTP MIDI stream via a MIDI DIN cable (or a software API emulation of a 821 MIDI DIN cable). In this case, an RTP-MIDI-aware system receives the 822 RTP MIDI stream and transcodes it onto the MIDI DIN cable (or its 823 emulation). Upon the receipt of the cancel sublist, the RTP-MIDI- aware 824 transcoder might have already sent the first part of the SysEx command 825 on the MIDI DIN cable to the receiver. 827 Unfortunately, the MIDI DIN cable protocol cannot directly code "cancel 828 SysEx in progress" semantics. However, MIDI DIN cable receivers begin 829 SysEx processing after the complete command arrives. The receiver 830 checks to see if it recognizes the command (coded in the first few 831 octets) and then checks to see if the command is the correct length. 832 Thus, in practice, a transcoder can cancel a SysEx command by sending an 833 0xF7 to (prematurely) end the SysEx command -- the receiver will detect 834 the incorrect command length and discard the command. 836 Appendix C.1 defines configuration tools that may be used to prohibit 837 SysEx command cancellation. 839 The relative ordering of SysEx command segments in a MIDI list must 840 match the relative ordering of the sublists in the original SysEx 841 command. By default, commands other than System Real-time MIDI commands 842 MUST NOT appear between SysEx command segments (Appendix C.1 defines 843 configuration tools to change this default, to let other commands types 844 appear between segments). If the command segments of a SysEx command 845 are placed in the MIDI lists of two or more RTP packets, the segment 846 ordering rules apply to the concatenation of all affected MIDI lists. 848 ----------------------------------------------------------- 849 | Sublist Position | Head Status Octet | Tail Status Octet | 850 |-----------------------------------------------------------| 851 | first | 0xF0 | 0xF0 | 852 |-----------------------------------------------------------| 853 | middle | 0xF7 | 0xF0 | 854 |-----------------------------------------------------------| 855 | last | 0xF7 | 0xF7 | 856 |-----------------------------------------------------------| 857 | cancel | 0xF7 | 0xF4 | 858 ----------------------------------------------------------- 860 Figure 5 -- Command segmentation status octets 862 [MIDI] permits 0xF7 octets that are not part of a (0xF0, 0xF7) pair to 863 appear on a MIDI 1.0 DIN cable. Unpaired 0xF7 octets have no semantic 864 meaning in MIDI, apart from cancelling running status. 866 Unpaired 0xF7 octets MUST NOT appear in the MIDI list of the MIDI 867 Command section. We impose this restriction to avoid interference with 868 the command segmentation coding defined in Figure 5. 870 SysEx commands carried on a MIDI 1.0 DIN cable may use the "dropped 871 0xF7" construction [MIDI]. In this coding method, the 0xF7 octet is 872 dropped from the end of the SysEx command, and the status octet of the 873 next MIDI command acts both to terminate the SysEx command and start the 874 next command. To encode this construction in the payload format, follow 875 these steps: 877 o Determine the appropriate delta times for the SysEx command and 878 the command that follows the SysEx command. 880 o Insert the "dropped" 0xF7 octet at the end of the SysEx command, 881 to form the standard SysEx syntax. 883 o Code both commands into the MIDI list using the rules above. 885 o Replace the 0xF7 octet that terminates the verbatim SysEx 886 encoding or the last segment of the segmented SysEx encoding 887 with a 0xF5 octet. This substitution informs the receiver 888 of the original dropped 0xF7 coding. 890 [MIDI] reserves the undefined System Common commands 0xF4 and 0xF5 and 891 the undefined System Real-time commands 0xF9 and 0xFD for future use. 892 By default, undefined commands MUST NOT appear in a MIDI Command field 893 in the MIDI list, with the exception of the 0xF5 octets used to code the 894 "dropped 0xF7" construction and the 0xF4 octets used by SysEx "cancel" 895 sublists. 897 During session configuration, a stream may be customized to transport 898 undefined commands (Appendix C.1). For this case, we now define how 899 senders encode undefined commands in the MIDI list. 901 An undefined System Real-time command MUST be coded using the System 902 Real-time rules. 904 If the undefined System Common commands are put to use in a future 905 version of [MIDI], the command will begin with an 0xF4 or 0xF5 status 906 octet, followed by an arbitrary number of data octets (i.e., zero or 907 more data bytes). To encode these commands, senders MUST terminate the 908 command with an 0xF7 octet and place the modified command into the MIDI 909 Command field. 911 Unfortunately, non-compliant uses of the undefined System Common 912 commands may appear in MIDI implementations. To model these commands, 913 we assume that the command begins with an 0xF4 or 0xF5 status octet, 914 followed by zero or more data octets, followed by zero or more trailing 915 0xF7 status octets. To encode the command, senders MUST first remove 916 all trailing 0xF7 status octets from the command. Then, senders MUST 917 terminate the command with an 0xF7 octet and place the modified command 918 into the MIDI Command field. 920 Note that we include the trailing octets in our model as a cautionary 921 measure: if such commands appeared in a non-compliant use of an 922 undefined System Common command, an RTP MIDI encoding of the command 923 that did not remove trailing octets could be mistaken for an encoding of 924 "middle" or "last" sublist of a segmented SysEx commands (Figure 5) 925 under certain packet loss conditions. 927 Original SysEx command: 929 0xF0 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0xF7 931 A two-segment segmentation: 933 0xF0 0x01 0x02 0x03 0x04 0xF0 935 0xF7 0x05 0x06 0x07 0x08 0xF7 937 A different two-segment segmentation: 939 0xF0 0x01 0xF0 941 0xF7 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0xF7 943 A three-segment segmentation: 945 0xF0 0x01 0x02 0xF0 947 0xF7 0x03 0x04 0xF0 949 0xF7 0x05 0x06 0x07 0x08 0xF7 951 The segmentation with the largest number of segments: 953 0xF0 0x01 0xF0 955 0xF7 0x02 0xF0 957 0xF7 0x03 0xF0 959 0xF7 0x04 0xF0 961 0xF7 0x05 0xF0 963 0xF7 0x06 0xF0 965 0xF7 0x07 0xF0 967 0xF7 0x08 0xF0 969 0xF7 0xF7 971 Figure 6 -- Example segmentations 973 4. The Recovery Journal System 975 The recovery journal is the default resiliency tool for unreliable 976 transport. In this section, we normatively define the roles that 977 senders and receivers play in the recovery journal system. 979 MIDI is a fragile code. A single lost command in a MIDI command stream 980 may produce an artifact in the rendered performance. We normatively 981 classify rendering artifacts into two categories: 983 o Transient artifacts. Transient artifacts produce immediate 984 but short-term glitches in the performance. For example, a lost 985 NoteOn (0x9) command produces a transient artifact: one note 986 fails to play, but the artifact does not extend beyond the end 987 of that note. 989 o Indefinite artifacts. Indefinite artifacts produce long-lasting 990 errors in the rendered performance. For example, a lost NoteOff 991 (0x8) command may produce an indefinite artifact: the note that 992 should have been ended by the lost NoteOff command may sustain 993 indefinitely. As a second example, the loss of a Control Change 994 (0xB) command for controller number 7 (Channel Volume) may 995 produce an indefinite artifact: after the loss, all notes on 996 the channel may play too softly or too loudly. 998 The purpose of the recovery journal system is to satisfy the recovery 999 journal mandate: the MIDI performance rendered from an RTP MIDI stream 1000 sent over unreliable transport MUST NOT contain indefinite artifacts. 1002 The recovery journal system does not use packet retransmission to 1003 satisfy this mandate. Instead, each packet includes a special section, 1004 called the recovery journal. 1006 The recovery journal codes the history of the stream, back to an earlier 1007 packet called the checkpoint packet. The range of coverage for the 1008 journal is called the checkpoint history. The recovery journal codes 1009 the information necessary to recover from the loss of an arbitrary 1010 number of packets in the checkpoint history. Appendix A.1 normatively 1011 defines the checkpoint packet and the checkpoint history. 1013 When a receiver detects a packet loss, it compares its own knowledge 1014 about the history of the stream with the history information coded in 1015 the recovery journal of the packet that ends the loss event. By noting 1016 the differences in these two versions of the past, a receiver is able to 1017 transform all indefinite artifacts in the rendered performance into 1018 transient artifacts, by executing MIDI commands to repair the stream. 1020 We now state the normative role for senders in the recovery journal 1021 system. 1023 Senders prepare a recovery journal for every packet in the stream. In 1024 doing so, senders choose the checkpoint packet identity for the journal. 1025 Senders make this choice by applying a sending policy. Appendix C.2.2 1026 normatively defines three sending policies: "closed- loop", "open-loop", 1027 and "anchor". 1029 By default, senders MUST use the closed-loop sending policy. If the 1030 session description overrides this default policy, by using the 1031 parameter j_update defined in Appendix C.2.2, senders MUST use the 1032 specified policy. 1034 After choosing the checkpoint packet identity for a packet, the sender 1035 creates the recovery journal. By default, this journal MUST conform to 1036 the normative semantics in Section 5 and Appendices A-B in this memo. 1037 In Appendix C.2.3, we define parameters that modify the normative 1038 semantics for recovery journals. If the session description uses these 1039 parameters, the journal created by the sender MUST conform to the 1040 modified semantics. 1042 Next, we state the normative role for receivers in the recovery journal 1043 system. 1045 A receiver MUST detect each RTP sequence number break in a stream. If 1046 the sequence number break is due to a packet loss event (as defined in 1047 [RFC3550]), the receiver MUST repair all indefinite artifacts in the 1048 rendered MIDI performance caused by the loss. If the sequence number 1049 break is due to an out-of-order packet (as defined in [RFC3550]), the 1050 receiver MUST NOT take actions that introduce indefinite artifacts 1051 (ignoring the out-of-order packet is a safe option). 1053 Receivers take special precautions when entering or exiting a session. 1054 A receiver MUST process the first received packet in a stream as if it 1055 were a packet that ends a loss event. Upon exiting a session, a 1056 receiver MUST ensure that the rendered MIDI performance does not end 1057 with indefinite artifacts. 1059 Receivers are under no obligation to perform indefinite artifact repairs 1060 at the moment a packet arrives. A receiver that uses a playout buffer 1061 may choose to wait until the moment of rendering before processing the 1062 recovery journal, as the "lost" packet may be a late packet that arrives 1063 in time to use. 1065 Next, we state the normative role for the creator of the session 1066 description in the recovery journal system. Depending on the 1067 application, the sender, the receivers, and other parties may take part 1068 in creating or approving the session description. 1070 A session description that specifies the default closed-loop sending 1071 policy and the default recovery journal semantics satisfies the recovery 1072 journal mandate. However, these default behaviors may not be 1073 appropriate for all sessions. If the creators of a session description 1074 use the parameters defined in Appendix C.2 to override these defaults, 1075 the creators MUST ensure that the parameters define a system that 1076 satisfies the recovery journal mandate. 1078 Finally, we note that this memo does not specify sender or receiver 1079 recovery journal algorithms. Implementations are free to use any 1080 algorithm that conforms to the requirements in this section. The non- 1081 normative [RFC4696] discusses sender and receiver algorithm design. 1083 5. Recovery Journal Format 1085 This section introduces the structure of the recovery journal and 1086 defines the bitfields of recovery journal headers. Appendices A-B 1087 complete the bitfield definition of the recovery journal. 1089 The recovery journal has a three-level structure: 1091 o Top-level header. 1093 o Channel and system journal headers. These headers encode 1094 recovery information for a single voice channel (channel 1095 journal) or for all systems commands (system journal). 1097 o Chapters. Chapters describe recovery information for a 1098 single MIDI command type. 1100 Figure 7 shows the top-level structure of the recovery journal. The 1101 recovery journals consists of a 3-octet header, followed by an optional 1102 system journal (labeled S-journal in Figure 7) and an optional list of 1103 channel journals. Figure 8 shows the recovery journal header format. 1105 0 1 2 3 1106 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 1107 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1108 | Recovery journal header | S-journal ... | 1109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1110 | Channel journals ... | 1111 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1113 Figure 7 -- Top-level recovery journal format 1115 0 1 2 1116 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 1117 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1118 |S|Y|A|H|TOTCHAN| Checkpoint Packet Seqnum | 1119 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1121 Figure 8 -- Recovery journal header 1123 If the Y header bit is set to 1, the system journal appears in the 1124 recovery journal, directly following the recovery journal header. 1126 If the A header bit is set to 1, the recovery journal ends with a list 1127 of (TOTCHAN + 1) channel journals (the 4-bit TOTCHAN header field is 1128 interpreted as an unsigned integer). 1130 A MIDI channel MAY be represented by (at most) one channel journal in a 1131 recovery journal. Channel journals MUST appear in the recovery journal 1132 in ascending channel-number order. 1134 If A and Y are both zero, the recovery journal only contains its 3- 1135 octet header and is considered to be an "empty" journal. 1137 The S (single-packet loss) bit appears in most recovery journal 1138 structures, including the recovery journal header. The S bit helps 1139 receivers efficiently parse the recovery journal in the common case of 1140 the loss of a single packet. Appendix A.1 defines S bit semantics. 1142 The H bit indicates if MIDI channels in the stream have been configured 1143 to use the enhanced Chapter C encoding (Appendix A.3.3). 1145 By default, the payload format does not use enhanced Chapter C encoding. 1146 In this default case, the H bit MUST be set to 0 for all packets in the 1147 stream. 1149 If the stream has been configured so that controller numbers for one or 1150 more MIDI channels use enhanced Chapter C encoding, the H bit MUST be 1151 set to 1 in all packets in the stream. In Appendix C.2.3, we show how 1152 to configure a stream to use enhanced Chapter C encoding. 1154 The 16-bit Checkpoint Packet Seqnum header field codes the sequence 1155 number of the checkpoint packet for this journal, in network byte order 1156 (big-endian). The choice of the checkpoint packet sets the depth of the 1157 checkpoint history for the journal (defined in Appendix A.1). 1159 Receivers may use the Checkpoint Packet Seqnum field of the packet that 1160 ends a loss event to verify that the journal checkpoint history covers 1161 the entire loss event. The checkpoint history covers the loss event if 1162 the Checkpoint Packet Seqnum field is less than or equal to one plus the 1163 highest RTP sequence number previously received on the stream (modulo 1164 2^16). 1166 0 1 2 3 1167 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 1168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1169 |S| CHAN |H| LENGTH |P|C|M|W|N|E|T|A| Chapters ... | 1170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1172 Figure 9 -- Channel journal format 1174 Figure 9 shows the structure of a channel journal: a 3-octet header, 1175 followed by a list of leaf elements called channel chapters. A channel 1176 journal encodes information about MIDI commands on the MIDI channel 1177 coded by the 4-bit CHAN header field. Note that CHAN uses the same bit 1178 encoding as the channel nibble in MIDI Channel Messages (the cccc field 1179 in Figure E.1 of Appendix E). 1181 The 10-bit LENGTH field codes the length of the channel journal. The 1182 semantics for LENGTH fields are uniform throughout the recovery journal, 1183 and are defined in Appendix A.1. 1185 The third octet of the channel journal header is the Table of Contents 1186 (TOC) of the channel journal. The TOC is a set of bits that encode the 1187 presence of a chapter in the journal. Each chapter contains information 1188 about a certain class of MIDI channel command: 1190 o Chapter P: MIDI Program Change (0xC) 1191 o Chapter C: MIDI Control Change (0xB) 1192 o Chapter M: MIDI Parameter System (part of 0xB) 1193 o Chapter W: MIDI Pitch Wheel (0xE) 1194 o Chapter N: MIDI NoteOff (0x8), NoteOn (0x9) 1195 o Chapter E: MIDI Note Command Extras (0x8, 0x9) 1196 o Chapter T: MIDI Channel Aftertouch (0xD) 1197 o Chapter A: MIDI Poly Aftertouch (0xA) 1199 Chapters appear in a list following the header, in order of their 1200 appearance in the TOC. Appendices A.2-9 describe the bitfield format 1201 for each chapter, and define the conditions under which a chapter type 1202 MUST appear in the recovery journal. If any chapter types are required 1203 for a channel, an associated channel journal MUST appear in the recovery 1204 journal. 1206 The H bit indicates if controller numbers on a MIDI channel have been 1207 configured to use the enhanced Chapter C encoding (Appendix A.3.3). 1209 By default, controller numbers on a MIDI channel do not use enhanced 1210 Chapter C encoding. In this default case, the H bit MUST be set to 0 1211 for all channel journal headers for the channel in the recovery journal, 1212 for all packets in the stream. 1214 However, if at least one controller number for a MIDI channel has been 1215 configured to use the enhanced Chapter C encoding, the H bit for its 1216 channel journal MUST be set to 1, for all packets in the stream. 1218 In Appendix C.2.3, we show how to configure a controller number to use 1219 enhanced Chapter C encoding. 1221 0 1 2 3 1222 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 1223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1224 |S|D|V|Q|F|X| LENGTH | System chapters ... | 1225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1227 Figure 10 -- System journal format 1229 Figure 10 shows the structure of the system journal: a 2-octet header, 1230 followed by a list of system chapters. Each chapter codes information 1231 about a specific class of MIDI Systems command: 1233 o Chapter D: Song Select (0xF3), Tune Request (0xF6), Reset (0xFF), 1234 undefined System commands (0xF4, 0xF5, 0xF9, 0xFD) 1235 o Chapter V: Active Sense (0xFE) 1236 o Chapter Q: Sequencer State (0xF2, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC) 1237 o Chapter F: MTC Tape Position (0xF1, 0xF0 0x7F 0xcc 0x01 0x01) 1238 o Chapter X: System Exclusive (all other 0xF0) 1240 The 10-bit LENGTH field codes the size of the system journal and 1241 conforms to semantics described in Appendix A.1. 1243 The D, V, Q, F, and X header bits form a Table of Contents (TOC) for the 1244 system journal. A TOC bit that is set to 1 codes the presence of a 1245 chapter in the journal. Chapters appear in a list following the header, 1246 in the order of their appearance in the TOC. 1248 Appendix B describes the bitfield format for the system chapters and 1249 defines the conditions under which a chapter type MUST appear in the 1250 recovery journal. If any system chapter type is required to appear in 1251 the recovery journal, the system journal MUST appear in the recovery 1252 journal. 1254 6. Session Description Protocol 1256 RTP does not perform session management. Instead, RTP works together 1257 with session management tools, such as the Session Initiation Protocol 1258 (SIP, [RFC3261]) and the Real Time Streaming Protocol (RTSP, [RFC2326]). 1260 RTP payload formats define media type parameters for use in session 1261 management (for example, this memo defines "rtp-midi" as the media type 1262 for native RTP MIDI streams). 1264 In most cases, session management tools use the media type parameters 1265 via another standard, the Session Description Protocol (SDP, [RFC4566]). 1267 SDP is a textual format for specifying session descriptions. Session 1268 descriptions specify the network transport and media encoding for RTP 1269 sessions. Session management tools coordinate the exchange of session 1270 descriptions between participants ("parties"). 1272 Some session management tools use SDP to negotiate details of media 1273 transport (network addresses, ports, etc.). We refer to this use of SDP 1274 as "negotiated usage". One example of negotiated usage is the 1275 Offer/Answer protocol ([RFC3264] and Appendix C.7.2 in this memo) as 1276 used by SIP. 1278 Other session management tools use SDP to declare the media encoding for 1279 the session but use other techniques to negotiate network transport. We 1280 refer to this use of SDP as "declarative usage". One example of 1281 declarative usage is RTSP ([RFC2326] and Appendix C.7.1 in this memo). 1283 Below, we show session description examples for native (Section 6.1) and 1284 mpeg4-generic (Section 6.2) streams. In Section 6.3, we introduce 1285 session configuration tools that may be used to customize streams. 1287 6.1. Session Descriptions for Native Streams 1289 The session description below defines a unicast UDP RTP session (via a 1290 media ("m=") line) whose sole payload type (96) is mapped to a minimal 1291 native RTP MIDI stream. 1293 v=0 1294 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 1295 s=Example 1296 t=0 0 1297 m=audio 5004 RTP/AVP 96 1298 c=IN IP4 192.0.2.94 1299 a=rtpmap:96 rtp-midi/44100 1301 The rtpmap attribute line uses the "rtp-midi" media type to specify an 1302 RTP MIDI native stream. The clock rate specified on the rtpmap line (in 1303 the example above, 44100 Hz) sets the scaling for the RTP timestamp 1304 header field (see Section 2.1, and also [RFC3550]). 1306 Note that this document does not specify a default clock rate value for 1307 RTP MIDI. When RTP MIDI is used with SDP, parties MUST use the rtpmap 1308 line to communicate the clock rate. Guidance for selecting the RTP MIDI 1309 clock rate value appears in Section 2.1. 1311 We consider the RTP MIDI stream shown above to be "minimal" because the 1312 session description does not customize the stream with parameters. 1313 Without such customization, a native RTP MIDI stream has these 1314 characteristics: 1316 1. If the stream uses unreliable transport (unicast UDP, multicast 1317 UDP, etc.), the recovery journal system is in use, and the RTP 1318 payload contains both the MIDI command section and the journal 1319 section. If the stream uses reliable transport (such as TCP), 1320 the stream does not use journalling, and the payload contains 1321 only the MIDI command section (Section 2.2). 1323 2. If the stream uses the recovery journal system, the recovery 1324 journal system uses the default sending policy and the default 1325 journal semantics (Section 4). 1327 3. In the MIDI command section of the payload, command timestamps 1328 use the default "comex" semantics (Section 3). 1330 4. The recommended temporal duration ("media time") of an RTP 1331 packet ranges from 0 to 200 ms, and the RTP timestamp 1332 difference between sequential packets in the stream may be 1333 arbitrarily large (Section 2.1). 1335 5. If more than one minimal rtp-midi stream appears in a session, 1336 the MIDI name spaces for these streams are independent: channel 1337 1 in the first stream does not reference the same MIDI channel 1338 as channel 1 in the second stream (see Appendix C.5 for a 1339 discussion of the independence of minimal rtp-midi streams). 1341 6. The rendering method for the stream is not specified. What the 1342 receiver "does" with a minimal native MIDI stream is "out of 1343 scope" of this memo. For example, in content creation 1344 environments, a user may manually configure client software to 1345 render the stream with a specific software package. 1347 As in standard in RTP, RTP sessions managed by SIP are sendrecv by 1348 default (parties send and receive MIDI), and RTP sessions managed by 1349 RTSP are recvonly by default (server sends and client receives). 1351 In sendrecv RTP MIDI sessions for the session description shown above, 1352 the 16 voice channel + systems MIDI name space is unique for each 1353 sender. Thus, in a two-party session, the voice channel 0 sent by one 1354 party is distinct from the voice channel 0 sent by the other party. 1356 This behavior corresponds to what occurs when two MIDI 1.0 DIN devices 1357 are cross-connected with two MIDI cables (one cable routing MIDI Out 1358 from the first device into MIDI In of the second device, a second cable 1359 routing MIDI In from the first device into MIDI Out of the second 1360 device). We define this "association" formally in Section 2.1. 1362 MIDI 1.0 DIN networks may be configured in a "party-line" multicast 1363 topology. For these networks, the MIDI protocol itself provides tools 1364 for addressing specific devices in transactions on a multicast network, 1365 and for device discovery. Thus, apart from providing a 1- to-many 1366 forward path and a many-to-1 reverse path, IETF protocols do not need to 1367 provide any special support for MIDI multicast networking. 1369 6.2. Session Descriptions for mpeg4-generic Streams 1371 An mpeg4-generic [RFC3640] RTP MIDI stream uses an MPEG 4 Audio Object 1372 Type to render MIDI into audio. Three Audio Object Types accept MIDI 1373 input: 1375 o General MIDI (Audio Object Type ID 15), based on the General 1376 MIDI rendering standard [MIDI]. 1378 o Wavetable Synthesis (Audio Object Type ID 14), based on the 1379 Downloadable Sounds Level 2 (DLS 2) rendering standard [DLS2]. 1381 o Main Synthetic (Audio Object Type ID 13), based on Structured 1382 Audio and the programming language SAOL [MPEGSA]. 1384 The primary service of an mpeg4-generic stream is to code Access Units 1385 (AUs). We define the mpeg4-generic RTP MIDI AU as the MIDI payload 1386 shown in Figure 1 of Section 2.1 of this memo: a MIDI command section 1387 optionally followed by a journal section. 1389 Exactly one RTP MIDI AU MUST be mapped to one mpeg4-generic RTP MIDI 1390 packet. The mpeg4-generic options for placing several AUs in an RTP 1391 packet MUST NOT be used with RTP MIDI. The mpeg4-generic options for 1392 fragmenting and interleaving AUs MUST NOT be used with RTP MIDI. The 1393 mpeg4-generic RTP packet payload (Figure 1 in [RFC3640]) MUST contain 1394 empty AU Header and Auxiliary sections. These rules yield mpeg4-generic 1395 packets that are structurally identical to native RTP MIDI packets, an 1396 essential property for the correct operation of the payload format. 1398 The session description that follows defines a unicast UDP RTP session 1399 (via a media ("m=") line) whose sole payload type (96) is mapped to a 1400 minimal mpeg4-generic RTP MIDI stream. This example uses the General 1401 MIDI Audio Object Type under Synthesis Profile @ Level 2. 1403 v=0 1404 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 1405 s=Example 1406 t=0 0 1407 m=audio 5004 RTP/AVP 96 1408 c=IN IP6 2001:DB80::7F2E:172A:1E24 1409 a=rtpmap:96 mpeg4-generic/44100 1410 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 1411 config=7A0A0000001A4D546864000000060000000100604D54726B0000 1412 000600FF2F000 1414 (The a=fmtp line has been wrapped to fit the page to accommodate memo 1415 formatting restrictions; it comprises a single line in SDP.) 1417 The fmtp attribute line codes the four parameters (streamtype, mode, 1418 profile-level-id, and config) that are required in all mpeg4-generic 1419 session descriptions [RFC3640]. For RTP MIDI streams, the streamtype 1420 parameter MUST be set to 5, the "mode" parameter MUST be set to "rtp- 1421 midi", and the "profile-level-id" parameter MUST be set to the MPEG-4 1422 Profile Level for the stream. For the Synthesis Profile, legal profile- 1423 level-id values are 11, 12, and 13, coding low (11), medium (12), or 1424 high (13) decoder computational complexity, as defined by MPEG 1425 conformance tests. 1427 In a minimal RTP MIDI session description, the config value MUST be a 1428 hexadecimal encoding [RFC3640] of the AudioSpecificConfig data block 1429 [MPEGAUDIO] for the stream. AudioSpecificConfig encodes the Audio 1430 Object Type for the stream and also encodes initialization data (SAOL 1431 programs, DLS 2 wave tables, etc.). Standard MIDI Files encoded in 1432 AudioSpecificConfig in a minimal session description MUST be ignored by 1433 the receiver. 1435 Receivers determine the rendering algorithm for the session by 1436 interpreting the first 5 bits of AudioSpecificConfig as an unsigned 1437 integer that codes the Audio Object Type. In our example above, the 1438 leading config string nibbles "7A" yield the Audio Object Type 15 1439 (General MIDI). In Appendix E.4, we derive the config string value in 1440 the session description shown above; the starting point of the 1441 derivation is the MPEG bitstreams defined in [MPEGSA] and [MPEGAUDIO]. 1443 We consider the stream to be "minimal" because the session description 1444 does not customize the stream through the use of parameters, other than 1445 the 4 required mpeg4-generic parameters described above. In Section 1446 6.1, we describe the behavior of a minimal native stream, as a numbered 1447 list of characteristics. Items 1-4 on that list also describe the 1448 minimal mpeg4-generic stream, but items 5 and 6 require restatements, as 1449 listed below: 1451 5. If more than one minimal mpeg4-generic stream appears in 1452 a session, each stream uses an independent instance of the 1453 Audio Object Type coded in the config parameter value. 1455 6. A minimal mpeg4-generic stream encodes the AudioSpecificConfig 1456 as an inline hexadecimal constant. If a session description 1457 is sent over UDP, it may be impossible to transport large 1458 AudioSpecificConfig blocks within the Maximum Transmission Size 1459 (MTU) of the underlying network (for Ethernet, the MTU is 1500 1460 octets). In some cases, the AudioSpecificConfig block may 1461 exceed the maximum size of the UDP packet itself. 1463 The comments in Section 6.1 on SIP and RTSP stream directional defaults, 1464 sendrecv MIDI channel usage, and MIDI 1.0 DIN multicast networks also 1465 apply to mpeg4-generic RTP MIDI sessions. 1467 In sendrecv sessions, each party's session description MUST use 1468 identical values for the mpeg4-generic parameters (including the 1469 required streamtype, mode, profile-level-id, and config parameters). As 1470 a consequence, each party uses an identically configured MPEG 4 Audio 1471 Object Type to render MIDI commands into audio. The preamble to 1472 Appendix C discusses a way to create "virtual sendrecv" sessions that do 1473 not have this restriction. 1475 6.3. Parameters 1477 This section introduces parameters for session configuration for RTP 1478 MIDI streams. In session descriptions, parameters modify the semantics 1479 of a payload type. Parameters are specified on an fmtp attribute line. 1480 See the session description example in Section 6.2 for an example of a 1481 fmtp attribute line. 1483 The parameters add features to the minimal streams described in Sections 1484 6.1-2, and support several types of services: 1486 o Stream subsetting. By default, all MIDI commands that 1487 are legal to appear on a MIDI 1.0 DIN cable may appear 1488 in an RTP MIDI stream. The cm_unused parameter overrides 1489 this default by prohibiting certain commands from appearing 1490 in the stream. The cm_used parameter is used in conjunction 1491 with cm_unused, to simplify the specification of complex 1492 exclusion rules. We describe cm_unused and cm_used in 1493 Appendix C.1. 1495 o Journal customization. The j_sec and j_update parameters 1496 configure the use of the journal section. The ch_default, 1497 ch_never, and ch_anchor parameters configure the semantics 1498 of the recovery journal chapters. These parameters are 1499 described in Appendix C.2 and override the default stream 1500 behaviors 1 and 2, listed in Section 6.1 and referenced in 1501 Section 6.2. 1503 o MIDI command timestamp semantics. The tsmode, octpos, 1504 mperiod, and linerate parameters customize the semantics 1505 of timestamps in the MIDI command section. These parameters 1506 let RTP MIDI accurately encode the implicit time coding of 1507 MIDI 1.0 DIN cables. These parameters are described in 1508 Appendix C.3 and override default stream behavior 3, 1509 listed in Section 6.1 and referenced in Section 6.2 1511 o Media time. The rtp_ptime and rtp_maxptime parameters define 1512 the temporal duration ("media time") of an RTP MIDI packet. 1513 The guardtime parameter sets the minimum sending rate of stream 1514 packets. These parameters are described in Appendix C.4 1515 and override default stream behavior 4, listed in Section 6.1 1516 and referenced in Section 6.2. 1518 o Stream description. The musicport parameter labels the 1519 MIDI name space of RTP streams in a multimedia session. 1520 Musicport is described in Appendix C.5. The musicport 1521 parameter overrides default stream behavior 5, in Sections 1522 6.1 and 6.2. 1524 o MIDI rendering. Several parameters specify the MIDI 1525 rendering method of a stream. These parameters are described 1526 in Appendix C.6 and override default stream behavior 6, in 1527 Sections 6.1 and 6.2. 1529 In Appendix C.7, we specify interoperability guidelines for two RTP MIDI 1530 application areas: content-streaming using RTSP (Appendix C.7.1) and 1531 network musical performance using SIP (Appendix C.7.2). 1533 7. Extensibility 1535 The payload format defined in this memo exclusively encodes all commands 1536 that may legally appear on a MIDI 1.0 DIN cable. 1538 Many worthy uses of MIDI over RTP do not fall within the narrow scope of 1539 the payload format. For example, the payload format does not support 1540 the direct transport of Standard MIDI File (SMF) meta-event and metric 1541 timing data. As a second example, the payload format does not define 1542 transport tools for user-defined commands (apart from tools to support 1543 System Exclusive commands [MIDI]). 1545 The payload format does not provide an extension mechanism to support 1546 new features of this nature, by design. Instead, we encourage the 1547 development of new payload formats for specialized musical applications. 1548 The IETF session management tools [RFC3264] [RFC2326] support codec 1549 negotiation, to facilitate the use of new payload formats in a backward- 1550 compatible way. 1552 However, the payload format does provide several extensibility tools, 1553 which we list below: 1555 o Journalling. As described in Appendix C.2, new token 1556 values for the j_sec and j_update parameters may 1557 be defined in IETF standards-track documents. This 1558 mechanism supports the design of new journal formats 1559 and the definition of new journal sending policies. 1561 o Rendering. The payload format may be extended to support 1562 new MIDI renderers (Appendix C.6.2). Certain general aspects 1563 of the RTP MIDI rendering process may also be extended, via 1564 the definition of new token values for the render (Appendix C.6) 1565 and smf_info (Appendix C.6.4.1) parameters. 1567 o Undefined commands. [MIDI] reserves 4 MIDI System commands 1568 for future use (0xF4, 0xF5, 0xF9, 0xFD). If updates 1569 to [MIDI] define the reserved commands, IETF standards-track 1570 documents may be defined to provide resiliency support for 1571 the commands. Opaque LEGAL fields appear in System Chapter 1572 D for this purpose (Appendix B.1.1). 1574 A final form of extensibility involves the inclusion of the payload 1575 format in framework documents. Framework documents describe how to 1576 combine protocols to form a platform for interoperable applications. 1577 For example, a stage and studio framework might define how to use SIP 1578 [RFC3261], RTSP [RFC2326], SDP [RFC4566], and RTP [RFC3550] to support 1579 media networking for professional audio equipment and electronic musical 1580 instruments. 1582 8. Congestion Control 1584 The RTP congestion control requirements defined in [RFC3550] apply to 1585 RTP MIDI sessions, and implementors should carefully read the congestion 1586 control section in [RFC3550]. As noted in [RFC3550], all transport 1587 protocols used on the Internet need to address congestion control in 1588 some way, and RTP is not an exception. 1590 In addition, the congestion control requirements defined in [RFC3551] 1591 applies to RTP MIDI sessions run under applicable profiles. The basic 1592 congestion control requirement defined in [RFC3551] is that RTP sessions 1593 that use UDP transport should monitor packet loss (via RTCP or other 1594 means) to ensure that the RTP stream competes fairly with TCP flows that 1595 share the network. 1597 Finally, RTP MIDI has congestion control issues that are unique for an 1598 audio RTP payload format. In applications such as network musical 1599 performance [NMP], the packet rate is linked to the gestural rate of a 1600 human performer. Senders MUST monitor the MIDI command source for 1601 patterns that result in excessive packet rates and take actions during 1602 RTP transcoding to reduce the RTP packet rate. [RFC4696] offers 1603 implementation guidance on this issue. 1605 9. Security Considerations 1607 Implementors should carefully read the Security Considerations sections 1608 of the RTP [RFC3550], AVP [RFC3551], and other RTP profile documents, as 1609 the issues discussed in these sections directly apply to RTP MIDI 1610 streams. Implementors should also review the Secure Real-time Transport 1611 Protocol (SRTP, [RFC3711]), an RTP profile that addresses the security 1612 issues discussed in [RFC3550] and [RFC3551]. 1614 Here, we discuss security issues that are unique to the RTP MIDI payload 1615 format. 1617 When using RTP MIDI, authentication of incoming RTP and RTCP packets is 1618 RECOMMENDED. Per-packet authentication may be provided by SRTP or by 1619 other means. Without the use of authentication, attackers could forge 1620 MIDI commands into an ongoing stream, damaging speakers and eardrums. 1621 An attacker could also craft RTP and RTCP packets to exploit known bugs 1622 in the client and take effective control of a client machine. 1624 Session management tools (such as SIP [RFC3261]) SHOULD use 1625 authentication during the transport of all session descriptions 1626 containing RTP MIDI media streams. For SIP, the Security Considerations 1627 section in [RFC3261] provides an overview of possible authentication 1628 mechanisms. RTP MIDI session descriptions should use authentication 1629 because the session descriptions may code initialization data using the 1630 parameters described in Appendix C. If an attacker inserts bogus 1631 initialization data into a session description, he can corrupt the 1632 session or forge an client attack. 1634 Session descriptions may also code renderer initialization data by 1635 reference, via the url (Appendix C.6.3) and smf_url (Appendix C.6.4.2) 1636 parameters. If the coded URL is spoofed, both session and client are 1637 open to attack, even if the session description itself is authenticated. 1638 Therefore, URLs specified in url and smf_url parameters SHOULD use 1639 [RFC2818]. 1641 Section 2.1 allows streams sent by a party in two RTP sessions to have 1642 the same SSRC value and the same RTP timestamp initialization value, 1643 under certain circumstances. Normally, these values are randomly chosen 1644 for each stream in a session, to make plaintext guessing harder to do if 1645 the payloads are encrypted. Thus, Section 2.1 weakens this aspect of 1646 RTP security. 