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'MIDI' -- Possible downref: Non-RFC (?) normative reference: ref. 'MPEGSA' ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) -- Possible downref: Non-RFC (?) normative reference: ref. 'MPEGAUDIO' -- Possible downref: Non-RFC (?) normative reference: ref. 'DLS2' ** Obsolete normative reference: RFC 2616 (Obsoleted by RFC 7230, RFC 7231, RFC 7232, RFC 7233, RFC 7234, RFC 7235) ** Obsolete normative reference: RFC 3388 (Obsoleted by RFC 5888) -- Possible downref: Non-RFC (?) normative reference: ref. 'RP015' ** Obsolete normative reference: RFC 4288 (Obsoleted by RFC 6838) -- Obsolete informational reference (is this intentional?): RFC 2326 (Obsoleted by RFC 7826) -- Obsolete informational reference (is this intentional?): RFC 2818 (Obsoleted by RFC 9110) Summary: 5 errors (**), 0 flaws (~~), 2 warnings (==), 17 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT J. Lazzaro 3 August 10, 2009 J. Wawrzynek 4 Expires: February 10, 2010 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 February 10, 2010. 33 Copyright Notice 35 Copyright (c) 2009 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents in effect on the date of 40 publication of this document (http://trustee.ietf.org/license-info). 41 Please review these documents carefully, as they describe your rights 42 and restrictions with respect to this document. 44 Abstract 46 This memo describes a Real-time Transport Protocol (RTP) payload 47 format for the MIDI (Musical Instrument Digital Interface) command 48 language. The format encodes all commands that may legally appear on 49 a MIDI 1.0 DIN cable. The format is suitable for interactive 50 applications (such as network musical performance) and content- 51 delivery applications (such as file streaming). The format may be 52 used over unicast and multicast UDP and TCP, and it defines tools for 53 graceful recovery from packet loss. Stream behavior, including the 54 MIDI rendering method, may be customized during session setup. The 55 format also serves as a mode for the mpeg4-generic format, to support 56 the MPEG 4 Audio Object Types for General MIDI, Downloadable Sounds 57 Level 2, and Structured Audio. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 5 62 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 63 1.2. Bitfield Conventions . . . . . . . . . . . . . . . . . . . 6 64 2. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . . . 7 65 2.1. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 7 66 2.2. MIDI Payload . . . . . . . . . . . . . . . . . . . . . . . 12 67 3. MIDI Command Section . . . . . . . . . . . . . . . . . . . . . . 14 68 3.1. Timestamps . . . . . . . . . . . . . . . . . . . . . . . . 15 69 3.2. Command Coding . . . . . . . . . . . . . . . . . . . . . . 17 70 4. The Recovery Journal System . . . . . . . . . . . . . . . . . . . 24 71 5. Recovery Journal Format . . . . . . . . . . . . . . . . . . . . . 26 72 6. Session Description Protocol . . . . . . . . . . . . . . . . . . 30 73 6.1. Session Descriptions for Native Streams . . . . . . . . . 31 74 6.2. Session Descriptions for mpeg4-generic Streams . . . . . . 33 75 6.3. Parameters . . . . . . . . . . . . . . . . . . . . . . . . 35 76 7. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . . . 37 77 8. Congestion Control . . . . . . . . . . . . . . . . . . . . . . . 38 78 9. Security Considerations . . . . . . . . . . . . . . . . . . . . . 39 79 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 40 80 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 40 81 11.1. rtp-midi Media Type Registration . . . . . . . . . . . . 41 82 11.1.1. Repository Request for "audio/rtp-midi" . . . . . 43 83 11.2. mpeg4-generic Media Type Registration . . . . . . . . . . 45 84 11.2.1. Repository Request for Mode rtp-midi for 85 mpeg4-generic . . . . . . . . . . . . . . . . . . 48 86 11.3. asc Media Type Registration . . . . . . . . . . . . . . . 49 87 A. The Recovery Journal Channel Chapters . . . . . . . . . . . . . . 52 88 A.1. Recovery Journal Definitions . . . . . . . . . . . . . . . 52 89 A.2. Chapter P: MIDI Program Change . . . . . . . . . . . . . . 57 90 A.3. Chapter C: MIDI Control Change . . . . . . . . . . . . . . 58 91 A.3.1. Log Inclusion Rules . . . . . . . . . . . . . . . . 58 92 A.3.2. Controller Log Format . . . . . . . . . . . . . . . 60 93 A.3.3. Log List Coding Rules . . . . . . . . . . . . . . . 62 94 A.3.4. The Parameter System . . . . . . . . . . . . . . . 65 95 A.4. Chapter M: MIDI Parameter System . . . . . . . . . . . . . 67 96 A.4.1. Log Inclusion Rules . . . . . . . . . . . . . . . . 68 97 A.4.2. Log Coding Rules . . . . . . . . . . . . . . . . . 70 98 A.4.2.1. The Value Tool . . . . . . . . . . . . . . . 71 99 A.4.2.2. The Count Tool . . . . . . . . . . . . . . . 75 100 A.5. Chapter W: MIDI Pitch Wheel . . . . . . . . . . . . . . . 76 101 A.6. Chapter N: MIDI NoteOff and NoteOn . . . . . . . . . . . . 77 102 A.6.1. Header Structure . . . . . . . . . . . . . . . . . 78 103 A.6.2. Note Structures . . . . . . . . . . . . . . . . . . 79 104 A.7. Chapter E: MIDI Note Command Extras . . . . . . . . . . . 81 105 A.7.1. Note Log Format . . . . . . . . . . . . . . . . . . 82 106 A.7.2. Log Inclusion Rules . . . . . . . . . . . . . . . . 82 107 A.8. Chapter T: MIDI Channel Aftertouch . . . . . . . . . . . . 83 108 A.9. Chapter A: MIDI Poly Aftertouch . . . . . . . . . . . . . 84 109 B. The Recovery Journal System Chapters . . . . . . . . . . . . . . 86 110 B.1. System Chapter D: Simple System Commands . . . . . . . . . 86 111 B.1.1. Undefined System Commands . . . . . . . . . . 87 112 B.2. System Chapter V: Active Sense Command . . . . . . . . . . 90 113 B.3. System Chapter Q: Sequencer State Commands . . . . . . . . 91 114 B.3.1. Non-compliant Sequencers . . . . . . . . . . . 93 115 B.4. System Chapter F: MIDI Time Code Tape Position . . . . . . 94 116 B.4.1. Partial Frames . . . . . . . . . . . . . . . . . . 96 117 B.5. System Chapter X: System Exclusive . . . . . . . . . . . . 98 118 B.5.1. Chapter Format . . . . . . . . . . . . . . . . 98 119 B.5.2. Log Inclusion Semantics . . . . . . . . . . . 101 120 B.5.3. TCOUNT and COUNT Fields . . . . . . . . . . . 103 121 C. Session Configuration Tools . . . . . . . . . . . . . . . . . . . 105 122 C.1. Configuration Tools: Stream Subsetting . . . . . . . . . . 106 123 C.2. Configuration Tools: The Journalling System . . . . . . . 110 124 C.2.1. The j_sec Parameter . . . . . . . . . . . . . . . . 111 125 C.2.2. The j_update Parameter . . . . . . . . . . . . . . 112 126 C.2.2.1. The anchor Sending Policy . . . . . . . . . 113 127 C.2.2.2. The closed-loop Sending Policy . . . . . . . 113 128 C.2.2.3. The open-loop Sending Policy . . . . . . . . 117 129 C.2.3. Recovery Journal Chapter Inclusion Parameters . . . 119 130 C.3. Configuration Tools: Timestamp Semantics . . . . . . . . . 124 131 C.3.1. The comex Algorithm . . . . . . . . . . . . . . . . 124 132 C.3.2. The async Algorithm . . . . . . . . . . . . . . . . 125 133 C.3.3. The buffer Algorithm . . . . . . . . . . . . . . . 126 134 C.4. Configuration Tools: Packet Timing Tools . . . . . . . . . 128 135 C.4.1. Packet Duration Tools . . . . . . . . . . . . . . . 128 136 C.4.2. The guardtime Parameter . . . . . . . . . . . . . . 129 137 C.5. Configuration Tools: Stream Description . . . . . . . . . 131 138 C.6. Configuration Tools: MIDI Rendering . . . . . . . . . . . 137 139 C.6.1. The multimode Parameter . . . . . . . . . . . . . . 138 140 C.6.2. Renderer Specification . . . . . . . . . . . . . . 138 141 C.6.3. Renderer Initialization . . . . . . . . . . . . . . 141 142 C.6.4. MIDI Channel Mapping . . . . . . . . . . . . . . . 143 143 C.6.4.1. The smf_info Parameter . . . . . . . . . . . 143 144 C.6.4.2. The smf_inline, smf_url, and smf_cid 145 Parameters . . . . . . . . . . . . . . . . . 145 146 C.6.4.3. The chanmask Parameter . . . . . . . . . . . 146 147 C.6.5. The audio/asc Media Type . . . . . . . . . . . . . 147 148 C.7. Interoperability . . . . . . . . . . . . . . . . . . . . . 149 149 C.7.1. MIDI Content Streaming Applications . . . . . . . 149 150 C.7.2. MIDI Network Musical Performance Applications . . . 152 151 D. Parameter Syntax Definitions . . . . . . . . . . . . . . . . . . 161 152 E. A MIDI Overview for Networking Specialists . . . . . . . . . . . 168 153 E.1. Commands Types . . . . . . . . . . . . . . . . . . . . . . 170 154 E.2. Running Status . . . . . . . . . . . . . . . . . . . . . . 170 155 E.3. Command Timing . . . . . . . . . . . . . . . . . . . . . . 171 156 E.4. AudioSpecificConfig Templates for MMA Renderers . . . . . 171 157 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 158 Normative References . . . . . . . . . . . . . . . . . . . . . 176 159 Informative References . . . . . . . . . . . . . . . . . . . . 177 160 Change Log for . . . . . . . . . 180 161 1. Introduction 163 The Internet Engineering Task Force (IETF) has developed a set of 164 focused tools for multimedia networking ([RFC3550] [RFC4566] [RFC3261] 165 [RFC2326]). These tools can be combined in different ways to support a 166 variety of real-time applications over Internet Protocol (IP) networks. 168 For example, a telephony application might use the Session Initiation 169 Protocol (SIP, [RFC3261]) to set up a phone call. Call setup would 170 include negotiations to agree on a common audio codec [RFC3264]. 171 Negotiations would use the Session Description Protocol (SDP, [RFC4566]) 172 to describe candidate codecs. 174 After a call is set up, audio data would flow between the parties using 175 the Real Time Protocol (RTP, [RFC3550]) under any applicable profile 176 (for example, the Audio/Visual Profile (AVP, [RFC3551])). The tools 177 used in this telephony example (SIP, SDP, RTP) might be combined in a 178 different way to support a content streaming application, perhaps in 179 conjunction with other tools, such as the Real Time Streaming Protocol 180 (RTSP, [RFC2326]). 182 The MIDI (Musical Instrument Digital Interface) command language [MIDI] 183 is widely used in musical applications that are analogous to the 184 examples described above. On stage and in the recording studio, MIDI is 185 used for the interactive remote control of musical instruments, an 186 application similar in spirit to telephony. On web pages, Standard MIDI 187 Files (SMFs, [MIDI]) rendered using the General MIDI standard [MIDI] 188 provide a low-bandwidth substitute for audio streaming. 190 This memo is motivated by a simple premise: if MIDI performances could 191 be sent as RTP streams that are managed by IETF session tools, a 192 hybridization of the MIDI and IETF application domains may occur. 194 For example, interoperable MIDI networking may foster network music 195 performance applications, in which a group of musicians, located at 196 different physical locations, interact over a network to perform as they 197 would if they were located in the same room [NMP]. As a second example, 198 the streaming community may begin to use MIDI for low- bitrate audio 199 coding, perhaps in conjunction with normative sound synthesis methods 200 [MPEGSA]. 202 To enable MIDI applications to use RTP, this memo defines an RTP payload 203 format and its media type. Sections 2-5 and Appendices A-B define the 204 RTP payload format. Section 6 and Appendices C-D define the media types 205 identifying the payload format, the parameters needed for configuration, 206 and how the parameters are utilized in SDP. 208 Appendix C also includes interoperability guidelines for the example 209 applications described above: network musical performance using SIP 210 (Appendix C.7.2) and content-streaming using RTSP (Appendix C.7.1). 212 Another potential application area for RTP MIDI is MIDI networking for 213 professional audio equipment and electronic musical instruments. We do 214 not offer interoperability guidelines for this application in this memo. 215 However, RTP MIDI has been designed with stage and studio applications 216 in mind, and we expect that efforts to define a stage and studio 217 framework will rely on RTP MIDI for MIDI transport services. 219 Some applications may require MIDI media delivery at a certain service 220 quality level (latency, jitter, packet loss, etc). RTP itself does not 221 provide service guarantees. However, applications may use lower-layer 222 network protocols to configure the quality of the transport services 223 that RTP uses. These protocols may act to reserve network resources for 224 RTP flows [RFC2205] or may simply direct RTP traffic onto a dedicated 225 "media network" in a local installation. Note that RTP and the MIDI 226 payload format do provide tools that applications may use to achieve the 227 best possible real-time performance at a given service level. 229 This memo normatively defines the syntax and semantics of the MIDI 230 payload format. However, this memo does not define algorithms for 231 sending and receiving packets. An ancillary document [RFC4696] provides 232 informative guidance on algorithms. Supplemental information may be 233 found in related conference publications [NMP] [GRAME]. 235 Throughout this memo, the phrase "native stream" refers to a stream that 236 uses the rtp-midi media type. The phrase "mpeg4-generic stream" refers 237 to a stream that uses the mpeg4-generic media type (in mode rtp-midi) to 238 operate in an MPEG 4 environment [RFC3640]. Section 6 describes this 239 distinction in detail. 241 1.1. Terminology 243 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 244 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 245 document are to be interpreted as described in BCP 14, RFC 2119 246 [RFC2119]. 248 1.2. Bitfield Conventions 250 In this document, the packet bitfields that share a common name often 251 have identical semantics. As most of these bitfields appear in 252 Appendices A-B, we define the common bitfield names in Appendix A.1. 254 However, a few of these common names also appear in the main text of 255 this document. For convenience, we list these definitions below: 257 o R flag bit. R flag bits are reserved for future use. Senders 258 MUST set R bits to 0. Receivers MUST ignore R bit values. 260 o LENGTH field. All fields named LENGTH (as distinct from LEN) 261 code the number of octets in the structure that contains it, 262 including the header it resides in and all hierarchical levels 263 below it. If a structure contains a LENGTH field, a receiver 264 MUST use the LENGTH field value to advance past the structure 265 during parsing, rather than use knowledge about the internal 266 format of the structure. 