1648 10. Acknowledgements 1650 We thank the networking, media compression, and computer music community 1651 members who have commented or contributed to the effort, including Kurt 1652 B, Cynthia Bruyns, Steve Casner, Paul Davis, Robin Davies, Joanne Dow, 1653 Tobias Erichsen, Nicolas Falquet, Dominique Fober, Philippe Gentric, 1654 Michael Godfrey, Chris Grigg, Todd Hager, Alfred Hoenes, Michel Jullian, 1655 Phil Kerr, Young-Kwon Lim, Jessica Little, Jan van der Meer, Colin 1656 Perkins, Charlie Richmond, Herbie Robinson, Larry Rowe, Eric Scheirer, 1657 Dave Singer, Martijn Sipkema, William Stewart, Kent Terry, Magnus 1658 Westerlund, Tom White, Jim Wright, Doug Wyatt, and Giorgio Zoia. We 1659 also thank the members of the San Francisco Bay Area music and audio 1660 community for creating the context for the work, including Don Buchla, 1661 Chris Chafe, Richard Duda, Dan Ellis, Adrian Freed, Ben Gold, Jaron 1662 Lanier, Roger Linn, Richard Lyon, Dana Massie, Max Mathews, Keith 1663 McMillen, Carver Mead, Nelson Morgan, Tom Oberheim, Malcolm Slaney, Dave 1664 Smith, Julius Smith, David Wessel, and Matt Wright. 1666 11. IANA Considerations 1668 This section makes a series of requests to IANA. The IANA has completed 1669 registration/assignments of the below requests. 1671 The sub-sections that follow hold the actual, detailed requests. All 1672 registrations in this section are in the IETF tree and follow the rules 1673 of [RFC4288] and [RFC4855], as appropriate. 1675 In Section 11.1, we request the registration of a new media type: 1676 "audio/rtp-midi". Paired with this request is a request for a 1677 repository for new values for several parameters associated with 1678 "audio/rtp-midi". We request this repository in Section 11.1.1. 1680 In Section 11.2, we request the registration of a new value ("rtp- 1681 midi") for the "mode" parameter of the "mpeg4-generic" media type. The 1682 "mpeg4-generic" media type is defined in [RFC3640], and [RFC3640] 1683 defines a repository for the "mode" parameter. However, we believe we 1684 are the first to request the registration of a "mode" value, so we 1685 believe the registry for "mode" has not yet been created by IANA. 1687 Paired with our "mode" parameter value request for "mpeg4-generic" is a 1688 request for a repository for new values for several parameters we have 1689 defined for use with the "rtp-midi" mode value. We request this 1690 repository in Section 11.2.1. 1692 In Section 11.3, we request the registration of a new media type: 1693 "audio/asc". No repository request is associated with this request. 1695 11.1. rtp-midi Media Type Registration 1697 This section requests the registration of the "rtp-midi" subtype for the 1698 "audio" media type. We request the registration of the parameters 1699 listed in the "optional parameters" section below (both the "non- 1700 extensible parameters" and the "extensible parameters" lists). We also 1701 request the creation of repositories for the "extensible parameters"; 1702 the details of this request appear in Section 11.1.1, below. 1704 Media type name: 1706 audio 1708 Subtype name: 1710 rtp-midi 1712 Required parameters: 1714 rate: The RTP timestamp clock rate. See Sections 2.1 and 6.1 1715 for usage details. 1717 Optional parameters: 1719 Non-extensible parameters: 1721 ch_anchor: See Appendix C.2.3 for usage details. 1722 ch_default: See Appendix C.2.3 for usage details. 1723 ch_never: See Appendix C.2.3 for usage details. 1724 cm_unused: See Appendix C.1 for usage details. 1725 cm_used: See Appendix C.1 for usage details. 1726 chanmask: See Appendix C.6.4.3 for usage details. 1727 cid: See Appendix C.6.3 for usage details. 1728 guardtime: See Appendix C.4.2 for usage details. 1729 inline: See Appendix C.6.3 for usage details. 1730 linerate: See Appendix C.3 for usage details. 1731 mperiod: See Appendix C.3 for usage details. 1732 multimode: See Appendix C.6.1 for usage details. 1733 musicport: See Appendix C.5 for usage details. 1734 octpos: See Appendix C.3 for usage details. 1735 rinit: See Appendix C.6.3 for usage details. 1736 rtp_maxptime: See Appendix C.4.1 for usage details. 1737 rtp_ptime: See Appendix C.4.1 for usage details. 1739 smf_cid: See Appendix C.6.4.2 for usage details. 1740 smf_inline: See Appendix C.6.4.2 for usage details. 1741 smf_url: See Appendix C.6.4.2 for usage details. 1742 tsmode: See Appendix C.3 for usage details. 1743 url: See Appendix C.6.3 for usage details. 1745 Extensible parameters: 1747 j_sec: See Appendix C.2.1 for usage details. See 1748 Section 11.1.1 for repository details. 1749 j_update: See Appendix C.2.2 for usage details. See 1750 Section 11.1.1 for repository details. 1751 render: See Appendix C.6 for usage details. See 1752 Section 11.1.1 for repository details. 1753 subrender: See Appendix C.6.2 for usage details. See 1754 Section 11.1.1 for repository details. 1755 smf_info: See Appendix C.6.4.1 for usage details. See 1756 Section 11.1.1 for repository details. 1758 Encoding considerations: 1760 The format for this type is framed and binary. 1762 Restrictions on usage: 1764 This type is only defined for real-time transfers of MIDI 1765 streams via RTP. Stored-file semantics for rtp-midi may 1766 be defined in the future. 1768 Security considerations: 1770 See Section 9 of this memo. 1772 Interoperability considerations: 1774 None. 1776 Published specification: 1778 This memo and [MIDI] serve as the normative specification. In 1779 addition, references [NMP], [GRAME], and [RFC4696] provide 1780 non-normative implementation guidance. 1782 Applications that use this media type: 1784 Audio content-creation hardware, such as MIDI controller piano 1785 keyboards and MIDI audio synthesizers. Audio content-creation 1786 software, such as music sequencers, digital audio workstations, 1787 and soft synthesizers. Computer operating systems, for network 1788 support of MIDI Application Programmer Interfaces. Content 1789 distribution servers and terminals may use this media type for 1790 low bit-rate music coding. 1792 Additional information: 1794 None. 1796 Person & email address to contact for further information: 1798 John Lazzaro 1800 Intended usage: 1802 COMMON. 1804 Author: 1806 John Lazzaro 1808 Change controller: 1810 IETF Audio/Video Transport Working Group delegated 1811 from the IESG. 1813 11.1.1. Repository Request for "audio/rtp-midi" 1815 For the "rtp-midi" subtype, we request the creation of repositories for 1816 extensions to the following parameters (which are those listed as 1817 "extensible parameters" in Section 11.1). 1819 j_sec: 1821 Registrations for this repository may only occur 1822 via an IETF standards-track document. Appendix C.2.1 1823 of this memo describes appropriate registrations for this 1824 repository. 1826 Initial values for this repository appear below: 1828 "none": Defined in Appendix C.2.1 of this memo. 1829 "recj": Defined in Appendix C.2.1 of this memo. 1831 j_update: 1833 Registrations for this repository may only occur 1834 via an IETF standards-track document. Appendix C.2.2 1835 of this memo describes appropriate registrations for this 1836 repository. 1838 Initial values for this repository appear below: 1840 "anchor": Defined in Appendix C.2.2 of this memo. 1841 "open-loop": Defined in Appendix C.2.2 of this memo. 1842 "closed-loop": Defined in Appendix C.2.2 of this memo. 1844 render: 1846 Registrations for this repository MUST include a 1847 specification of the usage of the proposed value. 1848 See text in the preamble of Appendix C.6 for details 1849 (the paragraph that begins "Other render token ..."). 1851 Initial values for this repository appear below: 1853 "unknown": Defined in Appendix C.6 of this memo. 1854 "synthetic": Defined in Appendix C.6 of this memo. 1855 "api": Defined in Appendix C.6 of this memo. 1856 "null": Defined in Appendix C.6 of this memo. 1858 subrender: 1860 Registrations for this repository MUST include a 1861 specification of the usage of the proposed value. 1862 See text Appendix C.6.2 for details (the paragraph 1863 that begins "Other subrender token ..."). 1865 Initial values for this repository appear below: 1867 "default": Defined in Appendix C.6.2 of this memo. 1869 smf_info: 1871 Registrations for this repository MUST include a 1872 specification of the usage of the proposed value. 1873 See text in Appendix C.6.4.1 for details (the 1874 paragraph that begins "Other smf_info token ..."). 1876 Initial values for this repository appear below: 1878 "ignore": Defined in Appendix C.6.4.1 of this memo. 1879 "sdp_start": Defined in Appendix C.6.4.1 of this memo. 1880 "identity": Defined in Appendix C.6.4.1 of this memo. 1882 11.2. mpeg4-generic Media Type Registration 1884 This section requests the registration of the "rtp-midi" value for the 1885 "mode" parameter of the "mpeg4-generic" media type. The "mpeg4- 1886 generic" media type is defined in [RFC3640], and [RFC3640] defines a 1887 repository for the "mode" parameter. We are registering mode rtp- midi 1888 to support the MPEG Audio codecs [MPEGSA] that use MIDI. 1890 In conjunction with this registration request, we request the 1891 registration of the parameters listed in the "optional parameters" 1892 section below (both the "non-extensible parameters" and the "extensible 1893 parameters" lists). We also request the creation of repositories for 1894 the "extensible parameters"; the details of this request appear in 1895 Appendix 11.2.1, below. 1897 Media type name: 1899 audio 1901 Subtype name: 1903 mpeg4-generic 1905 Required parameters: 1907 The "mode" parameter is required by [RFC3640]. [RFC3640] requests 1908 a repository for "mode", so that new values for mode 1909 may be added. We request that the value "rtp-midi" be 1910 added to the "mode" repository. 1912 In mode rtp-midi, the mpeg4-generic parameter rate is 1913 a required parameter. Rate specifies the RTP timestamp 1914 clock rate. See Sections 2.1 and 6.2 for usage details 1915 of rate in mode rtp-midi. 1917 Optional parameters: 1919 We request registration of the following parameters 1920 for use in mode rtp-midi for mpeg4-generic. 1922 Non-extensible parameters: 1924 ch_anchor: See Appendix C.2.3 for usage details. 1925 ch_default: See Appendix C.2.3 for usage details. 1926 ch_never: See Appendix C.2.3 for usage details. 1927 cm_unused: See Appendix C.1 for usage details. 1928 cm_used: See Appendix C.1 for usage details. 1929 chanmask: See Appendix C.6.4.3 for usage details. 1930 cid: See Appendix C.6.3 for usage details. 1931 guardtime: See Appendix C.4.2 for usage details. 1932 inline: See Appendix C.6.3 for usage details. 1933 linerate: See Appendix C.3 for usage details. 1934 mperiod: See Appendix C.3 for usage details. 1935 multimode: See Appendix C.6.1 for usage details. 1936 musicport: See Appendix C.5 for usage details. 1937 octpos: See Appendix C.3 for usage details. 1938 rinit: See Appendix C.6.3 for usage details. 1939 rtp_maxptime: See Appendix C.4.1 for usage details. 1940 rtp_ptime: See Appendix C.4.1 for usage details. 1941 smf_cid: See Appendix C.6.4.2 for usage details. 1942 smf_inline: See Appendix C.6.4.2 for usage details. 1943 smf_url: See Appendix C.6.4.2 for usage details. 1944 tsmode: See Appendix C.3 for usage details. 1945 url: See Appendix C.6.3 for usage details. 1947 Extensible parameters: 1949 j_sec: See Appendix C.2.1 for usage details. See 1950 Section 11.2.1 for repository details. 1951 j_update: See Appendix C.2.2 for usage details. See 1952 Section 11.2.1 for repository details. 1953 render: See Appendix C.6 for usage details. See 1954 Section 11.2.1 for repository details. 1955 subrender: See Appendix C.6.2 for usage details. See 1956 Section 11.2.1 for repository details. 1957 smf_info: See Appendix C.6.4.1 for usage details. See 1958 Section 11.2.1 for repository details. 1960 Encoding considerations: 1962 The format for this type is framed and binary. 1964 Restrictions on usage: 1966 Only defined for real-time transfers of audio/mpeg4-generic 1967 RTP streams with mode=rtp-midi. 1969 Security considerations: 1971 See Section 9 of this memo. 1973 Interoperability considerations: 1975 Except for the marker bit (Section 2.1), the packet formats 1976 for audio/rtp-midi and audio/mpeg4-generic (mode rtp-midi) 1977 are identical. The formats differ in use: audio/mpeg4-generic 1978 is for MPEG work, and audio/rtp-midi is for all other work. 1980 Published specification: 1982 This memo, [MIDI], and [MPEGSA] are the normative references. 1983 In addition, references [NMP], [GRAME], and [RFC4696] provide 1984 non-normative implementation guidance. 1986 Applications that use this media type: 1988 MPEG 4 servers and terminals that support [MPEGSA]. 1990 Additional information: 1992 None. 1994 Person & email address to contact for further information: 1996 John Lazzaro 1998 Intended usage: 2000 COMMON. 2002 Author: 2004 John Lazzaro 2006 Change controller: 2008 IETF Audio/Video Transport Working Group delegated 2009 from the IESG. 2011 11.2.1. Repository Request for Mode rtp-midi for mpeg4-generic 2013 For mode rtp-midi of the mpeg4-generic subtype, we request the creation 2014 of repositories for extensions to the following parameters (which are 2015 those listed as "extensible parameters" in Section 11.2). 2017 j_sec: 2019 Registrations for this repository may only occur 2020 via an IETF standards-track document. Appendix C.2.1 2021 of this memo describes appropriate registrations for this 2022 repository. 2024 Initial values for this repository appear below: 2026 "none": Defined in Appendix C.2.1 of this memo. 2027 "recj": Defined in Appendix C.2.1 of this memo. 2029 j_update: 2031 Registrations for this repository may only occur 2032 via an IETF standards-track document. Appendix C.2.2 2033 of this memo describes appropriate registrations for this 2034 repository. 2036 Initial values for this repository appear below: 2038 "anchor": Defined in Appendix C.2.2 of this memo. 2039 "open-loop": Defined in Appendix C.2.2 of this memo. 2040 "closed-loop": Defined in Appendix C.2.2 of this memo. 2042 render: 2044 Registrations for this repository MUST include a 2045 specification of the usage of the proposed value. 2046 See text in the preamble of Appendix C.6 for details 2047 (the paragraph that begins "Other render token ..."). 2049 Initial values for this repository appear below: 2051 "unknown": Defined in Appendix C.6 of this memo. 2052 "synthetic": Defined in Appendix C.6 of this memo. 2053 "null": Defined in Appendix C.6 of this memo. 2055 subrender: 2057 Registrations for this repository MUST include a 2058 specification of the usage of the proposed value. 2059 See text in Appendix C.6.2 for details (the paragraph 2060 that begins "Other subrender token ..." and 2061 subsequent paragraphs). Note that the text in 2062 Appendix C.6.2 contains restrictions on subrender 2063 registrations for mpeg4-generic ("Registrations 2064 for mpeg4-generic subrender values ..."). 2066 Initial values for this repository appear below: 2068 "default": Defined in Appendix C.6.2 of this memo. 2070 smf_info: 2072 Registrations for this repository MUST include a 2073 specification of the usage of the proposed value. 2074 See text in Appendix C.6.4.1 for details (the 2075 paragraph that begins "Other smf_info token ..."). 2077 Initial values for this repository appear below: 2079 "ignore": Defined in Appendix C.6.4.1 of this memo. 2080 "sdp_start": Defined in Appendix C.6.4.1 of this memo. 2081 "identity": Defined in Appendix C.6.4.1 of this memo. 2083 11.3. asc Media Type Registration 2085 This section registers "asc" as a subtype for the "audio" media type. 2086 We register this subtype to support the remote transfer of the "config" 2087 parameter of the mpeg4-generic media type [RFC3640] when it is used with 2088 mpeg4-generic mode rtp-midi (registered in Appendix 11.2 above). We 2089 explain the mechanics of using "audio/asc" to set the config parameter 2090 in Section 6.2 and Appendix C.6.5 of this document. 2092 Note that this registration is a new subtype registration and is not an 2093 addition to a repository defined by MPEG-related memos (such as 2094 [RFC3640]). Also note that this request for "audio/asc" does not 2095 register parameters, and does not request the creation of a repository. 2097 Media type name: 2099 audio 2101 Subtype name: 2103 asc 2105 Required parameters: 2107 None. 2109 Optional parameters: 2111 None. 2113 Encoding considerations: 2115 The native form of the data object is binary data, 2116 zero-padded to an octet boundary. 2118 Restrictions on usage: 2120 This type is only defined for data object (stored file) 2121 transfer. The most common transports for the type are 2122 HTTP and SMTP. 2124 Security considerations: 2126 See Section 9 of this memo. 2128 Interoperability considerations: 2130 None. 2132 Published specification: 2134 The audio/asc data object is the AudioSpecificConfig 2135 binary data structure, which is normatively defined in [MPEGAUDIO]. 2137 Applications that use this media type: 2139 MPEG 4 Audio servers and terminals that support 2140 audio/mpeg4-generic RTP streams for mode rtp-midi. 2142 Additional information: 2144 None. 2146 Person & email address to contact for further information: 2148 John Lazzaro 2150 Intended usage: 2152 COMMON. 2154 Author: 2156 John Lazzaro 2158 Change controller: 2160 IETF Audio/Video Transport Working Group delegated 2161 from the IESG. 2163 A. The Recovery Journal Channel Chapters 2165 A.1. Recovery Journal Definitions 2167 This appendix defines the terminology and the coding idioms that are 2168 used in the recovery journal bitfield descriptions in Section 5 (journal 2169 header structure), Appendices A.2 to A.9 (channel journal chapters) and 2170 Appendices B.1 to B.5 (system journal chapters). 2172 We assume that the recovery journal resides in the journal section of an 2173 RTP packet with sequence number I ("packet I") and that the Checkpoint 2174 Packet Seqnum field in the top-level recovery journal header refers to a 2175 previous packet with sequence number C (an exception is the self- 2176 referential C = I case). Unless stated otherwise, algorithms are 2177 assumed to use modulo 2^16 arithmetic for calculations on 16-bit 2178 sequence numbers and modulo 2^32 arithmetic for calculations on 32-bit 2179 extended sequence numbers. 2181 Several bitfield coding idioms appear throughout the recovery journal 2182 system, with consistent semantics. Most recovery journal elements begin 2183 with an "S" (Single-packet loss) bit. S bits are designed to help 2184 receivers efficiently parse through the recovery journal hierarchy in 2185 the common case of the loss of a single packet. 2187 As a rule, S bits MUST be set to 1. However, an exception applies if a 2188 recovery journal element in packet I encodes data about a command stored 2189 in the MIDI command section of packet I - 1. In this case, the S bit of 2190 the recovery journal element MUST be set to 0. If a recovery journal 2191 element has its S bit set to 0, all higher-level recovery journal 2192 elements that contain it MUST also have S bits that are set to 0, 2193 including the top-level recovery journal header. 2195 Other consistent bitfield coding idioms are described below: 2197 o R flag bit. R flag bits are reserved for future use. Senders 2198 MUST set R bits to 0. Receivers MUST ignore R bit values. 2200 o LENGTH field. All fields named LENGTH (as distinct from LEN) 2201 code the number of octets in the structure that contains it, 2202 including the header it resides in and all hierarchical levels 2203 below it. If a structure contains a LENGTH field, a receiver 2204 MUST use the LENGTH field value to advance past the structure 2205 during parsing, rather than use knowledge about the internal 2206 format of the structure. 2208 We now define normative terms used to describe recovery journal 2209 semantics. 2211 o Checkpoint history. The checkpoint history of a recovery journal 2212 is the concatenation of the MIDI command sections of packets C 2213 through I - 1. The final command in the MIDI command section for 2214 packet I - 1 is considered the most recent command; the first 2215 command in the MIDI command section for packet C is the oldest 2216 command. If command X is less recent than command Y, X is 2217 considered to be "before Y". A checkpoint history with no 2218 commands is considered to be empty. The checkpoint history 2219 never contains the MIDI command section of packet I (the 2220 packet containing the recovery journal), so if C == I, the 2221 checkpoint history is empty by definition. 2223 o Session history. The session history of a recovery journal is 2224 the concatenation of MIDI command sections from the first 2225 packet of the session up to packet I - 1. The definitions of 2226 command recency and history emptiness follow those in the 2227 checkpoint history. The session history never contains the 2228 MIDI command section of packet I, and so the session history of 2229 the first packet in the session is empty by definition. 2231 o Finished/unfinished commands. If all octets of a MIDI command 2232 appear in the session history, the command is defined as being 2233 finished. If some but not all octets of a command appear 2234 in the session history, the command is defined as being unfinished. 2235 Unfinished commands occur if segments of a SysEx command appear 2236 in several RTP packets. For example, if a SysEx command is coded 2237 as 3 segments, with segment 1 in packet K, segment 2 in packet 2238 K + 1, and segment 3 in packet K + 2, the session histories for 2239 packets K + 1 and K + 2 contain unfinished versions of the command. 2240 A session history contains a finished version of a cancelled SysEx 2241 command if the history contains the cancel sublist for the command. 2243 o Reset State commands. Reset State (RS) commands reset 2244 renderers to an initialized "powerup" condition. The 2245 RS commands are: System Reset (0xFF), General MIDI System Enable 2246 (0xF0 0x7E 0xcc 0x09 0x01 0xF7), General MIDI 2 System Enable 2247 (0xF0 0x7E 0xcc 0x09 0x03 0xF7), General MIDI System Disable 2248 (0xF0 0x7E 0xcc 0x09 0x00 0xF7), Turn DLS On (0xF0 0x7E 0xcc 0x0A 2249 0x01 0xF7), and Turn DLS Off (0xF0 0x7E 0xcc 0x0A 0x02 0xF7). 2250 Registrations of subrender parameter token values (Appendix C.6.2) 2251 and IETF standards-track documents MAY specify additional 2252 RS commands. 2254 o Active commands. Active command are MIDI commands that do not 2255 appear before a Reset State command in the session history. 2257 o N-active commands. N-active commands are MIDI commands that do 2258 not appear before one of the following commands in the session 2259 history: MIDI Control Change numbers 123-127 (numbers with All 2260 Notes Off semantics) or 120 (All Sound Off), and any Reset 2261 State command. 2263 o C-active commands. C-active commands are MIDI commands that do 2264 not appear before one of the following commands in the session 2265 history: MIDI Control Change number 121 (Reset All Controllers) 2266 and any Reset State command. 2268 o Oldest-first ordering rule. Several recovery journal chapters 2269 contain a list of elements, where each element is associated 2270 with a MIDI command that appears in the session history. In 2271 most cases, the chapter definition requires that list elements 2272 be ordered in accordance with the "oldest-first ordering rule". 2273 Below, we normatively define this rule: 2275 Elements associated with the most recent command in the session 2276 history coded in the list MUST appear at the end of the list. 2278 Elements associated with the oldest command in the session 2279 history coded in the list MUST appear at the start of the list. 2281 All other list elements MUST be arranged with respect to these 2282 boundary elements, to produce a list ordering that strictly 2283 reflects the relative session history recency of the commands 2284 coded by the elements in the list. 2286 o Parameter system. A MIDI feature that provides two sets of 2287 16,384 parameters to expand the 0-127 controller number space. 2288 The Registered Parameter Names (RPN) system and the Non-Registered 2289 Parameter Names (NRPN) system each provides 16,384 parameters. 2291 o Parameter system transaction. The value of RPNs and NRPNs are 2292 changed by a series of Control Change commands that form a 2293 parameter system transaction. A canonical transaction begins 2294 with two Control Change commands to set the parameter number 2295 (controller numbers 99 and 98 for NRPNs, controller numbers 101 2296 and 100 for RPNs). The transaction continues with an arbitrary 2297 number of Data Entry (controller numbers 6 and 38), Data Increment 2298 (controller number 96), and Data Decrement (controller number 2299 97) Control Change commands to set the parameter value. The 2300 transaction ends with a second pair of (99, 98) or (101, 100) 2301 Control Change commands that specify the null parameter (MSB 2302 value 0x7F, LSB value 0x7F). 2304 Several variants of the canonical transaction sequence are 2305 possible. Most commonly, the terminal pair of (99, 98) or 2306 (101, 100) Control Change commands may specify a parameter 2307 other than the null parameter. In this case, the command 2308 pair terminates the first transaction and starts a second 2309 transaction. The command pair is considered to be a part 2310 of both transactions. This variant is legal and recommended 2311 in [MIDI]. We refer to this variant as a "type 1 variant". 2313 Less commonly, the MSB (99 or 101) or LSB (98 or 100) command 2314 of a (99, 98) or (101, 100) Control Change pair may be omitted. 2316 If the MSB command is omitted, the transaction uses the MSB value 2317 of the most recent C-active Control Change command for controller 2318 number 99 or 101 that appears in the session history. We refer to 2319 this variant as a "type 2 variant". 2321 If the LSB command is omitted, the LSB value 0x00 is assumed. We 2322 refer to this variant as a "type 3 variant". The type 2 and type 3 2323 variants are defined as legal, but are not recommended, in [MIDI]. 2325 System real-time commands may appear at any point during 2326 a transaction (even between octets of individual commands 2327 in the transaction). More generally, [MIDI] does not forbid 2328 the appearance of unrelated MIDI commands during an open 2329 transaction. As a rule, these commands are considered to 2330 be "outside" the transaction and do not affect the status 2331 of the transaction in any way. Exceptions to this rule are 2332 commands whose semantics act to terminate transactions: 2333 Reset State commands, and Control Change (0xB) for controller 2334 number 121 (Reset All Controllers) [RP015]. 2336 o Initiated parameter system transaction. A canonical parameter 2337 system transaction whose (99, 98) or (101, 100) initial Control 2338 Change command pair appears in the session history is considered 2339 to be an initiated parameter system transaction. This definition 2340 also holds for type 1 variants. For type 2 variants (dropped MSB), 2341 a transaction whose initial LSB Control Change command appears in 2342 the session history is an initiated transaction. For type 3 2343 variants (dropped LSB), a transaction is considered to be 2344 initiated if at least one transaction command follows the initial 2345 MSB (99 or 101) Control Change command in the session history. 2346 The completion of a transaction does not nullify its "initiated" 2347 status. 2349 o Session history reference counts. Several recovery journal 2350 chapters include a reference count field, which codes the 2351 total number of commands of a type that appear in the session 2352 history. Examples include the Reset and Tune Request command 2353 logs (Chapter D, Appendix B.1) and the Active Sense command 2354 (Chapter V, Appendix B.2). Upon the detection of a loss event, 2355 reference count fields let a receiver deduce if any instances of 2356 the command have been lost, by comparing the journal reference 2357 count with its own reference count. Thus, a reference count 2358 field makes sense, even for command types in which knowing the 2359 NUMBER of lost commands is irrelevant (as is true with all of 2360 the example commands mentioned above). 2362 The chapter definitions in Appendices A.2 to A.9 and B.1 to B.5 reflect 2363 the default recovery journal behavior. The ch_default, ch_never, and 2364 ch_anchor parameters modify these definitions, as described in Appendix 2365 C.2.3. 2367 The chapter definitions specify if data MUST be present in the journal. 2368 Senders MAY also include non-required data in the journal. This 2369 optional data MUST comply with the normative chapter definition. For 2370 example, if a chapter definition states that a field codes data from the 2371 most recent active command in the session history, the sender MUST NOT 2372 code inactive commands or older commands in the field. 2374 Finally, we note that a channel journal only encodes information about 2375 MIDI commands appearing on the MIDI channel the journal protects. All 2376 references to MIDI commands in Appendices A.2 to A.9 should be read as 2377 "MIDI commands appearing on this channel." 2378 A.2. Chapter P: MIDI Program Change 2380 A channel journal MUST contain Chapter P if an active Program Change 2381 (0xC) command appears in the checkpoint history. Figure A.2.1 shows the 2382 format for Chapter P. 2384 0 1 2 2385 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 2386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2387 |S| PROGRAM |B| BANK-MSB |X| BANK-LSB | 2388 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2390 Figure A.2.1 -- Chapter P format 2392 The chapter has a fixed size of 24 bits. The PROGRAM field indicates 2393 the data value of the most recent active Program Change command in the 2394 session history. By default, the B, BANK-MSB, X, and BANK-LSB fields 2395 MUST be set to 0. Below, we define exceptions to this default 2396 condition. 2398 If an active Control Change (0xB) command for controller number 0 (Bank 2399 Select MSB) appears before the Program Change command in the session 2400 history, the B bit MUST be set to 1, and the BANK-MSB field MUST code 2401 the data value of the Control Change command. 2403 If B is set to 1, the BANK-LSB field MUST code the data value of the 2404 most recent Control Change command for controller number 32 (Bank Select 2405 LSB) that preceded the Program Change command coded in the PROGRAM field 2406 and followed the Control Change command coded in the BANK-MSB field. If 2407 no such Control Change command exists, the BANK-LSB field MUST be set to 2408 0. 2410 If B is set to 1, and if a Control Change command for controller number 2411 121 (Reset All Controllers) appears in the MIDI stream between the 2412 Control Change command coded by the BANK-MSB field and the Program 2413 Change command coded by the PROGRAM field, the X bit MUST be set to 1. 2415 Note that [RP015] specifies that Reset All Controllers does not reset 2416 the values of controller numbers 0 (Bank Select MSB) and 32 (Bank Select 2417 LSB). Thus, the X bit does not effect how receivers will use the BANK- 2418 LSB and BANK-MSB values when recovering from a lost Program Change 2419 command. The X bit serves to aid recovery in MIDI applications where 2420 controller numbers 0 and 32 are used in a non-standard way. 2422 A.3. Chapter C: MIDI Control Change 2424 Figure A.3.1 shows the format for Chapter C. 2426 0 1 2 3 2427 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 2428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2429 |S| LEN |S| NUMBER |A| VALUE/ALT |S| NUMBER | 2430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2431 |A| VALUE/ALT | .... | 2432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2434 Figure A.3.1 -- Chapter C format 2436 The chapter consists of a 1-octet header, followed by a variable length 2437 list of 2-octet controller logs. The list MUST contain at least one 2438 controller log. The 7-bit LEN field codes the number of controller logs 2439 in the list, minus one. We define the semantics of the controller log 2440 fields in Appendix A.3.2. 2442 A channel journal MUST contain Chapter C if the rules defined in this 2443 appendix require that one or more controller logs appear in the list. 2445 A.3.1. Log Inclusion Rules 2447 A controller log encodes information about a particular Control Change 2448 command in the session history. 2450 In the default use of the payload format, list logs MUST encode 2451 information about the most recent active command in the session history 2452 for a controller number. Logs encoding earlier commands MUST NOT appear 2453 in the list. 2455 Also, as a rule, the list MUST contain a log for the most recent active 2456 command for a controller number that appears in the checkpoint history. 2457 Below, we define exceptions to this rule: 2459 o MIDI streams may transmit 14-bit controller values using paired 2460 Most Significant Byte (MSB, controller numbers 0-31, 99, 101) and 2461 Least Significant Byte (LSB, controller numbers 32-63, 98, 100) 2462 Control Change commands [MIDI]. 2464 If the most recent active Control Change command in the session 2465 history for a 14-bit controller pair uses the MSB number, Chapter 2466 C MAY omit the controller log for the most recent active Control 2467 Change command for the associated LSB number, as the command 2468 ordering makes this LSB value irrelevant. However, this exception 2469 MUST NOT be applied if the sender is not certain that the MIDI 2470 source uses 14-bit semantics for the controller number pair. Note 2471 that some MIDI sources ignore 14-bit controller semantics and use 2472 the LSB controller numbers as independent 7-bit controllers. 2474 o If active Control Change commands for controller numbers 0 (Bank 2475 Select MSB) or 32 (Bank Select LSB) appear in the checkpoint 2476 history, and if the command instances are also coded in the 2477 BANK-MSB and BANK-LSB fields of the Chapter P (Appendix A.2), 2478 Chapter C MAY omit the controller logs for the commands. 2480 o Several controller number pairs are defined to be mutually 2481 exclusive. Controller numbers 124 (Omni Off) and 125 (Omni On) 2482 form a mutually exclusive pair, as do controller numbers 126 2483 (Mono) and 127 (Poly). 2485 If active Control Change commands for one or both members of 2486 a mutually exclusive pair appear in the checkpoint history, a 2487 log for the controller number of the most recent command for the 2488 pair in the checkpoint history MUST appear in the controller list. 2489 However, the list MAY omit the controller log for the most recent 2490 active command for the other number in the pair. 2492 If active Control Change commands for one or both members of a 2493 mutually exclusive pair appear in the session history, and if a 2494 log for the controller number of the most recent command for the 2495 pair does not appear in the controller list, a log for the most 2496 recent command for the other number of the pair MUST NOT appear 2497 in the controller list. 2499 o If an active Control Change command for controller number 121 2500 (Reset All Controllers) appears in the session history, the 2501 controller list MAY omit logs for Control Change commands that 2502 precede the Reset All Controllers command in the session history, 2503 under certain conditions. 2505 Namely, a log MAY be omitted if the sender is certain that a 2506 command stream follows the Reset All Controllers semantics 2507 defined in [RP015], and if the log codes a controller number 2508 for which [RP015] specifies a reset value. 2510 For example, [RP015] specifies that controller number 1 2511 (Modulation Wheel) is reset to the value 0, and thus 2512 a controller log for Modulation Wheel MAY be omitted 2513 from the controller log list. In contrast, [RP015] specifies 2514 that controller number 7 (Channel Volume) is not reset, 2515 and thus a controller log for Channel Volume MUST NOT 2516 be omitted from the controller log list. 2518 o Appendix A.3.4 defines exception rules for the MIDI Parameter 2519 System controller numbers 6, 38, and 96-101. 2521 A.3.2. Controller Log Format 2523 Figure A.3.2 shows the controller log structure of Chapter C. 2525 0 1 2526 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2527 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2528 |S| NUMBER |A| VALUE/ALT | 2529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2531 Figure A.3.2 -- Chapter C controller log 2533 The 7-bit NUMBER field identifies the controller number of the coded 2534 command. The 7-bit VALUE/ALT field codes recovery information for the 2535 command. The A bit sets the format of the VALUE/ALT field. 2537 A log encodes recovery information using one of the following tools: the 2538 value tool, the toggle tool, or the count tool. 2540 A log uses the value tool if the A bit is set to 0. The value tool 2541 codes the 7-bit data value of a command in the VALUE/ALT field. The 2542 value tool works best for controllers that code a continuous quantity, 2543 such as number 1 (Modulation Wheel). 2545 The A bit is set to 1 to code the toggle or count tool. These tools 2546 work best for controllers that code discrete actions. Figure A.3.3 2547 shows the controller log for these tools. 2549 0 1 2550 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2552 |S| NUMBER |1|T| ALT | 2553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2555 Figure A.3.3 -- Controller log for ALT tools 2557 A log uses the toggle tool if the T bit is set to 0. A log uses the 2558 count tool if the T bit is set to 1. Both methods use the 6-bit ALT 2559 field as an unsigned integer. 2561 The toggle tool works best for controllers that act as on/off switches, 2562 such as 64 (Damper Pedal (Sustain)). These controllers code the "off" 2563 state with control values 0-63 and the "on" state with 64-127. 2565 For the toggle tool, the ALT field codes the total number of toggles 2566 (off->on and on->off) due to Control Change commands in the session 2567 history, up to and including a toggle caused by the command coded by the 2568 log. The toggle count includes toggles caused by Control Change 2569 commands for controller number 121 (Reset All Controllers). 2571 Toggle counting is performed modulo 64. The toggle count is reset at 2572 the start of a session, and whenever a Reset State command (Appendix 2573 A.1) appears in the session history. When these reset events occur, the 2574 toggle count for a controller is set to 0 (for controllers whose default 2575 value is 0-63) or 1 (for controllers whose default value is 64-127). 2577 The Damper Pedal (Sustain) controller illustrates the benefits of the 2578 toggle tool over the value tool for switch controllers. As often used 2579 in piano applications, the "on" state of the controller lets notes 2580 resonate, while the "off" state immediately damps notes to silence. The 2581 loss of the "off" command in an "on->off->on" sequence results in 2582 ringing notes that should have been damped silent. The toggle tool lets 2583 receivers detect this lost "off" command, but the value tool does not. 2585 The count tool is conceptually similar to the toggle tool. For the 2586 count tool, the ALT field codes the total number of Control Change 2587 commands in the session history, up to and including the command coded 2588 by the log. Command counting is performed modulo 64. The command count 2589 is set to 0 at the start of the session and is reset to 0 whenever a 2590 Reset State command (Appendix A.1) appears in the session history. 2592 Because the count tool ignores the data value, it is a good match for 2593 controllers whose controller value is ignored, such as number 123 (All 2594 Notes Off). More generally, the count tool may be used to code a 2595 (modulo 64) identification number for a command. 2597 A.3.3. Log List Coding Rules 2599 In this section, we describe the organization of controller logs in the 2600 Chapter C log list. 2602 A log encodes information about a particular Control Change command in 2603 the session history. In most cases, a command SHOULD be coded by a 2604 single tool (and, thus, a single log). If a number is coded with a 2605 single tool and this tool is the count tool, recovery Control Change 2606 commands generated by a receiver SHOULD use the default control value 2607 for the controller. 2609 However, a command MAY be coded by several tool types (and, thus, 2610 several logs, each using a different tool). This technique may improve 2611 recovery performance for controllers with complex semantics, such as 2612 controller number 84 (Portamento Control) or controller number 121 2613 (Reset All Controllers) when used with a non-zero data octet (with the 2614 semantics described in [DLS2]). 2616 If a command is encoded by multiple tools, the logs MUST be placed in 2617 the list in the following order: count tool log (if any), followed by 2618 value tool log (if any), followed by toggle tool log (if any). 2620 The Chapter C log list MUST obey the oldest-first ordering rule (defined 2621 in Appendix A.1). Note that this ordering preserves the information 2622 necessary for the recovery of 14-bit controller values, without 2623 precluding the use of MSB and LSB controller pairs as independent 7-bit 2624 controllers. 2626 In the default use of the payload format, all logs that appear in the 2627 list for a controller number encode information about one Control Change 2628 command -- namely, the most recent active Control Change command in the 2629 session history for the number. 2631 This coding scheme provides good recovery performance for the standard 2632 uses of Control Change commands defined in [MIDI]. However, not all 2633 MIDI applications restrict the use of Control Change commands to those 2634 defined in [MIDI]. 2636 For example, consider the common MIDI encoding of rotary encoders 2637 ("infinite" rotation knobs). The mixing console MIDI convention defined 2638 in [LCP] codes the position of rotary encoders as a series of Control 2639 Change commands. Each command encodes a relative change of knob 2640 position from the last update (expressed as a clockwise or counter- 2641 clockwise knob turning angle). 2643 As the knob position is encoded incrementally over a series of Control 2644 Change commands, the best recovery performance is obtained if the log 2645 list encodes all Control Change commands for encoder controller numbers 2646 that appear in the checkpoint history, not only the most recent command. 2648 To support application areas that use Control Change commands in this 2649 way, Chapter C may be configured to encode information about several 2650 Control Change commands for a controller number. We use the term 2651 "enhanced" to describe this encoding method, which we describe below. 2653 In Appendix C.2.3, we show how to configure a stream to use enhanced 2654 Chapter C encoding for specific controller numbers. In Section 5 in the 2655 main text, we show how the H bits in the recovery journal header (Figure 2656 8) and in the channel journal header (Figure 9) indicate the use of 2657 enhanced Chapter C encoding. 2659 Here, we define how to encode a Chapter C log list that uses the 2660 enhanced encoding method. 2662 Senders that use the enhanced encoding method for a controller number 2663 MUST obey the rules below. These rules let a receiver determine which 2664 logs in the list correspond to lost commands. Note that these rules 2665 override the exceptions listed in Appendix A.3.1. 2667 o If N commands for a controller number are encoded in the list, 2668 the commands MUST be the N most recent commands for the controller 2669 number in the session history. For example, for N = 2, the sender 2670 MUST encode the most recent command and the second most recent 2671 command, not the most recent command and the third most recent 2672 command. 2674 o If a controller number uses enhanced encoding, the encoding 2675 of the least-recent command for the controller number in the 2676 log list MUST include a count tool log. In addition, if 2677 commands are encoded for the controller number whose logs 2678 have S bits set to 0, the encoding of the least-recent 2679 command with S = 0 logs MUST include a count tool log. 2681 The count tool is OPTIONAL for the other commands for the 2682 controller number encoded in the list, as a receiver is 2683 able to efficiently deduce the count tool value for these 2684 commands, for both single-packet and multi-packet loss events. 2686 o The use of the value and toggle tools MUST be identical for all 2687 commands for a controller number encoded in the list. For 2688 example, a value tool log either MUST appear for all commands 2689 for the controller number coded in the list, or alternatively, 2690 value tool logs for the controller number MUST NOT appear in 2691 the list. Likewise, a toggle tool log either MUST appear for 2692 all commands for the controller number coded in the list, or 2693 alternatively, toggle tool logs for the controller number MUST 2694 NOT appear in the list. 2696 o If a command is encoded by multiple tools, the logs MUST be 2697 placed in the list in the following order: count tool log 2698 (if any), followed by value tool log (if any), followed by 2699 toggle tool log (if any). 2701 These rules permit a receiver recovering from a packet loss to use the 2702 count tool log to match the commands encoded in the list with its own 2703 history of the stream, as we describe below. Note that the text below 2704 describes a non-normative algorithm; receivers are free to use any 2705 algorithm to match its history with the log list. 2707 In a typical implementation of the enhanced encoding method, a receiver 2708 computes and stores count, value, and toggle tool data field values for 2709 the most recent Control Change command it has received for a controller 2710 number. 2712 After a loss event, a receiver parses the Chapter C list and processes 2713 list logs for a controller number that uses enhanced encoding as 2714 follows. 2716 The receiver compares the count tool ALT field for the least-recent 2717 command for the controller number in the list against its stored count 2718 data for the controller number, to determine if recovery is necessary 2719 for the command coded in the list. The value and toggle tool logs (if 2720 any) that directly follow the count tool log are associated with this 2721 least-recent command. 2723 To check more-recent commands for the controller, the receiver detects 2724 additional value and/or toggle tool logs for the controller number in 2725 the list and infers count tool data for the command coded by these logs. 2726 This inferred data is used to determine if recovery is necessary for the 2727 command coded by the value and/or toggle tool logs. 2729 In this way, a receiver is able to execute only lost commands, without 2730 executing a command twice. While recovering from a single packet loss, 2731 a receiver may skip through S = 1 logs in the list, as the first S = 0 2732 log for an enhanced controller number is always a count tool log. 2734 Note that the requirements in Appendix C.2.2.2 for protective sender and 2735 receiver actions during session startup for multicast operation are of 2736 particular importance for enhanced encoding, as receivers need to 2737 initialize its count tool data structures with recovery journal data in 2738 order to match commands correctly after a loss event. 2740 Finally, we note in passing that in some applications of rotary 2741 encoders, a good user experience may be possible without the use of 2742 enhanced encoding. These applications are distinguished by visual 2743 feedback of encoding position that is driven by the post-recovery rotary 2744 encoding stream, and relatively low packet loss. In these domains, 2745 recovery performance may be acceptable for rotary encoders if the log 2746 list encodes only the most recent command, if both count and value logs 2747 appear for the command. 2749 A.3.4. The Parameter System 2751 Readers may wish to review the Appendix A.1 definitions of "parameter 2752 system", "parameter system transaction", and "initiated parameter system 2753 transaction" before reading this section. 2755 Parameter system transactions update a MIDI Registered Parameter Number 2756 (RPN) or Non-Registered Parameter Number (NRPN) value. A parameter 2757 system transaction is a sequence of Control Change commands that may use 2758 the following controllers numbers: 2760 o Data Entry MSB (6) 2761 o Data Entry LSB (38) 2762 o Data Increment (96) 2763 o Data Decrement (97) 2764 o Non-Registered Parameter Number (NRPN) LSB (98) 2765 o Non-Registered Parameter Number (NRPN) MSB (99) 2766 o Registered Parameter Number (RPN) LSB (100) 2767 o Registered Parameter Number (RPN) MSB (101) 2769 Control Change commands that are a part of a parameter system 2770 transaction MUST NOT be coded in Chapter C controller logs. Instead, 2771 these commands are coded in Chapter M, the MIDI Parameter chapter 2772 defined in Appendix A.4. 2774 However, Control Change commands that use the listed controllers as 2775 general-purpose controllers (i.e., outside of a parameter system 2776 transaction) MUST NOT be coded in Chapter M. 2778 Instead, the controllers are coded in Chapter C controller logs. The 2779 controller logs follow the coding rules stated in Appendix A.3.2 and 2780 A.3.3. The rules for coding paired LSB and MSB controllers, as defined 2781 in Appendix A.3.1, apply to the pairs (6, 38), (99, 98), and (101, 100) 2782 when coded in Chapter C. 2784 If active Control Change commands for controller numbers 6, 38, or 2785 96-101 appear in the checkpoint history, and these commands are used as 2786 general-purpose controllers, the most recent general-purpose command 2787 instance for these controller numbers MUST appear as entries in the 2788 Chapter C controller list. 2790 MIDI syntax permits a source to use controllers 6, 38, 96, and 97 as 2791 parameter-system controllers and general-purpose controllers in the same 2792 stream. An RTP MIDI sender MUST deduce the role of each Control Change 2793 command for these controller numbers by noting the placement of the 2794 command in the stream and MUST use this information to code the command 2795 in Chapter C or Chapter M, as appropriate. 2797 Specifically, active Control Change commands for controllers 6, 38, 96, 2798 and 97 act in a general-purpose way when 2800 o no active Control Change commands that set an RPN or 2801 NRPN parameter number appear in the session history, or 2803 o the most recent active Control Change commands in the session 2804 history that set an RPN or NRPN parameter number code the null 2805 parameter (MSB value 0x7F, LSB value 0x7F), or 2807 o a Control Change command for controller number 121 (Reset 2808 All Controllers) appears more recently in the session history 2809 than all active Control Change commands that set an RPN or 2810 NRPN parameter number (see [RP015] for details). 2812 Finally, we note that a MIDI source that follows the recommendations of 2813 [MIDI] exclusively uses numbers 98-101 as parameter system controllers. 2814 Alternatively, a MIDI source may exclusively use 98-101 as general- 2815 purpose controllers and lose the ability to perform parameter system 2816 transactions in a stream. 2818 In the language of [MIDI], the general-purpose use of controllers 98-101 2819 constitutes a non-standard controller assignment. As most real-world 2820 MIDI sources use the standard controller assignment for controller 2821 numbers 98-101, an RTP MIDI sender SHOULD assume these controllers act 2822 as parameter system controllers, unless it knows that a MIDI source uses 2823 controller numbers 98-101 in a general-purpose way. 2825 A.4. Chapter M: MIDI Parameter System 2827 Readers may wish to review the Appendix A.1 definitions for "C-active", 2828 "parameter system", "parameter system transaction", and "initiated 2829 parameter system transaction" before reading this appendix. 2831 Chapter M protects parameter system transactions for Registered 2832 Parameter Number (RPN) and Non-Registered Parameter Number (NRPN) 2833 values. Figure A.4.1 shows the format for Chapter M. 2835 0 1 2 3 2836 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 2837 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2838 |S|P|E|U|W|Z| LENGTH |Q| PENDING | Log list ... | 2839 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2841 Figure A.4.1 -- Top-level Chapter M format 2843 Chapter M begins with a 2-octet header. If the P header bit is set to 2844 1, a 1-octet field follows the header, coding the 7-bit PENDING value 2845 and its associated Q bit. 2847 The 10-bit LENGTH field codes the size of Chapter M and conforms to 2848 semantics described in Appendix A.1. 2850 Chapter M ends with a list of zero or more variable-length parameter 2851 logs. Appendix A.4.2 defines the bitfield format of a parameter log. 2852 Appendix A.4.1 defines the inclusion semantics of the log list. 2854 A channel journal MUST contain Chapter M if the rules defined in 2855 Appendix A.4.1 require that one or more parameter logs appear in the 2856 list. 2858 A channel journal also MUST contain Chapter M if the most recent C- 2859 active Control Change command involved in a parameter system transaction 2860 in the checkpoint history is 2862 o an RPN MSB (101) or NRPN MSB (99) controller, or 2864 o an RPN LSB (100) or NRPN LSB (98) controller that completes the 2865 coding of the null parameter (MSB value 0x7F, LSB value 0x7F). 2867 This rule provides loss protection for partially transmitted parameter 2868 numbers and for the null parameter numbers. 2870 If the most recent C-active Control Change command involved in a 2871 parameter system transaction in the session history is for the RPN MSB 2872 or NRPN MSB controller, the P header bit MUST be set to 1, and the 2873 PENDING field (and its associated Q bit) MUST follow the Chapter M 2874 header. Otherwise, the P header bit MUST be set to 0, and the PENDING 2875 field and Q bit MUST NOT appear in Chapter M. 2877 If PENDING codes an NRPN MSB, the Q bit MUST be set to 1. If PENDING 2878 codes an RPN MSB, the Q bit MUST be set to 0. 2880 The E header bit codes the current transaction state of the MIDI stream. 2881 If E = 1, an initiated transaction is in progress. Below, we define the 2882 rules for setting the E header bit: 2884 o If no C-active parameter system transaction Control Change 2885 commands appear in the session history, the E bit MUST be 2886 set to 0. 2888 o If the P header bit is set to 1, the E bit MUST be set to 0. 2890 o If the most recent C-active parameter system transaction 2891 Control Change command in the session history is for the 2892 NRPN LSB or RPN LSB controller number, and if this command 2893 acts to complete the coding of the null parameter (MSB 2894 value 0x7F, LSB value 0x7F), the E bit MUST be set to 0. 2896 o Otherwise, an initiated transaction is in progress, and the 2897 E bit MUST be set to 1. 2899 The U, W, and Z header bits code properties that are shared by all 2900 parameter logs in the list. If these properties are set, parameter logs 2901 may be coded with improved efficiency (we explain how in A.4.1). 2903 By default, the U, W, and Z bits MUST be set to 0. If all parameter 2904 logs in the list code RPN parameters, the U bit MAY be set to 1. If all 2905 parameter logs in the list code NRPN parameters, the W bit MAY be set to 2906 1. If the parameter numbers of all RPN and NRPN logs in the list lie in 2907 the range 0-127 (and thus have an MSB value of 0), the Z bit MAY be set 2908 to 1. 2910 Note that C-active semantics appear in the preceding paragraphs because 2911 [RP015] specifies that pending Parameter System transactions are closed 2912 by a Control Change command for controller number 121 (Reset All 2913 Controllers). 2915 A.4.1. Log Inclusion Rules 2917 Parameter logs code recovery information for a specific RPN or NRPN 2918 parameter. 2920 A parameter log MUST appear in the list if an active Control Change 2921 command that forms a part of an initiated transaction for the parameter 2922 appears in the checkpoint history. 2924 An exception to this rule applies if the checkpoint history only 2925 contains transaction Control Change commands for controller numbers 2926 98-101 that act to terminate the transaction. In this case, a log for 2927 the parameter MAY be omitted from the list. 2929 A log MAY appear in the list if an active Control Change command that 2930 forms a part of an initiated transaction for the parameter appears in 2931 the session history. Otherwise, a log for the parameter MUST NOT appear 2932 in the list. 2934 Multiple logs for the same RPN or NRPN parameter MUST NOT appear in the 2935 log list. 2937 The parameter log list MUST obey the oldest-first ordering rule (defined 2938 in Appendix A.1), with the phrase "parameter transaction" replacing the 2939 word "command" in the rule definition. 2941 Parameter logs associated with the RPN or NRPN null parameter (LSB = 2942 0x7F, MSB = 0x7F) MUST NOT appear in the log list. Chapter M uses the E 2943 header bit (Figure A.4.1) and the log list ordering rules to code null 2944 parameter semantics. 2946 Note that "active" semantics (rather than "C-active" semantics) appear 2947 in the preceding paragraphs because [RP015] specifies that pending 2948 Parameter System transactions are not reset by a Control Change command 2949 for controller number 121 (Reset All Controllers). However, the rule 2950 that follows uses C-active semantics, because it concerns the protection 2951 of the transaction system itself, and [RP015] specifies that Reset All 2952 Controllers acts to close a transaction in progress. 2954 In most cases, parameter logs for RPN and NRPN parameters that are 2955 assigned to the ch_never parameter (Appendix C.2.3) MAY be omitted from 2956 the list. An exception applies if 2958 o the log codes the most recent initiated transaction 2959 in the session history, and 2961 o a C-active command that forms a part of the transaction 2962 appears in the checkpoint history, and 2964 o the E header bit for the top-level Chapter M header (Figure 2965 A.4.1) is set to 1. 2967 In this case, a log for the parameter MUST appear in the list. This log 2968 informs receivers recovering from a loss that a transaction is in 2969 progress, so that the receiver is able to correctly interpret RPN or 2970 NRPN Control Change commands that follow the loss event. 2972 A.4.2. Log Coding Rules 2974 Figure A.4.2 shows the parameter log structure of Chapter M. 2976 0 1 2 3 2977 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 2978 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2979 |S| PNUM-LSB |Q| PNUM-MSB |J|K|L|M|N|T|V|R| Fields ... | 2980 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2982 Figure A.4.2 -- Parameter log format 2984 The log begins with a header, whose default size (as shown in Figure 2985 A.4.2) is 3 octets. If the Q header bit is set to 0, the log encodes an 2986 RPN parameter. If Q = 1, the log encodes an NRPN parameter. The 7-bit 2987 PNUM-MSB and PNUM-LSB fields code the parameter number and reflect the 2988 Control Change command data values for controllers 99 and 98 (for NRPNs) 2989 or 101 and 100 (for RPNs). 2991 The J, K, L, M, and N header bits form a Table of Contents (TOC) for the 2992 log and signal the presence of fixed-sized fields that follow the 2993 header. A header bit that is set to 1 codes the presence of a field in 2994 the log. The ordering of fields in the log follows the ordering of the 2995 header bits in the TOC. Appendices A.4.2.1-2 define the fields 2996 associated with each TOC header bit. 2998 The T and V header bits code information about the parameter log but are 2999 not part of the TOC. A set T or V bit does not signal the presence of 3000 any parameter log field. 3002 If the rules in Appendix A.4.1 state that a log for a given parameter 3003 MUST appear in Chapter M, the log MUST code sufficient information to 3004 protect the parameter from the loss of active parameter transaction 3005 Control Change commands in the checkpoint history. 3007 This rule does not apply if the parameter coded by the log is assigned 3008 to the ch_never parameter (Appendix C.2.3). In this case, senders MAY 3009 choose to set the J, K, L, M, and N TOC bits to 0, coding a parameter 3010 log with no fields. 3012 Note that logs to protect parameters that are assigned to ch_never are 3013 REQUIRED under certain conditions (see Appendix A.4.1). The purpose of 3014 the log is to inform receivers recovering from a loss that a transaction 3015 is in progress, so that the receiver is able to correctly interpret RPN 3016 or NRPN Control Change commands that follow the loss event. 3018 Parameter logs provide two tools for parameter protection: the value 3019 tool and the count tool. Depending on the semantics of the parameter, 3020 senders may use either tool, both tools, or neither tool to protect a 3021 given parameter. 3023 The value tool codes information a receiver may use to determine the 3024 current value of an RPN or NRPN parameter. If a parameter log uses the 3025 value tool, the V header bit MUST be set to 1, and the semantics defined 3026 in Appendices A.4.2.1 for setting the J, K, L, and M TOC bits MUST be 3027 followed. If a parameter log does not use the value tool, the V bit 3028 MUST be set to 0, and the J, K, L, and M TOC bits MUST also be set to 0. 3030 The count tool codes the number of transactions for an RPN or NRPN 3031 parameter. If a parameter log uses the count tool, the T header bit 3032 MUST be set to 1, and the semantics defined in Appendices A.4.2.2 for 3033 setting the N TOC bit MUST be followed. If a parameter log does not use 3034 the count tool, the T bit and the N TOC bit MUST be set to 0. 3036 Note that V and T are set if the sender uses value (V) or count (T) tool 3037 for the log on an ongoing basis. Thus, V may be set even if J = K = L = 3038 M = 0, and T may be set even if N = 0. 3040 In many cases, all parameters coded in the log list are of one type (RPN 3041 and NRPN), and all parameter numbers lie in the range 0-127. As 3042 described in Appendix A.4.1, senders MAY signal this condition by 3043 setting the top-level Chapter M header bit Z to 1 (to code the 3044 restricted range) and by setting the U or W bit to 1 (to code the 3045 parameter type). 3047 If the top-level Chapter M header codes Z = 1 and either U = 1 or W = 1, 3048 all logs in the parameter log list MUST use a modified header format. 3049 This modification deletes bits 8-15 of the bitfield shown in Figure 3050 A.4.2, to yield a 2-octet header. The values of the deleted PNUM-MSB 3051 and Q fields may be inferred from the U, W, and Z bit values. 3053 A.4.2.1. The Value Tool 3055 The value tool uses several fields to track the value of an RPN or NRPN 3056 parameter. 3058 The J TOC bit codes the presence of the octet shown in Figure A.4.3 in 3059 the field list. 3061 0 3062 0 1 2 3 4 5 6 7 3063 +-+-+-+-+-+-+-+-+ 3064 |X| ENTRY-MSB | 3065 +-+-+-+-+-+-+-+-+ 3067 Figure A.4.3 -- ENTRY-MSB field 3069 The 7-bit ENTRY-MSB field codes the data value of the most recent active 3070 Control Change command for controller number 6 (Data Entry MSB) in the 3071 session history that appears in a transaction for the log parameter. 3073 The X bit MUST be set to 1 if the command coded by ENTRY-MSB precedes 3074 the most recent Control Change command for controller 121 (Reset All 3075 Controllers) in the session history. Otherwise, the X bit MUST be set 3076 to 0. 3078 A parameter log that uses the value tool MUST include the ENTRY-MSB 3079 field if an active Control Change command for controller number 6 3080 appears in the checkpoint history. 3082 Note that [RP015] specifies that Control Change commands for controller 3083 121 (Reset All Controllers) do not reset RPN and NRPN values, and thus 3084 the X bit would not play a recovery role for MIDI systems that comply 3085 with [RP015]. 3087 However, certain renderers (such as DLS 2 [DLS2]) specify that certain 3088 RPN values are reset for some uses of Reset All Controllers. The X bit 3089 (and other bitfield features of this nature in this appendix) plays a 3090 role in recovery for renderers of this type. 3092 The K TOC bit codes the presence of the octet shown in Figure A.4.4 in 3093 the field list. 3095 0 3096 0 1 2 3 4 5 6 7 3097 +-+-+-+-+-+-+-+-+ 3098 |X| ENTRY-LSB | 3099 +-+-+-+-+-+-+-+-+ 3101 Figure A.4.4 -- ENTRY-LSB field 3103 The 7-bit ENTRY-LSB field codes the data value of the most recent active 3104 Control Change command for controller number 38 (Data Entry LSB) in the 3105 session history that appears in a transaction for the log parameter. 3107 The X bit MUST be set to 1 if the command coded by ENTRY-LSB precedes 3108 the most recent Control Change command for controller 121 (Reset All 3109 Controllers) in the session history. Otherwise, the X bit MUST be set 3110 to 0. 3112 As a rule, a parameter log that uses the value tool MUST include the 3113 ENTRY-LSB field if an active Control Change command for controller 3114 number 38 appears in the checkpoint history. However, the ENTRY-LSB 3115 field MUST NOT appear in a parameter log if the Control Change command 3116 associated with the ENTRY-LSB precedes a Control Change command for 3117 controller number 6 (Data Entry MSB) that appears in a transaction for 3118 the log parameter in the session history. 3120 The L TOC bit codes the presence of the octets shown in Figure A.4.5 in 3121 the field list. 3123 0 1 3124 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3126 |G|X| A-BUTTON | 3127 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3129 Figure A.4.5 -- A-BUTTON field 3131 The 14-bit A-BUTTON field codes a count of the number of active Control 3132 Change commands for controller numbers 96 and 97 (Data Increment and 3133 Data Decrement) in the session history that appear in a transaction for 3134 the log parameter. 3136 The M TOC bit codes the presence of the octets shown in Figure A.4.6 in 3137 the field list. 3139 0 1 3140 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3141 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3142 |G|R| C-BUTTON | 3143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3145 Figure A.4.6 -- C-BUTTON field 3147 The 14-bit C-BUTTON field has semantics identical to A-BUTTON, except 3148 that Data Increment and Data Decrement Control Change commands that 3149 precede the most recent Control Change command for controller 121 (Reset 3150 All Controllers) in the session history are not counted. 3152 For both A-BUTTON and C-BUTTON, Data Increment and Data Decrement 3153 Control Change commands are not counted if they precede Control Changes 3154 commands for controller numbers 6 (Data Entry MSB) or 38 (Data Entry 3155 LSB) that appear in a transaction for the log parameter in the session 3156 history. 3158 The A-BUTTON and C-BUTTON fields are interpreted as unsigned integers, 3159 and the G bit associated with the field codes the sign of the integer (G 3160 = 0 for positive or zero, G = 1 for negative). 3162 To compute and code the count value, initialize the count value to 0, 3163 add 1 for each qualifying Data Increment command, and subtract 1 for 3164 each qualifying Data Decrement command. After each add or subtract, 3165 limit the count magnitude to 16383. The G bit codes the sign of the 3166 count, and the A-BUTTON or C-BUTTON field codes the count magnitude. 3168 For the A-BUTTON field, if the most recent qualified Data Increment or 3169 Data Decrement command precedes the most recent Control Change command 3170 for controller 121 (Reset All Controllers) in the session history, the X 3171 bit associated with A-BUTTON field MUST be set to 1. Otherwise, the X 3172 bit MUST be set to 0. 3174 A parameter log that uses the value tool MUST include the A-BUTTON and 3175 C-BUTTON fields if an active Control Change command for controller 3176 numbers 96 or 97 appears in the checkpoint history. However, to improve 3177 coding efficiency, this rule has several exceptions: 3179 o If the log includes the A-BUTTON field, and if the X bit of 3180 the A-BUTTON field is set to 1, the C-BUTTON field (and its 3181 associated R and G bits) MAY be omitted from the log. 3183 o If the log includes the A-BUTTON field, and if the A-BUTTON 3184 and C-BUTTON fields (and their associated G bits) code identical 3185 values, the C-BUTTON field (and its associated R and G bits) 3186 MAY be omitted from the log. 3188 A.4.2.2. The Count Tool 3190 The count tool tracks the number of transactions for an RPN or NRPN 3191 parameter. The N TOC bit codes the presence of the octet shown in 3192 Figure A.4.7 in the field list. 3194 0 3195 0 1 2 3 4 5 6 7 3196 +-+-+-+-+-+-+-+-+ 3197 |X| COUNT | 3198 +-+-+-+-+-+-+-+-+ 3200 Figure A.4.7 -- COUNT field 3202 The 7-bit COUNT codes the number of initiated transactions for the log 3203 parameter that appear in the session history. Initiated transactions 3204 are counted if they contain one or more active Control Change commands, 3205 including commands for controllers 98-101 that initiate the parameter 3206 transaction. 3208 If the most recent counted transaction precedes the most recent Control 3209 Change command for controller 121 (Reset All Controllers) in the session 3210 history, the X bit associated with the COUNT field MUST be set to 1. 3211 Otherwise, the X bit MUST be set to 0. 3213 Transaction counting is performed modulo 128. The transaction count is 3214 set to 0 at the start of a session and is reset to 0 whenever a Reset 3215 State command (Appendix A.1) appears in the session history. 3217 A parameter log that uses the count tool MUST include the COUNT field if 3218 an active command that increments the transaction count (modulo 128) 3219 appears in the checkpoint history. 3221 A.5. Chapter W: MIDI Pitch Wheel 3223 A channel journal MUST contain Chapter W if a C-active MIDI Pitch Wheel 3224 (0xE) command appears in the checkpoint history. Figure A.5.1 shows the 3225 format for Chapter W. 3227 0 1 3228 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3230 |S| FIRST |R| SECOND | 3231 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3233 Figure A.5.1 -- Chapter W format 3235 The chapter has a fixed size of 16 bits. The FIRST and SECOND fields 3236 are the 7-bit values of the first and second data octets of the most 3237 recent active Pitch Wheel command in the session history. 3239 Note that Chapter W encodes C-active commands and thus does not encode 3240 active commands that are not C-active (see the second-to-last paragraph 3241 of Appendix A.1 for an explanation of chapter inclusion text in this 3242 regard). 3244 Chapter W does not encode "active but not C-active" commands because 3245 [RP015] declares that Control Change commands for controller number 121 3246 (Reset All Controllers) act to reset the Pitch Wheel value to 0. If 3247 Chapter W encoded "active but not C-active" commands, a repair operation 3248 following a Reset All Controllers command could incorrectly repair the 3249 stream with a stale Pitch Wheel value. 3251 A.6. Chapter N: MIDI NoteOff and NoteOn 3253 In this appendix, we consider NoteOn commands with zero velocity to be 3254 NoteOff commands. Readers may wish to review the Appendix A.1 3255 definition of "N-active commands" before reading this appendix. 3257 Chapter N completely protects note commands in streams that alternate 3258 between NoteOn and NoteOff commands for a particular note number. 3259 However, in rare applications, multiple overlapping NoteOn commands may 3260 appear for a note number. Chapter E, described in Appendix A.7, 3261 augments Chapter N to completely protect these streams. 3263 A channel journal MUST contain Chapter N if an N-active MIDI NoteOn 3264 (0x9) or NoteOff (0x8) command appears in the checkpoint history. 3265 Figure A.6.1 shows the format for Chapter N. 3267 0 1 2 3 3268 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 3269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3270 |B| LEN | LOW | HIGH |S| NOTENUM |Y| VELOCITY | 3271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3272 |S| NOTENUM |Y| VELOCITY | .... | 3273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3274 | OFFBITS | OFFBITS | .... | OFFBITS | 3275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3277 Figure A.6.1 -- Chapter N format 3279 Chapter N consists of a 2-octet header, followed by at least one of the 3280 following data structures: 3282 o A list of note logs to code NoteOn commands. 3283 o A NoteOff bitfield structure to code NoteOff commands. 3285 We define the header bitfield semantics in Appendix A.6.1. We define 3286 the note log semantics and the NoteOff bitfield semantics in Appendix 3287 A.6.2. 3289 If one or more N-active NoteOn or NoteOff commands in the checkpoint 3290 history reference a note number, the note number MUST be coded in either 3291 the note log list or the NoteOff bitfield structure. 3293 The note log list MUST contain an entry for all note numbers whose most 3294 recent checkpoint history appearance is in an N-active NoteOn command. 3295 The NoteOff bitfield structure MUST contain a set bit for all note 3296 numbers whose most recent checkpoint history appearance is in an N- 3297 active NoteOff command. 3299 A note number MUST NOT be coded in both structures. 3301 All note logs and NoteOff bitfield set bits MUST code the most recent N- 3302 active NoteOn or NoteOff reference to a note number in the session 3303 history. 3305 The note log list MUST obey the oldest-first ordering rule (defined in 3306 Appendix A.1). 3308 A.6.1. Header Structure 3310 The header for Chapter N, shown in Figure A.6.2, codes the size of the 3311 note list and bitfield structures. 3313 0 1 3314 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3316 |B| LEN | LOW | HIGH | 3317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3319 Figure A.6.2 -- Chapter N header 3321 The LEN field, a 7-bit integer value, codes the number of 2-octet note 3322 logs in the note list. Zero is a valid value for LEN and codes an empty 3323 note list. 3325 The 4-bit LOW and HIGH fields code the number of OFFBITS octets that 3326 follow the note log list. LOW and HIGH are unsigned integer values. If 3327 LOW <= HIGH, there are (HIGH - LOW + 1) OFFBITS octets in the chapter. 3328 The value pairs (LOW = 15, HIGH = 0) and (LOW = 15, HIGH = 1) code an 3329 empty NoteOff bitfield structure (i.e., no OFFBITS octets). Other (LOW 3330 > HIGH) value pairs MUST NOT appear in the header. 3332 The B bit provides S-bit functionality (Appendix A.1) for the NoteOff 3333 bitfield structure. By default, the B bit MUST be set to 1. However, 3334 if the MIDI command section of the previous packet (packet I - 1, with I 3335 as defined in Appendix A.1) includes a NoteOff command for the channel, 3336 the B bit MUST be set to 0. If the B bit is set to 0, the higher-level 3337 recovery journal elements that contain Chapter N MUST have S bits that 3338 are set to 0, including the top-level journal header. 3340 The LEN value of 127 codes a note list length of 127 or 128 note logs, 3341 depending on the values of LOW and HIGH. If LEN = 127, LOW = 15, and 3342 HIGH = 0, the note list holds 128 note logs, and the NoteOff bitfield 3343 structure is empty. For other values of LOW and HIGH, LEN = 127 codes 3344 that the note list contains 127 note logs. In this case, the chapter 3345 has (HIGH - LOW + 1) NoteOff OFFBITS octets if LOW <= HIGH and has no 3346 OFFBITS octets if LOW = 15 and HIGH = 1. 3348 A.6.2. Note Structures 3350 Figure A.6.3 shows the 2-octet note log structure. 3352 0 1 3353 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3355 |S| NOTENUM |Y| VELOCITY | 3356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3358 Figure A.6.3 -- Chapter N note log 3360 The 7-bit NOTENUM field codes the note number for the log. A note 3361 number MUST NOT be represented by multiple note logs in the note list. 3363 The 7-bit VELOCITY field codes the velocity value for the most recent N- 3364 active NoteOn command for the note number in the session history. 3365 Multiple overlapping NoteOns for a given note number may be coded using 3366 Chapter E, as discussed in Appendix A.7. 3368 VELOCITY is never zero; NoteOn commands with zero velocity are coded as 3369 NoteOff commands in the NoteOff bitfield structure. 3371 The note log does not code the execution time of the NoteOn command. 3372 However, the Y bit codes a hint from the sender about the NoteOn 3373 execution time. The Y bit codes a recommendation to play (Y = 1) or 3374 skip (Y = 0) the NoteOn command recovered from the note log. See 3375 Section 4.2 of [RFC4696] for non-normative guidance on the use of the Y 3376 bit. 3378 Figure A.6.1 shows the NoteOff bitfield structure, as the list of 3379 OFFBITS octets at the end of the chapter. A NoteOff OFFBITS octet codes 3380 NoteOff information for eight consecutive MIDI note numbers, with the 3381 most-significant bit representing the lowest note number. The most- 3382 significant bit of the first OFFBITS octet codes the note number 8*LOW; 3383 the most-significant bit of the last OFFBITS octet codes the note number 3384 8*HIGH. 3386 A set bit codes a NoteOff command for the note number. In the most 3387 efficient coding for the NoteOff bitfield structure, the first and last 3388 octets of the structure contain at least one set bit. Note that Chapter 3389 N does not code NoteOff velocity data. 3391 Note that in the general case, the recovery journal does not code the 3392 relative placement of a NoteOff command and a Change Control command for 3393 controller 64 (Damper Pedal (Sustain)). In many cases, a receiver 3394 processing a loss event may deduce this relative placement from the 3395 history of the stream and thus determine if a NoteOff note is sustained 3396 by the pedal. If such a determination is not possible, receivers SHOULD 3397 err on the side of silencing pedal sustains, as erroneously sustained 3398 notes may produce unpleasant (albeit transient) artifacts. 3400 A.7. Chapter E: MIDI Note Command Extras 3402 Readers may wish to review the Appendix A.1 definition of "N-active 3403 commands" before reading this appendix. In this appendix, a NoteOn 3404 command with a velocity of 0 is considered to be a NoteOff command with 3405 a release velocity value of 64. 3407 Chapter E encodes recovery information about MIDI NoteOn (0x9) and 3408 NoteOff (0x8) command features that rarely appear in MIDI streams. 3409 Receivers use Chapter E to reduce transient artifacts for streams where 3410 several NoteOn commands appear for a note number without an intervening 3411 NoteOff. Receivers also use Chapter E to reduce transient artifacts for 3412 streams that use NoteOff release velocity. Chapter E supplements the 3413 note information coded in Chapter N (Appendix A.6). 3415 Figure A.7.1 shows the format for Chapter E. 3417 0 1 2 3 3418 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 3419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3420 |S| LEN |S| NOTENUM |V| COUNT/VEL |S| NOTENUM | 3421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3422 |V| COUNT/VEL | .... | 3423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3425 Figure A.7.1 -- Chapter E format 3427 The chapter consists of a 1-octet header, followed by a variable-length 3428 list of 2-octet note logs. Appendix A.7.1 defines the bitfield format 3429 for a note log. 3431 The log list MUST contain at least one note log. The 7-bit LEN header 3432 field codes the number of note logs in the list, minus one. A channel 3433 journal MUST contain Chapter E if the rules defined in this appendix 3434 require that one or more note logs appear in the list. The note log 3435 list MUST obey the oldest-first ordering rule (defined in Appendix A.1). 3437 A.7.1. Note Log Format 3439 Figure A.7.2 reproduces the note log structure of Chapter E. 3441 0 1 3442 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3444 |S| NOTENUM |V| COUNT/VEL | 3445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3447 Figure A.7.2 -- Chapter E note log 3449 A note log codes information about the MIDI note number coded by the 3450 7-bit NOTENUM field. The nature of the information depends on the value 3451 of the V flag bit. 3453 If the V bit is set to 1, the COUNT/VEL field codes the release velocity 3454 value for the most recent N-active NoteOff command for the note number 3455 that appears in the session history. 3457 If the V bit is set to 0, the COUNT/VEL field codes a reference count of 3458 the number of NoteOn and NoteOff commands for the note number that 3459 appear in the session history. 3461 The reference count is set to 0 at the start of the session. NoteOn 3462 commands increment the count by 1. NoteOff commands decrement the count 3463 by 1. However, a decrement that generates a negative count value is not 3464 performed. 3466 If the reference count is in the range 0-126, the 7-bit COUNT/VEL field 3467 codes an unsigned integer representation of the count. If the count is 3468 greater than or equal to 127, COUNT/VEL is set to 127. 3470 By default, the count is reset to 0 whenever a Reset State command 3471 (Appendix A.1) appears in the session history, and whenever MIDI Control 3472 Change commands for controller numbers 123-127 (numbers with All Notes 3473 Off semantics) or 120 (All Sound Off) appear in the session history. 3475 A.7.2. Log Inclusion Rules 3477 If the most recent N-active NoteOn or NoteOff command for a note number 3478 in the checkpoint history is a NoteOff command with a release velocity 3479 value other than 64, a note log whose V bit is set to 1 MUST appear in 3480 Chapter E for the note number. 