268 2. Packet Format 270 In this section, we introduce the format of RTP MIDI packets. The 271 description includes some background information on RTP, for the benefit 272 of MIDI implementors new to IETF tools. Implementors should consult 273 [RFC3550] for an authoritative description of RTP. 275 This memo assumes that the reader is familiar with MIDI syntax and 276 semantics. Appendix E provides a MIDI overview, at a level of detail 277 sufficient to understand most of this memo. Implementors should consult 278 [MIDI] for an authoritative description of MIDI. 280 The MIDI payload format maps a MIDI command stream (16 voice channels + 281 systems) onto an RTP stream. An RTP media stream is a sequence of 282 logical packets that share a common format. Each packet consists of two 283 parts: the RTP header and the MIDI payload. Figure 1 shows this format 284 (vertical space delineates the header and payload). 286 We describe RTP packets as "logical" packets to highlight the fact that 287 RTP itself is not a network-layer protocol. Instead, RTP packets are 288 mapped onto network protocols (such as unicast UDP, multicast UDP, or 289 TCP) by an application [ALF]. The interleaved mode of the Real Time 290 Streaming Protocol (RTSP, [RFC2326]) is an example of an RTP mapping to 291 TCP transport, as is [RFC4571]. 293 2.1. RTP Header 295 [RFC3550] provides a complete description of the RTP header fields. In 296 this section, we clarify the role of a few RTP header fields for MIDI 297 applications. All fields are coded in network byte order (big- endian). 299 0 1 2 3 300 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 1 301 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 302 | V |P|X| CC |M| PT | Sequence number | 303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 304 | Timestamp | 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 | SSRC | 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 | MIDI command section ... | 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 | Journal section ... | 313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 315 Figure 1 -- Packet format 317 The behavior of the 1-bit M field depends on the media type of the 318 stream. For native streams, the M bit MUST be set to 1 if the MIDI 319 command section has a non-zero LEN field, and MUST be set to 0 320 otherwise. For mpeg4-generic streams, the M bit MUST be set to 1 for 321 all packets (to conform to [RFC3640]). 323 In an RTP MIDI stream, the 16-bit sequence number field is initialized 324 to a randomly chosen value and is incremented by one (modulo 2^16) for 325 each packet sent in the stream. A related quantity, the 32-bit extended 326 packet sequence number, may be computed by tracking rollovers of the 327 16-bit sequence number. Note that different receivers of the same 328 stream may compute different extended packet sequence numbers, depending 329 on when the receiver joined the session. 331 The 32-bit timestamp field sets the base timestamp value for the packet. 332 The payload codes MIDI command timing relative to this value. The 333 timestamp units are set by the clock rate parameter. For example, if 334 the clock rate has a value of 44100 Hz, two packets whose base timestamp 335 values differ by 2 seconds have RTP timestamp fields that differ by 336 88200. 338 Note that the clock rate parameter is not encoded within each RTP MIDI 339 packet. A receiver of an RTP MIDI stream becomes aware of the clock 340 rate as part of the session setup process. For example, if a session 341 management tool uses the Session Description Protocol (SDP, [RFC4566]) 342 to describe a media session, the clock rate parameter is set using the 343 rtpmap attribute. We show examples of session setup in Section 6. 345 For RTP MIDI streams destined to be rendered into audio, the clock rate 346 SHOULD be an audio sample rate of 32 KHz or higher. This recommendation 347 is due to the sensitivity of human musical perception to small timing 348 errors in musical note sequences, and due to the timbral changes that 349 occur when two near-simultaneous MIDI NoteOns are rendered with a 350 different timing than that desired by the content author due to clock 351 rate quantization. RTP MIDI streams that are not destined for audio 352 rendering (such as MIDI streams that control stage lighting) MAY use a 353 lower clock rate but SHOULD use a clock rate high enough to avoid timing 354 artifacts in the application. 356 For RTP MIDI streams destined to be rendered into audio, the clock rate 357 SHOULD be chosen from rates in common use in professional audio 358 applications or in consumer audio distribution. At the time of this 359 writing, these rates include 32 KHz, 44.1 KHz, 48 KHz, 64 KHz, 88.2 KHz, 360 96 KHz, 176.4 KHz, and 192 KHz. If the RTP MIDI session is a part of a 361 synchronized media session that includes another (non-MIDI) RTP audio 362 stream with a clock rate of 32 KHz or higher, the RTP MIDI stream SHOULD 363 use a clock rate that matches the clock rate of the other audio stream. 364 However, if the RTP MIDI stream is destined to be rendered into audio, 365 the RTP MIDI stream SHOULD NOT use a clock rate lower than 32 KHz, even 366 if this second stream has a clock rate less than 32 KHz. 368 Timestamps of consecutive packets do not necessarily increment at a 369 fixed rate, because RTP MIDI packets are not necessarily sent at a fixed 370 rate. The degree of packet transmission regularity reflects the 371 underlying application dynamics. Interactive applications may vary the 372 packet sending rate to track the gestural rate of a human performer, 373 whereas content-streaming applications may send packets at a fixed rate. 375 Therefore, the timestamps for two sequential RTP packets may be 376 identical, or the second packet may have a timestamp arbitrarily larger 377 than the first packet (modulo 2^32). Section 3 places additional 378 restrictions on the RTP timestamps for two sequential RTP packets, as 379 does the guardtime parameter (Appendix C.4.2). 381 We use the term "media time" to denote the temporal duration of the 382 media coded by an RTP packet. The media time coded by a packet is 383 computed by subtracting the last command timestamp in the MIDI command 384 section from the RTP timestamp (modulo 2^32). If the MIDI list of the 385 MIDI command section of a packet is empty, the media time coded by the 386 packet is 0 ms. Appendix C.4.1 discusses media time issues in detail. 388 We now define RTP session semantics, in the context of sessions 389 specified using the session description protocol [RFC4566]. A session 390 description media line ("m=") specifies an RTP session. An RTP session 391 has an independent space of 2^32 synchronization sources. 392 Synchronization source identifiers are coded in the SSRC header field of 393 RTP session packets. The payload types that may appear in the PT header 394 field of RTP session packets are listed at the end of the media line. 396 Several RTP MIDI streams may appear in an RTP session. Each stream is 397 distinguished by a unique SSRC value and has a unique sequence number 398 and RTP timestamp space. Multiple streams in the RTP session may be 399 sent by a single party. Multiple parties may send streams in the RTP 400 session. An RTP MIDI stream encodes data for a single MIDI command name 401 space (16 voice channels + Systems). 403 Streams in an RTP session may use different payload types, or they may 404 use the same payload type. However, each party may send, at most, one 405 RTP MIDI stream for each payload type mapped to an RTP MIDI payload 406 format in an RTP session. Recall that dynamic binding of payload type 407 numbers in [RFC4566] lets a party map many payload type numbers to the 408 RTP MIDI payload format; thus a party may send many RTP MIDI streams in 409 a single RTP session. Pairs of streams (unicast or multicast) that 410 communicate between two parties in an RTP session and that share a 411 payload type have the same association as a MIDI cable pair that cross- 412 connects two devices in a MIDI 1.0 DIN network. 414 The RTP session architecture described above is efficient in its use of 415 network ports, as one RTP session (using a port pair per party) supports 416 the transport of many MIDI name spaces (16 MIDI channels + systems). We 417 define tools for grouping and labelling MIDI name spaces across streams 418 and sessions in Appendix C.5 of this memo. 420 The RTP header timestamps for each stream in an RTP session have 421 separately and randomly chosen initialization values. Receivers use the 422 timing fields encoded in the RTP control protocol (RTCP, [RFC3550]) 423 sender reports to synchronize the streams sent by a party. The SSRC 424 values for each stream in an RTP session are also separately and 425 randomly chosen, as described in [RFC3550]. Receivers use the CNAME 426 field encoded in RTCP sender reports to verify that streams were sent by 427 the same party, and to detect SSRC collisions, as described in 428 [RFC3550]. 430 In some applications, a receiver renders MIDI commands into audio (or 431 into control actions, such as the rewind of a tape deck or the dimming 432 of stage lights). In other applications, a receiver presents a MIDI 433 stream to software programs via an Application Programmer Interface 434 (API). Appendix C.6 defines session configuration tools to specify what 435 receivers should do with a MIDI command stream. 437 If a multimedia session uses different RTP MIDI streams to send 438 different classes of media, the streams MUST be sent over different RTP 439 sessions. For example, if a multimedia session uses one MIDI stream for 440 audio and a second MIDI stream to control a lighting system, the audio 441 and lighting streams MUST be sent over different RTP sessions, each with 442 its own media line. 444 Session description tools defined in Appendix C.5 let a sending party 445 split a single MIDI name space (16 voice channels + systems) over 446 several RTP MIDI streams. Split transport of a MIDI command stream is a 447 delicate task, because correct command stream reconstruction by a 448 receiver depends on exact timing synchronization across the streams. 450 To support split name spaces, we define the following requirements: 452 o A party MUST NOT send several RTP MIDI streams that share a MIDI 453 name space in the same RTP session. Instead, each stream MUST 454 be sent from a different RTP session. 456 o If several RTP MIDI streams sent by a party share a MIDI name 457 space, all streams MUST use the same SSRC value and MUST use the 458 same randomly chosen RTP timestamp initialization value. 460 These rules let a receiver identify streams that share a MIDI name space 461 (by matching SSRC values) and also let a receiver accurately reconstruct 462 the source MIDI command stream (by using RTP timestamps to interleave 463 commands from the two streams). Care MUST be taken by senders to ensure 464 that SSRC changes due to collisions are reflected in both streams. 465 Receivers MUST regularly examine the RTCP CNAME fields associated with 466 the linked streams, to ensure that the assumed link is legitimate and 467 not the result of an SSRC collision by another sender. 469 Except for the special cases described above, a party may send many RTP 470 MIDI streams in the same session. However, it is sometimes advantageous 471 for two RTP MIDI streams to be sent over different RTP sessions. For 472 example, two streams may need different values for RTP session-level 473 attributes (such as the sendonly and recvonly attributes). As a second 474 example, two RTP sessions may be needed to send two unicast streams in a 475 multimedia session that originate on different computers (with different 476 IP numbers). Two RTP sessions are needed in this case because transport 477 addresses are specified on the RTP-session or multimedia-session level, 478 not on a payload type level. 480 On a final note, in some uses of MIDI, parties send bidirectional 481 traffic to conduct transactions (such as file exchange). These commands 482 were designed to work over MIDI 1.0 DIN cable networks may be configured 483 in a multicast topology, which use pure "party-line" signalling. Thus, 484 if a multimedia session ensures a multicast connection between all 485 parties, bidirectional MIDI commands will work without additional 486 support from the RTP MIDI payload format. 488 2.2. MIDI Payload 490 The payload (Figure 1) MUST begin with the MIDI command section. The 491 MIDI command section codes a (possibly empty) list of timestamped MIDI 492 commands, and provides the essential service of the payload format. 494 The payload MAY also contain a journal section. The journal section 495 provides resiliency by coding the recent history of the stream. A flag 496 in the MIDI command section codes the presence of a journal section in 497 the payload. 499 Section 3 defines the MIDI command section. Sections 4-5 and Appendices 500 A-B define the recovery journal, the default format for the journal 501 section. Here, we describe how these payload sections operate in a 502 stream in an RTP session. 504 The journalling method for a stream is set at the start of a session and 505 MUST NOT be changed thereafter. A stream may be set to use the recovery 506 journal, to use an alternative journal format (none are defined in this 507 memo), or not to use a journal. 509 The default journalling method of a stream is inferred from its 510 transport type. Streams that use unreliable transport (such as UDP) 511 default to using the recovery journal. Streams that use reliable 512 transport (such as TCP) default to not using a journal. Appendix C.2.1 513 defines session configuration tools for overriding these defaults. For 514 all types of transport, a sender MUST transmit an RTP packet stream with 515 consecutive sequence numbers (modulo 2^16). 517 If a stream uses the recovery journal, every payload in the stream MUST 518 include a journal section. If a stream does not use journalling, a 519 journal section MUST NOT appear in a stream payload. If a stream uses 520 an alternative journal format, the specification for the journal format 521 defines an inclusion policy. 523 If a stream is sent over UDP transport, the Maximum Transmission Unit 524 (MTU) of the underlying network limits the practical size of the payload 525 section (for example, an Ethernet MTU is 1500 octets), for applications 526 where predictable and minimal packet transmission latency is critical. 