3482 If the most recent N-active NoteOn or NoteOff command for a note number 3483 in the checkpoint history is a NoteOff command, and if the reference 3484 count for the note number is greater than 0, a note log whose V bit is 3485 set to 0 MUST appear in Chapter E for the note number. 3487 If the most recent N-active NoteOn or NoteOff command for a note number 3488 in the checkpoint history is a NoteOn command, and if the reference 3489 count for the note number is greater than 1, a note log whose V bit is 3490 set to 0 MUST appear in Chapter E for the note number. 3492 At most, two note logs MAY appear in Chapter E for a note number: one 3493 log whose V bit is set to 0, and one log whose V bit is set to 1. 3495 Chapter E codes a maximum of 128 note logs. If the log inclusion rules 3496 yield more than 128 REQUIRED logs, note logs whose V bit is set to 1 3497 MUST be dropped from Chapter E in order to reach the 128-log limit. 3498 Note logs whose V bit is set to 0 MUST NOT be dropped. 3500 Most MIDI streams do not use NoteOn and NoteOff commands in ways that 3501 would trigger the log inclusion rules. For these streams, Chapter E 3502 would never be REQUIRED to appear in a channel journal. 3504 The ch_never parameter (Appendix C.2.3) may be used to configure the log 3505 inclusion rules for Chapter E. 3507 A.8. Chapter T: MIDI Channel Aftertouch 3509 A channel journal MUST contain Chapter T if an N-active and C-active 3510 MIDI Channel Aftertouch (0xD) command appears in the checkpoint history. 3511 Figure A.8.1 shows the format for Chapter T. 3513 0 3514 0 1 2 3 4 5 6 7 3515 +-+-+-+-+-+-+-+-+ 3516 |S| PRESSURE | 3517 +-+-+-+-+-+-+-+-+ 3519 Figure A.8.1 -- Chapter T format 3521 The chapter has a fixed size of 8 bits. The 7-bit PRESSURE field holds 3522 the pressure value of the most recent N-active and C-active Channel 3523 Aftertouch command in the session history. 3525 Chapter T only encodes commands that are C-active and N-active. We 3526 define a C-active restriction because [RP015] declares that a Control 3527 Change command for controller 121 (Reset All Controllers) acts to reset 3528 the channel pressure to 0 (see the discussion at the end of Appendix A.5 3529 for a more complete rationale). 3531 We define an N-active restriction on the assumption that aftertouch 3532 commands are linked to note activity, and thus Channel Aftertouch 3533 commands that are not N-active are stale and should not be used to 3534 repair a stream. 3536 A.9. Chapter A: MIDI Poly Aftertouch 3538 A channel journal MUST contain Chapter A if a C-active Poly Aftertouch 3539 (0xA) command appears in the checkpoint history. Figure A.9.1 shows the 3540 format for Chapter A. 3542 0 1 2 3 3543 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 3544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3545 |S| LEN |S| NOTENUM |X| PRESSURE |S| NOTENUM | 3546 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3547 |X| PRESSURE | .... | 3548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3550 Figure A.9.1 -- Chapter A format 3552 The chapter consists of a 1-octet header, followed by a variable-length 3553 list of 2-octet note logs. A note log MUST appear for a note number if 3554 a C-active Poly Aftertouch command for the note number appears in the 3555 checkpoint history. A note number MUST NOT be represented by multiple 3556 note logs in the note list. The note log list MUST obey the oldest- 3557 first ordering rule (defined in Appendix A.1). 3559 The 7-bit LEN field codes the number of note logs in the list, minus 3560 one. Figure A.9.2 reproduces the note log structure of Chapter A. 3562 0 1 3563 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3564 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3565 |S| NOTENUM |X| PRESSURE | 3566 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3568 Figure A.9.2 -- Chapter A note log 3570 The 7-bit PRESSURE field codes the pressure value of the most recent C- 3571 active Poly Aftertouch command in the session history for the MIDI note 3572 number coded in the 7-bit NOTENUM field. 3574 As a rule, the X bit MUST be set to 0. However, the X bit MUST be set 3575 to 1 if the command coded by the log appears before one of the following 3576 commands in the session history: MIDI Control Change numbers 123-127 3577 (numbers with All Notes Off semantics) or 120 (All Sound Off). 3579 We define C-active restrictions for Chapter A because [RP015] declares 3580 that a Control Change command for controller 121 (Reset All Controllers) 3581 acts to reset the polyphonic pressure to 0 (see the discussion at the 3582 end of Appendix A.5 for a more complete rationale). 3584 B. The Recovery Journal System Chapters 3586 B.1. System Chapter D: Simple System Commands 3588 The system journal MUST contain Chapter D if an active MIDI Reset 3589 (0xFF), MIDI Tune Request (0xF6), MIDI Song Select (0xF3), undefined 3590 MIDI System Common (0xF4 and 0xF5), or undefined MIDI System Real-time 3591 (0xF9 and 0xFD) command appears in the checkpoint history. 3593 Figure B.1.1 shows the variable-length format for Chapter D. 3595 0 1 2 3 3596 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 3597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3598 |S|B|G|H|J|K|Y|Z| Command logs ... | 3599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3601 Figure B.1.1 -- System Chapter D format 3603 The chapter consists of a 1-octet header, followed by one or more 3604 command logs. Header flag bits indicate the presence of command logs 3605 for the Reset (B = 1), Tune Request (G = 1), Song Select (H = 1), 3606 undefined System Common 0xF4 (J = 1), undefined System Common 0xF5 (K = 3607 1), undefined System Real-time 0xF9 (Y = 1), or undefined System Real- 3608 time 0xFD (Z = 1) commands. 3610 Command logs appear in a list following the header, in the order that 3611 the flag bits appear in the header. 3613 Figure B.1.2 shows the 1-octet command log format for the Reset and Tune 3614 Request commands. 3616 0 3617 0 1 2 3 4 5 6 7 3618 +-+-+-+-+-+-+-+-+ 3619 |S| COUNT | 3620 +-+-+-+-+-+-+-+-+ 3622 Figure B.1.2 -- Command log for Reset and Tune Request 3624 Chapter D MUST contain the Reset command log if an active Reset command 3625 appears in the checkpoint history. The 7-bit COUNT field codes the 3626 total number of Reset commands (modulo 128) present in the session 3627 history. 3629 Chapter D MUST contain the Tune Request command log if an active Tune 3630 Request command appears in the checkpoint history. The 7-bit COUNT 3631 field codes the total number of Tune Request commands (modulo 128) 3632 present in the session history. 3634 For these commands, the COUNT field acts as a reference count. See the 3635 definition of "session history reference counts" in Appendix A.1 for 3636 more information. 3638 Figure B.1.3 shows the 1-octet command log format for the Song Select 3639 command. 3641 0 3642 0 1 2 3 4 5 6 7 3643 +-+-+-+-+-+-+-+-+ 3644 |S| VALUE | 3645 +-+-+-+-+-+-+-+-+ 3647 Figure B.1.3 -- Song Select command log format 3649 Chapter D MUST contain the Song Select command log if an active Song 3650 Select command appears in the checkpoint history. The 7-bit VALUE field 3651 codes the song number of the most recent active Song Select command in 3652 the session history. 3654 B.1.1. Undefined System Commands 3656 In this section, we define the Chapter D command logs for the undefined 3657 System commands. [MIDI] reserves the undefined System commands 0xF4, 3658 0xF5, 0xF9, and 0xFD for future use. At the time of this writing, any 3659 MIDI command stream that uses these commands is non-compliant with 3660 [MIDI]. However, future versions of [MIDI] may define these commands, 3661 and a few products do use these commands in a non-compliant manner. 3663 Figure B.1.4 shows the variable-length command log format for the 3664 undefined System Common commands (0xF4 and 0xF5). 3666 0 1 2 3 3667 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 3668 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3669 |S|C|V|L|DSZ| LENGTH | COUNT | VALUE ... | 3670 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3671 | LEGAL ... | 3672 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3674 Figure B.1.4 -- Undefined System Common command log format 3676 The command log codes a single command type (0xF4 or 0xF5, not both). 3677 Chapter D MUST contain a command log if an active 0xF4 command appears 3678 in the checkpoint history and MUST contain an independent command log if 3679 an active 0xF5 command appears in the checkpoint history. 3681 A Chapter D Undefined System Common command log consists of a two-octet 3682 header followed by a variable number of data fields. Header flag bits 3683 indicate the presence of the COUNT field (C = 1), the VALUE field (V = 3684 1), and the LEGAL field (L = 1). The 10-bit LENGTH field codes the size 3685 of the command log and conforms to semantics described in Appendix A.1. 3687 The 2-bit DSZ field codes the number of data octets in the command 3688 instance that appears most recently in the session history. If DSZ = 3689 0-2, the command has 0-2 data octets. If DSZ = 3, the command has 3 or 3690 more command data octets. 3692 We now define the default rules for the use of the COUNT, VALUE, and 3693 LEGAL fields. The session configuration tools defined in Appendix C.2.3 3694 may be used to override this behavior. 3696 By default, if the DSZ field is set to 0, the command log MUST include 3697 the COUNT field. The 8-bit COUNT field codes the total number of 3698 commands of the type coded by the log (0xF4 or 0xF5) present in the 3699 session history, modulo 256. 3701 By default, if the DSZ field is set to 1-3, the command log MUST include 3702 the VALUE field. The variable-length VALUE field codes a verbatim copy 3703 the data octets for the most recent use of the command type coded by the 3704 log (0xF4 or 0xF5) in the session history. The most-significant bit of 3705 the final data octet MUST be set to 1, and the most-significant bit of 3706 all other data octets MUST be set to 0. 3708 The LEGAL field is reserved for future use. If an update to [MIDI] 3709 defines the 0xF4 or 0xF5 command, an IETF standards-track document may 3710 define the LEGAL field. Until such a document appears, senders MUST NOT 3711 use the LEGAL field, and receivers MUST use the LENGTH field to skip 3712 over the LEGAL field. The LEGAL field would be defined by the IETF if 3713 the semantics of the new 0xF4 or 0xF5 command could not be protected 3714 from packet loss via the use of the COUNT and VALUE fields. 3716 Figure B.1.5 shows the variable-length command log format for the 3717 undefined System Real-time commands (0xF9 and 0xFD). 3719 0 1 2 3 3720 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 3721 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3722 |S|C|L| LENGTH | COUNT | LEGAL ... | 3723 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3725 Figure B.1.5 -- Undefined System Real-time command log format 3727 The command log codes a single command type (0xF9 or 0xFD, not both). 3728 Chapter D MUST contain a command log if an active 0xF9 command appears 3729 in the checkpoint history and MUST contain an independent command log if 3730 an active 0xFD command appears in the checkpoint history. 3732 A Chapter D Undefined System Real-time command log consists of a one- 3733 octet header followed by a variable number of data fields. Header flag 3734 bits indicate the presence of the COUNT field (C = 1) and the LEGAL 3735 field (L = 1). The 5-bit LENGTH field codes the size of the command log 3736 and conforms to semantics described in Appendix A.1. 3738 We now define the default rules for the use of the COUNT and LEGAL 3739 fields. The session configuration tools defined in Appendix C.2.3 may 3740 be used to override this behavior. 3742 The 8-bit COUNT field codes the total number of commands of the type 3743 coded by the log present in the session history, modulo 256. By 3744 default, the COUNT field MUST be present in the command log. 3746 The LEGAL field is reserved for future use. If an update to [MIDI] 3747 defines the 0xF9 or 0xFD command, an IETF standards-track document may 3748 define the LEGAL field to protect the command. Until such a document 3749 appears, senders MUST NOT use the LEGAL field, and receivers MUST use 3750 the LENGTH field to skip over the LEGAL field. The LEGAL field would be 3751 defined by the IETF if the semantics of the new 0xF9 or 0xFD command 3752 could not be protected from packet loss via the use of the COUNT field. 3754 Finally, we note that some non-standard uses of the undefined System 3755 Real-time commands act to implement non-compliant variants of the MIDI 3756 sequencer system. In Appendix B.3.1, we describe resiliency tools for 3757 the MIDI sequencer system that provide some protection in this case. 3759 B.2. System Chapter V: Active Sense Command 3761 The system journal MUST contain Chapter V if an active MIDI Active Sense 3762 (0xFE) command appears in the checkpoint history. Figure B.2.1 shows 3763 the format for Chapter V. 3765 0 3766 0 1 2 3 4 5 6 7 3767 +-+-+-+-+-+-+-+-+ 3768 |S| COUNT | 3769 +-+-+-+-+-+-+-+-+ 3771 Figure B.2.1 -- System Chapter V format 3773 The 7-bit COUNT field codes the total number of Active Sense commands 3774 (modulo 128) present in the session history. The COUNT field acts as a 3775 reference count. See the definition of "session history reference 3776 counts" in Appendix A.1 for more information. 3778 B.3. System Chapter Q: Sequencer State Commands 3780 This appendix describes Chapter Q, the system chapter for the MIDI 3781 sequencer commands. 3783 The system journal MUST contain Chapter Q if an active MIDI Song 3784 Position Pointer (0xF2), MIDI Clock (0xF8), MIDI Start (0xFA), MIDI 3785 Continue (0xFB), or MIDI Stop (0xFC) command appears in the checkpoint 3786 history, and if the rules defined in this appendix require a change in 3787 the Chapter Q bitfield contents because of the command appearance. 3789 Figure B.3.1 shows the variable-length format for Chapter Q. 3791 0 1 2 3 3792 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 3793 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3794 |S|N|D|C|T| TOP | CLOCK | TIMETOOLS ... | 3795 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3796 | ... | 3797 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3799 Figure B.3.1 -- System Chapter Q format 3801 Chapter Q consists of a 1-octet header followed by several optional 3802 fields, in the order shown in Figure B.3.1. 3804 Header flag bits signal the presence of the 16-bit CLOCK field (C = 1) 3805 and the 24-bit TIMETOOLS field (T = 1). The 3-bit TOP header field is 3806 interpreted as an unsigned integer, as are CLOCK and TIMETOOLS. We 3807 describe the TIMETOOLS field in Appendix B.3.1. 3809 Chapter Q encodes the most recent state of the sequencer system. 3810 Receivers use the chapter to re-synchronize the sequencer after a packet 3811 loss episode. Chapter fields encode the on/off state of the sequencer, 3812 the current position in the song, and the downbeat. 3814 The N header bit encodes the relative occurrence of the Start, Stop, and 3815 Continue commands in the session history. If an active Start or 3816 Continue command appears most recently, the N bit MUST be set to 1. If 3817 an active Stop appears most recently, or if no active Start, Stop, or 3818 Continue commands appear in the session history, the N bit MUST be set 3819 to 0. 3821 The C header flag, the TOP header field, and the CLOCK field act to code 3822 the current position in the sequence: 3824 o If C = 1, the 3-bit TOP header field and the 16-bit 3825 CLOCK field are combined to form the 19-bit unsigned quantity 3826 65536*TOP + CLOCK. This value encodes the song position 3827 in units of MIDI Clocks (24 clocks per quarter note), 3828 modulo 524288. Note that the maximum song position value 3829 that may be coded by the Song Position Pointer command is 3830 98303 clocks (which may be coded with 17 bits), and that 3831 MIDI-coded songs are generally constructed to avoid durations 3832 longer than this value. However, the 19-bit size may be useful 3833 for real-time applications, such as a drum machine MIDI output 3834 that is sending clock commands for long periods of time. 3836 o If C = 0, the song position is the start of the song. 3837 The C = 0 position is identical to the position coded 3838 by C = 1, TOP = 0, and CLOCK = 0, for the case where 3839 the song position is less than 524288 MIDI clocks. 3840 In certain situations (defined later in this section), 3841 normative text may require the C = 0 or the C = 1, 3842 TOP = 0, CLOCK = 0 encoding of the start of the song. 3844 The C, TOP, and CLOCK fields MUST be set to code the current song 3845 position, for both N = 0 and N = 1 conditions. If C = 0, the TOP field 3846 MUST be set to 0. See [MIDI] for a precise definition of a song 3847 position. 3849 The D header bit encodes information about the downbeat and acts to 3850 qualify the song position coded by the C, TOP, and CLOCK fields. 3852 If the D bit is set to 1, the song position represents the most recent 3853 position in the sequence that has played. If D = 1, the next Clock 3854 command (if N = 1) or the next (Continue, Clock) pair (if N = 0) acts to 3855 increment the song position by one clock, and to play the updated 3856 position. 3858 If the D bit is set to 0, the song position represents a position in the 3859 sequence that has not yet been played. If D = 0, the next Clock command 3860 (if N = 1) or the next (Continue, Clock) pair (if N = 0) acts to play 3861 the point in the song coded by the song position. The song position is 3862 not incremented. 3864 An example of a stream that uses D = 0 coding is one whose most recent 3865 sequence command is a Start or Song Position Pointer command (both N = 1 3866 conditions). However, it is also possible to construct examples where D 3867 = 0 and N = 0. A Start command immediately followed by a Stop command 3868 is coded in Chapter Q by setting C = 0, D = 0, N = 0, TOP = 0. 3870 If N = 1 (coding Start or Continue), D = 0 (coding that the downbeat has 3871 yet to be played), and the song position is at the start of the song, 3872 the C = 0 song position encoding MUST be used if a Start command occurs 3873 more recently than a Continue command in the session history, and the C 3874 = 1, TOP = 0, CLOCK = 0 song position encoding MUST be used if a 3875 Continue command occurs more recently than a Start command in the 3876 session history. 3878 B.3.1. Non-compliant Sequencers 3880 The Chapter Q description in this appendix assumes that the sequencer 3881 system counts off time with Clock commands, as mandated in [MIDI]. 3882 However, a few non-compliant products do not use Clock commands to count 3883 off time, but instead use non-standard methods. 3885 Chapter Q uses the TIMETOOLS field to provide resiliency support for 3886 these non-standard products. By default, the TIMETOOLS field MUST NOT 3887 appear in Chapter Q, and the T header bit MUST be set to 0. The session 3888 configuration tools described in Appendix C.2.3 may be used to select 3889 TIMETOOLS coding. 3891 Figure B.3.2 shows the format of the 24-bit TIMETOOLS field. 3893 0 1 2 3894 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 3895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3896 | TIME | 3897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3899 Figure B.3.2 -- TIMETOOLS format 3901 The TIME field is a 24-bit unsigned integer quantity, with units of 3902 milliseconds. TIME codes an additive correction term for the song 3903 position coded by the TOP, CLOCK, and C fields. TIME is coded in 3904 network byte order (big-endian). 3906 A receiver computes the correct song position by converting TIME into 3907 units of MIDI clocks and adding it to 65536*TOP + CLOCK (assuming C = 3908 1). Alternatively, a receiver may convert 65536*TOP + CLOCK into 3909 milliseconds (assuming C = 1) and add it to TIME. The downbeat (D 3910 header bit) semantics defined in Appendix B.3 apply to the corrected 3911 song position. 3913 B.4. System Chapter F: MIDI Time Code Tape Position 3915 This appendix describes Chapter F, the system chapter for the MIDI Time 3916 Code (MTC) commands. Readers may wish to review the Appendix A.1 3917 definition of "finished/unfinished commands" before reading this 3918 appendix. 3920 The system journal MUST contain Chapter F if an active System Common 3921 Quarter Frame command (0xF1) or an active finished System Exclusive 3922 (Universal Real Time) MTC Full Frame command (F0 7F cc 01 01 hr mn sc fr 3923 F7) appears in the checkpoint history. Otherwise, the system journal 3924 MUST NOT contain Chapter F. 3926 Figure B.4.1 shows the variable-length format for Chapter F. 3928 0 1 2 3 3929 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 3930 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3931 |S|C|P|Q|D|POINT| COMPLETE ... | 3932 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3933 | ... | PARTIAL ... | 3934 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3935 | ... | 3936 +-+-+-+-+-+-+-+-+ 3938 Figure B.4.1 -- System Chapter F format 3940 Chapter F holds information about recent MTC tape positions coded in the 3941 session history. Receivers use Chapter F to re-synchronize the MTC 3942 system after a packet loss episode. 3944 Chapter F consists of a 1-octet header followed by several optional 3945 fields, in the order shown in Figure B.4.1. The C and P header bits 3946 form a Table of Contents (TOC) and signal the presence of the 32-bit 3947 COMPLETE field (C = 1) and the 32-bit PARTIAL field (P = 1). 3949 The Q header bit codes information about the COMPLETE field format. If 3950 Chapter F does not contain a COMPLETE field, Q MUST be set to 0. 3952 The D header bit codes the tape movement direction. If the tape is 3953 moving forward, or if the tape direction is indeterminate, the D bit 3954 MUST be set to 0. If the tape is moving in the reverse direction, the D 3955 bit MUST be set to 1. In most cases, the ordering of commands in the 3956 session history clearly defines the tape direction. However, a few 3957 command sequences have an indeterminate direction (such as a session 3958 history consisting of one Full Frame command). 3960 The 3-bit POINT header field is interpreted as an unsigned integer. 3961 Appendix B.4.1 defines how the POINT field codes information about the 3962 contents of the PARTIAL field. If Chapter F does not contain a PARTIAL 3963 field, POINT MUST be set to 7 (if D = 0) or 0 (if D = 1). 3965 Chapter F MUST include the COMPLETE field if an active finished Full 3966 Frame command appears in the checkpoint history, or if an active Quarter 3967 Frame command that completes the encoding of a frame value appears in 3968 the checkpoint history. 3970 The COMPLETE field encodes the most recent active complete MTC frame 3971 value that appears in the session history. This frame value may take 3972 the form of a series of 8 active Quarter Frame commands (0xF1 0x0n 3973 through 0xF1 0x7n for forward tape movement, 0xF1 0x7n through 0xF1 0x0n 3974 for reverse tape movement) or may take the form of an active finished 3975 Full Frame command. 3977 If the COMPLETE field encodes a Quarter Frame command series, the Q 3978 header bit MUST be set to 1, and the COMPLETE field MUST have the format 3979 shown in Figure B.4.2. The 4-bit fields MT0 through MT7 code the data 3980 (lower) nibble for the Quarter Frame commands for Message Type 0 through 3981 Message Type 7 [MIDI]. These nibbles encode a complete frame value, in 3982 addition to fields reserved for future use by [MIDI]. 3984 0 1 2 3 3985 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 3986 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3987 | MT0 | MT1 | MT2 | MT3 | MT4 | MT5 | MT6 | MT7 | 3988 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3990 Figure B.4.2 -- COMPLETE field format, Q = 1 3992 In this usage, the frame value encoded in the COMPLETE field MUST be 3993 offset by 2 frames (relative to the frame value encoded in the Quarter 3994 Frame commands) if the frame value codes a 0xF1 0x0n through 0xF1 0x7n 3995 command sequence. This offset compensates for the two-frame latency of 3996 the Quarter Frame encoding for forward tape movement. No offset is 3997 applied if the frame value codes a 0xF1 0x7n through 0xF1 0x0n Quarter 3998 Frame command sequence. 4000 The most recent active complete MTC frame value may alternatively be 4001 encoded by an active finished Full Frame command. In this case, the Q 4002 header bit MUST be set to 0, and the COMPLETE field MUST have format 4003 shown in Figure B.4.3. The HR, MN, SC, and FR fields correspond to the 4004 hr, mn, sc, and fr data octets of the Full Frame command. 4006 0 1 2 3 4007 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 4008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4009 | HR | MN | SC | FR | 4010 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4012 Figure B.4.3 -- COMPLETE field format, Q = 0 4014 B.4.1. Partial Frames 4016 The most recent active session history command that encodes MTC frame 4017 value data may be a Quarter Frame command other than a forward-moving 4018 0xF1 0x7n command (which completes a frame value for forward tape 4019 movement) or a reverse-moving 0xF1 0x1n command (which completes a frame 4020 value for reverse tape movement). 4022 We consider this type of Quarter Frame command to be associated with a 4023 partial frame value. The Quarter Frame sequence that defines a partial 4024 frame value MUST either start at Message Type 0 and increment 4025 contiguously to an intermediate Message Type less than 7, or start at 4026 Message Type 7 and decrement contiguously to an intermediate Message 4027 type greater than 0. A Quarter Frame command sequence that does not 4028 follow this pattern is not associated with a partial frame value. 4030 Chapter F MUST include a PARTIAL field if the most recent active command 4031 in the checkpoint history that encodes MTC frame value data is a Quarter 4032 Frame command that is associated with a partial frame value. Otherwise, 4033 Chapter F MUST NOT include a PARTIAL field. 4035 The partial frame value consists of the data (lower) nibbles of the 4036 Quarter Frame command sequence. The PARTIAL field codes the partial 4037 frame value, using the format shown in Figure B.4.2. Message Type 4038 fields that are not associated with a Quarter Frame command MUST be set 4039 to 0. 4041 The POINT header field identifies the Message Type fields in the PARTIAL 4042 field that code valid data. If P = 1, the POINT field MUST encode the 4043 unsigned integer value formed by the lower 3 bits of the upper nibble of 4044 the data value of the most recent active Quarter Frame command in the 4045 session history. If D = 0 and P = 1, POINT MUST take on a value in the 4046 range 0-6. If D = 1 and P = 1, POINT MUST take on a value in the range 4047 1-7. 4049 If D = 0, MT fields (Figure B.4.2) in the inclusive range from 0 up to 4050 and including the POINT value encode the partial frame value. If D = 1, 4051 MT fields in the inclusive range from 7 down to and including the POINT 4052 value encode the partial frame value. Note that, unlike the COMPLETE 4053 field encoding, senders MUST NOT add a 2-frame offset to the partial 4054 frame value encoded in PARTIAL. 4056 For the default semantics, if a recovery journal contains Chapter F, and 4057 if the session history codes a legal [MIDI] series of Quarter Frame and 4058 Full Frame commands, the chapter always contains a COMPLETE or a PARTIAL 4059 field (and may contain both fields). Thus, a one-octet Chapter F (C = P 4060 = 0) always codes the presence of an illegal command sequence in the 4061 session history (under some conditions, the C = 1, P = 0 condition may 4062 also code the presence of an illegal command sequence). The illegal 4063 command sequence conditions are transient in nature and usually indicate 4064 that a Quarter Frame command sequence began with an intermediate Message 4065 Type. 4067 B.5. System Chapter X: System Exclusive 4069 This appendix describes Chapter X, the system chapter for MIDI System 4070 Exclusive (SysEx) commands (0xF0). Readers may wish to review the 4071 Appendix A.1 definition of "finished/unfinished commands" before reading 4072 this appendix. 4074 Chapter X consists of a list of one or more command logs. Each log in 4075 the list codes information about a specific finished or unfinished SysEx 4076 command that appears in the session history. The system journal MUST 4077 contain Chapter X if the rules defined in Appendix B.5.2 require that 4078 one or more logs appear in the list. 4080 The log list is not preceded by a header. Instead, each log implicitly 4081 encodes its own length. Given the length of the N'th list log, the 4082 presence of the (N+1)'th list log may be inferred from the LENGTH field 4083 of the system journal header (Figure 10 in Section 5 of the main text). 4084 The log list MUST obey the oldest-first ordering rule (defined in 4085 Appendix A.1). 4087 B.5.1. Chapter Format 4089 Figure B.5.1 shows the bitfield format for the Chapter X command logs. 4091 0 1 2 3 4092 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 4093 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4094 |S|T|C|F|D|L|STA| TCOUNT | COUNT | FIRST ... | 4095 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4096 | DATA ... | 4097 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4099 Figure B.5.1 -- Chapter X command log format 4101 A Chapter X command log consists of a 1-octet header, followed by the 4102 optional TCOUNT, COUNT, FIRST, and DATA fields. 4104 The T, C, F, and D header bits act as a Table of Contents (TOC) for the 4105 log. If T is set to 1, the 1-octet TCOUNT field appears in the log. If 4106 C is set to 1, the 1-octet COUNT field appears in the log. If F is set 4107 to 1, the variable-length FIRST field appears in the log. If D is set 4108 to 1, the variable-length DATA field appears in the log. 4110 The L header bit sets the coding tool for the log. We define the log 4111 coding tools in Appendix B.5.2. 4113 The STA field codes the status of the command coded by the log. The 4114 2-bit STA value is interpreted as an unsigned integer. If STA is 0, the 4115 log codes an unfinished command. Non-zero STA values code different 4116 classes of finished commands. An STA value of 1 codes a cancelled 4117 command, an STA value of 2 codes a command that uses the "dropped F7" 4118 construction, and an STA value of 3 codes all other finished commands. 4119 Section 3.2 in the main text describes cancelled and "dropped F7" 4120 commands. 4122 The S bit (Appendix A.1) of the first log in the list acts as the S bit 4123 for Chapter X. For the other logs in the list, the S bit refers to the 4124 log itself. The value of the "phantom" S bit associated with the first 4125 log is defined by the following rules: 4127 o If the list codes one log, the phantom S-bit value is 4128 the same as the Chapter X S-bit value. 4130 o If the list codes multiple logs, the phantom S-bit value is 4131 the logical OR of the S-bit value of the first and second 4132 command logs in the list. 4134 In all other respects, the S bit follows the semantics defined in 4135 Appendix A.1. 4137 The FIRST field (present if F = 1) encodes a variable-length unsigned 4138 integer value that sets the coverage of the DATA field. 4140 The FIRST field (present if F = 1) encodes a variable-length unsigned 4141 integer value that specifies which SysEx data bytes are encoded in the 4142 DATA field of the log. The FIRST field consists of an octet whose most- 4143 significant bit is set to 0, optionally preceded by one or more octets 4144 whose most-significant bit is set to 1. The algorithm shown in Figure 4145 B.5.2 decodes this format into an unsigned integer, to yield the value 4146 dec(FIRST). FIRST uses a variable-length encoding because dec(FIRST) 4147 references a data octet in a SysEx command, and a SysEx command may 4148 contain an arbitrary number of data octets. 4150 One-Octet FIRST value: 4152 Encoded form: 0ddddddd 4153 Decoded form: 00000000 00000000 00000000 0ddddddd 4155 Two-Octet FIRST value: 4157 Encoded form: 1ccccccc 0ddddddd 4158 Decoded form: 00000000 00000000 00cccccc cddddddd 4160 Three-Octet FIRST value: 4162 Encoded form: 1bbbbbbb 1ccccccc 0ddddddd 4163 Decoded form: 00000000 000bbbbb bbcccccc cddddddd 4165 Four-Octet FIRST value: 4167 Encoded form: 1aaaaaaa 1bbbbbbb 1ccccccc 0ddddddd 4168 Decoded form: 0000aaaa aaabbbbb bbcccccc cddddddd 4170 Figure B.5.2 -- Decoding FIRST field formats 4172 The DATA field (present if D = 1) encodes a modified version of the data 4173 octets of the SysEx command coded by the log. Status octets MUST NOT be 4174 coded in the DATA field. 4176 If F = 0, the DATA field begins with the first data octet of the SysEx 4177 command and includes all subsequent data octets for the command that 4178 appear in the session history. If F = 1, the DATA field begins with the 4179 (dec(FIRST) + 1)'th data octet of the SysEx command and includes all 4180 subsequent data octets for the command that appear in the session 4181 history. Note that the word "command" in the descriptions above refers 4182 to the original SysEx command as it appears in the source MIDI data 4183 stream, not to a particular MIDI list SysEx command segment. 4185 The length of the DATA field is coded implicitly, using the most- 4186 significant bit of each octet. The most-significant bit of the final 4187 octet of the DATA field MUST be set to 1. The most-significant bit of 4188 all other DATA octets MUST be set to 0. This coding method relies on 4189 the fact that the most-significant bit of a MIDI data octet is 0 by 4190 definition. Apart from this length-coding modification, the DATA field 4191 encodes a verbatim copy of all data octets it encodes. 4193 B.5.2. Log Inclusion Semantics 4195 Chapter X offers two tools to protect SysEx commands: the "recency" tool 4196 and the "list" tool. The tool definitions use the concept of the "SysEx 4197 type" of a command, which we now define. 4199 Each SysEx command instance in a session, excepting MTC Full Frame 4200 commands, is said to have a "SysEx type". Types are used in equality 4201 comparisons: two SysEx commands in a session are said to have "the same 4202 SysEx type" or "different SysEx types". 4204 If efficiency is not a concern, a sender may follow a simple typing 4205 rule: every SysEx command in the session history has a different SysEx 4206 type, and thus no two commands in the session have the same type. 4208 To improve efficiency, senders MAY implement exceptions to this rule. 4209 These exceptions declare that certain sets of SysEx command instances 4210 have the same SysEx type. Any command not covered by an exception 4211 follows the simple rule. We list exceptions below: 4213 o All commands with identical data octet fields (same number of 4214 data octets, same value for each data octet) have the same type. 4215 This rule MUST be applied to all SysEx commands in the session, 4216 or not at all. Note that the implementation of this exception 4217 requires no sender knowledge of the format and semantics of 4218 the SysEx commands in the stream, merely the ability to count 4219 and compare octets. 4221 o Two instances of the same command whose semantics set or report 4222 the value of the same "parameter" have the same type. The 4223 implementation of this exception requires specific knowledge of 4224 the format and semantics of SysEx commands. In practice, a 4225 sender implementation chooses to support this exception for 4226 certain classes of commands (such as the Universal System 4227 Exclusive commands defined in [MIDI]). If a sender supports 4228 this exception for a particular command in a class (for 4229 example, the Universal Real Time System Exclusive message 4230 for Master Volume, F0 F7 cc 04 01 vv vv F7, defined in [MIDI]), 4231 it MUST support the exception to all instances of this 4232 particular command in the session. 4234 We now use this definition of "SysEx type" to define the "recency" tool 4235 and the "list" tool for Chapter X. 4237 By default, the Chapter X log list MUST code sufficient information to 4238 protect the rendered MIDI performance from indefinite artifacts caused 4239 by the loss of all finished or unfinished active SysEx commands that 4240 appear in the checkpoint history (excluding finished MTC Full Frame 4241 commands, which are coded in Chapter F (Appendix B.4)). 4243 To protect a command of a specific SysEx type with the recency tool, 4244 senders MUST code a log in the log list for the most recent finished 4245 active instance of the SysEx type that appears in the checkpoint 4246 history. Additionally, if an unfinished active instance of the SysEx 4247 type appears in the checkpoint history, senders MUST code a log in the 4248 log list for the unfinished command instance. The L header bit of both 4249 command logs MUST be set to 0. 4251 To protect a command of a specific SysEx type with the list tool, 4252 senders MUST code a log in the Chapter X log list for each finished or 4253 unfinished active instance of the SysEx type that appears in the 4254 checkpoint history. The L header bit of list tool command logs MUST be 4255 set to 1. 4257 As a rule, a log REQUIRED by the list or recency tool MUST include a 4258 DATA field that codes all data octets that appear in the checkpoint 4259 history for the SysEx command instance associated with the log. The 4260 FIRST field MAY be used to configure a DATA field that minimally meets 4261 this requirement. 4263 An exception to this rule applies to cancelled commands (defined in 4264 Section 3.2). REQUIRED command logs associated with cancelled commands 4265 MAY be coded with no DATA field. However, if DATA appears in the log, 4266 DATA MUST code all data octets that appear in the checkpoint history for 4267 the command associated with the log. 4269 As defined by the preceding text in this section, by default all 4270 finished or unfinished active SysEx commands that appear in the 4271 checkpoint history (excluding finished MTC Full Frame commands) MUST be 4272 protected by the list tool or the recency tool. 4274 For some MIDI source streams, this default yields a Chapter X whose size 4275 is too large. For example, imagine that a sender begins to transcode a 4276 SysEx command with 10,000 data octets onto a UDP RTP stream "on the 4277 fly", by sending SysEx command segments as soon as data octets are 4278 delivered by the MIDI source. After 1000 octets have been sent, the 4279 expansion of Chapter X yields an RTP packet that is too large to fit in 4280 the Maximum Transmission Unit (MTU) for the stream. 4282 In this situation, if a sender uses the closed-loop sending policy for 4283 SysEx commands, the RTP packet size may always be capped by stalling the 4284 stream. In a stream stall, once the packet reaches a maximum size, the 4285 sender refrains from sending new packets with non-empty MIDI Command 4286 Sections until receiver feedback permits the trimming of Chapter X. If 4287 the stream permits arbitrary commands to appear between SysEx segments 4288 (selectable during configuration using the tools defined in Appendix 4289 C.1), the sender may stall the SysEx segment stream but continue to code 4290 other commands in the MIDI list. 4292 Stalls are a workable but sub-optimal solution to Chapter X size issues. 4293 As an alternative to stalls, senders SHOULD take preemptive action 4294 during session configuration to reduce the anticipated size of Chapter 4295 X, using the methods described below: 4297 o Partitioned transport. Appendix C.5 provides tools 4298 for sending a MIDI name space over several RTP streams. 4299 Senders may use these tools to map a MIDI source 4300 into a low-latency UDP RTP stream (for channel commands 4301 and short SysEx commands) and a reliable [RFC4571] TCP stream 4302 (for bulk-data SysEx commands). The cm_unused and 4303 cm_used parameters (Appendix C.1) may be used to 4304 communicate the nature of the SysEx command partition. 4305 As TCP is reliable, the RTP MIDI TCP stream would not 4306 use the recovery journal. To minimize transmission 4307 latency for short SysEx commands, senders may begin 4308 segmental transmission for all SysEx commands over the 4309 UDP stream and then cancel the UDP transmission of long 4310 commands (using tools described in Section 3.2) and 4311 resend the commands over the TCP stream. 4313 o Selective protection. Journal protection may not be 4314 necessary for all SysEx commands in a stream. The 4315 ch_never parameter (Appendix C.2) may be used to 4316 communicate which SysEx commands are excluded from 4317 Chapter X. 4319 B.5.3. TCOUNT and COUNT Fields 4321 If the T header bit is set to 1, the 8-bit TCOUNT field appears in the 4322 command log. If the C header bit is set to 1, the 8-bit COUNT field 4323 appears in the command log. TCOUNT and COUNT are interpreted as 4324 unsigned integers. 4326 The TCOUNT field codes the total number of SysEx commands of the SysEx 4327 type coded by the log that appear in the session history, at the moment 4328 after the (finished or unfinished) command coded by the log enters the 4329 session history. 4331 The COUNT field codes the total number of SysEx commands that appear in 4332 the session history, excluding commands that are excluded from Chapter X 4333 via the ch_never parameter (Appendix C.2), at the moment after the 4334 (finished or unfinished) command coded by the log enters the session 4335 history. 4337 Command counting for TCOUNT and COUNT uses modulo-256 arithmetic. MTC 4338 Full Frame command instances (Appendix B.4) are included in command 4339 counting if the TCOUNT and COUNT definitions warrant their inclusion, as 4340 are cancelled commands (Section 3.2). 4342 Senders use the TCOUNT and COUNT fields to track the identity and (for 4343 TCOUNT) the sequence position of a command instance. Senders MUST use 4344 the TCOUNT or COUNT fields if identity or sequence information is 4345 necessary to protect the command type coded by the log. 4347 If a sender uses the COUNT field in a session, the final command log in 4348 every Chapter X in the stream MUST code the COUNT field. This rule lets 4349 receivers resynchronize the COUNT value after a packet loss. 4351 C. Session Configuration Tools 4353 In Sections 6.1-2 of the main text, we show session descriptions for 4354 minimal native and mpeg4-generic RTP MIDI streams. Minimal streams lack 4355 the flexibility to support some applications. In this appendix, we 4356 describe how to customize stream behavior through the use of the payload 4357 format parameters. 4359 The appendix begins with 6 sections, each devoted to parameters that 4360 affect a particular aspect of stream behavior: 4362 o Appendix C.1 describes the stream subsetting system 4363 (cm_unused and cm_used). 4365 o Appendix C.2 describes the journalling system (ch_anchor, 4366 ch_default, ch_never, j_sec, j_update). 4368 o Appendix C.3 describes MIDI command timestamp semantics 4369 (linerate, mperiod, octpos, tsmode). 4371 o Appendix C.4 describes the temporal duration ("media time") 4372 of an RTP MIDI packet (guardtime, rtp_maxptime, rtp_ptime). 4374 o Appendix C.5 concerns stream description (musicport). 4376 o Appendix C.6 describes MIDI rendering (chanmask, cid, 4377 inline, multimode, render, rinit, subrender, smf_cid, 4378 smf_info, smf_inline, smf_url, url). 4380 The parameters listed above may optionally appear in session 4381 descriptions of RTP MIDI streams. If these parameters are used in an 4382 SDP session description, the parameters appear on an fmtp attribute 4383 line. This attribute line applies to the payload type associated with 4384 the fmtp line. 4386 The parameters listed above add extra functionality ("features") to 4387 minimal RTP MIDI streams. In Appendix C.7, we show how to use these 4388 features to support two classes of applications: content-streaming using 4389 RTSP (Appendix C.7.1) and network musical performance using SIP 4390 (Appendix C.7.2). 4392 The participants in a multimedia session MUST share a common view of all 4393 of the RTP MIDI streams that appear in an RTP session, as defined by a 4394 single media (m=) line. In some RTP MIDI applications, the "common 4395 view" restriction makes it difficult to use sendrecv streams (all 4396 parties send and receive), as each party has its own requirements. For 4397 example, a two-party network musical performance application may wish to 4398 customize the renderer on each host to match the CPU performance of the 4399 host [NMP]. 4401 We solve this problem by using two RTP MIDI streams -- one sendonly, one 4402 recvonly -- in lieu of one sendrecv stream. The data flows in the two 4403 streams travel in opposite directions, to control receivers configured 4404 to use different renderers. In the third example in Appendix C.5, we 4405 show how the musicport parameter may be used to define virtual sendrecv 4406 streams. 4408 As a general rule, the RTP MIDI protocol does not handle parameter 4409 changes during a session well, because the parameters describe 4410 heavyweight or stateful configuration that is not easily changed once a 4411 session has begun. Thus, parties SHOULD NOT expect that parameter 4412 change requests during a session will be accepted by other parties. 4413 However, implementors SHOULD support in-session parameter changes that 4414 are easy to handle (for example, the guardtime parameter defined in 4415 Appendix C.4) and SHOULD be capable of accepting requests for changes of 4416 those parameters, as received by its session management protocol (for 4417 example, re-offers in SIP [RFC3264]). 4419 Appendix D defines the Augmented Backus-Naur Form (ABNF, [RFC5234]) 4420 syntax for the payload parameters. Section 11 provides information to 4421 the Internet Assigned Numbers Authority (IANA) on the media types and 4422 parameters defined in this document. 4424 Appendix C.6.5 defines the media type "audio/asc", a stored object for 4425 initializing mpeg4-generic renderers. As described in Appendix C.6, the 4426 audio/asc media type is assigned to the "rinit" parameter to specify an 4427 initialization data object for the default mpeg4-generic renderer. Note 4428 that RTP stream semantics are not defined for "audio/asc". Therefore, 4429 the "asc" subtype MUST NOT appear on the rtpmap line of a session 4430 description. 4432 C.1. Configuration Tools: Stream Subsetting 4434 As defined in Section 3.2 in the main text, the MIDI list of an RTP MIDI 4435 packet may encode any MIDI command that may legally appear on a MIDI 1.0 4436 DIN cable. 4438 In this appendix, we define two parameters (cm_unused and cm_used) that 4439 modify this default condition, by excluding certain types of MIDI 4440 commands from the MIDI list of all packets in a stream. For example, if 4441 a multimedia session partitions a MIDI name space into two RTP MIDI 4442 streams, the parameters may be used to define which commands appear in 4443 each stream. 4445 In this appendix, we define a simple language for specifying MIDI 4446 command types. If a command type is assigned to cm_unused, the commands 4447 coded by the string MUST NOT appear in the MIDI list. If a command type 4448 is assigned to cm_used, the commands coded by the string MAY appear in 4449 the MIDI list. 4451 The parameter list may code multiple assignments to cm_used and 4452 cm_unused. Assignments have a cumulative effect and are applied in the 4453 order of appearance in the parameter list. A later assignment of a 4454 command type to the same parameter expands the scope of the earlier 4455 assignment. A later assignment of a command type to the opposite 4456 parameter cancels (partially or completely) the effect of an earlier 4457 assignment. 4459 To initialize the stream subsetting system, "implicit" assignments to 4460 cm_unused and cm_used are processed before processing the actual 4461 assignments that appear in the parameter list. The System Common 4462 undefined commands (0xF4, 0xF5) and the System Real-Time Undefined 4463 commands (0xF9, 0xFD) are implicitly assigned to cm_unused. All other 4464 command types are implicitly assigned to cm_used. 4466 Note that the implicit assignments code the default behavior of an RTP 4467 MIDI stream as defined in Section 3.2 in the main text (namely, that all 4468 commands that may legally appear on a MIDI 1.0 DIN cable may appear in 4469 the stream). Also note that assignments of the System Common undefined 4470 commands (0xF4, 0xF5) apply to the use of these commands in the MIDI 4471 source command stream, not the special use of 0xF4 and 0xF5 in SysEx 4472 segment encoding defined in Section 3.2 in the main text. 4474 As a rule, parameter assignments obey the following syntax (see Appendix 4475 D for ABNF): 4477 = [channel list][field list] 4479 The command-type list is mandatory; the channel and field lists are 4480 optional. 4482 The command-type list specifies the MIDI command types for which the 4483 parameter applies. The command-type list is a concatenated sequence of 4484 one or more of the letters (ABCFGHJKMNPQTVWXYZ). The letters code the 4485 following command types: 4487 o A: Poly Aftertouch (0xA) 4488 o B: System Reset (0xFF) 4489 o C: Control Change (0xB) 4490 o F: System Time Code (0xF1) 4491 o G: System Tune Request (0xF6) 4492 o H: System Song Select (0xF3) 4493 o J: System Common Undefined (0xF4) 4494 o K: System Common Undefined (0xF5) 4495 o N: NoteOff (0x8), NoteOn (0x9) 4496 o P: Program Change (0xC) 4497 o Q: System Sequencer (0xF2, 0xF8, 0xFA, 0xFB, 0xFC) 4498 o T: Channel Aftertouch (0xD) 4499 o V: System Active Sense (0xFE) 4500 o W: Pitch Wheel (0xE) 4501 o X: SysEx (0xF0, 0xF7) 4502 o Y: System Real-Time Undefined (0xF9) 4503 o Z: System Real-Time Undefined (0xFD) 4505 In addition to the letters above, the letter M may also appear in the 4506 command-type list. The letter M refers to the MIDI parameter system 4507 (see definition in Appendix A.1 and in [MIDI]). An assignment of M to 4508 cm_unused codes that no RPN or NRPN transactions may appear in the MIDI 4509 list. 4511 Note that if cm_unused is assigned the letter M, Control Change (0xB) 4512 commands for the controller numbers in the standard controller 4513 assignment might still appear in the MIDI list. For an explanation, see 4514 Appendix A.3.4 for a discussion of the "general-purpose" use of 4515 parameter system controller numbers. 4517 In the text below, rules that apply to "MIDI voice channel commands" 4518 also apply to the letter M. 4520 The letters in the command-type list MUST be uppercase and MUST appear 4521 in alphabetical order. Letters other than (ABCFGHJKMNPQTVWXYZ) that 4522 appear in the list MUST be ignored. 4524 For MIDI voice channel commands, the channel list specifies the MIDI 4525 channels for which the parameter applies. If no channel list is 4526 provided, the parameter applies to all MIDI channels (0-15). The 4527 channel list takes the form of a list of channel numbers (0 through 15) 4528 and dash-separated channel number ranges (i.e., 0-5, 8-12, etc.). Dots 4529 (i.e., "." characters) separate elements in the channel list. 4531 Recall that System commands do not have a MIDI channel associated with 4532 them. Thus, for most command-type letters that code System commands (B, 4533 F, G, H, J, K, Q, V, Y, and Z), the channel list is ignored. 4535 For the command-type letter X, the appearance of certain numbers in the 4536 channel list codes special semantics. 4538 o The digit 0 codes that SysEx "cancel" sublists (Section 4539 3.2 in the main text) MUST NOT appear in the MIDI list. 4541 o The digit 1 codes that cancel sublists MAY appear in the 4542 MIDI list (the default condition). 4544 o The digit 2 codes that commands other than System 4545 Real-time MIDI commands MUST NOT appear between SysEx 4546 command segments in the MIDI list (the default condition). 4548 o The digit 3 codes that any MIDI command type may 4549 appear between SysEx command segments in the MIDI list, 4550 with the exception of the segmented encoding of a second 4551 SysEx command (verbatim SysEx commands are OK). 4553 For command-type X, the channel list MUST NOT contain both digits 0 and 4554 1, and it MUST NOT contain both digits 2 and 3. For command-type X, 4555 channel list numbers other than the numbers defined above are ignored. 4556 If X does not have a channel list, the semantics marked "the default 4557 condition" in the list above apply. 4559 The syntax for field lists in a parameter assignment follows the syntax 4560 for channel lists. If no field list is provided, the parameter applies 4561 to all controller or note numbers. 4563 For command-type C (Control Change), the field list codes the controller 4564 numbers (0-255) for which the parameter applies. 4566 For command-type M (Parameter System), the field list codes the 4567 Registered Parameter Numbers (RPNs) and Non-Registered Parameter Numbers 4568 (NRPNs) for which the parameter applies. The number range 0-16383 4569 specifies RPNs, the number range 16384-32767 specifies NRPNs (16384 4570 corresponds to NRPN 0, 32767 corresponds to NRPN 16383). 4572 For command-types N (NoteOn and NoteOff) and A (Poly Aftertouch), the 4573 field list codes the note numbers for which the parameter applies. 4575 For command-types J and K (System Common Undefined), the field list 4576 consists of a single digit, which specifies the number of data octets 4577 that follow the command octet. 4579 For command-type X (SysEx), the field list codes the number of data 4580 octets that may appear in a SysEx command. Thus, the field list 0-255 4581 specifies SysEx commands with 255 or fewer data octets, the field list 4582 256-4294967295 specifies SysEx commands with more than 255 data octets 4583 but excludes commands with 255 or fewer data octets, and the field list 4584 0 excludes all commands. 4586 A secondary parameter assignment syntax customizes command-type X (see 4587 Appendix D for complete ABNF): 4589 = "__" *( "_" ) "__" 4591 The assignment defines the class of SysEx commands that obeys the 4592 semantics of the assigned parameter. The command class is specified by 4593 listing the permitted values of the first N data octets that follow the 4594 SysEx 0xF0 command octet. Any SysEx command whose first N data octets 4595 match the list is a member of the class. 4597 Each defines a data octet of the command, as a dot-separated 4598 (".") list of one or more hexadecimal constants (such as "7F") or dash- 4599 separated hexadecimal ranges (such as "01-1F"). Underscores ("_") 4600 separate each . Double-underscores ("__") delineate the data 4601 octet list. 4603 Using this syntax, each assignment specifies a single SysEx command 4604 class. Session descriptions may use several assignments to cm_used and 4605 cm_unused to specify complex behaviors. 4607 The example session description below illustrates the use of the stream 4608 subsetting parameters: 4610 v=0 4611 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 4612 s=Example 4613 t=0 0 4614 m=audio 5004 RTP/AVP 96 4615 c=IN IP6 2001:DB80::7F2E:172A:1E24 4616 a=rtpmap:96 rtp-midi/44100 4617 a=fmtp:96 cm_unused=ACGHJKNMPTVWXYZ; cm_used=__7F_00-7F_01_01__ 4619 The session description configures the stream for use in clock 4620 applications. All voice channels are unused, as are all System Commands 4621 except those used for MIDI Time Code (command-type F, and the Full Frame 4622 SysEx command that is matched by the string assigned to cm_used), the 4623 System Sequencer commands (command-type Q), and System Reset (command- 4624 type B). 4626 C.2. Configuration Tools: The Journalling System 4628 In this appendix, we define the payload format parameters that configure 4629 stream journalling and the recovery journal system. 4631 The j_sec parameter (Appendix C.2.1) sets the journalling method for the 4632 stream. The j_update parameter (Appendix C.2.2) sets the recovery 4633 journal sending policy for the stream. Appendix C.2.2 also defines the 4634 sending policies of the recovery journal system. 4636 Appendix C.2.3 defines several parameters that modify the recovery 4637 journal semantics. These parameters change the default recovery journal 4638 semantics as defined in Section 5 and Appendices A-B. 4640 The journalling method for a stream is set at the start of a session and 4641 MUST NOT be changed thereafter. This requirement forbids changes to the 4642 j_sec parameter once a session has begun. 4644 A related requirement, defined in the appendix sections below, forbids 4645 the acceptance of parameter values that would violate the recovery 4646 journal mandate. In many cases, a change in one of the parameters 4647 defined in this appendix during an ongoing session would result in a 4648 violation of the recovery journal mandate for an implementation; in this 4649 case, the parameter change MUST NOT be accepted. 4651 C.2.1. The j_sec Parameter 4653 Section 2.2 defines the default journalling method for a stream. 4654 Streams that use unreliable transport (such as UDP) default to using the 4655 recovery journal. Streams that use reliable transport (such as TCP) 4656 default to not using a journal. 4658 The parameter j_sec may be used to override this default. This memo 4659 defines two symbolic values for j_sec: "none", to indicate that all 4660 stream payloads MUST NOT contain a journal section, and "recj", to 4661 indicate that all stream payloads MUST contain a journal section that 4662 uses the recovery journal format. 4664 For example, the j_sec parameter might be set to "none" for a UDP stream 4665 that travels between two hosts on a local network that is known to 4666 provide reliable datagram delivery. 4668 The session description below configures a UDP stream that does not use 4669 the recovery journal: 4671 v=0 4672 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 4673 s=Example 4674 t=0 0 4675 m=audio 5004 RTP/AVP 96 4676 c=IN IP4 192.0.2.94 4677 a=rtpmap:96 rtp-midi/44100 4678 a=fmtp:96 j_sec=none 4680 Other IETF standards-track documents may define alternative journal 4681 formats. These documents MUST define new symbolic values for the j_sec 4682 parameter to signal the use of the format. 4684 Parties MUST NOT accept a j_sec value that violates the recovery journal 4685 mandate (see Section 4 for details). If a session description uses a 4686 j_sec value unknown to the recipient, the recipient MUST NOT accept the 4687 description. 4689 Special j_sec issues arise when sessions are managed by session 4690 management tools (like RTSP, [RFC2326]) that use SDP for "declarative 4691 usage" purposes (see the preamble of Section 6 for details). For these 4692 session management tools, SDP does not code transport details (such as 4693 UDP or TCP) for the session. Instead, server and client negotiate 4694 transport details via other means (for RTSP, the SETUP method). 4696 In this scenario, the use of the j_sec parameter may be ill-advised, as 4697 the creator of the session description may not yet know the transport 4698 type for the session. In this case, the session description SHOULD 4699 configure the journalling system using the parameters defined in the 4700 remainder of Appendix C.2, but it SHOULD NOT use j_sec to set the 4701 journalling status. Recall that if j_sec does not appear in the session 4702 description, the default method for choosing the journalling method is 4703 in effect (no journal for reliable transport, recovery journal for 4704 unreliable transport). 4706 However, in declarative usage situations where the creator of the 4707 session description knows that journalling is always required or never 4708 required, the session description SHOULD use the j_sec parameter. 4710 C.2.2. The j_update Parameter 4712 In Section 4, we use the term "sending policy" to describe the method a 4713 sender uses to choose the checkpoint packet identity for each recovery 4714 journal in a stream. In the sub-sections that follow, we normatively 4715 define three sending policies: anchor, closed-loop, and open-loop. 4717 As stated in Section 4, the default sending policy for a stream is the 4718 closed-loop policy. The j_update parameter may be used to override this 4719 default. 4721 We define three symbolic values for j_update: "anchor", to indicate that 4722 the stream uses the anchor sending policy, "open-loop", to indicate that 4723 the stream uses the open-loop sending policy, and "closed-loop", to 4724 indicate that the stream uses the closed-loop sending policy. See 4725 Appendix C.2.3 for examples session descriptions that use the j_update 4726 parameter. 4728 Parties MUST NOT accept a j_update value that violates the recovery 4729 journal mandate (Section 4). 4731 Other IETF standards-track documents may define additional sending 4732 policies for the recovery journal system. These documents MUST define 4733 new symbolic values for the j_update parameter to signal the use of the 4734 new policy. If a session description uses a j_update value unknown to 4735 the recipient, the recipient MUST NOT accept the description. 4737 C.2.2.1. The anchor Sending Policy 4739 In the anchor policy, the sender uses the first packet in the stream as 4740 the checkpoint packet for all packets in the stream. The anchor policy 4741 satisfies the recovery journal mandate (Section 4), as the checkpoint 4742 history always covers the entire stream. 4744 The anchor policy does not require the use of the RTP control protocol 4745 (RTCP, [RFC3550]) or other feedback from receiver to sender. Senders do 4746 not need to take special actions to ensure that received streams start 4747 up free of artifacts, as the recovery journal always covers the entire 4748 history of the stream. Receivers are relieved of the responsibility of 4749 tracking the changing identity of the checkpoint packet, because the 4750 checkpoint packet never changes. 4752 The main drawback of the anchor policy is bandwidth efficiency. Because 4753 the checkpoint history covers the entire stream, the size of the 4754 recovery journals produced by this policy usually exceeds the journal 4755 size of alternative policies. For single-channel MIDI data streams, the 4756 bandwidth overhead of the anchor policy is often acceptable (see 4757 Appendix A.4 of [NMP]). For dense streams, the closed-loop or open-loop 4758 policies may be more appropriate. 4760 C.2.2.2. The closed-loop Sending Policy 4762 The closed-loop policy is the default policy of the recovery journal 4763 system. For each packet in the stream, the policy lets senders choose 4764 the smallest possible checkpoint history that satisfies the recovery 4765 journal mandate. As smaller checkpoint histories generally yield 4766 smaller recovery journals, the closed-loop policy reduces the bandwidth 4767 of a stream, relative to the anchor policy. 4769 The closed-loop policy relies on feedback from receiver to sender. The 4770 policy assumes that a receiver periodically informs the sender of the 4771 highest sequence number it has seen so far in the stream, coded in the 4772 32-bit extension format defined in [RFC3550]. For RTCP, receivers 4773 transmit this information in the Extended Highest Sequence Number 4774 Received (EHSNR) field of Receiver Reports. RTCP Sender or Receiver 4775 Reports MUST be sent by any participant in a session with closed loop 4776 sending policy, unless another feedback mechanism has been agreed upon. 4778 The sender may safely use receiver sequence number feedback to guide 4779 checkpoint history management, because Section 4 requires that receivers 4780 repair indefinite artifacts whenever a packet loss event occur. 4782 We now normatively define the closed-loop policy. At the moment a 4783 sender prepares an RTP packet for transmission, the sender is aware of R 4784 >= 0 receivers for the stream. Senders may become aware of a receiver 4785 via RTCP traffic from the receiver, via RTP packets from a paired stream 4786 sent by the receiver to the sender, via messages from a session 4787 management tool, or by other means. As receivers join and leave a 4788 session, the value of R changes. 4790 Each known receiver k (1 <= k <= R) is associated with a 32-bit extended 4791 packet sequence number M(k), where the extension reflects the sequence 4792 number rollover count of the sender. 4794 If the sender has received at least one feedback report from receiver k, 4795 M(k) is the most recent report of the highest RTP packet sequence number 4796 seen by the receiver, normalized to reflect the rollover count of the 4797 sender. 4799 If the sender has not received a feedback report from the receiver, M(k) 4800 is the extended sequence number of the last packet the sender 4801 transmitted before it became aware of the receiver. If the sender 4802 became aware of this receiver before it sent the first packet in the 4803 stream, M(k) is the extended sequence number of the first packet in the 4804 stream. 4806 Given this definition of M(), we now state the closed-loop policy. When 4807 preparing a new packet for transmission, a sender MUST choose a 4808 checkpoint packet with extended sequence number N, such that M(k) >= (N 4809 - 1) for all k, 1 <= k <= R, where R >= 1. The policy does not restrict 4810 sender behavior in the R == 0 (no known receivers) case. 4812 Under the closed-loop policy as defined above, a sender may transmit 4813 packets whose checkpoint history is shorter than the session history (as 4814 defined in Appendix A.1). In this event, a new receiver that joins the 4815 stream may experience indefinite artifacts. 4817 For example, if a Control Change (0xB) command for Channel Volume 4818 (controller number 7) was sent early in a stream, and later a new 4819 receiver joins the session, the closed-loop policy may permit all 4820 packets sent to the new receiver to use a checkpoint history that does 4821 not include the Channel Volume Control Change command. As a result, the 4822 new receiver experiences an indefinite artifact, and plays all notes on 4823 a channel too loudly or too softly. 4825 To address this issue, the closed-loop policy states that whenever a 4826 sender becomes aware of a new receiver, the sender MUST determine if the 4827 receiver would be subject to indefinite artifacts under the closed-loop 4828 policy. If so, the sender MUST ensure that the receiver starts the 4829 session free of indefinite artifacts. For example, to solve the Channel 4830 Volume issue described above, the sender may code the current state of 4831 the Channel Volume controller numbers in the recovery journal Chapter C, 4832 until it receives the first RTCP RR report that signals that a packet 4833 containing this Chapter C has been received. 4835 In satisfying this requirement, senders MAY infer the initial MIDI state 4836 of the receiver from the session description. For example, the stream 4837 example in Section 6.2 has the initial state defined in [MIDI] for 4838 General MIDI. 4840 In a unicast RTP session, a receiver may safely assume that the sender 4841 is aware of its presence as a receiver from the first packet sent in the 4842 RTP stream. However, in other types of RTP sessions (multicast, 4843 conference focus, RTP translator/mixer), a receiver is often not able to 4844 determine if the sender is initially aware of its presence as a 4845 receiver. 4847 To address this issue, the closed-loop policy states that if a receiver 4848 participates in a session where it may have access to a stream whose 4849 sender is not aware of the receiver, the receiver MUST take actions to 4850 ensure that its rendered MIDI performance does not contain indefinite 4851 artifacts. These protections will be necessarily incomplete. For 4852 example, a receiver may monitor the Checkpoint Packet Seqnum for 4853 uncovered loss events, and "err on the side of caution" with respect to 4854 handling stuck notes due to lost MIDI NoteOff commands, but the receiver 4855 is not able to compensate for the lack of Channel Volume initialization 4856 data in the recovery journal. 4858 The receiver MUST NOT discontinue these protective actions until it is 4859 certain that the sender is aware of its presence. If a receiver is not 4860 able to ascertain sender awareness, the receiver MUST continue these 4861 protective actions for the duration of the session. 4863 Note that in a multicast session where all parties are expected to send 4864 and receive, the reception of RTCP receiver reports from the sender 4865 about the RTP stream a receiver is multicasting back is evidence of the 4866 sender's awareness that the RTP stream multicast by the sender is being 4867 monitored by the receiver. Receivers may also obtain sender awareness 4868 evidence from session management tools, or by other means. In practice, 4869 ongoing observation of the Checkpoint Packet Seqnum to determine if the 4870 sender is taking actions to prevent loss events for a receiver is a good 4871 indication of sender awareness, as is the sudden appearance of recovery 4872 journal chapters with numerous Control Change controller data that was 4873 not foreshadowed by recent commands coded in the MIDI list shortly after 4874 sending an RTCP RR. 4876 The final set of normative closed-loop policy requirements concerns how 4877 senders and receivers handle unplanned disruptions of RTCP feedback from 4878 a receiver to a sender. By "unplanned", we refer to disruptions that 4879 are not due to the signalled termination of an RTP stream, via an RTCP 4880 BYE or via session management tools. 4882 As defined earlier in this section, the closed-loop policy states that a 4883 sender MUST choose a checkpoint packet with extended sequence number N, 4884 such that M(k) >= (N - 1) for all k, 1 <= k <= R, where R >= 1. If the 4885 sender has received at least one feedback report from receiver k, M(k) 4886 is the most recent report of the highest RTP packet sequence number seen 4887 by the receiver, normalized to reflect the rollover count of the sender. 4889 If this receiver k stops sending feedback to the sender, the M(k) value 4890 used by the sender reflects the last feedback report from the receiver. 4891 As time progresses without feedback from receiver k, this fixed M(k) 4892 value forces the sender to increase the size of the checkpoint history, 4893 and thus increases the bandwidth of the stream. 4895 At some point, the sender may need to take action in order to limit the 4896 bandwidth of the stream. In most envisioned uses of RTP MIDI, long 4897 before this point is reached, the SSRC time-out mechanism defined in 4898 [RFC3550] will remove the uncooperative receiver from the session (note 4899 that the closed-loop policy does not suggest or require any special 4900 sender behavior upon an SSRC time-out, other than the sender actions 4901 related to changing R, described earlier in this section). 4903 However, in rare situations, the bandwidth of the stream (due to a lack 4904 of feedback reports from the sender) may become too large to continue 4905 sending the stream to the receiver before the SSRC time-out occurs for 4906 the receiver. In this case, the closed-loop policy states that the 4907 sender should invoke the SSRC time-out for the receiver early. 4909 We now discuss receiver responsibilities in the case of unplanned 4910 disruptions of RTCP feedback from receiver to sender. 4912 In the unicast case, if a sender invokes the SSRC time-out mechanism for 4913 a receiver, the receiver stops receiving packets from the sender. The 4914 sender behavior imposed by the guardtime parameter (Appendix C.4.2) lets 4915 the receiver conclude that an SSRC time-out has occurred in a reasonable 4916 time period. 4918 In this case of a time-out, a receiver MUST keep sending RTCP feedback, 4919 in order to re-establish the RTP flow from the sender. Unless the 4920 receiver expects a prompt recovery of the RTP flow, the receiver MUST 4921 take actions to ensure that the rendered MIDI performance does not 4922 exhibit "very long transient artifacts" (for example, by silencing 4923 NoteOns to prevent stuck notes) while awaiting reconnection of the flow. 4925 In the multicast case, if a sender invokes the SSRC time-out mechanism 4926 for a receiver, the receiver may continue to receive packets, but the 4927 sender will no longer be using the M(k) feedback from the receiver to 4928 choose each checkpoint packet. If the receiver does not have additional 4929 information that precludes an SSRC time-out (such as RTCP Receiver 4930 Reports from the sender about an RTP stream the receiver is multicasting 4931 back to the sender), the receiver MUST monitor the Checkpoint Packet 4932 Seqnum to detect an SSRC time-out. If an SSRC time-out is detected, the 4933 receiver MUST follow the instructions for SSRC time-outs described for 4934 the unicast case above. 4936 Finally, we note that the closed-loop policy is suitable for use in 4937 RTP/RTCP sessions that use multicast transport. However, aspects of the 4938 closed-loop policy do not scale well to sessions with large numbers of 4939 participants. The sender state scales linearly with the number of 4940 receivers, as the sender needs to track the identity and M(k) value for 4941 each receiver k. The average recovery journal size is not independent 4942 of the number of receivers, as the RTCP reporting interval backoff slows 4943 down the rate of a full update of M(k) values. The backoff algorithm 4944 may also increase the amount of ancillary state used by implementations 4945 of the normative sender and receiver behaviors defined in Section 4. 4947 C.2.2.3. The open-loop Sending Policy 4949 The open-loop policy is suitable for sessions that are not able to 4950 implement the receiver-to-sender feedback required by the closed-loop 4951 policy, and that are also not able to use the anchor policy because of 4952 bandwidth constraints. 4954 The open-loop policy does not place constraints on how a sender chooses 4955 the checkpoint packet for each packet in the stream. In the absence of 4956 such constraints, a receiver may find that the recovery journal in the 4957 packet that ends a loss event has a checkpoint history that does not 4958 cover the entire loss event. We refer to loss events of this type as 4959 uncovered loss events. 4961 To ensure that uncovered loss events do not compromise the recovery 4962 journal mandate, the open-loop policy assigns specific recovery tasks to 4963 senders, receivers, and the creators of session descriptions. The 4964 underlying premise of the open-loop policy is that the indefinite 4965 artifacts produced during uncovered loss events fall into two classes. 4967 One class of artifacts is recoverable indefinite artifacts. Receivers 4968 are able to repair recoverable artifacts that occur during an uncovered 4969 loss event without intervention from the sender, at the potential cost 4970 of unpleasant transient artifacts. 4972 For example, after an uncovered loss event, receivers are able to repair 4973 indefinite artifacts due to NoteOff (0x8) commands that may have 4974 occurred during the loss event, by executing NoteOff commands for all 4975 active NoteOns commands. This action causes a transient artifact (a 4976 sudden silent period in the performance), but ensures that no stuck 4977 notes sound indefinitely. We refer to MIDI commands that are amenable 4978 to repair in this fashion as recoverable MIDI commands. 4980 A second class of artifacts is unrecoverable indefinite artifacts. If 4981 this class of artifact occurs during an uncovered loss event, the 4982 receiver is not able to repair the stream. 4984 For example, after an uncovered loss event, receivers are not able to 4985 repair indefinite artifacts due to Control Change (0xB) Channel Volume 4986 (controller number 7) commands that have occurred during the loss event. 4987 A repair is impossible because the receiver has no way of determining 4988 the data value of a lost Channel Volume command. We refer to MIDI 4989 commands that are fragile in this way as unrecoverable MIDI commands. 4991 The open-loop policy does not specify how to partition the MIDI command 4992 set into recoverable and unrecoverable commands. Instead, it assumes 4993 that the creators of the session descriptions are able to come to 4994 agreement on a suitable recoverable/unrecoverable MIDI command partition 4995 for an application. 4997 Given these definitions, we now state the normative requirements for the 4998 open-loop policy. 5000 In the open-loop policy, the creators of the session description MUST 5001 use the ch_anchor parameter (defined in Appendix C.2.3) to protect all 5002 unrecoverable MIDI command types from indefinite artifacts, or 5003 alternatively MUST use the cm_unused parameter (defined in Appendix C.1) 5004 to exclude the command types from the stream. These options act to 5005 shield command types from artifacts during an uncovered loss event. 5007 In the open-loop policy, receivers MUST examine the Checkpoint Packet 5008 Seqnum field of the recovery journal header after every loss event, to 5009 check if the loss event is an uncovered loss event. Section 5 shows how 5010 to perform this check. If an uncovered loss event has occurred, a 5011 receiver MUST perform indefinite artifact recovery for all MIDI command 5012 types that are not shielded by ch_anchor and cm_unused parameter 5013 assignments in the session description. 5015 The open-loop policy does not place specific constraints on the sender. 5016 However, the open-loop policy works best if the sender manages the size 5017 of the checkpoint history to ensure that uncovered losses occur 5018 infrequently, by taking into account the delay and loss characteristics 5019 of the network. Also, as each checkpoint packet change incurs the risk 5020 of an uncovered loss, senders should only move the checkpoint if it 5021 reduces the size of the journal. 5023 C.2.3. Recovery Journal Chapter Inclusion Parameters 5025 The recovery journal chapter definitions (Appendices A-B) specify under 5026 what conditions a chapter MUST appear in the recovery journal. In most 5027 cases, the definition states that if a certain command appears in the 5028 checkpoint history, a certain chapter type MUST appear in the recovery 5029 journal to protect the command. 5031 In this section, we describe the chapter inclusion parameters. These 5032 parameters modify the conditions under which a chapter appears in the 5033 journal. These parameters are essential to the use of the open-loop 5034 policy (Appendix C.2.2.3) and may also be used to simplify 5035 implementations of the closed-loop (Appendix C.2.2.2) and anchor 5036 (Appendix C.2.2.1) policies. 5038 Each parameter represents a type of chapter inclusion semantics. An 5039 assignment to a parameter declares which chapters (or chapter subsets) 5040 obey the inclusion semantics. We describe the assignment syntax for 5041 these parameters later in this section. 5043 A party MUST NOT accept chapter inclusion parameter values that violate 5044 the recovery journal mandate (Section 4). All assignments of the 5045 subsetting parameters (cm_used and cm_unused) MUST precede the first 5046 assignment of a chapter inclusion parameter in the parameter list. 5048 Below, we normatively define the semantics of the chapter inclusion 5049 parameters. For clarity, we define the action of parameters on complete 5050 chapters. If a parameter is assigned a subset of a chapter, the 5051 definition applies only to the chapter subset. 5053 o ch_never. A chapter assigned to the ch_never parameter MUST 5054 NOT appear in the recovery journal (Appendix A.4.1-2 defines 5055 exceptions to this rule for Chapter M). To signal the exclusion 5056 of a chapter from the journal, an assignment to ch_never MUST 5057 be made, even if the commands coded by the chapter are assigned 5058 to cm_unused. This rule simplifies the handling of commands 5059 types that may be coded in several chapters. 5061 o ch_default. A chapter assigned to the ch_default parameter 5062 MUST follow the default semantics for the chapter, as defined 5063 in Appendices A-B. 5065 o ch_anchor. A chapter assigned to the ch_anchor MUST obey a 5066 modified version of the default chapter semantics. In the 5067 modified semantics, all references to the checkpoint history 5068 are replaced with references to the session history, and all 5069 references to the checkpoint packet are replaced with 5070 references to the first packet sent in the stream. 5072 Parameter assignments obey the following syntax (see Appendix D for 5073 ABNF): 5075 = [channel list][field list] 5077 The chapter list is mandatory; the channel and field lists are optional. 5078 Multiple assignments to parameters have a cumulative effect and are 5079 applied in the order of parameter appearance in a media description. 5081 To determine the semantics of a list of chapter inclusion parameter 5082 assignments, we begin by assuming an implicit assignment of all channel 5083 and system chapters to the ch_default parameter, with the default values 5084 for the channel list and field list for each chapter that are defined 5085 below. 5087 We then interpret the semantics of the actual parameter assignments, 5088 using the rules below. 5090 A later assignment of a chapter to the same parameter expands the scope 5091 of the earlier assignment. In most cases, a later assignment of a 5092 chapter to a different parameter cancels (partially or completely) the 5093 effect of an earlier assignment. 