527 A sender SHOULD NOT create RTP MIDI UDP packets whose size exceeds the 528 MTU of the underlying network. Instead, the sender SHOULD take steps to 529 keep the maximum packet size under the MTU limit. 531 These steps may take many forms. The default closed-loop recovery 532 journal sending policy (defined in Appendix C.2.2.2) uses RTP control 533 protocol (RTCP, [RFC3550]) feedback to manage the RTP MIDI packet size. 534 In addition, Section 3.2 and Appendix B.5.2 provide specific tools for 535 managing the size of packets that code MIDI System Exclusive (0xF0) 536 commands. Appendix C.5 defines session configuration tools that may be 537 used to split a dense MIDI name space into several UDP streams (each 538 sent in a different RTP session, per Section 2.1) so that the payload 539 fits comfortably into an MTU. Another option is to use TCP. Section 540 4.3 of [RFC4696] provides non-normative advice for packet size 541 management. 543 3. MIDI Command Section 545 Figure 2 shows the format of the MIDI command section. 547 0 1 2 3 548 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 1 549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 550 |B|J|Z|P|LEN... | MIDI list ... | 551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 553 Figure 2 -- MIDI command section 555 The MIDI command section begins with a variable-length header. 557 The header field LEN codes the number of octets in the MIDI list that 558 follow the header. If the header flag B is 0, the header is one octet 559 long, and LEN is a 4-bit field, supporting a maximum MIDI list length of 560 15 octets. 562 If B is 1, the header is two octets long, and LEN is a 12-bit field, 563 supporting a maximum MIDI list length of 4095 octets. LEN is coded in 564 network byte order (big-endian): the 4 bits of LEN that appear in the 565 first header octet code the most significant 4 bits of the 12-bit LEN 566 value. 568 A LEN value of 0 is legal, and it codes an empty MIDI list. 570 If the J header bit is set to 1, a journal section MUST appear after the 571 MIDI command section in the payload. If the J header bit is set to 0, 572 the payload MUST NOT contain a journal section. 574 We define the semantics of the P header bit in Section 3.2. 576 If the LEN header field is nonzero, the MIDI list has the structure 577 shown in Figure 3. 579 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 580 | Delta Time 0 (1-4 octets long, or 0 octets if Z = 1) | 581 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 582 | MIDI Command 0 (1 or more octets long) | 583 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 584 | Delta Time 1 (1-4 octets long) | 585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 586 | MIDI Command 1 (1 or more octets long) | 587 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 588 | ... | 589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 590 | Delta Time N (1-4 octets long) | 591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 592 | MIDI Command N (0 or more octets long) | 593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 595 Figure 3 -- MIDI list structure 597 If the header flag Z is 1, the MIDI list begins with a complete MIDI 598 command (coded in the MIDI Command 0 field, in Figure 3) preceded by a 599 delta time (coded in the Delta Time 0 field). If Z is 0, the Delta Time 600 0 field is not present in the MIDI list, and the command coded in the 601 MIDI Command 0 field has an implicit delta time of 0. 603 The MIDI list structure may also optionally encode a list of N 604 additional complete MIDI commands, each coded in a MIDI Command K field. 605 Each additional command MUST be preceded by a Delta Time K field, which 606 codes the command's delta time. We discuss exceptions to the "command 607 fields code complete MIDI commands" rule in Section 3.2. 609 The final MIDI command field (i.e., the MIDI Command N field, shown in 610 Figure 3) in the MIDI list MAY be empty. Moreover, a MIDI list MAY 611 consist a single delta time (encoded in the Delta Time 0 field) without 612 an associated command (which would have been encoded in the MIDI Command 613 0 field). These rules enable MIDI coding features that are explained in 614 Section 3.1. We delay the explanations because an understanding of RTP 615 MIDI timestamps is necessary to describe the features. 617 3.1. Timestamps 619 In this section, we describe how RTP MIDI encodes a timestamp for each 620 MIDI list command. Command timestamps have the same units as RTP packet 621 header timestamps (described in Section 2.1 and [RFC3550]). Recall that 622 RTP timestamps have units of seconds, whose scaling is set during 623 session configuration (see Section 6.1 and [RFC4566]). 625 As shown in Figure 3, the MIDI list encodes time using a compact delta- 626 time format. The RTP MIDI delta time syntax is a modified form of the 627 MIDI File delta time syntax [MIDI]. RTP MIDI delta times use 1-4 octet 628 fields to encode 32-bit unsigned integers. Figure 4 shows the encoded 629 and decoded forms of delta times. Note that delta time values may be 630 legally encoded in multiple formats; for example, there are four legal 631 ways to encode the zero delta time (0x00, 0x8000, 0x808000, 0x80808000). 633 RTP MIDI uses delta times to encode a timestamp for each MIDI command. 634 The timestamp for MIDI Command K is the summation (modulo 2^32) of the 635 RTP timestamp and decoded delta times 0 through K. This cumulative 636 coding technique, borrowed from MIDI File delta time coding, is 637 efficient because it reduces the number of multi-octet delta times. 639 All command timestamps in a packet MUST be less than or equal to the RTP 640 timestamp of the next packet in the stream (modulo 2^32). 642 This restriction ensures that a particular RTP MIDI packet in a stream 643 is uniquely responsible for encoding time starting at the moment after 644 the RTP timestamp encoded in the RTP packet header, and ending at the 645 moment before the final command timestamp encoded in the MIDI list. The 646 "moment before" and "moment after" qualifiers acknowledge the "less than 647 or equal" semantics (as opposed to "strictly less than") in the sentence 648 above this paragraph. 650 Note that it is possible to "pad" the end of an RTP MIDI packet with 651 time that is guaranteed to be void of MIDI commands, by setting the 652 "Delta Time N" field of the MIDI list to the end of the void time, and 653 by omitting its corresponding "MIDI Command N" field (a syntactic 654 construction the preamble of Section 3 expressly made legal). 656 In addition, it is possible to code an RTP MIDI packet to express that a 657 period of time in the stream is void of MIDI commands. The RTP 658 timestamp in the header would code the start of the void time. The MIDI 659 list of this packet would consist of a "Delta Time 0" field that coded 660 the end of the void time. No other fields would be present in the MIDI 661 list (a syntactic construction the preamble of Section 3 also expressly 662 made legal). 664 By default, a command timestamp indicates the execution time for the 665 command. The difference between two timestamps indicates the time delay 666 between the execution of the commands. This difference may be zero, 667 coding simultaneous execution. In this memo, we refer to this 668 interpretation of timestamps as "comex" (COMmand EXecution) semantics. 669 We formally define comex semantics in Appendix C.3. 671 The comex interpretation of timestamps works well for transcoding a 672 Standard MIDI File (SMF) into an RTP MIDI stream, as SMFs code a 673 timestamp for each MIDI command stored in the file. To transcode an SMF 674 that uses metric time markers, use the SMF tempo map (encoded in the SMF 675 as meta-events) to convert metric SMF timestamp units into seconds-based 676 RTP timestamp units. 678 The comex interpretation also works well for MIDI hardware controllers 679 that are coding raw sensor data directly onto an RTP MIDI stream. Note 680 that this controller design is preferable to a design that converts raw 681 sensor data into a MIDI 1.0 cable command stream and then transcodes the 682 stream onto an RTP MIDI stream. 684 The comex interpretation of timestamps is usually not the best timestamp 685 interpretation for transcoding a MIDI source that uses implicit command 686 timing (such as MIDI 1.0 DIN cables) into an RTP MIDI stream. Appendix 687 C.3 defines alternatives to comex semantics and describes session 688 configuration tools for selecting the timestamp interpretation semantics 689 for a stream. 691 One-Octet Delta Time: 693 Encoded form: 0ddddddd 694 Decoded form: 00000000 00000000 00000000 0ddddddd 696 Two-Octet Delta Time: 698 Encoded form: 1ccccccc 0ddddddd 699 Decoded form: 00000000 00000000 00cccccc cddddddd 701 Three-Octet Delta Time: 703 Encoded form: 1bbbbbbb 1ccccccc 0ddddddd 704 Decoded form: 00000000 000bbbbb bbcccccc cddddddd 706 Four-Octet Delta Time: 708 Encoded form: 1aaaaaaa 1bbbbbbb 1ccccccc 0ddddddd 709 Decoded form: 0000aaaa aaabbbbb bbcccccc cddddddd 711 Figure 4 -- Decoding delta time formats 713 3.2. Command Coding 715 Each non-empty MIDI Command field in the MIDI list codes one of the MIDI 716 command types that may legally appear on a MIDI 1.0 DIN cable. Standard 717 MIDI File meta-events do not fit this definition and MUST NOT appear in 718 the MIDI list. As a rule, each MIDI Command field codes a complete 719 command, in the binary command format defined in [MIDI]. In the 720 remainder of this section, we describe exceptions to this rule. 722 The first MIDI channel command in the MIDI list MUST include a status 723 octet. Running status coding, as defined in [MIDI], MAY be used for all 724 subsequent MIDI channel commands in the list. As in [MIDI], System 725 Common and System Exclusive messages (0xF0 ... 0xF7) cancel the running 726 status state, but System Real-time messages (0xF8 ... 0xFF) do not 727 affect the running status state. All System commands in the MIDI list 728 MUST include a status octet. 730 As we note above, the first channel command in the MIDI list MUST 731 include a status octet. However, the corresponding command in the 732 original MIDI source data stream might not have a status octet (in this 733 case, the source would be coding the command using running status). If 734 the status octet of the first channel command in the MIDI list does not 735 appear in the source data stream, the P (phantom) header bit MUST be set 736 to 1. In all other cases, the P bit MUST be set to 0. 738 Note that the P bit describes the MIDI source data stream, not the MIDI 739 list encoding; regardless of the state of the P bit, the MIDI list MUST 740 include the status octet. 742 As receivers MUST be able to decode running status, sender implementors 743 should feel free to use running status to improve bandwidth efficiency. 744 However, senders SHOULD NOT introduce timing jitter into an existing 745 MIDI command stream through an inappropriate use or removal of running 746 status coding. This warning primarily applies to senders whose RTP MIDI 747 streams may be transcoded onto a MIDI 1.0 DIN cable [MIDI] by the 748 receiver: both the timestamps and the command coding (running status or 749 not) must comply with the physical restrictions of implicit time coding 750 over a slow serial line. 752 On a MIDI 1.0 DIN cable [MIDI], a System Real-time command may be 753 embedded inside of another "host" MIDI command. This syntactic 754 construction is not supported in the payload format: a MIDI Command 755 field in the MIDI list codes exactly one MIDI command (partially or 756 completely). 758 To encode an embedded System Real-time command, senders MUST extract the 759 command from its host and code it in the MIDI list as a separate 760 command. The host command and System Real-time command SHOULD appear in 761 the same MIDI list. The delta time of the System Real-time command 762 SHOULD result in a command timestamp that encodes the System Real-time 763 command placement in its original embedded position. 765 Two methods are provided for encoding MIDI System Exclusive (SysEx) 766 commands in the MIDI list. A SysEx command may be encoded in a MIDI 767 Command field verbatim: a 0xF0 octet, followed by an arbitrary number of 768 data octets, followed by a 0xF7 octet. 770 Alternatively, a SysEx command may be encoded as multiple segments. The 771 command is divided into two or more SysEx command segments; each segment 772 is encoded in its own MIDI Command field in the MIDI list. 774 The payload format supports segmentation in order to encode SysEx 775 commands that encode information in the temporal pattern of data octets. 776 By encoding these commands as a series of segments, each data octet may 777 be associated with a distinct delta time. Segmentation also supports 778 the coding of large SysEx commands across several packets. 780 To segment a SysEx command, first partition its data octet list into two 781 or more sublists. The last sublist MAY be empty (i.e., contain no 782 octets); all other sublists MUST contain at least one data octet. To 783 complete the segmentation, add the status octets defined in Figure 5 to 784 the head and tail of the first, last, and any "middle" sublists. Figure 785 6 shows example segmentations of a SysEx command. 787 A sender MAY cancel a segmented SysEx command transmission that is in 788 progress, by sending the "cancel" sublist shown in Figure 5. A "cancel" 789 sublist MAY follow a "first" or "middle" sublist in the transmission, 790 but MUST NOT follow a "last" sublist. The cancel MUST be empty (thus, 791 0xF7 0xF4 is the only legal cancel sublist). 793 The cancellation feature is needed because Appendix C.1 defines 794 configuration tools that let session parties exclude certain SysEx 795 commands in the stream. Senders that transcode a MIDI source onto an 796 RTP MIDI stream under these constraints have the responsibility of 797 excluding undesired commands from the RTP MIDI stream. 799 The cancellation feature lets a sender start the transmission of a 800 command before the MIDI source has sent the entire command. If a sender 801 determines that the command whose transmission is in progress should not 802 appear on the RTP stream, it cancels the command. Without a method for 803 cancelling a SysEx command transmission, senders would be forced to use 804 a high-latency store-and-forward approach to transcoding SysEx commands 805 onto RTP MIDI packets, in order to validate each SysEx command before 806 transmission. 