5095 The chapter list specifies the channel or system chapters for which the 5096 parameter applies. The chapter list is a concatenated sequence of one 5097 or more of the letters corresponding to the chapter types 5098 (ACDEFMNPQTVWX). In addition, the list may contain one or more of the 5099 letters for the sub-chapter types (BGHJKYZ) of System Chapter D. 5101 The letters in a chapter list MUST be uppercase and MUST appear in 5102 alphabetical order. Letters other than (ABCDEFGHJKMNPQTVWXYZ) that 5103 appear in the chapter list MUST be ignored. 5105 The channel list specifies the channel journals for which this parameter 5106 applies; if no channel list is provided, the parameter applies to all 5107 channel journals. The channel list takes the form of a list of channel 5108 numbers (0 through 15) and dash-separated channel number ranges (i.e., 5109 0-5, 8-12, etc.). Dots (i.e., "." characters) separate elements in the 5110 channel list. 5112 Several of the systems chapters may be configured to have special 5113 semantics. Configuration occurs by specifying a channel list for the 5114 systems channel, using the coding described below (note that MIDI 5115 Systems commands do not have a "channel", and thus the original purpose 5116 of the channel list does not apply to systems chapters). The expression 5117 "the digit N" in the text below refers to the inclusion of N as a 5118 "channel" in the channel list for a systems chapter. 5120 For the J and K Chapter D sub-chapters (undefined System Common), the 5121 digit 0 codes that the parameter applies to the LEGAL field of the 5122 associated command log (Figure B.1.4 of Appendix B.1), the digit 1 codes 5123 that the parameter applies to the VALUE field of the command log, and 5124 the digit 2 codes that the parameter applies to the COUNT field of the 5125 command log. 5127 For the Y and Z Chapter D sub-chapters (undefined System Real-time), the 5128 digit 0 codes that the parameter applies to the LEGAL field of the 5129 associated command log (Figure B.1.5 of Appendix B.1) and the digit 1 5130 codes that the parameter applies to the COUNT field of the command log. 5132 For Chapter Q (Sequencer State Commands), the digit 0 codes that the 5133 parameter applies to the default Chapter Q definition, which forbids the 5134 TIME field. The digit 1 codes that the parameter applies to the 5135 optional Chapter Q definition, which supports the TIME field. 5137 The syntax for field lists follows the syntax for channel lists. If no 5138 field list is provided, the parameter applies to all controller or note 5139 numbers. For Chapter C, if no field list is provided, the controller 5140 numbers do not use enhanced Chapter C encoding (Appendix A.3.3). 5142 For Chapter C, the field list may take on values in the range 0 to 255. 5143 A field value X in the range 0-127 refers to a controller number X, and 5144 indicates that the controller number does not use enhanced Chapter C 5145 encoding. A field value X in the range 128-255 refers to a controller 5146 number "X minus 128" and indicates the controller number does use the 5147 enhanced Chapter C encoding. 5149 Assignments made to configure the Chapter C encoding method for a 5150 controller number MUST be made to the ch_default or ch_anchor 5151 parameters, as assignments to ch_never act to exclude the number from 5152 the recovery journal (and thus the indicated encoding method is 5153 irrelevant). 5155 A Chapter C field list MUST NOT encode conflicting information about the 5156 enhanced encoding status of a particular controller number. For 5157 example, values 0 and 128 MUST NOT both be coded by a field list. 5159 For Chapter M, the field list codes the Registered Parameter Numbers 5160 (RPNs) and Non-Registered Parameter Numbers (NRPNs) for which the 5161 parameter applies. The number range 0-16383 specifies RPNs, the number 5162 range 16384-32767 specifies NRPNs (16384 corresponds to NRPN 0, 32767 5163 corresponds to NRPN 16383). 5165 For Chapters N and A, the field list codes the note numbers for which 5166 the parameter applies. The note number range specified for Chapter N 5167 also applies to Chapter E. 5169 For Chapter E, the digit 0 codes that the parameter applies to Chapter E 5170 note logs whose V bit is set to 0, and the digit 1 codes that the 5171 parameter applies to note logs whose V bit is set to 1. 5173 For Chapter X, the field list codes the number of data octets that may 5174 appear in a SysEx command that is coded in the chapter. Thus, the field 5175 list 0-255 specifies SysEx commands with 255 or fewer data octets, the 5176 field list 256-4294967295 specifies SysEx commands with more than 255 5177 data octets but excludes commands with 255 or fewer data octets, and the 5178 field list 0 excludes all commands. 5180 A secondary parameter assignment syntax customizes Chapter X (see 5181 Appendix D for complete ABNF): 5183 = "__" *( "_" ) "__" 5185 The assignment defines a class of SysEx commands whose Chapter X coding 5186 obeys the semantics of the assigned parameter. The command class is 5187 specified by listing the permitted values of the first N data octets 5188 that follow the SysEx 0xF0 command octet. Any SysEx command whose first 5189 N data octets match the list is a member of the class. 5191 Each defines a data octet of the command, as a dot-separated 5192 (".") list of one or more hexadecimal constants (such as "7F") or dash- 5193 separated hexadecimal ranges (such as "01-1F"). Underscores ("_") 5194 separate each . Double-underscores ("__") delineate the data 5195 octet list. 5197 Using this syntax, each assignment specifies a single SysEx command 5198 class. Session descriptions may use several assignments to the same (or 5199 different) parameters to specify complex Chapter X behaviors. The 5200 ordering behavior of multiple assignments follows the guidelines for 5201 chapter parameter assignments described earlier in this section. 5203 The example session description below illustrates the use of the chapter 5204 inclusion parameters: 5206 v=0 5207 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5208 s=Example 5209 t=0 0 5210 m=audio 5004 RTP/AVP 96 5211 c=IN IP6 2001:DB80::7F2E:172A:1E24 5212 a=rtpmap:96 rtp-midi/44100 5213 a=fmtp:96 j_update=open-loop; cm_unused=ABCFGHJKMQTVWXYZ; 5214 cm_used=__7E_00-7F_09_01.02.03__; 5215 cm_used=__7F_00-7F_04_01.02__; cm_used=C7.64; 5216 ch_never=ABCDEFGHJKMQTVWXYZ; ch_never=4.11-13N; 5217 ch_anchor=P; ch_anchor=C7.64; 5218 ch_anchor=__7E_00-7F_09_01.02.03__; 5219 ch_anchor=__7F_00-7F_04_01.02__ 5221 (The a=fmtp line has been wrapped to fit the page to accommodate 5222 memo formatting restrictions; it comprises a single line in SDP.) 5224 The j_update parameter codes that the stream uses the open-loop policy. 5225 Most MIDI command-types are assigned to cm_unused and thus do not appear 5226 in the stream. As a consequence, the assignments to the first ch_never 5227 parameter reflect that most chapters are not in use. 5229 Chapter N for several MIDI channels is assigned to ch_never. Chapter N 5230 for MIDI channels other than 4, 11, 12, and 13 may appear in the 5231 recovery journal, using the (default) ch_default semantics. In 5232 practice, this assignment pattern would reflect knowledge about a 5233 resilient rendering method in use for the excluded channels. 5235 The MIDI Program Change command and several MIDI Control Change 5236 controller numbers are assigned to ch_anchor. Note that the ordering of 5237 the ch_anchor chapter C assignment after the ch_never command acts to 5238 override the ch_never assignment for the listed controller numbers (7 5239 and 64). 5241 The assignment of command-type X to cm_unused excludes most SysEx 5242 commands from the stream. Exceptions are made for General MIDI System 5243 On/Off commands and for the Master Volume and Balance commands, via the 5244 use of the secondary assignment syntax. The cm_used assignment codes 5245 the exception, and the ch_anchor assignment codes how these commands are 5246 protected in Chapter X. 5248 C.3. Configuration Tools: Timestamp Semantics 5250 The MIDI command section of the payload format consists of a list of 5251 commands, each with an associated timestamp. The semantics of command 5252 timestamps may be set during session configuration, using the parameters 5253 we describe in this section 5255 The parameter "tsmode" specifies the timestamp semantics for a stream. 5256 The parameter takes on one of three token values: "comex", "async", or 5257 "buffer". 5259 The default "comex" value specifies that timestamps code the execution 5260 time for a command (Appendix C.3.1) and supports the accurate 5261 transcoding of Standard MIDI Files (SMFs, [MIDI]). The "comex" value is 5262 also RECOMMENDED for new MIDI user-interface controller designs. The 5263 "async" value specifies an asynchronous timestamp sampling algorithm for 5264 time-of-arrival sources (Appendix C.3.2). The "buffer" value specifies 5265 a synchronous timestamp sampling algorithm (Appendix C.3.3) for time-of- 5266 arrival sources. 5268 Ancillary parameters MAY follow tsmode in a media description. We 5269 define these parameters in Appendices C.3.2-3 below. 5271 C.3.1. The comex Algorithm 5273 The default "comex" (COMmand EXecution) tsmode value specifies the 5274 execution time for the command. With comex, the difference between two 5275 timestamps indicates the time delay between the execution of the 5276 commands. This difference may be zero, coding simultaneous execution. 5278 The comex interpretation of timestamps works well for transcoding a 5279 Standard MIDI File (SMF, [MIDI]) into an RTP MIDI stream, as SMFs code a 5280 timestamp for each MIDI command stored in the file. To transcode an SMF 5281 that uses metric time markers, use the SMF tempo map (encoded in the SMF 5282 as meta-events) to convert metric SMF timestamp units into seconds-based 5283 RTP timestamp units. 5285 New MIDI controller designs (piano keyboard, drum pads, etc.) that 5286 support RTP MIDI and that have direct access to sensor data SHOULD use 5287 comex interpretation for timestamps, so that simultaneous gestural 5288 events may be accurately coded by RTP MIDI. 5290 Comex is a poor choice for transcoding MIDI 1.0 DIN cables [MIDI], for a 5291 reason that we will now explain. A MIDI DIN cable is an asynchronous 5292 serial protocol (320 microseconds per MIDI byte). MIDI commands on a 5293 DIN cable are not tagged with timestamps. Instead, MIDI DIN receivers 5294 infer command timing from the time of arrival of the bytes. Thus, two 5295 two-byte MIDI commands that occur at a source simultaneously are encoded 5296 on a MIDI 1.0 DIN cable with a 640 microsecond time offset. A MIDI DIN 5297 receiver is unable to tell if this time offset existed in the source 5298 performance or is an artifact of the serial speed of the cable. 5299 However, the RTP MIDI comex interpretation of timestamps declares that a 5300 timestamp offset between two commands reflects the timing of the source 5301 performance. 5303 This semantic mismatch is the reason that comex is a poor choice for 5304 transcoding MIDI DIN cables. Note that the choice of the RTP timestamp 5305 rate (Section 6.1-2 in the main text) cannot fix this inaccuracy issue. 5306 In the sections that follow, we describe two alternative timestamp 5307 interpretations ("async" and "buffer") that are a better match to MIDI 5308 1.0 DIN cable timing, and to other MIDI time-of-arrival sources. 5310 The "octpos", "linerate", and "mperiod" ancillary parameters (defined 5311 below) SHOULD NOT be used with comex. 5313 C.3.2. The async Algorithm 5315 The "async" tsmode value specifies the asynchronous sampling of a MIDI 5316 time-of-arrival source. In asynchronous sampling, the moment an octet 5317 is received from a source, it is labelled with a wall-clock time value. 5318 The time value has RTP timestamp units. 5320 The "octpos" ancillary parameter defines how RTP command timestamps are 5321 derived from octet time values. If octpos has the token value "first", 5322 a timestamp codes the time value of the first octet of the command. If 5323 octpos has the token value "last", a timestamp codes the time value of 5324 the last octet of the command. If the octpos parameter does not appear 5325 in the media description, the sender does not know which octet of the 5326 command the timestamp references (for example, the sender may be relying 5327 on an operating system service that does not specify this information). 5329 The octpos semantics refer to the first or last octet of a command as it 5330 appears on a time-of-arrival MIDI source, not as it appears in an RTP 5331 MIDI packet. This distinction is significant because the RTP coding may 5332 contain octets that are not present in the source. For example, the 5333 status octet of the first MIDI command in a packet may have been added 5334 to the MIDI stream during transcoding, to comply with the RTP MIDI 5335 running status requirements (Section 3.2). 5337 The "linerate" ancillary parameter defines the timespan of one MIDI 5338 octet on the transmission medium of the MIDI source to be sampled (such 5339 as a MIDI 1.0 DIN cable). The parameter has units of nanoseconds, and 5340 takes on integral values. For MIDI 1.0 DIN cables, the correct linerate 5341 value is 320000 (this value is also the default value for the 5342 parameter). 5344 We now show a session description example for the async algorithm. 5345 Consider a sender that is transcoding a MIDI 1.0 DIN cable source into 5346 RTP. The sender runs on a computing platform that assigns time values 5347 to every incoming octet of the source, and the sender uses the time 5348 values to label the first octet of each command in the RTP packet. This 5349 session description describes the transcoding: 5351 v=0 5352 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5353 s=Example 5354 t=0 0 5355 m=audio 5004 RTP/AVP 96 5356 c=IN IP4 192.0.2.94 5357 a=rtpmap:96 rtp-midi/44100 5358 a=sendonly 5359 a=fmtp:96 tsmode=async; linerate=320000; octpos=first 5361 C.3.3. The buffer Algorithm 5363 The "buffer" tsmode value specifies the synchronous sampling of a MIDI 5364 time-of-arrival source. 5366 In synchronous sampling, octets received from a source are placed in a 5367 holding buffer upon arrival. At periodic intervals, the RTP sender 5368 examines the buffer. The sender removes complete commands from the 5369 buffer and codes those commands in an RTP packet. The command timestamp 5370 codes the moment of buffer examination, expressed in RTP timestamp 5371 units. Note that several commands may have the same timestamp value. 5373 The "mperiod" ancillary parameter defines the nominal periodic sampling 5374 interval. The parameter takes on positive integral values and has RTP 5375 timestamp units. 5377 The "octpos" ancillary parameter, defined in Appendix C.3.1 for 5378 asynchronous sampling, plays a different role in synchronous sampling. 5379 In synchronous sampling, the parameter specifies the timestamp semantics 5380 of a command whose octets span several sampling periods. 5382 If octpos has the token value "first", the timestamp reflects the 5383 arrival period of the first octet of the command. If octpos has the 5384 token value "last", the timestamp reflects the arrival period of the 5385 last octet of the command. The octpos semantics refer to the first or 5386 last octet of the command as it appears on a time-of-arrival source, not 5387 as it appears in the RTP packet. 5389 If the octpos parameter does not appear in the media description, the 5390 timestamp MAY reflect the arrival period of any octet of the command; 5391 senders use this option to signal a lack of knowledge about the timing 5392 details of the buffering process at sub-command granularity. 5394 We now show a session description example for the buffer algorithm. 5395 Consider a sender that is transcoding a MIDI 1.0 DIN cable source into 5396 RTP. The sender runs on a computing platform that places source data 5397 into a buffer upon receipt. The sender polls the buffer 1000 times a 5398 second, extracts all complete commands from the buffer, and places the 5399 commands in an RTP packet. This session description describes the 5400 transcoding: 5402 v=0 5403 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5404 s=Example 5405 t=0 0 5406 m=audio 5004 RTP/AVP 96 5407 c=IN IP6 2001:DB80::7F2E:172A:1E24 5408 a=rtpmap:96 rtp-midi/44100 5409 a=sendonly 5410 a=fmtp:96 tsmode=buffer; linerate=320000; octpos=last; mperiod=44 5412 The mperiod value of 44 is derived by dividing the clock rate specified 5413 by the rtpmap attribute (44100 Hz) by the 1000 Hz buffer sampling rate 5414 and rounding to the nearest integer. Command timestamps might not 5415 increment by exact multiples of 44, as the actual sampling period might 5416 not precisely match the nominal mperiod value. 5418 C.4. Configuration Tools: Packet Timing Tools 5420 In this appendix, we describe session configuration tools for 5421 customizing the temporal behavior of MIDI stream packets. 5423 C.4.1. Packet Duration Tools 5425 Senders control the granularity of a stream by setting the temporal 5426 duration ("media time") of the packets in the stream. Short media times 5427 (20 ms or less) often imply an interactive session. Longer media times 5428 (100 ms or more) usually indicate a content streaming session. The RTP 5429 AVP profile [RFC3551] recommends audio packet media times in a range 5430 from 0 to 200 ms. 5432 By default, an RTP receiver dynamically senses the media time of packets 5433 in a stream and chooses the length of its playout buffer to match the 5434 stream. A receiver typically sizes its playout buffer to fit several 5435 audio packets and adjusts the buffer length to reflect the network 5436 jitter and the sender timing fidelity. 5438 Alternatively, the packet media time may be statically set during 5439 session configuration. Session descriptions MAY use the RTP MIDI 5440 parameter "rtp_ptime" to set the recommended media time for a packet. 5441 Session descriptions MAY also use the RTP MIDI parameter "rtp_maxptime" 5442 to set the maximum media time for a packet permitted in a stream. Both 5443 parameters MAY be used together to configure a stream. 5445 The values assigned to the rtp_ptime and rtp_maxptime parameters have 5446 the units of the RTP timestamp for the stream, as set by the rtpmap 5447 attribute (see Section 6.1). Thus, if rtpmap sets the clock rate of a 5448 stream to 44100 Hz, a maximum packet media time of 10 ms is coded by 5449 setting rtp_maxptime=441. As stated in the Appendix C preamble, the 5450 senders and receivers of a stream MUST agree on common values for 5451 rtp_ptime and rtp_maxptime if the parameters appear in the media 5452 description for the stream. 5454 0 ms is a reasonable media time value for MIDI packets and is often used 5455 in low-latency interactive applications. In a packet with a 0 ms media 5456 time, all commands execute at the instant they are coded by the packet 5457 timestamp. The session description below configures all packets in the 5458 stream to have 0 ms media time: 5460 v=0 5461 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5462 s=Example 5463 t=0 0 5464 m=audio 5004 RTP/AVP 96 5465 c=IN IP4 192.0.2.94 5466 a=rtpmap:96 rtp-midi/44100 5467 a=fmtp:96 rtp_ptime=0; rtp_maxptime=0 5469 The session attributes ptime and maxptime [RFC4566] MUST NOT be used to 5470 configure an RTP MIDI stream. Sessions MUST use rtp_ptime in lieu of 5471 ptime and MUST use rtp_maxptime in lieu of maxptime. RTP MIDI defines 5472 its own parameters for media time configuration because 0 ms values for 5473 ptime and maxptime are forbidden by [RFC3264] but are essential for 5474 certain applications of RTP MIDI. 5476 See the Appendix C.7 examples for additional discussion about using 5477 rtp_ptime and rtp_maxptime for session configuration. 5479 C.4.2. The guardtime Parameter 5481 RTP permits a sender to stop sending audio packets for an arbitrary 5482 period of time during a session. When sending resumes, the RTP sequence 5483 number series continues unbroken, and the RTP timestamp value reflects 5484 the media time silence gap. 5486 This RTP feature has its roots in telephony, but it is also well matched 5487 to interactive MIDI sessions, as players may fall silent for several 5488 seconds during (or between) songs. 5490 Certain MIDI applications benefit from a slight enhancement to this RTP 5491 feature. In interactive applications, receivers may use on-line network 5492 models to guide heuristics for handling lost and late RTP packets. 5493 These models may work poorly if a sender ceases packet transmission for 5494 long periods of time. 5496 Session descriptions may use the parameter "guardtime" to set a minimum 5497 sending rate for a media session. The value assigned to guardtime codes 5498 the maximum separation time between two sequential packets, as expressed 5499 in RTP timestamp units. 5501 Typical guardtime values are 500-2000 ms. This value range is not a 5502 normative bound, and parties SHOULD be prepared to process values 5503 outside this range. 5505 The congestion control requirements for sender implementations 5506 (described in Section 8 and [RFC3550]) take precedence over the 5507 guardtime parameter. Thus, if the guardtime parameter requests a 5508 minimum sending rate, but sending at this rate would violate the 5509 congestion control requirements, senders MUST ignore the guardtime 5510 parameter value. In this case, senders SHOULD use the lowest minimum 5511 sending rate that satisfies the congestion control requirements. 5513 Below, we show a session description that uses the guardtime parameter. 5515 v=0 5516 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5517 s=Example 5518 t=0 0 5519 m=audio 5004 RTP/AVP 96 5520 c=IN IP6 2001:DB80::7F2E:172A:1E24 5521 a=rtpmap:96 rtp-midi/44100 5522 a=fmtp:96 guardtime=44100; rtp_ptime=0; rtp_maxptime=0 5523 C.5. Configuration Tools: Stream Description 5525 As we discussed in Section 2.1, a party may send several RTP MIDI 5526 streams in the same RTP session, and several RTP sessions that carry 5527 MIDI may appear in a multimedia session. 5529 By default, the MIDI name space (16 channels + systems) of each RTP 5530 stream sent by a party in a multimedia session is independent. By 5531 independent, we mean three distinct things: 5533 o If a party sends two RTP MIDI streams (A and B), MIDI voice 5534 channel 0 in stream A is a different "channel 0" than MIDI 5535 voice channel 0 in stream B. 5537 o MIDI voice channel 0 in stream B is not considered to be 5538 "channel 16" of a 32-channel MIDI voice channel space whose 5539 "channel 0" is channel 0 of stream A. 5541 o Streams sent by different parties over different RTP sessions, 5542 or over the same RTP session but with different payload type 5543 numbers, do not share the association that is shared by a MIDI 5544 cable pair that cross-connects two devices in a MIDI 1.0 DIN 5545 network. By default, this association is only held by streams 5546 sent by different parties in the same RTP session that use the 5547 same payload type number. 5549 In this appendix, we show how to express that specific RTP MIDI streams 5550 in a multimedia session are not independent but instead are related in 5551 one of the three ways defined above. We use two tools to express these 5552 relations: 5554 o The musicport parameter. This parameter is assigned a 5555 non-negative integer value between 0 and 4294967295. It 5556 appears in the fmtp lines of payload types. 5558 o The FID grouping attribute [RFC3388] signals that several RTP 5559 sessions in a multimedia session are using the musicport 5560 parameter to express an inter-session relationship. 5562 If a multimedia session has several payload types whose musicport 5563 parameters are assigned the same integer value, streams using these 5564 payload types share an "identity relationship" (including streams that 5565 use the same payload type). Streams in an identity relationship share 5566 two properties: 5568 o Identity relationship streams sent by the same party 5569 target the same MIDI name space. Thus, if streams A 5570 and B share an identity relationship, voice channel 0 5571 in stream A is the same "channel 0" as voice channel 5572 0 in stream B. 5574 o Pairs of identity relationship streams that are sent by 5575 different parties share the association that is shared 5576 by a MIDI cable pair that cross-connects two devices in 5577 a MIDI 1.0 DIN network. 5579 A party MUST NOT send two RTP MIDI streams that share an identity 5580 relationship in the same RTP session. Instead, each stream MUST be in a 5581 separate RTP session. As explained in Section 2.1, this restriction is 5582 necessary to support the RTP MIDI method for the synchronization of 5583 streams that share a MIDI name space. 5585 If a multimedia session has several payload types whose musicport 5586 parameters are assigned sequential values (i.e., i, i+1, ... i+k), the 5587 streams using the payload types share an "ordered relationship". For 5588 example, if payload type A assigns 2 to musicport and payload type B 5589 assigns 3 to musicport, A and B are in an ordered relationship. 5591 Streams in an ordered relationship that are sent by the same party are 5592 considered by renderers to form a single larger MIDI space. For 5593 example, if stream A has a musicport value of 2 and stream B has a 5594 musicport value of 3, MIDI voice channel 0 in stream B is considered to 5595 be voice channel 16 in the larger MIDI space formed by the relationship. 5596 Note that it is possible for streams to participate in both an identity 5597 relationship and an ordered relationship. 5599 We now state several rules for using musicport: 5601 o If streams from several RTP sessions in a multimedia 5602 session use the musicport parameter, the RTP sessions 5603 MUST be grouped using the FID grouping attribute 5604 defined in [RFC3388]. 5606 o An ordered or identity relationship MUST NOT 5607 contain both native RTP MIDI streams and 5608 mpeg4-generic RTP MIDI streams. An exception applies 5609 if a relationship consists of sendonly and recvonly 5610 (but not sendrecv) streams. In this case, the sendonly 5611 streams MUST NOT contain both types of streams, and the 5612 recvonly streams MUST NOT contain both types of streams. 5614 o It is possible to construct identity relationships 5615 that violate the recovery journal mandate (for example, 5616 sending NoteOns for a voice channel on stream A and 5617 NoteOffs for the same voice channel on stream B). 5618 Parties MUST NOT generate (or accept) session 5619 descriptions that exhibit this flaw. 5621 o Other payload formats MAY define musicport media type 5622 parameters. Formats would define these parameters so that 5623 their sessions could be bundled into RTP MIDI name spaces. 5624 The parameter definitions MUST be compatible with the 5625 musicport semantics defined in this appendix. 5627 As a rule, at most one payload type in a relationship may specify a MIDI 5628 renderer. An exception to the rule applies to relationships that 5629 contain sendonly and recvonly streams but no sendrecv streams. In this 5630 case, one sendonly session and one recvonly session may each define a 5631 renderer. 5633 Renderer specification in a relationship may be done using the tools 5634 described in Appendix C.6. These tools work for both native streams and 5635 mpeg4-generic streams. An mpeg4-generic stream that uses the Appendix 5636 C.6 tools MUST set all "config" parameters to the empty string (""). 5638 Alternatively, for mpeg4-generic streams, renderer specification may be 5639 done by setting one "config" parameter in the relationship to the 5640 renderer configuration string, and all other config parameters to the 5641 empty string (""). 5643 We now define sender and receiver rules that apply when a party sends 5644 several streams that target the same MIDI name space. 5646 Senders MAY use the subsetting parameters (Appendix C.1) to predefine 5647 the partitioning of commands between streams, or they MAY use a dynamic 5648 partitioning strategy. 5650 Receivers that merge identity relationship streams into a single MIDI 5651 command stream MUST maintain the structural integrity of the MIDI 5652 commands coded in each stream during the merging process, in the same 5653 way that software that merges traditional MIDI 1.0 DIN cable flows is 5654 responsible for creating a merged command flow compatible with [MIDI]. 5656 Senders MUST partition the name space so that the rendered MIDI 5657 performance does not contain indefinite artifacts (as defined in Section 5658 4). This responsibility holds even if all streams are sent over 5659 reliable transport, as different stream latencies may yield indefinite 5660 artifacts. For example, stuck notes may occur in a performance split 5661 over two TCP streams, if NoteOn commands are sent on one stream and 5662 NoteOff commands are sent on the other. 5664 Senders MUST NOT split a Registered Parameter Name (RPN) or Non- 5665 Registered Parameter Name (NRPN) transaction appearing on a MIDI channel 5666 across multiple identity relationship sessions. Receivers MUST assume 5667 that the RPN/NRPN transactions that appear on different identity 5668 relationship sessions are independent and MUST preserve transactional 5669 integrity during the MIDI merge. 5671 A simple way to safely partition voice channel commands is to place all 5672 MIDI commands for a particular voice channel into the same session. 5673 Safe partitioning of MIDI Systems commands may be more complicated for 5674 sessions that extensively use System Exclusive. 5676 We now show several session description examples that use the musicport 5677 parameter. 5679 Our first session description example shows two RTP MIDI streams that 5680 drive the same General MIDI decoder. The sender partitions MIDI 5681 commands between the streams dynamically. The musicport values indicate 5682 that the streams share an identity relationship. 5684 v=0 5685 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5686 s=Example 5687 t=0 0 5688 a=group:FID 1 2 5689 c=IN IP4 192.0.2.94 5690 m=audio 5004 RTP/AVP 96 5691 a=rtpmap:96 mpeg4-generic/44100 5692 a=mid:1 5693 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5694 config=7A0A0000001A4D546864000000060000000100604D54726B0 5695 000000600FF2F000; musicport=12 5696 m=audio 5006 RTP/AVP 96 5697 a=rtpmap:96 mpeg4-generic/44100 5698 a=mid:2 5699 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 5700 musicport=12 5702 (The a=fmtp lines have been wrapped to fit the page to accommodate 5703 memo formatting restrictions; they comprise single lines in SDP.) 5705 Recall that Section 2.1 defines rules for streams that target the same 5706 MIDI name space. Those rules, implemented in the example above, require 5707 that each stream resides in a separate RTP session, and that the 5708 grouping mechanisms defined in [RFC3388] signal an inter-session 5709 relationship. The "group" and "mid" attribute lines implement this 5710 grouping mechanism. 5712 A variant on this example, whose session description is not shown, would 5713 use two streams in an identity relationship driving the same MIDI 5714 renderer, each with a different transport type. One stream would use 5715 UDP and would be dedicated to real-time messages. A second stream would 5716 use TCP [RFC4571] and would be used for SysEx bulk data messages. 5718 In the next example, two mpeg4-generic streams form an ordered 5719 relationship to drive a Structured Audio decoder with 32 MIDI voice 5720 channels. Both streams reside in the same RTP session. 5722 v=0 5723 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5724 s=Example 5725 t=0 0 5726 m=audio 5006 RTP/AVP 96 97 5727 c=IN IP6 2001:DB80::7F2E:172A:1E24 5728 a=rtpmap:96 mpeg4-generic/44100 5729 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=13; 5730 musicport=5 5731 a=rtpmap:97 mpeg4-generic/44100 5732 a=fmtp:97 streamtype=5; mode=rtp-midi; config=""; profile-level-id=13; 5733 musicport=6; render=synthetic; rinit="audio/asc"; 5734 url="http://example.com/cardinal.asc"; 5735 cid="azsldkaslkdjqpwojdkmsldkfpe" 5737 (The a=fmtp lines have been wrapped to fit the page to accommodate 5738 memo formatting restrictions; they comprise single lines in SDP.) 5740 The sequential musicport values for the two sessions establish the 5741 ordered relationship. The musicport=5 session maps to Structured Audio 5742 extended channels range 0-15, the musicport=6 session maps to Structured 5743 Audio extended channels range 16-31. 5745 Both config strings are empty. The configuration data is specified by 5746 parameters that appear in the fmtp line of the second media description. 5747 We define this configuration method in Appendix C.6. 5749 The next example shows two RTP MIDI streams (one recvonly, one sendonly) 5750 that form a "virtual sendrecv" session. Each stream resides in a 5751 different RTP session (a requirement because sendonly and recvonly are 5752 RTP session attributes). 5754 v=0 5755 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5756 s=Example 5757 t=0 0 5758 a=group:FID 1 2 5759 c=IN IP4 192.0.2.94 5760 m=audio 5004 RTP/AVP 96 5761 a=sendonly 5762 a=rtpmap:96 mpeg4-generic/44100 5763 a=mid:1 5764 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5765 config=7A0A0000001A4D546864000000060000000100604D54726B0 5766 000000600FF2F000; musicport=12 5767 m=audio 5006 RTP/AVP 96 5768 a=recvonly 5769 a=rtpmap:96 mpeg4-generic/44100 5770 a=mid:2 5771 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5772 config=7A0A0000001A4D546864000000060000000100604D54726B0 5773 000000600FF2F000; musicport=12 5775 (The a=fmtp lines have been wrapped to fit the page to accommodate 5776 memo formatting restrictions; they comprise single lines in SDP.) 5778 To signal the "virtual sendrecv" semantics, the two streams assign 5779 musicport to the same value (12). As defined earlier in this section, 5780 pairs of identity relationship streams that are sent by different 5781 parties share the association that is shared by a MIDI cable pair that 5782 cross-connects two devices in a MIDI 1.0 network. We use the term 5783 "virtual sendrecv" because streams sent by different parties in a true 5784 sendrecv session also have this property. 5786 As discussed in the preamble to Appendix C, the primary advantage of the 5787 virtual sendrecv configuration is that each party can customize the 5788 property of the stream it receives. In the example above, each stream 5789 defines its own "config" string that could customize the rendering 5790 algorithm for each party (in fact, the particular strings shown in this 5791 example are identical, because General MIDI is not a configurable MPEG 4 5792 renderer). 5794 C.6. Configuration Tools: MIDI Rendering 5796 This appendix defines the session configuration tools for rendering. 5798 The "render" parameter specifies a rendering method for a stream. The 5799 parameter is assigned a token value that signals the top-level rendering 5800 class. This memo defines four token values for render: "unknown", 5801 "synthetic", "api", and "null": 5803 o An "unknown" renderer is a renderer whose nature is unspecified. 5804 It is the default renderer for native RTP MIDI streams. 5806 o A "synthetic" renderer transforms the MIDI stream into audio 5807 output (or sometimes into stage lighting changes or other 5808 actions). It is the default renderer for mpeg4-generic 5809 RTP MIDI streams. 5811 o An "api" renderer presents the command stream to applications 5812 via an Application Programmer Interface (API). 5814 o The "null" renderer discards the MIDI stream. 5816 The "null" render value plays special roles during Offer/Answer 5817 negotiations [RFC3264]. A party uses the "null" value in an answer to 5818 reject an offered renderer. Note that rejecting a renderer is 5819 independent from rejecting a payload type (coded by removing the payload 5820 type from a media line) and rejecting a media stream (coded by zeroing 5821 the port of a media line that uses the renderer). 5823 Other render token values MAY be registered with IANA. The token value 5824 MUST adhere to the ABNF for render tokens defined in Appendix D. 5825 Registrations MUST include a complete specification of parameter value 5826 usage, similar in depth to the specifications that appear throughout 5827 Appendix C.6 for "synthetic" and "api" render values. If a party is 5828 offered a session description that uses a render token value that is not 5829 known to the party, the party MUST NOT accept the renderer. Options 5830 include rejecting the renderer (using the "null" value), the payload 5831 type, the media stream, or the session description. 5833 Other parameters MAY follow a render parameter in a parameter list. The 5834 additional parameters act to define the exact nature of the renderer. 5835 For example, the "subrender" parameter (defined in Appendix C.6.2) 5836 specifies the exact nature of the renderer. 5838 Special rules apply to using the render parameter in an mpeg4-generic 5839 stream. We define these rules in Appendix C.6.5. 5841 C.6.1. The multimode Parameter 5843 A media description MAY contain several render parameters. By default, 5844 if a parameter list includes several render parameters, a receiver MUST 5845 choose exactly one renderer from the list to render the stream. The 5846 "multimode" parameter may be used to override this default. We define 5847 two token values for multimode: "one" and "all": 5849 o The default "one" value requests rendering by exactly one of 5850 the listed renderers. 5852 o The "all" value requests the synchronized rendering of the RTP 5853 MIDI stream by all listed renderers, if possible. 5855 If the multimode parameter appears in a parameter list, it MUST appear 5856 before the first render parameter assignment. 5858 Render parameters appear in the parameter list in order of decreasing 5859 priority. A receiver MAY use the priority ordering to decide which 5860 renderer(s) to retain in a session. 5862 If the "offer" in an Offer/Answer-style negotiation [RFC3264] contains a 5863 parameter list with one or more render parameters, the "answer" MUST set 5864 the render parameters of all unchosen renderers to "null". 5866 C.6.2. Renderer Specification 5868 The render parameter (Appendix C.6 preamble) specifies, in a broad 5869 sense, what a renderer does with a MIDI stream. In this appendix, we 5870 describe the "subrender" parameter. The token value assigned to 5871 subrender defines the exact nature of the renderer. Thus, "render" and 5872 "subrender" combine to define a renderer, in the same way as MIME types 5873 and MIME subtypes combine to define a type of media [RFC2045]. 5875 If the subrender parameter is used for a renderer definition, it MUST 5876 appear immediately after the render parameter in the parameter list. At 5877 most one subrender parameter may appear in a renderer definition. 5879 This document defines one value for subrender: the value "default". The 5880 "default" token specifies the use of the default renderer for the stream 5881 type (native or mpeg4-generic). The default renderer for native RTP 5882 MIDI streams is a renderer whose nature is unspecified (see point 6 in 5883 Section 6.1 for details). The default renderer for mpeg4-generic RTP 5884 MIDI streams is an MPEG 4 Audio Object Type whose ID number is 13, 14, 5885 or 15 (see Section 6.2 for details). 5887 If a renderer definition does not use the subrender parameter, the value 5888 "default" is assumed for subrender. 5890 Other subrender token values may be registered with IANA. We now 5891 discuss guidelines for registering subrender values. 5893 A subrender value is registered for a specific stream type (native or 5894 mpeg4-generic) and a specific render value (excluding "null" and 5895 "unknown"). Registrations for mpeg4-generic subrender values are 5896 restricted to new MPEG 4 Audio Object Types that accept MIDI input. The 5897 syntax of the token MUST adhere to the token definition in Appendix D. 5899 For "render=synthetic" renderers, a subrender value registration 5900 specifies an exact method for transforming the MIDI stream into audio 5901 (or sometimes into video or control actions, such as stage lighting). 5902 For standardized renderers, this specification is usually a pointer to a 5903 standards document, perhaps supplemented by RTP-MIDI-specific 5904 information. For commercial products and open-source projects, this 5905 specification usually takes the form of instructions for interfacing the 5906 RTP MIDI stream with the product or project software. A 5907 "render=synthetic" registration MAY specify additional Reset State 5908 commands for the renderer (Appendix A.1). 