808 The recommended receiver reaction to a cancellation depends on the 809 capabilities of the receiver. For example, a sound synthesizer that is 810 directly parsing RTP MIDI packets and rendering them to audio will be 811 aware of the fact that SysEx commands may be cancelled in RTP MIDI. 812 These receivers SHOULD detect a SysEx cancellation in the MIDI list and 813 act as if they had never received the SysEx command. 815 As a second example, a synthesizer may be receiving MIDI data from an 816 RTP MIDI stream via a MIDI DIN cable (or a software API emulation of a 817 MIDI DIN cable). In this case, an RTP-MIDI-aware system receives the 818 RTP MIDI stream and transcodes it onto the MIDI DIN cable (or its 819 emulation). Upon the receipt of the cancel sublist, the RTP-MIDI- aware 820 transcoder might have already sent the first part of the SysEx command 821 on the MIDI DIN cable to the receiver. 823 Unfortunately, the MIDI DIN cable protocol cannot directly code "cancel 824 SysEx in progress" semantics. However, MIDI DIN cable receivers begin 825 SysEx processing after the complete command arrives. The receiver 826 checks to see if it recognizes the command (coded in the first few 827 octets) and then checks to see if the command is the correct length. 828 Thus, in practice, a transcoder can cancel a SysEx command by sending an 829 0xF7 to (prematurely) end the SysEx command -- the receiver will detect 830 the incorrect command length and discard the command. 832 Appendix C.1 defines configuration tools that may be used to prohibit 833 SysEx command cancellation. 835 The relative ordering of SysEx command segments in a MIDI list must 836 match the relative ordering of the sublists in the original SysEx 837 command. By default, commands other than System Real-time MIDI commands 838 MUST NOT appear between SysEx command segments (Appendix C.1 defines 839 configuration tools to change this default, to let other commands types 840 appear between segments). If the command segments of a SysEx command 841 are placed in the MIDI lists of two or more RTP packets, the segment 842 ordering rules apply to the concatenation of all affected MIDI lists. 844 ----------------------------------------------------------- 845 | Sublist Position | Head Status Octet | Tail Status Octet | 846 |-----------------------------------------------------------| 847 | first | 0xF0 | 0xF0 | 848 |-----------------------------------------------------------| 849 | middle | 0xF7 | 0xF0 | 850 |-----------------------------------------------------------| 851 | last | 0xF7 | 0xF7 | 852 |-----------------------------------------------------------| 853 | cancel | 0xF7 | 0xF4 | 854 ----------------------------------------------------------- 856 Figure 5 -- Command segmentation status octets 858 [MIDI] permits 0xF7 octets that are not part of a (0xF0, 0xF7) pair to 859 appear on a MIDI 1.0 DIN cable. Unpaired 0xF7 octets have no semantic 860 meaning in MIDI, apart from cancelling running status. 862 Unpaired 0xF7 octets MUST NOT appear in the MIDI list of the MIDI 863 Command section. We impose this restriction to avoid interference with 864 the command segmentation coding defined in Figure 5. 866 SysEx commands carried on a MIDI 1.0 DIN cable may use the "dropped 867 0xF7" construction [MIDI]. In this coding method, the 0xF7 octet is 868 dropped from the end of the SysEx command, and the status octet of the 869 next MIDI command acts both to terminate the SysEx command and start the 870 next command. To encode this construction in the payload format, follow 871 these steps: 873 o Determine the appropriate delta times for the SysEx command and 874 the command that follows the SysEx command. 876 o Insert the "dropped" 0xF7 octet at the end of the SysEx command, 877 to form the standard SysEx syntax. 879 o Code both commands into the MIDI list using the rules above. 881 o Replace the 0xF7 octet that terminates the verbatim SysEx 882 encoding or the last segment of the segmented SysEx encoding 883 with a 0xF5 octet. This substitution informs the receiver 884 of the original dropped 0xF7 coding. 886 [MIDI] reserves the undefined System Common commands 0xF4 and 0xF5 and 887 the undefined System Real-time commands 0xF9 and 0xFD for future use. 888 By default, undefined commands MUST NOT appear in a MIDI Command field 889 in the MIDI list, with the exception of the 0xF5 octets used to code the 890 "dropped 0xF7" construction and the 0xF4 octets used by SysEx "cancel" 891 sublists. 893 During session configuration, a stream may be customized to transport 894 undefined commands (Appendix C.1). For this case, we now define how 895 senders encode undefined commands in the MIDI list. 897 An undefined System Real-time command MUST be coded using the System 898 Real-time rules. 900 If the undefined System Common commands are put to use in a future 901 version of [MIDI], the command will begin with an 0xF4 or 0xF5 status 902 octet, followed by an arbitrary number of data octets (i.e., zero or 903 more data bytes). To encode these commands, senders MUST terminate the 904 command with an 0xF7 octet and place the modified command into the MIDI 905 Command field. 907 Unfortunately, non-compliant uses of the undefined System Common 908 commands may appear in MIDI implementations. To model these commands, 909 we assume that the command begins with an 0xF4 or 0xF5 status octet, 910 followed by zero or more data octets, followed by zero or more trailing 911 0xF7 status octets. To encode the command, senders MUST first remove 912 all trailing 0xF7 status octets from the command. Then, senders MUST 913 terminate the command with an 0xF7 octet and place the modified command 914 into the MIDI Command field. 916 Note that we include the trailing octets in our model as a cautionary 917 measure: if such commands appeared in a non-compliant use of an 918 undefined System Common command, an RTP MIDI encoding of the command 919 that did not remove trailing octets could be mistaken for an encoding of 920 "middle" or "last" sublist of a segmented SysEx commands (Figure 5) 921 under certain packet loss conditions. 923 Original SysEx command: 925 0xF0 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0xF7 927 A two-segment segmentation: 929 0xF0 0x01 0x02 0x03 0x04 0xF0 931 0xF7 0x05 0x06 0x07 0x08 0xF7 933 A different two-segment segmentation: 935 0xF0 0x01 0xF0 937 0xF7 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0xF7 939 A three-segment segmentation: 941 0xF0 0x01 0x02 0xF0 943 0xF7 0x03 0x04 0xF0 945 0xF7 0x05 0x06 0x07 0x08 0xF7 947 The segmentation with the largest number of segments: 949 0xF0 0x01 0xF0 951 0xF7 0x02 0xF0 953 0xF7 0x03 0xF0 955 0xF7 0x04 0xF0 957 0xF7 0x05 0xF0 959 0xF7 0x06 0xF0 961 0xF7 0x07 0xF0 963 0xF7 0x08 0xF0 965 0xF7 0xF7 967 Figure 6 -- Example segmentations 969 4. The Recovery Journal System 971 The recovery journal is the default resiliency tool for unreliable 972 transport. In this section, we normatively define the roles that 973 senders and receivers play in the recovery journal system. 975 MIDI is a fragile code. A single lost command in a MIDI command stream 976 may produce an artifact in the rendered performance. We normatively 977 classify rendering artifacts into two categories: 979 o Transient artifacts. Transient artifacts produce immediate 980 but short-term glitches in the performance. For example, a lost 981 NoteOn (0x9) command produces a transient artifact: one note 982 fails to play, but the artifact does not extend beyond the end 983 of that note. 985 o Indefinite artifacts. Indefinite artifacts produce long-lasting 986 errors in the rendered performance. For example, a lost NoteOff 987 (0x8) command may produce an indefinite artifact: the note that 988 should have been ended by the lost NoteOff command may sustain 989 indefinitely. As a second example, the loss of a Control Change 990 (0xB) command for controller number 7 (Channel Volume) may 991 produce an indefinite artifact: after the loss, all notes on 992 the channel may play too softly or too loudly. 994 The purpose of the recovery journal system is to satisfy the recovery 995 journal mandate: the MIDI performance rendered from an RTP MIDI stream 996 sent over unreliable transport MUST NOT contain indefinite artifacts. 998 The recovery journal system does not use packet retransmission to 999 satisfy this mandate. Instead, each packet includes a special section, 1000 called the recovery journal. 1002 The recovery journal codes the history of the stream, back to an earlier 1003 packet called the checkpoint packet. The range of coverage for the 1004 journal is called the checkpoint history. The recovery journal codes 1005 the information necessary to recover from the loss of an arbitrary 1006 number of packets in the checkpoint history. Appendix A.1 normatively 1007 defines the checkpoint packet and the checkpoint history. 1009 When a receiver detects a packet loss, it compares its own knowledge 1010 about the history of the stream with the history information coded in 1011 the recovery journal of the packet that ends the loss event. By noting 1012 the differences in these two versions of the past, a receiver is able to 1013 transform all indefinite artifacts in the rendered performance into 1014 transient artifacts, by executing MIDI commands to repair the stream. 1016 We now state the normative role for senders in the recovery journal 1017 system. 1019 Senders prepare a recovery journal for every packet in the stream. In 1020 doing so, senders choose the checkpoint packet identity for the journal. 1021 Senders make this choice by applying a sending policy. Appendix C.2.2 1022 normatively defines three sending policies: "closed- loop", "open-loop", 1023 and "anchor". 1025 By default, senders MUST use the closed-loop sending policy. If the 1026 session description overrides this default policy, by using the 1027 parameter j_update defined in Appendix C.2.2, senders MUST use the 1028 specified policy. 1030 After choosing the checkpoint packet identity for a packet, the sender 1031 creates the recovery journal. By default, this journal MUST conform to 1032 the normative semantics in Section 5 and Appendices A-B in this memo. 1033 In Appendix C.2.3, we define parameters that modify the normative 1034 semantics for recovery journals. If the session description uses these 1035 parameters, the journal created by the sender MUST conform to the 1036 modified semantics. 1038 Next, we state the normative role for receivers in the recovery journal 1039 system. 1041 A receiver MUST detect each RTP sequence number break in a stream. If 1042 the sequence number break is due to a packet loss event (as defined in 1043 [RFC3550]), the receiver MUST repair all indefinite artifacts in the 1044 rendered MIDI performance caused by the loss. If the sequence number 1045 break is due to an out-of-order packet (as defined in [RFC3550]), the 1046 receiver MUST NOT take actions that introduce indefinite artifacts 1047 (ignoring the out-of-order packet is a safe option). 1049 Receivers take special precautions when entering or exiting a session. 1050 A receiver MUST process the first received packet in a stream as if it 1051 were a packet that ends a loss event. Upon exiting a session, a 1052 receiver MUST ensure that the rendered MIDI performance does not end 1053 with indefinite artifacts. 1055 Receivers are under no obligation to perform indefinite artifact repairs 1056 at the moment a packet arrives. A receiver that uses a playout buffer 1057 may choose to wait until the moment of rendering before processing the 1058 recovery journal, as the "lost" packet may be a late packet that arrives 1059 in time to use. 1061 Next, we state the normative role for the creator of the session 1062 description in the recovery journal system. Depending on the 1063 application, the sender, the receivers, and other parties may take part 1064 in creating or approving the session description. 1066 A session description that specifies the default closed-loop sending 1067 policy and the default recovery journal semantics satisfies the recovery 1068 journal mandate. However, these default behaviors may not be 1069 appropriate for all sessions. If the creators of a session description 1070 use the parameters defined in Appendix C.2 to override these defaults, 1071 the creators MUST ensure that the parameters define a system that 1072 satisfies the recovery journal mandate. 1074 Finally, we note that this memo does not specify sender or receiver 1075 recovery journal algorithms. Implementations are free to use any 1076 algorithm that conforms to the requirements in this section. The non- 1077 normative [RFC4696] discusses sender and receiver algorithm design. 1079 5. Recovery Journal Format 1081 This section introduces the structure of the recovery journal and 1082 defines the bitfields of recovery journal headers. Appendices A-B 1083 complete the bitfield definition of the recovery journal. 1085 The recovery journal has a three-level structure: 1087 o Top-level header. 1089 o Channel and system journal headers. These headers encode 1090 recovery information for a single voice channel (channel 1091 journal) or for all systems commands (system journal). 1093 o Chapters. Chapters describe recovery information for a 1094 single MIDI command type. 1096 Figure 7 shows the top-level structure of the recovery journal. The 1097 recovery journals consists of a 3-octet header, followed by an optional 1098 system journal (labeled S-journal in Figure 7) and an optional list of 1099 channel journals. Figure 8 shows the recovery journal header format. 1101 0 1 2 3 1102 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 1103 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1104 | Recovery journal header | S-journal ... | 1105 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1106 | Channel journals ... | 1107 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1109 Figure 7 -- Top-level recovery journal format 1111 0 1 2 1112 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 1113 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1114 |S|Y|A|H|TOTCHAN| Checkpoint Packet Seqnum | 1115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1117 Figure 8 -- Recovery journal header 1119 If the Y header bit is set to 1, the system journal appears in the 1120 recovery journal, directly following the recovery journal header. 1122 If the A header bit is set to 1, the recovery journal ends with a list 1123 of (TOTCHAN + 1) channel journals (the 4-bit TOTCHAN header field is 1124 interpreted as an unsigned integer). 1126 A MIDI channel MAY be represented by (at most) one channel journal in a 1127 recovery journal. Channel journals MUST appear in the recovery journal 1128 in ascending channel-number order. 1130 If A and Y are both zero, the recovery journal only contains its 3- 1131 octet header and is considered to be an "empty" journal. 1133 The S (single-packet loss) bit appears in most recovery journal 1134 structures, including the recovery journal header. The S bit helps 1135 receivers efficiently parse the recovery journal in the common case of 1136 the loss of a single packet. Appendix A.1 defines S bit semantics. 1138 The H bit indicates if MIDI channels in the stream have been configured 1139 to use the enhanced Chapter C encoding (Appendix A.3.3). 1141 By default, the payload format does not use enhanced Chapter C encoding. 1142 In this default case, the H bit MUST be set to 0 for all packets in the 1143 stream. 1145 If the stream has been configured so that controller numbers for one or 1146 more MIDI channels use enhanced Chapter C encoding, the H bit MUST be 1147 set to 1 in all packets in the stream. In Appendix C.2.3, we show how 1148 to configure a stream to use enhanced Chapter C encoding. 1150 The 16-bit Checkpoint Packet Seqnum header field codes the sequence 1151 number of the checkpoint packet for this journal, in network byte order 1152 (big-endian). The choice of the checkpoint packet sets the depth of the 1153 checkpoint history for the journal (defined in Appendix A.1). 1155 Receivers may use the Checkpoint Packet Seqnum field of the packet that 1156 ends a loss event to verify that the journal checkpoint history covers 1157 the entire loss event. The checkpoint history covers the loss event if 1158 the Checkpoint Packet Seqnum field is less than or equal to one plus the 1159 highest RTP sequence number previously received on the stream (modulo 1160 2^16). 1162 0 1 2 3 1163 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 1164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1165 |S| CHAN |H| LENGTH |P|C|M|W|N|E|T|A| Chapters ... | 1166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1168 Figure 9 -- Channel journal format 1170 Figure 9 shows the structure of a channel journal: a 3-octet header, 1171 followed by a list of leaf elements called channel chapters. A channel 1172 journal encodes information about MIDI commands on the MIDI channel 1173 coded by the 4-bit CHAN header field. Note that CHAN uses the same bit 1174 encoding as the channel nibble in MIDI Channel Messages (the cccc field 1175 in Figure E.1 of Appendix E). 1177 The 10-bit LENGTH field codes the length of the channel journal. The 1178 semantics for LENGTH fields are uniform throughout the recovery journal, 1179 and are defined in Appendix A.1. 1181 The third octet of the channel journal header is the Table of Contents 1182 (TOC) of the channel journal. The TOC is a set of bits that encode the 1183 presence of a chapter in the journal. Each chapter contains information 1184 about a certain class of MIDI channel command: 1186 o Chapter P: MIDI Program Change (0xC) 1187 o Chapter C: MIDI Control Change (0xB) 1188 o Chapter M: MIDI Parameter System (part of 0xB) 1189 o Chapter W: MIDI Pitch Wheel (0xE) 1190 o Chapter N: MIDI NoteOff (0x8), NoteOn (0x9) 1191 o Chapter E: MIDI Note Command Extras (0x8, 0x9) 1192 o Chapter T: MIDI Channel Aftertouch (0xD) 1193 o Chapter A: MIDI Poly Aftertouch (0xA) 1195 Chapters appear in a list following the header, in order of their 1196 appearance in the TOC. Appendices A.2-9 describe the bitfield format 1197 for each chapter, and define the conditions under which a chapter type 1198 MUST appear in the recovery journal. If any chapter types are required 1199 for a channel, an associated channel journal MUST appear in the recovery 1200 journal. 1202 The H bit indicates if controller numbers on a MIDI channel have been 1203 configured to use the enhanced Chapter C encoding (Appendix A.3.3). 1205 By default, controller numbers on a MIDI channel do not use enhanced 1206 Chapter C encoding. In this default case, the H bit MUST be set to 0 1207 for all channel journal headers for the channel in the recovery journal, 1208 for all packets in the stream. 1210 However, if at least one controller number for a MIDI channel has been 1211 configured to use the enhanced Chapter C encoding, the H bit for its 1212 channel journal MUST be set to 1, for all packets in the stream. 1214 In Appendix C.2.3, we show how to configure a controller number to use 1215 enhanced Chapter C encoding. 1217 0 1 2 3 1218 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 1219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1220 |S|D|V|Q|F|X| LENGTH | System chapters ... | 1221 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1223 Figure 10 -- System journal format 1225 Figure 10 shows the structure of the system journal: a 2-octet header, 1226 followed by a list of system chapters. Each chapter codes information 1227 about a specific class of MIDI Systems command: 1229 o Chapter D: Song Select (0xF3), Tune Request (0xF6), Reset (0xFF), 1230 undefined System commands (0xF4, 0xF5, 0xF9, 0xFD) 1231 o Chapter V: Active Sense (0xFE) 1232 o Chapter Q: Sequencer State (0xF2, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC) 1233 o Chapter F: MTC Tape Position (0xF1, 0xF0 0x7F 0xcc 0x01 0x01) 1234 o Chapter X: System Exclusive (all other 0xF0) 1236 The 10-bit LENGTH field codes the size of the system journal and 1237 conforms to semantics described in Appendix A.1. 1239 The D, V, Q, F, and X header bits form a Table of Contents (TOC) for the 1240 system journal. A TOC bit that is set to 1 codes the presence of a 1241 chapter in the journal. Chapters appear in a list following the header, 1242 in the order of their appearance in the TOC. 1244 Appendix B describes the bitfield format for the system chapters and 1245 defines the conditions under which a chapter type MUST appear in the 1246 recovery journal. If any system chapter type is required to appear in 1247 the recovery journal, the system journal MUST appear in the recovery 1248 journal. 1250 6. Session Description Protocol 1252 RTP does not perform session management. Instead, RTP works together 1253 with session management tools, such as the Session Initiation Protocol 1254 (SIP, [RFC3261]) and the Real Time Streaming Protocol (RTSP, [RFC2326]). 1256 RTP payload formats define media type parameters for use in session 1257 management (for example, this memo defines "rtp-midi" as the media type 1258 for native RTP MIDI streams). 1260 In most cases, session management tools use the media type parameters 1261 via another standard, the Session Description Protocol (SDP, [RFC4566]). 1263 SDP is a textual format for specifying session descriptions. Session 1264 descriptions specify the network transport and media encoding for RTP 1265 sessions. Session management tools coordinate the exchange of session 1266 descriptions between participants ("parties"). 1268 Some session management tools use SDP to negotiate details of media 1269 transport (network addresses, ports, etc.). We refer to this use of SDP 1270 as "negotiated usage". One example of negotiated usage is the 1271 Offer/Answer protocol ([RFC3264] and Appendix C.7.2 in this memo) as 1272 used by SIP. 1274 Other session management tools use SDP to declare the media encoding for 1275 the session but use other techniques to negotiate network transport. We 1276 refer to this use of SDP as "declarative usage". One example of 1277 declarative usage is RTSP ([RFC2326] and Appendix C.7.1 in this memo). 1279 Below, we show session description examples for native (Section 6.1) and 1280 mpeg4-generic (Section 6.2) streams. In Section 6.3, we introduce 1281 session configuration tools that may be used to customize streams. 1283 6.1. Session Descriptions for Native Streams 1285 The session description below defines a unicast UDP RTP session (via a 1286 media ("m=") line) whose sole payload type (96) is mapped to a minimal 1287 native RTP MIDI stream. 1289 v=0 1290 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 1291 s=Example 1292 t=0 0 1293 m=audio 5004 RTP/AVP 96 1294 c=IN IP4 192.0.2.94 1295 a=rtpmap:96 rtp-midi/44100 1297 The rtpmap attribute line uses the "rtp-midi" media type to specify an 1298 RTP MIDI native stream. The clock rate specified on the rtpmap line (in 1299 the example above, 44100 Hz) sets the scaling for the RTP timestamp 1300 header field (see Section 2.1, and also [RFC3550]). 1302 Note that this document does not specify a default clock rate value for 1303 RTP MIDI. When RTP MIDI is used with SDP, parties MUST use the rtpmap 1304 line to communicate the clock rate. Guidance for selecting the RTP MIDI 1305 clock rate value appears in Section 2.1. 1307 We consider the RTP MIDI stream shown above to be "minimal" because the 1308 session description does not customize the stream with parameters. 1309 Without such customization, a native RTP MIDI stream has these 1310 characteristics: 1312 1. If the stream uses unreliable transport (unicast UDP, multicast 1313 UDP, etc.), the recovery journal system is in use, and the RTP 1314 payload contains both the MIDI command section and the journal 1315 section. If the stream uses reliable transport (such as TCP), 1316 the stream does not use journalling, and the payload contains 1317 only the MIDI command section (Section 2.2). 1319 2. If the stream uses the recovery journal system, the recovery 1320 journal system uses the default sending policy and the default 1321 journal semantics (Section 4). 1323 3. In the MIDI command section of the payload, command timestamps 1324 use the default "comex" semantics (Section 3). 1326 4. The recommended temporal duration ("media time") of an RTP 1327 packet ranges from 0 to 200 ms, and the RTP timestamp 1328 difference between sequential packets in the stream may be 1329 arbitrarily large (Section 2.1). 1331 5. If more than one minimal rtp-midi stream appears in a session, 1332 the MIDI name spaces for these streams are independent: channel 1333 1 in the first stream does not reference the same MIDI channel 1334 as channel 1 in the second stream (see Appendix C.5 for a 1335 discussion of the independence of minimal rtp-midi streams). 1337 6. The rendering method for the stream is not specified. What the 1338 receiver "does" with a minimal native MIDI stream is "out of 1339 scope" of this memo. For example, in content creation 1340 environments, a user may manually configure client software to 1341 render the stream with a specific software package. 1343 As in standard in RTP, RTP sessions managed by SIP are sendrecv by 1344 default (parties send and receive MIDI), and RTP sessions managed by 1345 RTSP are recvonly by default (server sends and client receives). 1347 In sendrecv RTP MIDI sessions for the session description shown above, 1348 the 16 voice channel + systems MIDI name space is unique for each 1349 sender. Thus, in a two-party session, the voice channel 0 sent by one 1350 party is distinct from the voice channel 0 sent by the other party. 1352 This behavior corresponds to what occurs when two MIDI 1.0 DIN devices 1353 are cross-connected with two MIDI cables (one cable routing MIDI Out 1354 from the first device into MIDI In of the second device, a second cable 1355 routing MIDI In from the first device into MIDI Out of the second 1356 device). We define this "association" formally in Section 2.1. 1358 MIDI 1.0 DIN networks may be configured in a "party-line" multicast 1359 topology. For these networks, the MIDI protocol itself provides tools 1360 for addressing specific devices in transactions on a multicast network, 1361 and for device discovery. Thus, apart from providing a 1- to-many 1362 forward path and a many-to-1 reverse path, IETF protocols do not need to 1363 provide any special support for MIDI multicast networking. 1365 6.2. Session Descriptions for mpeg4-generic Streams 1367 An mpeg4-generic [RFC3640] RTP MIDI stream uses an MPEG 4 Audio Object 1368 Type to render MIDI into audio. Three Audio Object Types accept MIDI 1369 input: 1371 o General MIDI (Audio Object Type ID 15), based on the General 1372 MIDI rendering standard [MIDI]. 1374 o Wavetable Synthesis (Audio Object Type ID 14), based on the 1375 Downloadable Sounds Level 2 (DLS 2) rendering standard [DLS2]. 1377 o Main Synthetic (Audio Object Type ID 13), based on Structured 1378 Audio and the programming language SAOL [MPEGSA]. 1380 The primary service of an mpeg4-generic stream is to code Access Units 1381 (AUs). We define the mpeg4-generic RTP MIDI AU as the MIDI payload 1382 shown in Figure 1 of Section 2.1 of this memo: a MIDI command section 1383 optionally followed by a journal section. 1385 Exactly one RTP MIDI AU MUST be mapped to one mpeg4-generic RTP MIDI 1386 packet. The mpeg4-generic options for placing several AUs in an RTP 1387 packet MUST NOT be used with RTP MIDI. The mpeg4-generic options for 1388 fragmenting and interleaving AUs MUST NOT be used with RTP MIDI. The 1389 mpeg4-generic RTP packet payload (Figure 1 in [RFC3640]) MUST contain 1390 empty AU Header and Auxiliary sections. These rules yield mpeg4-generic 1391 packets that are structurally identical to native RTP MIDI packets, an 1392 essential property for the correct operation of the payload format. 1394 The session description that follows defines a unicast UDP RTP session 1395 (via a media ("m=") line) whose sole payload type (96) is mapped to a 1396 minimal mpeg4-generic RTP MIDI stream. This example uses the General 1397 MIDI Audio Object Type under Synthesis Profile @ Level 2. 1399 v=0 1400 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 1401 s=Example 1402 t=0 0 1403 m=audio 5004 RTP/AVP 96 1404 c=IN IP6 2001:DB80::7F2E:172A:1E24 1405 a=rtpmap:96 mpeg4-generic/44100 1406 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 1407 config=7A0A0000001A4D546864000000060000000100604D54726B0000 1408 000600FF2F000 1410 (The a=fmtp line has been wrapped to fit the page to accommodate memo 1411 formatting restrictions; it comprises a single line in SDP.) 1413 The fmtp attribute line codes the four parameters (streamtype, mode, 1414 profile-level-id, and config) that are required in all mpeg4-generic 1415 session descriptions [RFC3640]. For RTP MIDI streams, the streamtype 1416 parameter MUST be set to 5, the "mode" parameter MUST be set to "rtp- 1417 midi", and the "profile-level-id" parameter MUST be set to the MPEG-4 1418 Profile Level for the stream. For the Synthesis Profile, legal profile- 1419 level-id values are 11, 12, and 13, coding low (11), medium (12), or 1420 high (13) decoder computational complexity, as defined by MPEG 1421 conformance tests. 