5910 A "render=api" subrender value registration specifies how an RTP MIDI 5911 stream interfaces with an API (Application Programmers Interface). This 5912 specification is usually a pointer to programmer's documentation for the 5913 API, perhaps supplemented by RTP-MIDI-specific information. 5915 A subrender registration MAY specify an initialization file (referred to 5916 in this document as an initialization data object) for the stream. The 5917 initialization data object MAY be encoded in the parameter list 5918 (verbatim or by reference) using the coding tools defined in Appendix 5919 C.6.3. An initialization data object MUST have a registered [RFC4288] 5920 media type and subtype [RFC2045]. 5922 For "render=synthetic" renderers, the data object usually encodes 5923 initialization data for the renderer (sample files, synthesis patch 5924 parameters, reverberation room impulse responses, etc.). 5926 For "render=api" renderers, the data object usually encodes data about 5927 the stream used by the API (for example, for an RTP MIDI stream 5928 generated by a piano keyboard controller, the manufacturer and model 5929 number of the keyboard, for use in GUI presentation). 5931 Usually, only one initialization object is encoded for a renderer. If a 5932 renderer uses multiple data objects, the correct receiver interpretation 5933 of multiple data objects MUST be defined in the subrender registration. 5935 A subrender value registration may also specify additional parameters, 5936 to appear in the parameter list immediately after subrender. These 5937 parameter names MUST begin with the subrender value, followed by an 5938 underscore ("_"), to avoid name space collisions with future RTP MIDI 5939 parameter names (for example, a parameter "foo_bar" defined for 5940 subrender value "foo"). 5942 We now specify guidelines for interpreting the subrender parameter 5943 during session configuration. 5945 If a party is offered a session description that uses a renderer whose 5946 subrender value is not known to the party, the party MUST NOT accept the 5947 renderer. Options include rejecting the renderer (using the "null" 5948 value), the payload type, the media stream, or the session description. 5950 Receivers MUST be aware of the Reset State commands (Appendix A.1) for 5951 the renderer specified by the subrender parameter and MUST insure that 5952 the renderer does not experience indefinite artifacts due to the 5953 presence (or the loss) of a Reset State command. 5955 C.6.3. Renderer Initialization 5957 If the renderer for a stream uses an initialization data object, an 5958 "rinit" parameter MUST appear in the parameter list immediately after 5959 the "subrender" parameter. If the renderer parameter list does not 5960 include a subrender parameter (recall the semantics for "default" in 5961 Appendix C.6.2), the "rinit" parameter MUST appear immediately after the 5962 "render" parameter. 5964 The value assigned to the rinit parameter MUST be the media type/subtype 5965 [RFC2045] for the initialization data object. If an initialization 5966 object type is registered with several media types, including audio, the 5967 assignment to rinit MUST use the audio media type. 5969 RTP MIDI supports several parameters for encoding initialization data 5970 objects for renderers in the parameter list: "inline", "url", and "cid". 5972 If the "inline", "url", and/or "cid" parameters are used by a renderer, 5973 these parameters MUST immediately follow the "rinit" parameter. 5975 If a "url" parameter appears for a renderer, an "inline" parameter MUST 5976 NOT appear. If an "inline" parameter appears for a renderer, a "url" 5977 parameter MUST NOT appear. However, neither "url" or "inline" is 5978 required to appear. If neither "url" or "inline" parameters follow 5979 "rinit", the "cid" parameter MUST follow "rinit". 5981 The "inline" parameter supports the inline encoding of the data object. 5982 The parameter is assigned a double-quoted Base64 [RFC2045] encoding of 5983 the binary data object, with no line breaks. Appendix E.4 shows an 5984 example that constructs an inline parameter value. 5986 The "url" parameter is assigned a double-quoted string representation of 5987 a Uniform Resource Locator (URL) for the data object. The string MUST 5988 specify either a HyperText Transport Protocol URI (HTTP, [RFC2616]) or 5989 an HTTP over TLS URI (HTTPS, [RFC2818]). The media type/subtype for the 5990 data object SHOULD be specified in the appropriate HTTP or HTTPS 5991 transport header. 5993 The "url" parameter is assigned a double-quoted string representation of 5994 a Uniform Resource Locator (URL) for the data object. The string MUST 5995 specify a HyperText Transport Protocol URL (HTTP, [RFC2616]). HTTP MAY 5996 be used over TCP or MAY be used over a secure network transport, such as 5997 the method described in [RFC2818]. The media type/subtype for the data 5998 object SHOULD be specified in the appropriate HTTP transport header. 6000 The "cid" parameter supports data object caching. The parameter is 6001 assigned a double-quoted string value that encodes a globally unique 6002 identifier for the data object. 6004 A cid parameter MAY immediately follow an inline parameter, in which 6005 case the cid identifier value MUST be associated with the inline data 6006 object. 6008 If a url parameter is present, and if the data object for the URL is 6009 expected to be unchanged for the life of the URL, a cid parameter MAY 6010 immediately follow the url parameter. The cid identifier value MUST be 6011 associated with the data object for the URL. A cid parameter assigned 6012 to the same identifier value SHOULD be specified following the data 6013 object type/subtype in the appropriate HTTP transport header. 6015 If a url parameter is present, and if the data object for the URL is 6016 expected to change during the life of the URL, a cid parameter MUST NOT 6017 follow the url parameter. A receiver interprets the presence of a cid 6018 parameter as an indication that it is safe to use a cached copy of the 6019 url data object; the absence of a cid parameter is an indication that it 6020 is not safe to use a cached copy, as it may change. 6022 Finally, the cid parameter MAY be used without the inline and url 6023 parameters. In this case, the identifier references a local or 6024 distributed catalog of data objects. 6026 In most cases, only one data object is coded in the parameter list for 6027 each renderer. For example, the default renderer for mpeg4-generic 6028 streams uses a single data object (see Appendix C.6.5 for example 6029 usage). 6031 However, a subrender registration MAY permit the use of multiple data 6032 objects for a renderer. If multiple data objects are encoded for a 6033 renderer, each object encoding begins with an "rinit" parameter, 6034 followed by "inline", "url", and/or "cid" parameters. 6036 Initialization data objects MAY encapsulate a Standard MIDI File (SMF). 6037 By default, the SMFs that are encapsulated in a data object MUST be 6038 ignored by an RTP MIDI receiver. We define parameters to override this 6039 default in Appendix C.6.4. 6041 To end this section, we offer guidelines for registering media types for 6042 initialization data objects. These guidelines are in addition to the 6043 information in [RFC4288]. 6045 Some initialization data objects are also capable of encoding MIDI note 6046 information and thus complete audio performances. These objects SHOULD 6047 be registered using the "audio" media type, so that the objects may also 6048 be used for store-and-forward rendering, and "application" media type, 6049 to support editing tools. Initialization objects without note storage, 6050 or initialization objects for non-audio renderers, SHOULD be registered 6051 only for an "application" media type. 6053 C.6.4. MIDI Channel Mapping 6055 In this appendix, we specify how to map MIDI name spaces (16 voice 6056 channels + systems) onto a renderer. 6058 In the general case: 6060 o A session may define an ordered relationship (Appendix C.5) 6061 that presents more than one MIDI name space to a renderer. 6063 o A renderer may accept an arbitrary number of MIDI name spaces, 6064 or it may expect a specific number of MIDI name spaces. 6066 A session description SHOULD provide a compatible MIDI name space to 6067 each renderer in the session. If a receiver detects that a session 6068 description has too many or too few MIDI name spaces for a renderer, 6069 MIDI data from extra stream name spaces MUST be discarded, and extra 6070 renderer name spaces MUST NOT be driven with MIDI data (except as 6071 described in Appendix C.6.4.1, below). 6073 If a parameter list defines several renderers and assigns the "all" 6074 token value to the multimode parameter, the same name space is presented 6075 to each renderer. However, the "chanmask" parameter may be used to mask 6076 out selected voice channels to each renderer. We define "chanmask" and 6077 other MIDI management parameters in the sub-sections below. 6079 C.6.4.1. The smf_info Parameter 6081 The smf_info parameter defines the use of the SMFs encapsulated in 6082 renderer data objects (if any). The smf_info parameter also defines the 6083 use of SMFs coded in the smf_inline, smf_url, and smf_cid parameters 6084 (defined in Appendix C.6.4.2). 6086 The smf_info parameter describes the "render" parameter that most 6087 recently precedes it in the parameter list. The smf_info parameter MUST 6088 NOT appear in parameter lists that do not use the "render" parameter, 6089 and MUST NOT appear before the first use of "render" in the parameter 6090 list. 6092 We define three token values for smf_info: "ignore", "sdp_start", and 6093 "identity": 6095 o The "ignore" value indicates that the SMFs MUST be discarded. 6096 This behavior is the default SMF rendering behavior. 6098 o The "sdp_start" value codes that SMFs MUST be rendered, 6099 and that the rendering MUST begin upon the acceptance of 6100 the session description. If a receiver is offered a session 6101 description with a renderer that uses an smf_info parameter 6102 set to sdp_start, and if the receiver does not support 6103 rendering SMFs, the receiver MUST NOT accept the renderer 6104 associated with the smf_info parameter. Options include 6105 rejecting the renderer (by setting the "render" parameter 6106 to "null"), the payload type, the media stream, or the 6107 entire session description. 6109 o The "identity" value indicates that the SMFs code the identity 6110 of the renderer. The value is meant for use with the 6111 "unknown" renderer (see Appendix C.6 preamble). The MIDI commands 6112 coded in the SMF are informational in nature and MUST NOT be 6113 presented to a renderer for audio presentation. In 6114 typical use, the SMF would use SysEx Identity Reply 6115 commands (F0 7E nn 06 02, as defined in [MIDI]) to identify 6116 devices, and use device-specific SysEx commands to describe 6117 current state of the devices (patch memory contents, etc.). 6119 Other smf_info token values MAY be registered with IANA. The token 6120 value MUST adhere to the ABNF for render tokens defined in Appendix D. 6121 Registrations MUST include a complete specification of parameter usage, 6122 similar in depth to the specifications that appear in this appendix for 6123 "sdp_start" and "identity". 6125 If a party is offered a session description that uses an smf_info 6126 parameter value that is not known to the party, the party MUST NOT 6127 accept the renderer associated with the smf_info parameter. Options 6128 include rejecting the renderer, the payload type, the media stream, or 6129 the entire session description. 6131 We now define the rendering semantics for the "sdp_start" token value in 6132 detail. 6134 The SMFs and RTP MIDI streams in a session description share the same 6135 MIDI name space(s). In the simple case of a single RTP MIDI stream and 6136 a single SMF, the SMF MIDI commands and RTP MIDI commands are merged 6137 into a single name space and presented to the renderer. The indefinite 6138 artifact responsibilities for merged MIDI streams defined in Appendix 6139 C.5 also apply to merging RTP and SMF MIDI data. 6141 If a payload type codes multiple SMFs, the SMF name spaces are presented 6142 as an ordered entity to the renderer. To determine the ordering of SMFs 6143 for a renderer (which SMF is "first", which is "second", etc.), use the 6144 following rules: 6146 o If the renderer uses a single data object, the order of 6147 appearance of the SMFs in the object's internal structure 6148 defines the order of the SMFs (the earliest SMF in the object 6149 is "first", the next SMF in the object is "second", etc.). 6151 o If multiple data objects are encoded for a renderer, the 6152 appearance of each data object in the parameter list 6153 sets the relative order of the SMFs encoded in each 6154 data object (SMFs encoded in parameters that appear 6155 earlier in the list are ordered before SMFs encoded 6156 in parameters that appear later in the list). 6158 o If SMFs are encoded in data objects parameters and in 6159 the parameters defined in C.6.4.2, the relative order 6160 of the data object parameters and C.6.4.2 parameters 6161 in the parameter list sets the relative order of SMFs 6162 (SMFs encoded in parameters that appear earlier in the 6163 list are ordered before SMFs in parameters that appear 6164 later in the list). 6166 Given this ordering of SMFs, we now define the mapping of SMFs to 6167 renderer name spaces. The SMF that appears first for a renderer maps to 6168 the first renderer name space. The SMF that appears second for a 6169 renderer maps to the second renderer name space, etc. If the associated 6170 RTP MIDI streams also form an ordered relationship, the first SMF is 6171 merged with the first name space of the relationship, the second SMF is 6172 merged to the second name space of the relationship, etc. 6174 Unless the streams and the SMFs both use MIDI Time Code, the time offset 6175 between SMF and stream data is unspecified. This restriction limits the 6176 use of SMFs to applications where synchronization is not critical, such 6177 as the transport of System Exclusive commands for renderer 6178 initialization, or human-SMF interactivity. 6180 Finally, we note that each SMF in the sdp_start discussion above encodes 6181 exactly one MIDI name space (16 voice channels + systems). Thus, the 6182 use of the Device Name SMF meta event to specify several MIDI name 6183 spaces in an SMF is not supported for sdp_start. 6185 C.6.4.2. The smf_inline, smf_url, and smf_cid Parameters 6187 In some applications, the renderer data object may not encapsulate SMFs, 6188 but an application may wish to use SMFs in the manner defined in 6189 Appendix C.6.4.1. 6191 The "smf_inline", "smf_url", and "smf_cid" parameters address this 6192 situation. These parameters use the syntax and semantics of the inline, 6193 url, and cid parameters defined in Appendix C.6.3, except that the 6194 encoded data object is an SMF. 6196 The "smf_inline", "smf_url", and "smf_cid" parameters belong to the 6197 "render" parameter that most recently precedes it in the session 6198 description. The "smf_inline", "smf_url", and "smf_cid" parameters MUST 6199 NOT appear in parameter lists that do not use the "render" parameter and 6200 MUST NOT appear before the first use of "render" in the parameter list. 6201 If several "smf_inline", "smf_url", or "smf_cid" parameters appear for a 6202 renderer, the order of the parameters defines the SMF name space 6203 ordering. 6205 C.6.4.3. The chanmask Parameter 6207 The chanmask parameter instructs the renderer to ignore all MIDI voice 6208 commands for certain channel numbers. The parameter value is a 6209 concatenated string of "1" and "0" digits. Each string position maps to 6210 a MIDI voice channel number (system channels may not be masked). A "1" 6211 instructs the renderer to process the voice channel; a "0" instructs the 6212 renderer to ignore the voice channel. 6214 The string length of the chanmask parameter value MUST be 16 (for a 6215 single stream or an identity relationship) or a multiple of 16 (for an 6216 ordered relationship). 6218 The chanmask parameter describes the "render" parameter that most 6219 recently precedes it in the session description; chanmask MUST NOT 6220 appear in parameter lists that do not use the "render" parameter and 6221 MUST NOT appear before the first use of "render" in the parameter list. 6223 The chanmask parameter describes the final MIDI name spaces presented to 6224 the renderer. The SMF and stream components of the MIDI name spaces may 6225 not be independently masked. 6227 If a receiver is offered a session description with a renderer that uses 6228 the chanmask parameter, and if the receiver does not implement the 6229 semantics of the chanmask parameter, the receiver MUST NOT accept the 6230 renderer unless the chanmask parameter value contains only "1"s. 6232 C.6.5. The audio/asc Media Type 6234 In Appendix 11.3, we register the audio/asc media type. The data object 6235 for audio/asc is a binary encoding of the AudioSpecificConfig data block 6236 used to initialize mpeg4-generic streams (Section 6.2 and [MPEGAUDIO]). 6238 An mpeg4-generic parameter list MAY use the render, subrender, and rinit 6239 parameters with the audio/asc media type for renderer configuration. 6240 Several restrictions apply to the use of these parameters in 6241 mpeg4-generic parameter lists: 6243 o An mpeg4-generic media description that uses the render parameter 6244 MUST assign the empty string ("") to the mpeg4-generic "config" 6245 parameter. The use of the streamtype, mode, and profile-level-id 6246 parameters MUST follow the normative text in Section 6.2. 6248 o Sessions that use identity or ordered relationships MUST follow 6249 the mpeg4-generic configuration restrictions in Appendix C.5. 6251 o The render parameter MUST be assigned the value "synthetic", 6252 "unknown", "null", or a render value that has been added to 6253 the IANA repository for use with mpeg4-generic RTP MIDI 6254 streams. The "api" token value for render MUST NOT be used. 6256 o If a subrender parameter is present, it MUST immediately follow 6257 the render parameter, and it MUST be assigned the token value 6258 "default" or assigned a subrender value added to the IANA 6259 repository for use with mpeg4-generic RTP MIDI streams. A 6260 subrender parameter assignment may be left out of the renderer 6261 configuration, in which case the implied value of subrender 6262 is the default value of "default". 6264 o If the render parameter is assigned the value "synthetic" 6265 and the subrender parameter has the value "default" (assigned 6266 or implied), the rinit parameter MUST be assigned the value 6267 "audio/asc", and an AudioSpecificConfig data object MUST be encoded 6268 using the mechanisms defined in C.6.2-3. The AudioSpecificConfig 6269 data MUST encode one of the MPEG 4 Audio Object Types defined for 6270 use with mpeg4-generic in Section 6.2. If the subrender value is 6271 other than "default", refer to the subrender registration 6272 for information on the use of "audio/asc" with the renderer. 6274 o If the render parameter is assigned the value "null" or 6275 "unknown", the data object MAY be omitted. 6277 Several general restrictions apply to the use of the audio/asc media 6278 type in RTP MIDI: 6280 o A native stream MUST NOT assign "audio/asc" to rinit. The 6281 audio/asc media type is not intended to be a general-purpose 6282 container for rendering systems outside of MPEG usage. 6284 o The audio/asc media type defines a stored object type; it does 6285 not define semantics for RTP streams. Thus, audio/asc MUST NOT 6286 appear on an rtpmap line of a session description. 6288 Below, we show session description examples for audio/asc. The session 6289 description below uses the inline parameter to code the 6290 AudioSpecificConfig block for a mpeg4-generic General MIDI stream. We 6291 derive the value assigned to the inline parameter in Appendix E.4. The 6292 subrender token value of "default" is implied by the absence of the 6293 subrender parameter in the parameter list. 6295 v=0 6296 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 6297 s=Example 6298 t=0 0 6299 m=audio 5004 RTP/AVP 96 6300 c=IN IP4 192.0.2.94 6301 a=rtpmap:96 mpeg4-generic/44100 6302 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6303 render=synthetic; rinit="audio/asc"; 6304 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6306 (The a=fmtp line has been wrapped to fit the page to accommodate 6307 memo formatting restrictions; it comprises a single line in SDP.) 6309 The session description below uses the url parameter to code the 6310 AudioSpecificConfig block for the same General MIDI stream: 6312 v=0 6313 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 6314 s=Example 6315 t=0 0 6316 m=audio 5004 RTP/AVP 96 6317 c=IN IP4 192.0.2.94 6318 a=rtpmap:96 mpeg4-generic/44100 6319 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6320 render=synthetic; rinit="audio/asc"; url="http://example.net/oski.asc"; 6321 cid="xjflsoeiurvpa09itnvlduihgnvet98pa3w9utnuighbuk" 6323 (The a=fmtp line has been wrapped to fit the page to accommodate 6324 memo formatting restrictions; it comprises a single line in SDP.) 6326 C.7. Interoperability 6328 In this appendix, we define interoperability guidelines for two 6329 application areas: 6331 o MIDI content-streaming applications. RTP MIDI is added to 6332 RTSP-based content-streaming servers, so that viewers may 6333 experience MIDI performances (produced by a specified client- 6334 side renderer) in synchronization with other streams (video, 6335 audio). 6337 o Long-distance network musical performance applications. RTP 6338 MIDI is added to SIP-based voice chat or videoconferencing 6339 programs, as an alternative, or as an addition, to audio and/or 6340 video RTP streams. 6342 For each application, we define a core set of functionality that all 6343 implementations MUST implement. 6345 The applications we address in this section are not an exhaustive list 6346 of potential RTP MIDI uses. We expect framework documents for other 6347 applications to be developed, within the IETF or within other 6348 organizations. We discuss other potential application areas for RTP 6349 MIDI in Section 1 of the main text of this memo. 6351 C.7.1. MIDI Content Streaming Applications 6353 In content-streaming applications, a user invokes an RTSP client to 6354 initiate a request to an RTSP server to view a multimedia session. For 6355 example, clicking on a web page link for an Internet Radio channel 6356 launches an RTSP client that uses the link's RTSP URL to contact the 6357 RTSP server hosting the radio channel. 6359 The content may be pre-recorded (for example, on-demand replay of 6360 yesterday's football game) or "live" (for example, football game 6361 coverage as it occurs), but in either case the user is usually an 6362 "audience member" as opposed to a "participant" (as the user would be in 6363 telephony). 6365 Note that these examples describe the distribution of audio content to 6366 an audience member. The interoperability guidelines in this appendix 6367 address RTP MIDI applications of this nature, not applications such as 6368 the transmission of raw MIDI command streams for use in a professional 6369 environment (recording studio, performance stage, etc.). 6371 In an RTSP session, a client accesses a session description that is 6372 "declared" by the server, either via the RTSP DESCRIBE method, or via 6373 other means, such as HTTP or email. The session description defines the 6374 session from the perspective of the client. For example, if a media 6375 line in the session description contains a non-zero port number, it 6376 encodes the server's preference for the client's port numbers for RTP 6377 and RTCP reception. Once media flow begins, the server sends an RTP 6378 MIDI stream to the client, which renders it for presentation, perhaps in 6379 synchrony with video or other audio streams. 6381 We now define the interoperability text for content-streaming RTSP 6382 applications. 6384 In most cases, server interoperability responsibilities are described in 6385 terms of limits on the "reference" session description a server provides 6386 for a performance if it has no information about the capabilities of the 6387 client. The reference session is a "lowest common denominator" session 6388 that maximizes the odds that a client will be able to view the session. 6389 If a server is aware of the capabilities of the client, the server is 6390 free to provide a session description customized for the client in the 6391 DESCRIBE reply. 6393 Clients MUST support unicast UDP RTP MIDI streams that use the recovery 6394 journal with the closed-loop or the anchor sending policies. Clients 6395 MUST be able to interpret stream subsetting and chapter inclusion 6396 parameters in the session description that qualify the sending policies. 6397 Client support of enhanced Chapter C encoding is OPTIONAL. 6399 The reference session description offered by a server MUST send all RTP 6400 MIDI UDP streams as unicast streams that use the recovery journal and 6401 the closed-loop or anchor sending policies. Servers SHOULD use the 6402 stream subsetting and chapter inclusion parameters in the reference 6403 session description, to simplify the rendering task of the client. 6404 Server support of enhanced Chapter C encoding is OPTIONAL. 6406 Clients and servers MUST support the use of RTSP interleaved mode (a 6407 method for interleaving RTP onto the RTSP TCP transport). 6409 Clients MUST be able to interpret the timestamp semantics signalled by 6410 the "comex" value of the tsmode parameter (i.e., the timestamp semantics 6411 of Standard MIDI Files [MIDI]). Servers MUST use the "comex" value for 6412 the "tsmode" parameter in the reference session description. 6414 Clients MUST be able to process an RTP MIDI stream whose packets encode 6415 an arbitrary temporal duration ("media time"). Thus, in practice, 6416 clients MUST implement a MIDI playout buffer. Clients MUST NOT depend 6417 on the presence of rtp_ptime, rtp_maxtime, and guardtime parameters in 6418 the session description in order to process packets, but they SHOULD be 6419 able to use these parameters to improve packet processing. 6421 Servers SHOULD strive to send RTP MIDI streams in the same way media 6422 servers send conventional audio streams: a sequence of packets that 6423 either all code the same temporal duration (non-normative example: 50 ms 6424 packets) or that code one of an integral number of temporal durations 6425 (non-normative example: 50 ms, 100 ms, 250 ms, or 500 ms packets). 6426 Servers SHOULD encode information about the packetization method in the 6427 rtp_ptime and rtp_maxtime parameters in the session description. 6429 Clients MUST be able to examine the render and subrender parameter, to 6430 determine if a multimedia session uses a renderer it supports. Clients 6431 MUST be able to interpret the default "one" value of the "multimode" 6432 parameter, to identify supported renderers from a list of renderer 6433 descriptions. Clients MUST be able to interpret the musicport 6434 parameter, to the degree that it is relevant to the renderers it 6435 supports. Clients MUST be able to interpret the chanmask parameter. 6437 Clients supporting renderers whose data object (as encoded by a 6438 parameter value for "inline") could exceed 300 octets in size MUST 6439 support the url and cid parameters and thus must implement the HTTP 6440 protocol in addition to RTSP. HTTP over TLS [RFC2818] support for data 6441 objects is OPTIONAL. 6443 Servers MUST specify complete rendering systems for RTP MIDI streams. 6444 Note that a minimal RTP MIDI native stream does not meet this 6445 requirement (Section 6.1), as the rendering method for such streams is 6446 "not specified". 6448 At the time of this memo, the only way for servers to specify a complete 6449 rendering system is to specify an mpeg4-generic RTP MIDI stream in mode 6450 rtp-midi (Section 6.2 and C.6.5). As a consequence, the only rendering 6451 systems that may be presently used are General MIDI [MIDI], DLS 2 6452 [DLS2], or Structured Audio [MPEGSA]. Note that the maximum inline 6453 value for General MIDI is well under 300 octets (and thus clients need 6454 not support the "url" parameter), and that the maximum inline values for 6455 DLS 2 and Structured Audio may be much larger than 300 octets (and thus 6456 clients MUST support the url parameter). 6458 We anticipate that the owners of rendering systems (both standardized 6459 and proprietary) will register subrender parameters for their renderers. 6460 Once registration occurs, native RTP MIDI sessions may use render and 6461 subrender (Appendix C.6.2) to specify complete rendering systems for 6462 RTSP content-streaming multimedia sessions. 6464 Servers MUST NOT use the sdp_start value for the smf_info parameter in 6465 the reference session description, as this use would require that 6466 clients be able to parse and render Standard MIDI Files. 6468 Clients MUST support mpeg4-generic mode rtp-midi General MIDI (GM) 6469 sessions, at a polyphony limited by the hardware capabilities of the 6470 client. This requirement provides a "lowest common denominator" 6471 rendering system for content providers to target. Note that this 6472 requirement does not force implementors of a non-GM renderer (such as 6473 DLS 2 or Structured Audio) to add a second rendering engine. Instead, a 6474 client may satisfy the requirement by including a set of voice patches 6475 that implement the GM instrument set, and using this emulation for 6476 mpeg4-generic GM sessions. 6478 It is RECOMMENDED that servers use General MIDI as the renderer for the 6479 reference session description, because clients are REQUIRED to support 6480 it. We do not require General MIDI as the reference renderer, because 6481 for normative applications it is an inappropriate choice. Servers using 6482 General MIDI as a "lowest common denominator" renderer SHOULD use 6483 Universal Real-Time SysEx MIP messages [SPMIDI] to communicate the 6484 priority of voices to polyphony-limited clients. 6486 C.7.2. MIDI Network Musical Performance Applications 6488 In Internet telephony and videoconferencing applications, parties 6489 interact over an IP network as they would face-to-face. Good user 6490 experiences require low end-to-end audio latency and tight audiovisual 6491 synchronization (for "lip-sync"). The Session Initiation Protocol (SIP, 6492 [RFC3261]) is used for session management. 6494 In this appendix section, we define interoperability guidelines for 6495 using RTP MIDI streams in interactive SIP applications. Our primary 6496 interest is supporting Network Musical Performances (NMP), where 6497 musicians in different locations interact over the network as if they 6498 were in the same room. See [NMP] for background information on NMP, and 6499 see [RFC4696] for a discussion of low-latency RTP MIDI implementation 6500 techniques for NMP. 6502 Note that the goal of NMP applications is telepresence: the parties 6503 should hear audio that is close to what they would hear if they were in 6504 the same room. The interoperability guidelines in this appendix address 6505 RTP MIDI applications of this nature, not applications such as the 6506 transmission of raw MIDI command streams for use in a professional 6507 environment (recording studio, performance stage, etc.). 6509 We focus on session management for two-party unicast sessions that 6510 specify a renderer for RTP MIDI streams. Within this limited scope, the 6511 guidelines defined here are sufficient to let applications interoperate. 6512 We define the REQUIRED capabilities of RTP MIDI senders and receivers in 6513 NMP sessions and define how session descriptions exchanged are used to 6514 set up network musical performance sessions. 6516 SIP lets parties negotiate details of the session, using the 6517 Offer/Answer protocol [RFC3264]. However, RTP MIDI has so many 6518 parameters that "blind" negotiations between two parties using different 6519 applications might not yield a common session configuration. 6521 Thus, we now define a set of capabilities that NMP parties MUST support. 6522 Session description offers whose options lie outside the envelope of 6523 REQUIRED party behavior risk negotiation failure. We also define 6524 session description idioms that the RTP MIDI part of an offer MUST 6525 follow, in order to structure the offer for simpler analysis. 6527 We use the term "offerer" for the party making a SIP offer, and 6528 "answerer" for the party answering the offer. Finally, we note that 6529 unless it is qualified by the adjective "sender" or "receiver", a 6530 statement that a party MUST support X implies that it MUST support X for 6531 both sending and receiving. 6533 If an offerer wishes to define a "sendrecv" RTP MIDI stream, it may use 6534 a true sendrecv session or the "virtual sendrecv" construction described 6535 in the preamble to Appendix C and in Appendix C.5. A true sendrecv 6536 session indicates that the offerer wishes to participate in a session 6537 where both parties use identically configured renderers. A virtual 6538 sendrecv session indicates that the offerer is willing to participate in 6539 a session where the two parties may be using different renderer 6540 configurations. Thus, parties MUST be prepared to see both real and 6541 virtual sendrecv sessions in an offer. 6543 Parties MUST support unicast UDP transport of RTP MIDI streams. These 6544 streams MUST use the recovery journal with the closed-loop or anchor 6545 sending policies. These streams MUST use the stream subsetting and 6546 chapter inclusion parameters to declare the types of MIDI commands that 6547 will be sent on the stream (for sendonly streams) or will be processed 6548 (for recvonly streams), including the size limits on System Exclusive 6549 commands. Support of enhanced Chapter C encoding is OPTIONAL. 6551 Note that both TCP and multicast UDP support are OPTIONAL. We make TCP 6552 OPTIONAL because we expect NMP renderers to rely on data objects 6553 (signalled by "rinit" and associated parameters) for initialization at 6554 the start of the session, and only to use System Exclusive commands for 6555 interactive control during the session. These interactive commands are 6556 small enough to be protected via the recovery journal mechanism of RTP 6557 MIDI UDP streams. 6559 We now discuss timestamps, packet timing, and packet sending algorithms. 6561 Recall that the tsmode parameter controls the semantics of command 6562 timestamps in the MIDI list of RTP packets. 6564 Parties MUST support clock rates of 44.1 kHz, 48 kHz, 88.2 kHz, and 96 6565 kHz. Parties MUST support streams using the "comex", "async", and 6566 "buffer" tsmode values. Recvonly offers MUST offer the default "comex". 6568 Parties MUST support a wide range of packet temporal durations: from 6569 rtp_ptime and rtp_maxptime values of 0, to rtp_ptime and rtp_maxptime 6570 values that code 100 ms. Thus, receivers MUST be able to implement a 6571 playout buffer. 6573 Offers and answers MUST present rtp_ptime, rtp_maxptime, and guardtime 6574 values that support the latency that users would expect in the 6575 application, subject to bandwidth constraints. As senders MUST abide by 6576 values set for these parameters in a session description, a receiver 6577 SHOULD use these values to size its playout buffer to produce the lowest 6578 reliable latency for a session. Implementers should refer to [RFC4696] 6579 for information on packet sending algorithms for latency-sensitive 6580 applications. Parties MUST be able to implement the semantics of the 6581 guardtime parameter, for times from 5 ms to 5000 ms. 6583 We now discuss the use of the render parameter. 6585 Sessions MUST specify complete rendering systems for all RTP MIDI 6586 streams. Note that a minimal RTP MIDI native stream does not meet this 6587 requirement (Section 6.1), as the rendering method for such streams is 6588 "not specified". 6590 At the time this writing, the only way for parties to specify a complete 6591 rendering system is to specify an mpeg4-generic RTP MIDI stream in mode 6592 rtp-midi (Section 6.2 and C.6.5). We anticipate that the owners of 6593 rendering systems (both standardized and proprietary) will register 6594 subrender values for their renderers. Once IANA registration occurs, 6595 native RTP MIDI sessions may use render and subrender (Appendix C.6.2) 6596 to specify complete rendering systems for SIP network musical 6597 performance multimedia sessions. 6599 All parties MUST support General MIDI (GM) sessions, at a polyphony 6600 limited by the hardware capabilities of the party. This requirement 6601 provides a "lowest common denominator" rendering system, without which 6602 practical interoperability will be quite difficult. When using GM, 6603 parties SHOULD use Universal Real-Time SysEx MIP messages [SPMIDI] to 6604 communicate the priority of voices to polyphony-limited clients. 6606 Note that this requirement does not force implementors of a non-GM 6607 renderer (for mpeg4-generic sessions, DLS 2, or Structured Audio) to add 6608 a second rendering engine. Instead, a client may satisfy the 6609 requirement by including a set of voice patches that implement the GM 6610 instrument set, and using this emulation for mpeg4-generic GM sessions. 6611 We require GM support so that an offerer that wishes to maximize 6612 interoperability may do so by offering GM if its preferred renderer is 6613 not accepted by the answerer. 6615 Offerers MUST NOT present several renderers as options in a session 6616 description by listing several payload types on a media line, as Section 6617 2.1 uses this construct to let a party send several RTP MIDI streams in 6618 the same RTP session. 6620 Instead, an offerer wishing to present rendering options SHOULD offer a 6621 single payload type that offers several renderers. In this construct, 6622 the parameter list codes a list of render parameters (each followed by 6623 its support parameters). As discussed in Appendix C.6.1, the order of 6624 renderers in the list declares the offerer's preference. The "unknown" 6625 and "null" values MUST NOT appear in the offer. The answer MUST set all 6626 render values except the desired renderer to "null". Thus, "unknown" 6627 MUST NOT appear in the answer. 6629 We use SHOULD instead of MUST in the first sentence in the paragraph 6630 above, because this technique does not work in all situations (example: 6631 an offerer wishes to offer both mpeg4-generic renderers and native RTP 6632 MIDI renderers as options). In this case, the offerer MUST present a 6633 series of session descriptions, each offering a single renderer, until 6634 the answerer accepts a session description. 6636 Parties MUST support the musicport, chanmask, subrender, rinit, and 6637 inline parameters. Parties supporting renderers whose data object (as 6638 encoded by a parameter value for "inline") could exceed 300 octets in 6639 size MUST support the url and cid parameters and thus must implement the 6640 HTTP protocol. HTTP over TLS [RFC2818] support for data objects is 6641 OPTIONAL. Note that in mpeg4-generic, General MIDI data objects cannot 6642 exceed 300 octets, but DLS 2 and Structured Audio data objects may. 6643 Support for the other rendering parameters (smf_cif, smf_info, 6644 smf_inline, smf_url) is OPTIONAL. 6646 Thus far in this document, our discussion has assumed that the only MIDI 6647 flows that drive a renderer are the network flows described in the 6648 session description. In NMP applications, this assumption would require 6649 two rendering engines: one for local use by a party, a second for the 6650 remote party. 6652 In practice, applications may wish to have both parties share a single 6653 rendering engine. In this case, the session description MUST use a 6654 virtual sendrecv session and MUST use the stream subsetting and chapter 6655 inclusion parameters to allocate which MIDI channels are intended for 6656 use by a party. If two parties are sharing a MIDI channel, the 6657 application MUST ensure that appropriate MIDI merging occurs at the 6658 input to the renderer. 6660 We now discuss the use of (non-MIDI) audio streams in the session. 6662 Audio streams may be used for two purposes: as a "talkback" channel for 6663 parties to converse, or as a way to conduct a performance that includes 6664 MIDI and audio channels. In the latter case, offers MUST use sample 6665 rates and the packet temporal durations for the audio and MIDI streams 6666 that support low-latency synchronized rendering. 6668 We now show an example of an offer/answer exchange in a network musical 6669 performance application (next page). 