1423 In a minimal RTP MIDI session description, the config value MUST be a 1424 hexadecimal encoding [RFC3640] of the AudioSpecificConfig data block 1425 [MPEGAUDIO] for the stream. AudioSpecificConfig encodes the Audio 1426 Object Type for the stream and also encodes initialization data (SAOL 1427 programs, DLS 2 wave tables, etc.). Standard MIDI Files encoded in 1428 AudioSpecificConfig in a minimal session description MUST be ignored by 1429 the receiver. 1431 Receivers determine the rendering algorithm for the session by 1432 interpreting the first 5 bits of AudioSpecificConfig as an unsigned 1433 integer that codes the Audio Object Type. In our example above, the 1434 leading config string nibbles "7A" yield the Audio Object Type 15 1435 (General MIDI). In Appendix E.4, we derive the config string value in 1436 the session description shown above; the starting point of the 1437 derivation is the MPEG bitstreams defined in [MPEGSA] and [MPEGAUDIO]. 1439 We consider the stream to be "minimal" because the session description 1440 does not customize the stream through the use of parameters, other than 1441 the 4 required mpeg4-generic parameters described above. In Section 1442 6.1, we describe the behavior of a minimal native stream, as a numbered 1443 list of characteristics. Items 1-4 on that list also describe the 1444 minimal mpeg4-generic stream, but items 5 and 6 require restatements, as 1445 listed below: 1447 5. If more than one minimal mpeg4-generic stream appears in 1448 a session, each stream uses an independent instance of the 1449 Audio Object Type coded in the config parameter value. 1451 6. A minimal mpeg4-generic stream encodes the AudioSpecificConfig 1452 as an inline hexadecimal constant. If a session description 1453 is sent over UDP, it may be impossible to transport large 1454 AudioSpecificConfig blocks within the Maximum Transmission Size 1455 (MTU) of the underlying network (for Ethernet, the MTU is 1500 1456 octets). In some cases, the AudioSpecificConfig block may 1457 exceed the maximum size of the UDP packet itself. 1459 The comments in Section 6.1 on SIP and RTSP stream directional defaults, 1460 sendrecv MIDI channel usage, and MIDI 1.0 DIN multicast networks also 1461 apply to mpeg4-generic RTP MIDI sessions. 1463 In sendrecv sessions, each party's session description MUST use 1464 identical values for the mpeg4-generic parameters (including the 1465 required streamtype, mode, profile-level-id, and config parameters). As 1466 a consequence, each party uses an identically configured MPEG 4 Audio 1467 Object Type to render MIDI commands into audio. The preamble to 1468 Appendix C discusses a way to create "virtual sendrecv" sessions that do 1469 not have this restriction. 1471 6.3. Parameters 1473 This section introduces parameters for session configuration for RTP 1474 MIDI streams. In session descriptions, parameters modify the semantics 1475 of a payload type. Parameters are specified on an fmtp attribute line. 1476 See the session description example in Section 6.2 for an example of a 1477 fmtp attribute line. 1479 The parameters add features to the minimal streams described in Sections 1480 6.1-2, and support several types of services: 1482 o Stream subsetting. By default, all MIDI commands that 1483 are legal to appear on a MIDI 1.0 DIN cable may appear 1484 in an RTP MIDI stream. The cm_unused parameter overrides 1485 this default by prohibiting certain commands from appearing 1486 in the stream. The cm_used parameter is used in conjunction 1487 with cm_unused, to simplify the specification of complex 1488 exclusion rules. We describe cm_unused and cm_used in 1489 Appendix C.1. 1491 o Journal customization. The j_sec and j_update parameters 1492 configure the use of the journal section. The ch_default, 1493 ch_never, and ch_anchor parameters configure the semantics 1494 of the recovery journal chapters. These parameters are 1495 described in Appendix C.2 and override the default stream 1496 behaviors 1 and 2, listed in Section 6.1 and referenced in 1497 Section 6.2. 1499 o MIDI command timestamp semantics. The tsmode, octpos, 1500 mperiod, and linerate parameters customize the semantics 1501 of timestamps in the MIDI command section. These parameters 1502 let RTP MIDI accurately encode the implicit time coding of 1503 MIDI 1.0 DIN cables. These parameters are described in 1504 Appendix C.3 and override default stream behavior 3, 1505 listed in Section 6.1 and referenced in Section 6.2 1507 o Media time. The rtp_ptime and rtp_maxptime parameters define 1508 the temporal duration ("media time") of an RTP MIDI packet. 1509 The guardtime parameter sets the minimum sending rate of stream 1510 packets. These parameters are described in Appendix C.4 1511 and override default stream behavior 4, listed in Section 6.1 1512 and referenced in Section 6.2. 1514 o Stream description. The musicport parameter labels the 1515 MIDI name space of RTP streams in a multimedia session. 1516 Musicport is described in Appendix C.5. The musicport 1517 parameter overrides default stream behavior 5, in Sections 1518 6.1 and 6.2. 1520 o MIDI rendering. Several parameters specify the MIDI 1521 rendering method of a stream. These parameters are described 1522 in Appendix C.6 and override default stream behavior 6, in 1523 Sections 6.1 and 6.2. 1525 In Appendix C.7, we specify interoperability guidelines for two RTP MIDI 1526 application areas: content-streaming using RTSP (Appendix C.7.1) and 1527 network musical performance using SIP (Appendix C.7.2). 1529 7. Extensibility 1531 The payload format defined in this memo exclusively encodes all commands 1532 that may legally appear on a MIDI 1.0 DIN cable. 1534 Many worthy uses of MIDI over RTP do not fall within the narrow scope of 1535 the payload format. For example, the payload format does not support 1536 the direct transport of Standard MIDI File (SMF) meta-event and metric 1537 timing data. As a second example, the payload format does not define 1538 transport tools for user-defined commands (apart from tools to support 1539 System Exclusive commands [MIDI]). 1541 The payload format does not provide an extension mechanism to support 1542 new features of this nature, by design. Instead, we encourage the 1543 development of new payload formats for specialized musical applications. 1544 The IETF session management tools [RFC3264] [RFC2326] support codec 1545 negotiation, to facilitate the use of new payload formats in a backward- 1546 compatible way. 1548 However, the payload format does provide several extensibility tools, 1549 which we list below: 1551 o Journalling. As described in Appendix C.2, new token 1552 values for the j_sec and j_update parameters may 1553 be defined in IETF standards-track documents. This 1554 mechanism supports the design of new journal formats 1555 and the definition of new journal sending policies. 1557 o Rendering. The payload format may be extended to support 1558 new MIDI renderers (Appendix C.6.2). Certain general aspects 1559 of the RTP MIDI rendering process may also be extended, via 1560 the definition of new token values for the render (Appendix C.6) 1561 and smf_info (Appendix C.6.4.1) parameters. 1563 o Undefined commands. [MIDI] reserves 4 MIDI System commands 1564 for future use (0xF4, 0xF5, 0xF9, 0xFD). If updates 1565 to [MIDI] define the reserved commands, IETF standards-track 1566 documents may be defined to provide resiliency support for 1567 the commands. Opaque LEGAL fields appear in System Chapter 1568 D for this purpose (Appendix B.1.1). 1570 A final form of extensibility involves the inclusion of the payload 1571 format in framework documents. Framework documents describe how to 1572 combine protocols to form a platform for interoperable applications. 1573 For example, a stage and studio framework might define how to use SIP 1574 [RFC3261], RTSP [RFC2326], SDP [RFC4566], and RTP [RFC3550] to support 1575 media networking for professional audio equipment and electronic musical 1576 instruments. 1578 8. Congestion Control 1580 The RTP congestion control requirements defined in [RFC3550] apply to 1581 RTP MIDI sessions, and implementors should carefully read the congestion 1582 control section in [RFC3550]. As noted in [RFC3550], all transport 1583 protocols used on the Internet need to address congestion control in 1584 some way, and RTP is not an exception. 1586 In addition, the congestion control requirements defined in [RFC3551] 1587 applies to RTP MIDI sessions run under applicable profiles. The basic 1588 congestion control requirement defined in [RFC3551] is that RTP sessions 1589 that use UDP transport should monitor packet loss (via RTCP or other 1590 means) to ensure that the RTP stream competes fairly with TCP flows that 1591 share the network. 1593 Finally, RTP MIDI has congestion control issues that are unique for an 1594 audio RTP payload format. In applications such as network musical 1595 performance [NMP], the packet rate is linked to the gestural rate of a 1596 human performer. Senders MUST monitor the MIDI command source for 1597 patterns that result in excessive packet rates and take actions during 1598 RTP transcoding to reduce the RTP packet rate. [RFC4696] offers 1599 implementation guidance on this issue. 1601 9. Security Considerations 1603 Implementors should carefully read the Security Considerations sections 1604 of the RTP [RFC3550], AVP [RFC3551], and other RTP profile documents, as 1605 the issues discussed in these sections directly apply to RTP MIDI 1606 streams. Implementors should also review the Secure Real-time Transport 1607 Protocol (SRTP, [RFC3711]), an RTP profile that addresses the security 1608 issues discussed in [RFC3550] and [RFC3551]. 1610 Here, we discuss security issues that are unique to the RTP MIDI payload 1611 format. 1613 When using RTP MIDI, authentication of incoming RTP and RTCP packets is 1614 RECOMMENDED. Per-packet authentication may be provided by SRTP or by 1615 other means. Without the use of authentication, attackers could forge 1616 MIDI commands into an ongoing stream, damaging speakers and eardrums. 1617 An attacker could also craft RTP and RTCP packets to exploit known bugs 1618 in the client and take effective control of a client machine. 1620 Session management tools (such as SIP [RFC3261]) SHOULD use 1621 authentication during the transport of all session descriptions 1622 containing RTP MIDI media streams. For SIP, the Security Considerations 1623 section in [RFC3261] provides an overview of possible authentication 1624 mechanisms. RTP MIDI session descriptions should use authentication 1625 because the session descriptions may code initialization data using the 1626 parameters described in Appendix C. If an attacker inserts bogus 1627 initialization data into a session description, he can corrupt the 1628 session or forge an client attack. 1630 Session descriptions may also code renderer initialization data by 1631 reference, via the url (Appendix C.6.3) and smf_url (Appendix C.6.4.2) 1632 parameters. If the coded URL is spoofed, both session and client are 1633 open to attack, even if the session description itself is authenticated. 1634 Therefore, URLs specified in url and smf_url parameters SHOULD use 1635 [RFC2818]. 1637 Section 2.1 allows streams sent by a party in two RTP sessions to have 1638 the same SSRC value and the same RTP timestamp initialization value, 1639 under certain circumstances. Normally, these values are randomly chosen 1640 for each stream in a session, to make plaintext guessing harder to do if 1641 the payloads are encrypted. Thus, Section 2.1 weakens this aspect of 1642 RTP security. 1644 10. Acknowledgements 1646 We thank the networking, media compression, and computer music community 1647 members who have commented or contributed to the effort, including Kurt 1648 B, Cynthia Bruyns, Steve Casner, Paul Davis, Robin Davies, Joanne Dow, 1649 Tobias Erichsen, Nicolas Falquet, Dominique Fober, Philippe Gentric, 1650 Michael Godfrey, Chris Grigg, Todd Hager, Alfred Hoenes, Michel Jullian, 1651 Phil Kerr, Young-Kwon Lim, Jessica Little, Jan van der Meer, Colin 1652 Perkins, Charlie Richmond, Herbie Robinson, Larry Rowe, Eric Scheirer, 1653 Dave Singer, Martijn Sipkema, William Stewart, Kent Terry, Magnus 1654 Westerlund, Tom White, Jim Wright, Doug Wyatt, and Giorgio Zoia. We 1655 also thank the members of the San Francisco Bay Area music and audio 1656 community for creating the context for the work, including Don Buchla, 1657 Chris Chafe, Richard Duda, Dan Ellis, Adrian Freed, Ben Gold, Jaron 1658 Lanier, Roger Linn, Richard Lyon, Dana Massie, Max Mathews, Keith 1659 McMillen, Carver Mead, Nelson Morgan, Tom Oberheim, Malcolm Slaney, Dave 1660 Smith, Julius Smith, David Wessel, and Matt Wright. 1662 11. IANA Considerations 1664 This section makes a series of requests to IANA. The IANA has completed 1665 registration/assignments of the below requests. 1667 The sub-sections that follow hold the actual, detailed requests. All 1668 registrations in this section are in the IETF tree and follow the rules 1669 of [RFC4288] and [RFC4855], as appropriate. 1671 In Section 11.1, we request the registration of a new media type: 1672 "audio/rtp-midi". Paired with this request is a request for a 1673 repository for new values for several parameters associated with 1674 "audio/rtp-midi". We request this repository in Section 11.1.1. 1676 In Section 11.2, we request the registration of a new value ("rtp- 1677 midi") for the "mode" parameter of the "mpeg4-generic" media type. The 1678 "mpeg4-generic" media type is defined in [RFC3640], and [RFC3640] 1679 defines a repository for the "mode" parameter. However, we believe we 1680 are the first to request the registration of a "mode" value, so we 1681 believe the registry for "mode" has not yet been created by IANA. 1683 Paired with our "mode" parameter value request for "mpeg4-generic" is a 1684 request for a repository for new values for several parameters we have 1685 defined for use with the "rtp-midi" mode value. We request this 1686 repository in Section 11.2.1. 1688 In Section 11.3, we request the registration of a new media type: 1689 "audio/asc". No repository request is associated with this request. 1691 11.1. rtp-midi Media Type Registration 1693 This section requests the registration of the "rtp-midi" subtype for the 1694 "audio" media type. We request the registration of the parameters 1695 listed in the "optional parameters" section below (both the "non- 1696 extensible parameters" and the "extensible parameters" lists). We also 1697 request the creation of repositories for the "extensible parameters"; 1698 the details of this request appear in Section 11.1.1, below. 1700 Media type name: 1702 audio 1704 Subtype name: 1706 rtp-midi 1708 Required parameters: 1710 rate: The RTP timestamp clock rate. See Sections 2.1 and 6.1 1711 for usage details. 1713 Optional parameters: 1715 Non-extensible parameters: 1717 ch_anchor: See Appendix C.2.3 for usage details. 1718 ch_default: See Appendix C.2.3 for usage details. 1719 ch_never: See Appendix C.2.3 for usage details. 1720 cm_unused: See Appendix C.1 for usage details. 1721 cm_used: See Appendix C.1 for usage details. 1722 chanmask: See Appendix C.6.4.3 for usage details. 1723 cid: See Appendix C.6.3 for usage details. 1724 guardtime: See Appendix C.4.2 for usage details. 1725 inline: See Appendix C.6.3 for usage details. 1726 linerate: See Appendix C.3 for usage details. 1727 mperiod: See Appendix C.3 for usage details. 1728 multimode: See Appendix C.6.1 for usage details. 1729 musicport: See Appendix C.5 for usage details. 1730 octpos: See Appendix C.3 for usage details. 1731 rinit: See Appendix C.6.3 for usage details. 1732 rtp_maxptime: See Appendix C.4.1 for usage details. 1733 rtp_ptime: See Appendix C.4.1 for usage details. 1735 smf_cid: See Appendix C.6.4.2 for usage details. 1736 smf_inline: See Appendix C.6.4.2 for usage details. 1737 smf_url: See Appendix C.6.4.2 for usage details. 1738 tsmode: See Appendix C.3 for usage details. 1739 url: See Appendix C.6.3 for usage details. 1741 Extensible parameters: 1743 j_sec: See Appendix C.2.1 for usage details. See 1744 Section 11.1.1 for repository details. 1745 j_update: See Appendix C.2.2 for usage details. See 1746 Section 11.1.1 for repository details. 1747 render: See Appendix C.6 for usage details. See 1748 Section 11.1.1 for repository details. 1749 subrender: See Appendix C.6.2 for usage details. See 1750 Section 11.1.1 for repository details. 1751 smf_info: See Appendix C.6.4.1 for usage details. See 1752 Section 11.1.1 for repository details. 1754 Encoding considerations: 1756 The format for this type is framed and binary. 1758 Restrictions on usage: 1760 This type is only defined for real-time transfers of MIDI 1761 streams via RTP. Stored-file semantics for rtp-midi may 1762 be defined in the future. 1764 Security considerations: 1766 See Section 9 of this memo. 1768 Interoperability considerations: 1770 None. 1772 Published specification: 1774 This memo and [MIDI] serve as the normative specification. In 1775 addition, references [NMP], [GRAME], and [RFC4696] provide 1776 non-normative implementation guidance. 1778 Applications that use this media type: 1780 Audio content-creation hardware, such as MIDI controller piano 1781 keyboards and MIDI audio synthesizers. Audio content-creation 1782 software, such as music sequencers, digital audio workstations, 1783 and soft synthesizers. Computer operating systems, for network 1784 support of MIDI Application Programmer Interfaces. Content 1785 distribution servers and terminals may use this media type for 1786 low bit-rate music coding. 1788 Additional information: 1790 None. 1792 Person & email address to contact for further information: 1794 John Lazzaro 1796 Intended usage: 1798 COMMON. 1800 Author: 1802 John Lazzaro 1804 Change controller: 1806 IETF Audio/Video Transport Working Group delegated 1807 from the IESG. 1809 11.1.1. Repository Request for "audio/rtp-midi" 1811 For the "rtp-midi" subtype, we request the creation of repositories for 1812 extensions to the following parameters (which are those listed as 1813 "extensible parameters" in Section 11.1). 1815 j_sec: 1817 Registrations for this repository may only occur 1818 via an IETF standards-track document. Appendix C.2.1 1819 of this memo describes appropriate registrations for this 1820 repository. 1822 Initial values for this repository appear below: 1824 "none": Defined in Appendix C.2.1 of this memo. 1825 "recj": Defined in Appendix C.2.1 of this memo. 1827 j_update: 1829 Registrations for this repository may only occur 1830 via an IETF standards-track document. Appendix C.2.2 1831 of this memo describes appropriate registrations for this 1832 repository. 1834 Initial values for this repository appear below: 1836 "anchor": Defined in Appendix C.2.2 of this memo. 1837 "open-loop": Defined in Appendix C.2.2 of this memo. 1838 "closed-loop": Defined in Appendix C.2.2 of this memo. 1840 render: 1842 Registrations for this repository MUST include a 1843 specification of the usage of the proposed value. 1844 See text in the preamble of Appendix C.6 for details 1845 (the paragraph that begins "Other render token ..."). 1847 Initial values for this repository appear below: 1849 "unknown": Defined in Appendix C.6 of this memo. 1850 "synthetic": Defined in Appendix C.6 of this memo. 1851 "api": Defined in Appendix C.6 of this memo. 1852 "null": Defined in Appendix C.6 of this memo. 1854 subrender: 1856 Registrations for this repository MUST include a 1857 specification of the usage of the proposed value. 1858 See text Appendix C.6.2 for details (the paragraph 1859 that begins "Other subrender token ..."). 1861 Initial values for this repository appear below: 1863 "default": Defined in Appendix C.6.2 of this memo. 1865 smf_info: 1867 Registrations for this repository MUST include a 1868 specification of the usage of the proposed value. 1869 See text in Appendix C.6.4.1 for details (the 1870 paragraph that begins "Other smf_info token ..."). 1872 Initial values for this repository appear below: 1874 "ignore": Defined in Appendix C.6.4.1 of this memo. 1875 "sdp_start": Defined in Appendix C.6.4.1 of this memo. 1876 "identity": Defined in Appendix C.6.4.1 of this memo. 1878 11.2. mpeg4-generic Media Type Registration 1880 This section requests the registration of the "rtp-midi" value for the 1881 "mode" parameter of the "mpeg4-generic" media type. The "mpeg4- 1882 generic" media type is defined in [RFC3640], and [RFC3640] defines a 1883 repository for the "mode" parameter. We are registering mode rtp- midi 1884 to support the MPEG Audio codecs [MPEGSA] that use MIDI. 1886 In conjunction with this registration request, we request the 1887 registration of the parameters listed in the "optional parameters" 1888 section below (both the "non-extensible parameters" and the "extensible 1889 parameters" lists). We also request the creation of repositories for 1890 the "extensible parameters"; the details of this request appear in 1891 Appendix 11.2.1, below. 1893 Media type name: 1895 audio 1897 Subtype name: 1899 mpeg4-generic 1901 Required parameters: 1903 The "mode" parameter is required by [RFC3640]. [RFC3640] requests 1904 a repository for "mode", so that new values for mode 1905 may be added. We request that the value "rtp-midi" be 1906 added to the "mode" repository. 1908 In mode rtp-midi, the mpeg4-generic parameter rate is 1909 a required parameter. Rate specifies the RTP timestamp 1910 clock rate. See Sections 2.1 and 6.2 for usage details 1911 of rate in mode rtp-midi. 1913 Optional parameters: 1915 We request registration of the following parameters 1916 for use in mode rtp-midi for mpeg4-generic. 1918 Non-extensible parameters: 1920 ch_anchor: See Appendix C.2.3 for usage details. 1921 ch_default: See Appendix C.2.3 for usage details. 1922 ch_never: See Appendix C.2.3 for usage details. 1923 cm_unused: See Appendix C.1 for usage details. 1924 cm_used: See Appendix C.1 for usage details. 1925 chanmask: See Appendix C.6.4.3 for usage details. 1926 cid: See Appendix C.6.3 for usage details. 1927 guardtime: See Appendix C.4.2 for usage details. 1928 inline: See Appendix C.6.3 for usage details. 1929 linerate: See Appendix C.3 for usage details. 1930 mperiod: See Appendix C.3 for usage details. 1931 multimode: See Appendix C.6.1 for usage details. 1932 musicport: See Appendix C.5 for usage details. 1933 octpos: See Appendix C.3 for usage details. 1934 rinit: See Appendix C.6.3 for usage details. 1935 rtp_maxptime: See Appendix C.4.1 for usage details. 1936 rtp_ptime: See Appendix C.4.1 for usage details. 1937 smf_cid: See Appendix C.6.4.2 for usage details. 1938 smf_inline: See Appendix C.6.4.2 for usage details. 1939 smf_url: See Appendix C.6.4.2 for usage details. 1940 tsmode: See Appendix C.3 for usage details. 1941 url: See Appendix C.6.3 for usage details. 1943 Extensible parameters: 1945 j_sec: See Appendix C.2.1 for usage details. See 1946 Section 11.2.1 for repository details. 1947 j_update: See Appendix C.2.2 for usage details. See 1948 Section 11.2.1 for repository details. 1949 render: See Appendix C.6 for usage details. See 1950 Section 11.2.1 for repository details. 1951 subrender: See Appendix C.6.2 for usage details. See 1952 Section 11.2.1 for repository details. 1953 smf_info: See Appendix C.6.4.1 for usage details. See 1954 Section 11.2.1 for repository details. 1956 Encoding considerations: 1958 The format for this type is framed and binary. 1960 Restrictions on usage: 1962 Only defined for real-time transfers of audio/mpeg4-generic 1963 RTP streams with mode=rtp-midi. 1965 Security considerations: 1967 See Section 9 of this memo. 1969 Interoperability considerations: 1971 Except for the marker bit (Section 2.1), the packet formats 1972 for audio/rtp-midi and audio/mpeg4-generic (mode rtp-midi) 1973 are identical. The formats differ in use: audio/mpeg4-generic 1974 is for MPEG work, and audio/rtp-midi is for all other work. 1976 Published specification: 1978 This memo, [MIDI], and [MPEGSA] are the normative references. 1979 In addition, references [NMP], [GRAME], and [RFC4696] provide 1980 non-normative implementation guidance. 1982 Applications that use this media type: 1984 MPEG 4 servers and terminals that support [MPEGSA]. 1986 Additional information: 1988 None. 1990 Person & email address to contact for further information: 1992 John Lazzaro 1994 Intended usage: 1996 COMMON. 1998 Author: 2000 John Lazzaro 2002 Change controller: 2004 IETF Audio/Video Transport Working Group delegated 2005 from the IESG. 2007 11.2.1. Repository Request for Mode rtp-midi for mpeg4-generic 2009 For mode rtp-midi of the mpeg4-generic subtype, we request the creation 2010 of repositories for extensions to the following parameters (which are 2011 those listed as "extensible parameters" in Section 11.2). 2013 j_sec: 2015 Registrations for this repository may only occur 2016 via an IETF standards-track document. Appendix C.2.1 2017 of this memo describes appropriate registrations for this 2018 repository. 2020 Initial values for this repository appear below: 2022 "none": Defined in Appendix C.2.1 of this memo. 2023 "recj": Defined in Appendix C.2.1 of this memo. 2025 j_update: 2027 Registrations for this repository may only occur 2028 via an IETF standards-track document. Appendix C.2.2 2029 of this memo describes appropriate registrations for this 2030 repository. 2032 Initial values for this repository appear below: 2034 "anchor": Defined in Appendix C.2.2 of this memo. 2035 "open-loop": Defined in Appendix C.2.2 of this memo. 2036 "closed-loop": Defined in Appendix C.2.2 of this memo. 2038 render: 2040 Registrations for this repository MUST include a 2041 specification of the usage of the proposed value. 2042 See text in the preamble of Appendix C.6 for details 2043 (the paragraph that begins "Other render token ..."). 2045 Initial values for this repository appear below: 2047 "unknown": Defined in Appendix C.6 of this memo. 2048 "synthetic": Defined in Appendix C.6 of this memo. 2049 "null": Defined in Appendix C.6 of this memo. 2051 subrender: 2053 Registrations for this repository MUST include a 2054 specification of the usage of the proposed value. 2055 See text in Appendix C.6.2 for details (the paragraph 2056 that begins "Other subrender token ..." and 2057 subsequent paragraphs). Note that the text in 2058 Appendix C.6.2 contains restrictions on subrender 2059 registrations for mpeg4-generic ("Registrations 2060 for mpeg4-generic subrender values ..."). 2062 Initial values for this repository appear below: 2064 "default": Defined in Appendix C.6.2 of this memo. 2066 smf_info: 2068 Registrations for this repository MUST include a 2069 specification of the usage of the proposed value. 2070 See text in Appendix C.6.4.1 for details (the 2071 paragraph that begins "Other smf_info token ..."). 2073 Initial values for this repository appear below: 2075 "ignore": Defined in Appendix C.6.4.1 of this memo. 2076 "sdp_start": Defined in Appendix C.6.4.1 of this memo. 2077 "identity": Defined in Appendix C.6.4.1 of this memo. 2079 11.3. asc Media Type Registration 2081 This section registers "asc" as a subtype for the "audio" media type. 2082 We register this subtype to support the remote transfer of the "config" 2083 parameter of the mpeg4-generic media type [RFC3640] when it is used with 2084 mpeg4-generic mode rtp-midi (registered in Appendix 11.2 above). We 2085 explain the mechanics of using "audio/asc" to set the config parameter 2086 in Section 6.2 and Appendix C.6.5 of this document. 2088 Note that this registration is a new subtype registration and is not an 2089 addition to a repository defined by MPEG-related memos (such as 2090 [RFC3640]). Also note that this request for "audio/asc" does not 2091 register parameters, and does not request the creation of a repository. 2093 Media type name: 2095 audio 2097 Subtype name: 2099 asc 2101 Required parameters: 2103 None. 2105 Optional parameters: 2107 None. 2109 Encoding considerations: 2111 The native form of the data object is binary data, 2112 zero-padded to an octet boundary. 2114 Restrictions on usage: 2116 This type is only defined for data object (stored file) 2117 transfer. The most common transports for the type are 2118 HTTP and SMTP. 2120 Security considerations: 2122 See Section 9 of this memo. 2124 Interoperability considerations: 2126 None. 2128 Published specification: 2130 The audio/asc data object is the AudioSpecificConfig 2131 binary data structure, which is normatively defined in [MPEGAUDIO]. 2133 Applications that use this media type: 2135 MPEG 4 Audio servers and terminals that support 2136 audio/mpeg4-generic RTP streams for mode rtp-midi. 2138 Additional information: 2140 None. 2142 Person & email address to contact for further information: 2144 John Lazzaro 2146 Intended usage: 2148 COMMON. 