6671 Below, we show an offer that complies with the interoperability text in 6672 this appendix section. 6674 v=0 6675 o=first 2520644554 2838152170 IN IP4 first.example.net 6676 s=Example 6677 t=0 0 6678 a=group:FID 1 2 6679 c=IN IP4 192.0.2.94 6680 m=audio 16112 RTP/AVP 96 6681 a=recvonly 6682 a=mid:1 6683 a=rtpmap:96 mpeg4-generic/44100 6684 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6685 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=2NPTW; 6686 cm_used=2C0.1.7.10.11.64.121.123; cm_used=2M0.1.2; 6687 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6688 ch_default=2NPTW; ch_default=2C0.1.7.10.11.64.121.123; 6689 ch_default=2M0.1.2; cm_default=X0-16; 6690 rtp_ptime=0; rtp_maxptime=0; guardtime=44100; 6691 musicport=1; render=synthetic; rinit="audio/asc"; 6692 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6693 m=audio 16114 RTP/AVP 96 6694 a=sendonly 6695 a=mid:2 6696 a=rtpmap:96 mpeg4-generic/44100 6697 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6698 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=1NPTW; 6699 cm_used=1C0.1.7.10.11.64.121.123; cm_used=1M0.1.2; 6700 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6701 ch_default=1NPTW; ch_default=1C0.1.7.10.11.64.121.123; 6702 ch_default=1M0.1.2; cm_default=X0-16; 6703 rtp_ptime=0; rtp_maxptime=0; guardtime=44100; 6704 musicport=1; render=synthetic; rinit="audio/asc"; 6705 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6707 (The a=fmtp lines have been wrapped to fit the page to accommodate 6708 memo formatting restrictions; it comprises a single line in SDP.) 6710 The owner line (o=) identifies the session owner as "first". 6712 The session description defines two MIDI streams: a recvonly stream on 6713 which "first" receives a performance, and a sendonly stream that "first" 6714 uses to send a performance. The recvonly port number encodes the ports 6715 on which "first" wishes to receive RTP (16112) and RTCP (16113) media at 6716 IP4 address 192.0.2.94. The sendonly port number encodes the port on 6717 which "first" wishes to receive RTCP for the stream (16115). 6719 The musicport parameters code that the two streams share and identity 6720 relationship and thus form a virtual sendrecv stream. 6722 Both streams are mpeg4-generic RTP MIDI streams that specify a General 6723 MIDI renderer. The stream subsetting parameters code that the recvonly 6724 stream uses MIDI channel 1 exclusively for voice commands, and that the 6725 sendonly stream uses MIDI channel 2 exclusively for voice commands. 6726 This mapping permits the application software to share a single renderer 6727 for local and remote performers. 6729 We now show the answer to the offer. 6731 v=0 6732 o=second 2520644554 2838152170 IN IP4 second.example.net 6733 s=Example 6734 t=0 0 6735 a=group:FID 1 2 6736 c=IN IP4 192.0.2.105 6737 m=audio 5004 RTP/AVP 96 6738 a=sendonly 6739 a=mid:1 6740 a=rtpmap:96 mpeg4-generic/44100 6741 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6742 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=2NPTW; 6743 cm_used=2C0.1.7.10.11.64.121.123; cm_used=2M0.1.2; 6744 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6745 ch_default=2NPTW; ch_default=2C0.1.7.10.11.64.121.123; 6746 ch_default=2M0.1.2; cm_default=X0-16; 6747 rtp_ptime=0; rtp_maxptime=882; guardtime=44100; 6748 musicport=1; render=synthetic; rinit="audio/asc"; 6749 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6750 m=audio 5006 RTP/AVP 96 6751 a=recvonly 6752 a=mid:2 6753 a=rtpmap:96 mpeg4-generic/44100 6754 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6755 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=1NPTW; 6756 cm_used=1C0.1.7.10.11.64.121.123; cm_used=1M0.1.2; 6757 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6758 ch_default=1NPTW; ch_default=1C0.1.7.10.11.64.121.123; 6759 ch_default=1M0.1.2; cm_default=X0-16; 6760 rtp_ptime=0; rtp_maxptime=0; guardtime=88200; 6761 musicport=1; render=synthetic; rinit="audio/asc"; 6762 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6764 (The a=fmtp lines have been wrapped to fit the page to accommodate 6765 memo formatting restrictions; they comprise single lines in SDP.) 6767 The owner line (o=) identifies the session owner as "second". 6769 The port numbers for both media streams are non-zero; thus, "second" has 6770 accepted the session description. The stream marked "sendonly" in the 6771 offer is marked "recvonly" in the answer, and vice versa, coding the 6772 different view of the session held by "session". The IP4 number 6773 (192.0.2.105) and the RTP (5004 and 5006) and RTCP (5005 and 5007) have 6774 been changed by "second" to match its transport wishes. 6776 In addition, "second" has made several parameter changes: rtp_maxptime 6777 for the sendonly stream has been changed to code 2 ms (441 in clock 6778 units), and the guardtime for the recvonly stream has been doubled. As 6779 these parameter modifications request capabilities that are REQUIRED to 6780 be implemented by interoperable parties, "second" can make these changes 6781 with confidence that "first" can abide by them. 6783 D. Parameter Syntax Definitions 6785 In this appendix, we define the syntax for the RTP MIDI media type 6786 parameters in Augmented Backus-Naur Form (ABNF, [RFC5234]). When using 6787 these parameters with SDP, all parameters MUST appear on a single fmtp 6788 attribute line of an RTP MIDI media description. For mpeg4-generic RTP 6789 MIDI streams, this line MUST also include any mpeg4-generic parameters 6790 (usage described in Section 6.2). An fmtp attribute line may be defined 6791 (after [RFC3640]) as: 6793 ; 6794 ; SDP fmtp line definition 6795 ; 6797 fmtp = "a=fmtp:" token SP param-assign 0*(";" SP param-assign) CRLF 6799 where codes the RTP payload type. Note that white space MUST 6800 NOT appear between the "a=fmtp:" and the RTP payload type. 6802 We now define the syntax of the parameters defined in Appendix C. The 6803 definition takes the form of the incremental assembly of the token. See [RFC3640] for the syntax of the mpeg4-generic 6805 parameters discussed in Section 6.2. 6807 ; 6808 ; 6809 ; top-level definition for all parameters 6810 ; 6811 ; 6813 ; 6814 ; Parameters defined in Appendix C.1 6816 param-assign = ("cm_unused=" (([channel-list] command-type 6817 [f-list]) / sysex-data)) 6819 param-assign =/ ("cm_used=" (([channel-list] command-type 6820 [f-list]) / sysex-data)) 6822 ; 6823 ; Parameters defined in Appendix C.2 6825 param-assign =/ ("j_sec=" ("none" / "recj" / ietf-extension)) 6827 param-assign =/ ("j_update=" ("anchor" / "closed-loop" / 6828 "open-loop" / ietf-extension)) 6830 param-assign =/ ("ch_default=" (([channel-list] chapter-list 6831 [f-list]) / sysex-data)) 6833 param-assign =/ ("ch_never=" (([channel-list] chapter-list 6834 [f-list]) / sysex-data)) 6836 param-assign =/ ("ch_anchor=" (([channel-list] chapter-list 6837 [f-list]) / sysex-data)) 6839 ; 6840 ; Parameters defined in Appendix C.3 6842 param-assign =/ ("tsmode=" ("comex" / "async" / "buffer")) 6844 param-assign =/ ("linerate=" nonzero-four-octet) 6846 param-assign =/ ("octpos=" ("first" / "last")) 6848 param-assign =/ ("mperiod=" nonzero-four-octet) 6850 ; 6851 ; Parameter defined in Appendix C.4 6853 param-assign =/ ("guardtime=" nonzero-four-octet) 6855 param-assign =/ ("rtp_ptime=" four-octet) 6857 param-assign =/ ("rtp_maxptime=" four-octet) 6859 ; 6860 ; Parameters defined in Appendix C.5 6862 param-assign =/ ("musicport=" four-octet) 6864 ; 6865 ; Parameters defined in Appendix C.6 6867 param-assign =/ ("chanmask=" 1*( 16(BIT) )) 6869 param-assign =/ ("cid=" DQUOTE cid-block DQUOTE) 6871 param-assign =/ ("inline=" DQUOTE base-64-block DQUOTE) 6873 param-assign =/ ("multimode=" ("all" / "one")) 6875 param-assign =/ ("render=" ("synthetic" / "api" / "null" / 6876 "unknown" / extension)) 6878 param-assign =/ ("rinit=" mime-type "/" mime-subtype) 6880 param-assign =/ ("smf_cid=" DQUOTE cid-block DQUOTE) 6882 param-assign =/ ("smf_info=" ("ignore" / "identity" / 6883 "sdp_start" / extension)) 6885 param-assign =/ ("smf_inline=" DQUOTE base-64-block DQUOTE) 6887 param-assign =/ ("smf_url=" DQUOTE uri-element DQUOTE) 6889 param-assign =/ ("subrender=" ("default" / extension)) 6891 param-assign =/ ("url=" DQUOTE uri-element DQUOTE) 6893 ; 6894 ; list definitions for the cm_ command-type 6895 ; 6897 command-type = [A] [B] [C] [F] [G] [H] [J] [K] [M] 6898 [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 6900 ; 6901 ; list definitions for the ch_ chapter-list 6902 ; 6904 chapter-list = [A] [B] [C] [D] [E] [F] [G] [H] [J] [K] 6905 [M] [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 6907 ; 6908 ; list definitions for the channel-list (used in ch_* / cm_* params) 6909 ; 6911 channel-list = midi-chan-element *("." midi-chan-element) 6913 midi-chan-element = midi-chan / midi-chan-range 6915 midi-chan-range = midi-chan "-" midi-chan 6916 ; 6917 ; decimal value of left midi-chan 6918 ; MUST be strictly less than 6919 ; decimal value of right midi-chan 6921 midi-chan = DIGIT / ("1" %x30-35) ; "0" .. "15" 6922 ; 6923 ; list definitions for the ch_ field list (f-list) 6924 ; 6926 f-list = midi-field-element *("." midi-field-element) 6928 midi-field-element = midi-field / midi-field-range 6930 midi-field-range = midi-field "-" midi-field 6931 ; 6932 ; decimal value of left midi-field 6933 ; MUST be strictly less than 6934 ; decimal value of right midi-field 6936 midi-field = four-octet 6937 ; 6938 ; large range accommodates Chapter M 6939 ; RPN (0-16383) and NRPN (16384-32767) 6940 ; parameters, and Chapter X octet sizes. 6942 ; 6943 ; definitions for ch_ sysex-data 6944 ; 6946 sysex-data = "__" h-list *("_" h-list) "__" 6948 h-list = hex-field-element *("." hex-field-element) 6950 hex-field-element = hex-octet / hex-field-range 6952 hex-field-range = hex-octet "-" hex-octet 6953 ; 6954 ; hexadecimal value of left hex-octet 6955 ; MUST be strictly less than hexadecimal 6956 ; value of right hex-octet 6958 hex-octet = %x30-37 U-HEXDIG 6959 ; 6960 ; rewritten special case of hex-octet in [RFC2045] 6961 ; (page 23). 6962 ; note that a-f are not permitted, only A-F. 6963 ; hex-octet values MUST NOT exceed 0x7F. 6965 ; 6966 ; definitions for rinit parameter 6967 ; 6969 mime-type = "audio" / "application" 6970 mime-subtype = token 6971 ; 6972 ; See Appendix C.6.2 for registration 6973 ; requirements for rinit type/subtypes. 6975 ; 6976 ; definitions for base64 encoding 6977 ; copied from [RFC4566] 6978 ; changes from [RFC4566] to improve automatic syntax checking 6979 ; 6981 base-64-block = *base64-unit [base64-pad] 6983 base64-unit = 4(base64-char) 6985 base64-pad = (2(base64-char) "==") / (3(base64-char) "=") 6987 base64-char = %x41-5A / %x61-7A / %x30-39 / "+" / "/" 6988 ; A-Z, a-z, 0-9, "+" and "/" 6990 ; 6991 ; generic rules 6992 ; 6994 ietf-extension = token 6995 ; 6996 ; may only be defined in standards-track RFCs 6998 extension = token 6999 ; 7000 ; may be defined 7001 ; by filing a registration with IANA 7003 nonzero-four-octet = (NZ-DIGIT 0*8(DIGIT)) 7004 / (%x30-33 9(DIGIT)) 7005 / ("4" %x30-31 8(DIGIT)) 7006 / ("42" %x30-38 7(DIGIT)) 7007 / ("429" %x30-33 6(DIGIT)) 7008 / ("4294" %x30-38 5(DIGIT)) 7009 / ("42949" %x30-35 4(DIGIT)) 7010 / ("429496" %x30-36 3(DIGIT)) 7011 / ("4294967" %x30-31 2(DIGIT)) 7012 / ("42949672" %x30-38 (DIGIT)) 7013 / ("429496729" %x30-34) 7014 ; 7015 ; unsigned encoding of non-zero 32-bit value: 7016 ; 1 .. 4294967295 7018 four-octet = "0" / nonzero-four-octet 7019 ; 7020 ; unsigned encoding of 32-bit value: 7021 ; 0 .. 4294967295 7023 uri-element = URI-reference 7024 ; as defined in [RFC3986] 7026 token = 1*token-char 7027 ; copied from [RFC4566] 7029 token-char = %x21 / %x23-27 / %x2A-2B / %x2D-2E / 7030 %x30-39 / %x41-5A / %x5E-7E 7031 ; copied from [RFC4566] 7033 cid-block = 1*cid-char 7035 cid-char = token-char 7036 cid-char =/ "@" 7037 cid-char =/ "," 7038 cid-char =/ ";" 7039 cid-char =/ ":" 7040 cid-char =/ "\" 7041 cid-char =/ "/" 7042 cid-char =/ "[" 7043 cid-char =/ "]" 7044 cid-char =/ "?" 7045 cid-char =/ "=" 7046 ; 7047 ; - add back in the tspecials [RFC2045], except 7048 ; for DQUOTE and the non-email safe ( ) < > 7049 ; - note that the definitions above ensure that 7050 ; cid-block is always enclosed with DQUOTEs 7052 A = %x41 ; uppercase only letters used above 7053 B = %x42 7054 C = %x43 7055 D = %x44 7056 E = %x45 7057 F = %x46 7058 G = %x47 7059 H = %x48 7060 J = %x4A 7061 K = %x4B 7062 M = %x4D 7063 N = %x4E 7064 P = %x50 7065 Q = %x51 7066 T = %x54 7067 V = %x56 7068 W = %x57 7069 X = %x58 7070 Y = %x59 7071 Z = %x5A 7073 NZ-DIGIT = %x31-39 ; non-zero decimal digit 7075 U-HEXDIG = DIGIT / A / B / C / D / E / F 7076 ; variant of HEXDIG [RFC5234] : 7077 ; hexadecimal digit using uppercase A-F only 7079 ; the rules below are from the Core Rules from [RFC5234] 7081 BIT = "0" / "1" 7083 DQUOTE = %x22 ; " (Double Quote) 7085 DIGIT = %x30-39 ; 0-9 7087 ; external references 7088 ; URI-reference: from [RFC3986] 7090 ; 7091 ; End of ABNF 7093 The mpeg4-generic RTP payload [RFC3640] defines a "mode" parameter that 7094 signals the type of MPEG stream in use. We add a new mode value, "rtp- 7095 midi", using the ABNF rule below: 7097 ; 7098 ; mpeg4-generic mode parameter extension 7099 ; 7101 mode =/ "rtp-midi" 7102 ; as described in Section 6.2 of this memo 7104 E. A MIDI Overview for Networking Specialists 7106 This appendix presents an overview of the MIDI standard, for the benefit 7107 of networking specialists new to musical applications. Implementors 7108 should consult [MIDI] for a normative description of MIDI. 7110 Musicians make music by performing a controlled sequence of physical 7111 movements. For example, a pianist plays by coordinating a series of key 7112 presses, key releases, and pedal actions. MIDI represents a musical 7113 performance by encoding these physical gestures as a sequence of MIDI 7114 commands. This high-level musical representation is compact but 7115 fragile: one lost command may be catastrophic to the performance. 7117 MIDI commands have much in common with the machine instructions of a 7118 microprocessor. MIDI commands are defined as binary elements. 7119 Bitfields within a MIDI command have a regular structure and a 7120 specialized purpose. For example, the upper nibble of the first command 7121 octet (the opcode field) codes the command type. MIDI commands may 7122 consist of an arbitrary number of complete octets, but most MIDI 7123 commands are 1, 2, or 3 octets in length. 7125 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7126 | Channel Voice Messages | Bitfield Pattern | 7127 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7128 | NoteOff (end a note) | 1000cccc 0nnnnnnn 0vvvvvvv | 7129 |-------------------------------------------------------------| 7130 | NoteOn (start a note) | 1001cccc 0nnnnnnn 0vvvvvvv | 7131 |-------------------------------------------------------------| 7132 | PTouch (Polyphonic Aftertouch) | 1010cccc 0nnnnnnn 0aaaaaaa | 7133 |-------------------------------------------------------------| 7134 | CControl (Controller Change) | 1011cccc 0xxxxxxx 0yyyyyyy | 7135 |-------------------------------------------------------------| 7136 | PChange (Program Change) | 1100cccc 0ppppppp | 7137 |-------------------------------------------------------------| 7138 | CTouch (Channel Aftertouch) | 1101cccc 0aaaaaaa | 7139 |-------------------------------------------------------------| 7140 | PWheel (Pitch Wheel) | 1110cccc 0xxxxxxx 0yyyyyyy | 7141 ------------------------------------------------------------- 7143 Figure E.1 -- MIDI Channel Messages 7145 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7146 | System Common Messages | Bitfield Pattern | 7147 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7148 | System Exclusive | 11110000, followed by a | 7149 | | list of 0xxxxxx octets, | 7150 | | followed by 11110111 | 7151 |-------------------------------------------------------------| 7152 | MIDI Time Code Quarter Frame | 11110001 0xxxxxxx | 7153 |-------------------------------------------------------------| 7154 | Song Position Pointer | 11110010 0xxxxxxx 0yyyyyyy | 7155 |-------------------------------------------------------------| 7156 | Song Select | 11110011 0xxxxxxx | 7157 |-------------------------------------------------------------| 7158 | Undefined | 11110100 | 7159 |-------------------------------------------------------------| 7160 | Undefined | 11110101 | 7161 |-------------------------------------------------------------| 7162 | Tune Request | 11110110 | 7163 |-------------------------------------------------------------| 7164 | System Exclusive End Marker | 11110111 | 7165 ------------------------------------------------------------- 7167 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7168 | System Realtime Messages | Bitfield Pattern | 7169 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7170 | Clock | 11111000 | 7171 |-------------------------------------------------------------| 7172 | Undefined | 11111001 | 7173 |-------------------------------------------------------------| 7174 | Start | 11111010 | 7175 |-------------------------------------------------------------| 7176 | Continue | 11111011 | 7177 |-------------------------------------------------------------| 7178 | Stop | 11111100 | 7179 |-------------------------------------------------------------| 7180 | Undefined | 11111101 | 7181 |-------------------------------------------------------------| 7182 | Active Sense | 11111110 | 7183 |-------------------------------------------------------------| 7184 | System Reset | 11111111 | 7185 ------------------------------------------------------------- 7187 Figure E.2 -- MIDI System Messages 7189 Figure E.1 and E.2 show the MIDI command family. There are three major 7190 classes of commands: voice commands (opcode field values in the range 7191 0x8 through 0xE), system common commands (opcode field 0xF, commands 7192 0xF0 through 0xF7), and system real-time commands (opcode field 0xF, 7193 commands 0xF8 through 0xFF). Voice commands code the musical gestures 7194 for each timbre in a composition. Systems commands perform functions 7195 that usually affect all voice channels, such as System Reset (0xFF). 7197 E.1. Commands Types 7199 Voice commands execute on one of 16 MIDI channels, as coded by its 4-bit 7200 channel field (field cccc in Figure E.1). In most applications, notes 7201 for different timbres are assigned to different channels. To support 7202 applications that require more than 16 channels, MIDI systems use 7203 several MIDI command streams in parallel, to yield 32, 48, or 64 MIDI 7204 channels. 7206 As an example of a voice command, consider a NoteOn command (opcode 7207 0x9), with binary encoding 1001cccc 0nnnnnnn 0aaaaaaa. This command 7208 signals the start of a musical note on MIDI channel cccc. The note has 7209 a pitch coded by the note number nnnnnnn, and an onset amplitude coded 7210 by note velocity aaaaaaa. 7212 Other voice commands signal the end of notes (NoteOff, opcode 0x8), map 7213 a specific timbre to a MIDI channel (PChange, opcode 0xC), or set the 7214 value of parameters that modulate the timbral quality (all other voice 7215 commands). The exact meaning of most voice channel commands depends on 7216 the rendering algorithms the MIDI receiver uses to generate sound. In 7217 most applications, a MIDI sender has a model (in some sense) of the 7218 rendering method used by the receiver. 7220 System commands perform a variety of global tasks in the stream, 7221 including "sequencer" playback control of pre-recorded MIDI commands 7222 (the Song Position Pointer, Song Select, Clock, Start, Continue, and 7223 Stop messages), SMPTE time code (the MIDI Time Code Quarter Frame 7224 command), and the communication of device-specific data (the System 7225 Exclusive messages). 7227 E.2. Running Status 7229 All MIDI command bitfields share a special structure: the leading bit of 7230 the first octet is set to 1, and the leading bit of all subsequent 7231 octets is set to 0. This structure supports a data compression system, 7232 called running status [MIDI], that improves the coding efficiency of 7233 MIDI. 7235 In running status coding, the first octet of a MIDI voice command may be 7236 dropped if it is identical to the first octet of the previous MIDI voice 7237 command. This rule, in combination with a convention to consider NoteOn 7238 commands with a null third octet as NoteOff commands, supports the 7239 coding of note sequences using two octets per command. 7241 Running status coding is only used for voice commands. The presence of 7242 a system common message in the stream cancels running status mode for 7243 the next voice command. However, system real-time messages do not 7244 cancel running status mode. 7246 E.3. Command Timing 7248 The bitfield formats in Figures E.1 and E.2 do not encode the execution 7249 time for a command. Timing information is not a part of the MIDI 7250 command syntax itself; different applications of the MIDI command 7251 language use different methods to encode timing. 7253 For example, the MIDI command set acts as the transport layer for MIDI 7254 1.0 DIN cables [MIDI]. MIDI cables are short asynchronous serial lines 7255 that facilitate the remote operation of musical instruments and audio 7256 equipment. Timestamps are not sent over a MIDI 1.0 DIN cable. Instead, 7257 the standard uses an implicit "time of arrival" code. Receivers execute 7258 MIDI commands at the moment of arrival. 7260 In contrast, Standard MIDI Files (SMFs, [MIDI]), a file format for 7261 representing complete musical performances, add an explicit timestamp to 7262 each MIDI command, using a delta encoding scheme that is optimized for 7263 statistics of musical performance. SMF timestamps usually code timing 7264 using the metric notation of a musical score. SMF meta-events are used 7265 to add a tempo map to the file, so that score beats may be accurately 7266 converted into units of seconds during rendering. 7268 E.4. AudioSpecificConfig Templates for MMA Renderers 7270 In Section 6.2 and Appendix C.6.5, we describe how session descriptions 7271 include an AudioSpecificConfig data block to specify a MIDI rendering 7272 algorithm for mpeg4-generic RTP MIDI streams. 7274 The bitfield format of AudioSpecificConfig is defined in [MPEGAUDIO]. 7275 StructuredAudioSpecificConfig, a key data structure coded in 7276 AudioSpecificConfig, is defined in [MPEGSA]. 7278 For implementors wishing to specify Structured Audio renderers, a full 7279 understanding of [MPEGSA] and [MPEGAUDIO] is essential. However, many 7280 implementors will limit their rendering options to the two MIDI 7281 Manufacturers Association renderers that may be specified in 7282 AudioSpecificConfig: General MIDI (GM, [MIDI]) and Downloadable Sounds 2 7283 (DLS 2, [DLS2]). 7285 To aid these implementors, we reproduce the AudioSpecificConfig bitfield 7286 formats for a GM renderer and a DLS 2 renderer below. We have checked 7287 these bitfields carefully and believe they are correct. However, we 7288 stress that the material below is informative, and that [MPEGAUDIO] and 7289 [MPEGSA] are the normative definitions for AudioSpecificConfig. 7291 As described in Section 6.2, a minimal mpeg4-generic session description 7292 encodes the AudioSpecificConfig binary bitfield as a hexadecimal string 7293 (whose format is defined in [RFC3640]) that is assigned to the "config" 7294 parameter. As described in Appendix C.6.3, a session description that 7295 uses the render parameter encodes the AudioSpecificConfig binary 7296 bitfield as a Base64-encoded string assigned to the "inline" parameter, 7297 or in the body of an HTTP URL assigned to the "url" parameter. 7299 Below, we show a simplified binary AudioSpecificConfig bitfield format, 7300 suitable for sending and receiving GM and DLS 2 data: 7302 0 1 2 3 7303 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 7304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7305 | AOTYPE |FREQIDX|CHANNEL|SACNK| FILE_BLK 1 (required) ... | 7306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7307 |1|SACNK| FILE_BLK 2 (optional) ... | 7308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7309 | ... |1|SACNK| FILE_BLK N (optional) ... | 7310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7311 |0|0| (first "0" bit terminates FILE_BLK list) 7312 +-+-+ 7314 Figure E.3 -- Simplified AudioSpecificConfig 7316 The 5-bit AOTYPE field specifies the Audio Object Type as an unsigned 7317 integer. The legal values for use with mpeg4-generic RTP MIDI streams 7318 are "15" (General MIDI), "14" (DLS 2), and "13" (Structured Audio). 7319 Thus, receivers that do not support all three mpeg4-generic renderers 7320 may parse the first 5 bits of an AudioSpecificConfig coded in a session 7321 description and reject sessions that specify unsupported renderers. 7323 The 4-bit FREQIDX field specifies the sampling rate of the renderer. We 7324 show the mapping of FREQIDX values to sampling rates in Figure E.4. 7325 Senders MUST specify a sampling frequency that matches the RTP clock 7326 rate, if possible; if not, senders MUST specify the escape value. 7327 Receivers MUST consult the RTP clock parameter for the true sampling 7328 rate if the escape value is specified. 7330 FREQIDX Sampling Frequency 7332 0x0 96000 7333 0x1 88200 7334 0x2 64000 7335 0x3 48000 7336 0x4 44100 7337 0x5 32000 7338 0x6 24000 7339 0x7 22050 7340 0x8 16000 7341 0x9 12000 7342 0xa 11025 7343 0xb 8000 7344 0xc reserved 7345 0xd reserved 7346 0xe reserved 7347 0xf escape value 7349 Figure E.4 -- FreqIdx encoding 7351 The 4-bit CHANNEL field specifies the number of audio channels for the 7352 renderer. The values 0x1 to 0x5 specify 1 to 5 audio channels; the 7353 value 0x6 specifies 5+1 surround sound, and the value 0x7 specifies 7+1 7354 surround sound. If the rtpmap line in the session description specifies 7355 one of these formats, CHANNEL MUST be set to the corresponding value. 7356 Otherwise, CHANNEL MUST be set to 0x0. 7358 The CHANNEL field is followed by a list of one or more binary file data 7359 blocks. The 3-bit SACNK field (the chunk_type field in class 7360 StructuredAudioSpecificConfig, defined in [MPEGSA]) specifies the type 7361 of each data block. 7363 For General MIDI, only Standard MIDI Files may appear in the list (SACNK 7364 field value 2). For DLS 2, only Standard MIDI Files and DLS 2 RIFF 7365 files (SACNK field value 4) may appear. For both of these file types, 7366 the FILE_BLK field has the format shown in Figure E.5: a 32-bit unsigned 7367 integer value (FILE_LEN) coding the number of bytes in the SMF or RIFF 7368 file, followed by FILE_LEN bytes coding the file data. 7370 0 1 2 3 7371 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 7372 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7373 | FILE_LEN (32-bit, a byte count SMF file or RIFF file) | 7374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7375 | FILE_DATA (file contents, a list of FILE_LEN bytes) ... | 7376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7378 Figure E.5 -- The FILE_BLK field format 7380 Note that several files may follow the CHANNEL field. The "1" constant 7381 fields in Figure E.3 code the presence of another file; the "0" constant 7382 field codes the end of the list. The final "0" bit in Figure E.3 codes 7383 the absence of special coding tools (see [MPEGAUDIO] for details). 7384 Senders not using these tools MUST append this "0" bit; receivers that 7385 do not understand these coding tools MUST ignore all data following a 7386 "1" in this position. 7388 The StructuredAudioSpecificConfig bitfield structure requires the 7389 presence of one FILE_BLK. For mpeg4-generic RTP MIDI use of DLS 2, 7390 FILE_BLKs MUST code RIFF files or SMF files. For mpeg4-generic RTP MIDI 7391 use of General MIDI, FILE_BLKs MUST code SMF files. By default, this 7392 SMF will be ignored (Appendix C.6.4.1). In this default case, a GM 7393 StructuredAudioSpecificConfig bitfield SHOULD code a FILE_BLK whose 7394 FILE_LEN is 0, and whose FILE_DATA is empty. 7396 To complete this appendix, we derive the StructuredAudioSpecificConfig 7397 that we use in the General MIDI session examples in this memo. 7398 Referring to Figure E.3, we note that for GM, AOTYPE = 15. Our examples 7399 use a 44,100 Hz sample rate (FREQIDX = 4) and are in mono (CHANNEL = 1). 7400 For GM, a single SMF is encoded (SACNK = 2), using the SMF shown in 7401 Figure E.6 (a 26 byte file). 7403 -------------------------------------------- 7404 | MIDI File =
| 7405 -------------------------------------------- 7407
= 7408 4D 54 68 64 00 00 00 06 00 00 00 01 00 60 7410 = 7411 4D 54 72 6B 00 00 00 04 00 FF 2F 00 7413 Figure E.6 -- SMF file encoded in the example 7415 Placing these constants in binary format into the data structure shown 7416 in Figure E.3 yields the constant shown in Figure E.7. 7418 0 1 2 3 7419 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 7420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7421 |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| 7422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7423 |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| 7424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7425 |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| 7426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7427 |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| 7428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7429 |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| 7430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7431 |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| 7432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7433 |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| 7434 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7435 |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| 7436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7437 |0|0| 7438 +-+-+ 7440 Figure E.7 -- AudioSpecificConfig used in GM examples 7442 Expressing this bitfield as an ASCII hexadecimal string yields: 7444 7A0A0000001A4D546864000000060000000100604D54726B0000000600FF2F000 7446 This string is assigned to the "config" parameter in the minimal 7447 mpeg4-generic General MIDI examples in this memo (such as the example in 7448 Section 6.2). Expressing this string in Base64 [RFC2045] yields: 7450 egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA 7452 This string is assigned to the "inline" parameter in the General MIDI 7453 example shown in Appendix C.6.5. 7455 References 7457 Normative References 7459 [MIDI] MIDI Manufacturers Association. "The Complete MIDI 1.0 7460 Detailed Specification", 1996. 7462 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 7463 Jacobson, "RTP: A Transport Protocol for Real-Time 7464 Applications", STD 64, RFC 3550, July 2003. 7466 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 7467 Video Conferences with Minimal Control", STD 65, RFC 7468 3551, July 2003. 7470 [RFC3640] van der Meer, J., Mackie, D., Swaminathan, V., Singer, 7471 D., and P. Gentric, "RTP Payload Format for Transport of 7472 MPEG-4 Elementary Streams", RFC 3640, November 2003. 7474 [MPEGSA] International Standards Organization. "ISO/IEC 14496 7475 MPEG-4", Part 3 (Audio), Subpart 5 (Structured Audio), 7476 2001. 7478 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 7479 Description Protocol", RFC 4566, July 2006. 7481 [MPEGAUDIO] International Standards Organization. "ISO 14496 MPEG- 7482 4", Part 3 (Audio), 2001. 7484 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 7485 Extensions (MIME) Part One: Format of Internet Message 7486 Bodies", RFC 2045, November 1996. 7488 [DLS2] MIDI Manufacturers Association. "The MIDI Downloadable 7489 Sounds Specification", v98.2, 1998. 7491 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 7492 Specifications: ABNF", RFC 5234, January 2008. 7494 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 7495 Requirement Levels", BCP 14, RFC 2119, March 1997. 7497 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 7498 Norrman, "The Secure Real-time Transport Protocol 7499 (SRTP)", RFC 3711, March 2004. 7501 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 7502 with Session Description Protocol (SDP)", RFC 3264, June 7503 2002. 7505 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 7506 Resource Identifier (URI): Generic Syntax", STD 66, RFC 7507 3986, January 2005. 7509 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 7510 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 7511 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 7513 [RFC3388] Camarillo, G., Eriksson, G., Holler, J., and H. 7514 Schulzrinne, "Grouping of Media Lines in the Session 7515 Description Protocol (SDP)", RFC 3388, December 2002. 7517 [RP015] MIDI Manufacturers Association. "Recommended Practice 7518 015 (RP-015): Response to Reset All Controllers", 11/98. 7520 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 7521 Registration Procedures", BCP 13, RFC 4288, December 7522 2005. 7524 [RFC4855] Casner, S., "MIME Type Registration of RTP 7525 Payload Formats", RFC 4855, February 2007. 7527 Informative References 7529 [NMP] Lazzaro, J. and J. Wawrzynek. "A Case for Network 7530 Musical Performance", 11th International Workshop on 7531 Network and Operating Systems Support for Digital Audio 7532 and Video (NOSSDAV 2001) June 25-26, 2001, Port 7533 Jefferson, New York. 7535 [GRAME] Fober, D., Orlarey, Y. and S. Letz. "Real Time Musical 7536 Events Streaming over Internet", Proceedings of the 7537 International Conference on WEB Delivering of Music 2001, 7538 pages 147-154. 7540 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 7541 A., Peterson, J., Sparks, R., Handley, M., and E. 7542 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 7543 June 2002. 7545 [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time 7546 Streaming Protocol (RTSP)", RFC 2326, April 1998. 7548 [ALF] Clark, D. D. and D. L. Tennenhouse. "Architectural 7549 considerations for a new generation of protocols", 7550 SIGCOMM Symposium on Communications Architectures and 7551 Protocols , (Philadelphia, Pennsylvania), pp. 200--208, 7552 ACM, Sept. 1990. 7554 [RFC4696] Lazzaro, J. and J. Wawrzynek, "An Implementation Guide 7555 for RTP MIDI", RFC 4696, November 2006. 7557 [RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S., and S. 7558 Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 7559 Functional Specification", RFC 2205, September 1997. 7561 [RFC4571] Lazzaro, J. "Framing Real-time Transport Protocol (RTP) 7562 and RTP Control Protocol (RTCP) Packets over Connection- 7563 Oriented Transport", RFC 4571, July 2006. 7565 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 7567 [SPMIDI] MIDI Manufacturers Association. "Scalable Polyphony 7568 MIDI, Specification and Device Profiles", Document 7569 Version 1.0a, 2002. 7571 [LCP] Apple Computer. "Logic 7 Dedicated Control Surface 7572 Support", Appendix B. Product manual available from 7573 www.apple.com. 7575 Authors' Addresses 7577 John Lazzaro (corresponding author) 7578 UC Berkeley 7579 CS Division 7580 315 Soda Hall 7581 Berkeley CA 94720-1776 7582 EMail: lazzaro@cs.berkeley.edu 7584 John Wawrzynek 7585 UC Berkeley 7586 CS Division 7587 631 Soda Hall 7588 Berkeley CA 94720-1776 7589 EMail: johnw@cs.berkeley.edu 7591 Full Copyright Statement 7593 Copyright (c) 2010 IETF Trust and the persons identified as the 7594 document authors. All rights reserved. 7596 This document is subject to BCP 78 and the IETF Trust's Legal Provisions 7597 Relating to IETF Documents (http://trustee.ietf.org/license-info) 7598 in effect on the date of publication of this document. Please 7599 review these documents carefully, as they describe your rights and 7600 restrictions with respect to this document. Code Components 7601 extracted from this document must include Simplified BSD License 7602 text as described in Section 4.e of the Trust Legal Provisions and 7603 are provided without warranty as described in the Simplified BSD 7604 License. 7606 Copyright (c) 2010 IETF Trust and the persons identified as the 7607 document authors. All rights reserved. 7609 Acknowledgement 7611 Funding for the RFC Editor function is currently provided by the 7612 Internet Society. 7614 Change Log for 7616 This I-D is a modified version of RFC 4695. For every error found to 7617 date in RFC 4695, the I-D has been modified to fix the error. 7619 Below, we list the errors found in RFC 4695 that are most likely to 7620 confuse implementors. The fixes to Appendix D ABNF errors listed 7621 below are presented without comments; see Appendix D to see the 7622 commented rule in context. The list below includes the fixes for all 7623 normative errors; most fixes for other types of errors are not listed. 7624 However, the I-D itself contains fixes for all known errors. 7626 -- 7628 03-08.txt changes: 7630 No errata has been reported for RFC 4695 in the past year. 7631 Apart from updates in the document name and expiration dates, 7632 03-08.txt contains no changes from 02.txt 7634 -- 7636 02.txt changes: 7638 No errata has been reported for RFC 4695 in the past six months. 7639 Apart from updates in the document name and expiration dates, 7640 02.txt contains no changes from 01.txt 7642 -- 7644 01.txt changes: 7646 A typo was fixed in the Appendix D ABNF. P and Q are now 7647 correctly defined as: 7649 P = %x50 7650 Q = %x51 7652 Thanks to Alfred Hoenes for these changes. 7654 -- 7656 00.txt changes: 7658 Thanks to Alfred Hoenes for these changes. 7660 [1] In Appendix C.1 and Appendix C.2.3 of RFC 4695, an ABNF rule 7661 related to System Chapter X is incorrectly defined as: 7663 = "__" ["_" ] "__" 7665 The correct version of this rule is: 7667 = "__" *( "_" ) "__" 7669 [2] In Appendix C.6.3 of RFC 4695, the URIs permitted to be assigned 7670 to the "url" parameter are not stated clearly. URIs assigned to "url" 7671 MUST specify either HTTP or HTTP over TLS transport protocols. 7673 In Appendix C.7.1 and C.7.2 of RFC 4695, the transport 7674 interoperability requirements for the "url" parameter are not stated 7675 clearly. For both C.7.1 and C.7.2, HTTP is REQUIRED and HTTP over TLS 7676 is OPTIONAL. 7678 [3] Both fmtp lines in both session description examples in Appendix 7679 C.7.2 of RFC 4695 contain instances of the same syntax error (a 7680 missing ";" at a line wrap after "cm_used=2M0.1.2"). 7682 [4] In Appendix D of RFC 4695, all uses of "*ietf-extension" in rules 7683 are in error, and should be replaced with "ietf-extension". Likewise, 7684 all uses of "*extension" are in error, and should be replaced with 7685 "extension". This bug incorrectly lets the null token be assigned to 7686 the j_sec, j_update, render, smf_info, and subrender parameters. 7688 [5] In Appendix D of RFC 4695, the definitions of the 7689 and incorrectly allow lowercase letters to appear in 7690 these strings. The correct definitions of these rules appear below: 7692 command-type = [A] [B] [C] [F] [G] [H] [J] [K] [M] 7693 [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 7695 chapter-list = [A] [B] [C] [D] [E] [F] [G] [H] [J] [K] 7696 [M] [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 7698 A = %x41 7699 B = %x42 7700 C = %x43 7701 D = %x44 7702 E = %x45 7703 F = %x46 7704 G = %x47 7705 H = %x48 7706 J = %x4A 7707 K = %x4B 7708 M = %x4D 7709 N = %x4E 7710 P = %x50 ; correct as shown, these values were 7711 Q = %x51 ; incorrect in the -00.txt I-D version 7712 T = %x54 7713 V = %x56 7714 W = %x57 7715 X = %x58 7716 Y = %x59 7717 Z = %x5A 7719 [5] In Appendix D of RFC 4695, the definitions of the , 7720 , and are incorrect. The correct 7721 definitions of these rules appear below: 7723 nonzero-four-octet = (NZ-DIGIT 0*8(DIGIT)) 7724 / (%x30-33 9(DIGIT)) 7725 / ("4" %x30-31 8(DIGIT)) 7726 / ("42" %x30-38 7(DIGIT)) 7727 / ("429" %x30-33 6(DIGIT)) 7728 / ("4294" %x30-38 5(DIGIT)) 7729 / ("42949" %x30-35 4(DIGIT)) 7730 / ("429496" %x30-36 3(DIGIT)) 7731 / ("4294967" %x30-31 2(DIGIT)) 7732 / ("42949672" %x30-38 (DIGIT)) 7733 / ("429496729" %x30-34) 7735 four-octet = "0" / nonzero-four-octet 7736 midi-chan = DIGIT / ("1" %x30-35) 7738 DIGIT = %x30-39 7739 NZ-DIGIT = %x31-39 7741 [6] In Appendix D of RFC4695, the rule is 7742 incorrect. The correct definition of this rule appears below. 7744 hex-octet = %x30-37 U-HEXDIG 7745 U-HEXDIG = DIGIT / A / B / C / D / E / F 7747 ; DIGIT as defined in [5] above 7748 ; A, B, C, D, E, F as defined in [4] above 7750 [7] In Appendix D of RFC4695, the rules and 7751 are defined unclearly. The rewritten rules 7752 appear below: 7754 base64-unit = 4(base64-char) 7755 base64-pad = (2(base64-char) "==") / (3(base64-char) "=") 7757 ---