2150 Author: 2152 John Lazzaro 2154 Change controller: 2156 IETF Audio/Video Transport Working Group delegated 2157 from the IESG. 2159 A. The Recovery Journal Channel Chapters 2161 A.1. Recovery Journal Definitions 2163 This appendix defines the terminology and the coding idioms that are 2164 used in the recovery journal bitfield descriptions in Section 5 (journal 2165 header structure), Appendices A.2 to A.9 (channel journal chapters) and 2166 Appendices B.1 to B.5 (system journal chapters). 2168 We assume that the recovery journal resides in the journal section of an 2169 RTP packet with sequence number I ("packet I") and that the Checkpoint 2170 Packet Seqnum field in the top-level recovery journal header refers to a 2171 previous packet with sequence number C (an exception is the self- 2172 referential C = I case). Unless stated otherwise, algorithms are 2173 assumed to use modulo 2^16 arithmetic for calculations on 16-bit 2174 sequence numbers and modulo 2^32 arithmetic for calculations on 32-bit 2175 extended sequence numbers. 2177 Several bitfield coding idioms appear throughout the recovery journal 2178 system, with consistent semantics. Most recovery journal elements begin 2179 with an "S" (Single-packet loss) bit. S bits are designed to help 2180 receivers efficiently parse through the recovery journal hierarchy in 2181 the common case of the loss of a single packet. 2183 As a rule, S bits MUST be set to 1. However, an exception applies if a 2184 recovery journal element in packet I encodes data about a command stored 2185 in the MIDI command section of packet I - 1. In this case, the S bit of 2186 the recovery journal element MUST be set to 0. If a recovery journal 2187 element has its S bit set to 0, all higher-level recovery journal 2188 elements that contain it MUST also have S bits that are set to 0, 2189 including the top-level recovery journal header. 2191 Other consistent bitfield coding idioms are described below: 2193 o R flag bit. R flag bits are reserved for future use. Senders 2194 MUST set R bits to 0. Receivers MUST ignore R bit values. 2196 o LENGTH field. All fields named LENGTH (as distinct from LEN) 2197 code the number of octets in the structure that contains it, 2198 including the header it resides in and all hierarchical levels 2199 below it. If a structure contains a LENGTH field, a receiver 2200 MUST use the LENGTH field value to advance past the structure 2201 during parsing, rather than use knowledge about the internal 2202 format of the structure. 2204 We now define normative terms used to describe recovery journal 2205 semantics. 2207 o Checkpoint history. The checkpoint history of a recovery journal 2208 is the concatenation of the MIDI command sections of packets C 2209 through I - 1. The final command in the MIDI command section for 2210 packet I - 1 is considered the most recent command; the first 2211 command in the MIDI command section for packet C is the oldest 2212 command. If command X is less recent than command Y, X is 2213 considered to be "before Y". A checkpoint history with no 2214 commands is considered to be empty. The checkpoint history 2215 never contains the MIDI command section of packet I (the 2216 packet containing the recovery journal), so if C == I, the 2217 checkpoint history is empty by definition. 2219 o Session history. The session history of a recovery journal is 2220 the concatenation of MIDI command sections from the first 2221 packet of the session up to packet I - 1. The definitions of 2222 command recency and history emptiness follow those in the 2223 checkpoint history. The session history never contains the 2224 MIDI command section of packet I, and so the session history of 2225 the first packet in the session is empty by definition. 2227 o Finished/unfinished commands. If all octets of a MIDI command 2228 appear in the session history, the command is defined as being 2229 finished. If some but not all octets of a command appear 2230 in the session history, the command is defined as being unfinished. 2231 Unfinished commands occur if segments of a SysEx command appear 2232 in several RTP packets. For example, if a SysEx command is coded 2233 as 3 segments, with segment 1 in packet K, segment 2 in packet 2234 K + 1, and segment 3 in packet K + 2, the session histories for 2235 packets K + 1 and K + 2 contain unfinished versions of the command. 2236 A session history contains a finished version of a cancelled SysEx 2237 command if the history contains the cancel sublist for the command. 2239 o Reset State commands. Reset State (RS) commands reset 2240 renderers to an initialized "powerup" condition. The 2241 RS commands are: System Reset (0xFF), General MIDI System Enable 2242 (0xF0 0x7E 0xcc 0x09 0x01 0xF7), General MIDI 2 System Enable 2243 (0xF0 0x7E 0xcc 0x09 0x03 0xF7), General MIDI System Disable 2244 (0xF0 0x7E 0xcc 0x09 0x00 0xF7), Turn DLS On (0xF0 0x7E 0xcc 0x0A 2245 0x01 0xF7), and Turn DLS Off (0xF0 0x7E 0xcc 0x0A 0x02 0xF7). 2246 Registrations of subrender parameter token values (Appendix C.6.2) 2247 and IETF standards-track documents MAY specify additional 2248 RS commands. 2250 o Active commands. Active command are MIDI commands that do not 2251 appear before a Reset State command in the session history. 2253 o N-active commands. N-active commands are MIDI commands that do 2254 not appear before one of the following commands in the session 2255 history: MIDI Control Change numbers 123-127 (numbers with All 2256 Notes Off semantics) or 120 (All Sound Off), and any Reset 2257 State command. 2259 o C-active commands. C-active commands are MIDI commands that do 2260 not appear before one of the following commands in the session 2261 history: MIDI Control Change number 121 (Reset All Controllers) 2262 and any Reset State command. 2264 o Oldest-first ordering rule. Several recovery journal chapters 2265 contain a list of elements, where each element is associated 2266 with a MIDI command that appears in the session history. In 2267 most cases, the chapter definition requires that list elements 2268 be ordered in accordance with the "oldest-first ordering rule". 2269 Below, we normatively define this rule: 2271 Elements associated with the most recent command in the session 2272 history coded in the list MUST appear at the end of the list. 2274 Elements associated with the oldest command in the session 2275 history coded in the list MUST appear at the start of the list. 2277 All other list elements MUST be arranged with respect to these 2278 boundary elements, to produce a list ordering that strictly 2279 reflects the relative session history recency of the commands 2280 coded by the elements in the list. 2282 o Parameter system. A MIDI feature that provides two sets of 2283 16,384 parameters to expand the 0-127 controller number space. 2284 The Registered Parameter Names (RPN) system and the Non-Registered 2285 Parameter Names (NRPN) system each provides 16,384 parameters. 2287 o Parameter system transaction. The value of RPNs and NRPNs are 2288 changed by a series of Control Change commands that form a 2289 parameter system transaction. A canonical transaction begins 2290 with two Control Change commands to set the parameter number 2291 (controller numbers 99 and 98 for NRPNs, controller numbers 101 2292 and 100 for RPNs). The transaction continues with an arbitrary 2293 number of Data Entry (controller numbers 6 and 38), Data Increment 2294 (controller number 96), and Data Decrement (controller number 2295 97) Control Change commands to set the parameter value. The 2296 transaction ends with a second pair of (99, 98) or (101, 100) 2297 Control Change commands that specify the null parameter (MSB 2298 value 0x7F, LSB value 0x7F). 2300 Several variants of the canonical transaction sequence are 2301 possible. Most commonly, the terminal pair of (99, 98) or 2302 (101, 100) Control Change commands may specify a parameter 2303 other than the null parameter. In this case, the command 2304 pair terminates the first transaction and starts a second 2305 transaction. The command pair is considered to be a part 2306 of both transactions. This variant is legal and recommended 2307 in [MIDI]. We refer to this variant as a "type 1 variant". 2309 Less commonly, the MSB (99 or 101) or LSB (98 or 100) command 2310 of a (99, 98) or (101, 100) Control Change pair may be omitted. 2312 If the MSB command is omitted, the transaction uses the MSB value 2313 of the most recent C-active Control Change command for controller 2314 number 99 or 101 that appears in the session history. We refer to 2315 this variant as a "type 2 variant". 2317 If the LSB command is omitted, the LSB value 0x00 is assumed. We 2318 refer to this variant as a "type 3 variant". The type 2 and type 3 2319 variants are defined as legal, but are not recommended, in [MIDI]. 2321 System real-time commands may appear at any point during 2322 a transaction (even between octets of individual commands 2323 in the transaction). More generally, [MIDI] does not forbid 2324 the appearance of unrelated MIDI commands during an open 2325 transaction. As a rule, these commands are considered to 2326 be "outside" the transaction and do not affect the status 2327 of the transaction in any way. Exceptions to this rule are 2328 commands whose semantics act to terminate transactions: 2329 Reset State commands, and Control Change (0xB) for controller 2330 number 121 (Reset All Controllers) [RP015]. 2332 o Initiated parameter system transaction. A canonical parameter 2333 system transaction whose (99, 98) or (101, 100) initial Control 2334 Change command pair appears in the session history is considered 2335 to be an initiated parameter system transaction. This definition 2336 also holds for type 1 variants. For type 2 variants (dropped MSB), 2337 a transaction whose initial LSB Control Change command appears in 2338 the session history is an initiated transaction. For type 3 2339 variants (dropped LSB), a transaction is considered to be 2340 initiated if at least one transaction command follows the initial 2341 MSB (99 or 101) Control Change command in the session history. 2342 The completion of a transaction does not nullify its "initiated" 2343 status. 2345 o Session history reference counts. Several recovery journal 2346 chapters include a reference count field, which codes the 2347 total number of commands of a type that appear in the session 2348 history. Examples include the Reset and Tune Request command 2349 logs (Chapter D, Appendix B.1) and the Active Sense command 2350 (Chapter V, Appendix B.2). Upon the detection of a loss event, 2351 reference count fields let a receiver deduce if any instances of 2352 the command have been lost, by comparing the journal reference 2353 count with its own reference count. Thus, a reference count 2354 field makes sense, even for command types in which knowing the 2355 NUMBER of lost commands is irrelevant (as is true with all of 2356 the example commands mentioned above). 2358 The chapter definitions in Appendices A.2 to A.9 and B.1 to B.5 reflect 2359 the default recovery journal behavior. The ch_default, ch_never, and 2360 ch_anchor parameters modify these definitions, as described in Appendix 2361 C.2.3. 2363 The chapter definitions specify if data MUST be present in the journal. 2364 Senders MAY also include non-required data in the journal. This 2365 optional data MUST comply with the normative chapter definition. For 2366 example, if a chapter definition states that a field codes data from the 2367 most recent active command in the session history, the sender MUST NOT 2368 code inactive commands or older commands in the field. 2370 Finally, we note that a channel journal only encodes information about 2371 MIDI commands appearing on the MIDI channel the journal protects. All 2372 references to MIDI commands in Appendices A.2 to A.9 should be read as 2373 "MIDI commands appearing on this channel." 2374 A.2. Chapter P: MIDI Program Change 2376 A channel journal MUST contain Chapter P if an active Program Change 2377 (0xC) command appears in the checkpoint history. Figure A.2.1 shows the 2378 format for Chapter P. 2380 0 1 2 2381 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 2382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2383 |S| PROGRAM |B| BANK-MSB |X| BANK-LSB | 2384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2386 Figure A.2.1 -- Chapter P format 2388 The chapter has a fixed size of 24 bits. The PROGRAM field indicates 2389 the data value of the most recent active Program Change command in the 2390 session history. By default, the B, BANK-MSB, X, and BANK-LSB fields 2391 MUST be set to 0. Below, we define exceptions to this default 2392 condition. 2394 If an active Control Change (0xB) command for controller number 0 (Bank 2395 Select MSB) appears before the Program Change command in the session 2396 history, the B bit MUST be set to 1, and the BANK-MSB field MUST code 2397 the data value of the Control Change command. 2399 If B is set to 1, the BANK-LSB field MUST code the data value of the 2400 most recent Control Change command for controller number 32 (Bank Select 2401 LSB) that preceded the Program Change command coded in the PROGRAM field 2402 and followed the Control Change command coded in the BANK-MSB field. If 2403 no such Control Change command exists, the BANK-LSB field MUST be set to 2404 0. 2406 If B is set to 1, and if a Control Change command for controller number 2407 121 (Reset All Controllers) appears in the MIDI stream between the 2408 Control Change command coded by the BANK-MSB field and the Program 2409 Change command coded by the PROGRAM field, the X bit MUST be set to 1. 2411 Note that [RP015] specifies that Reset All Controllers does not reset 2412 the values of controller numbers 0 (Bank Select MSB) and 32 (Bank Select 2413 LSB). Thus, the X bit does not effect how receivers will use the BANK- 2414 LSB and BANK-MSB values when recovering from a lost Program Change 2415 command. The X bit serves to aid recovery in MIDI applications where 2416 controller numbers 0 and 32 are used in a non-standard way. 2418 A.3. Chapter C: MIDI Control Change 2420 Figure A.3.1 shows the format for Chapter C. 2422 0 1 2 3 2423 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 2424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2425 |S| LEN |S| NUMBER |A| VALUE/ALT |S| NUMBER | 2426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2427 |A| VALUE/ALT | .... | 2428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2430 Figure A.3.1 -- Chapter C format 2432 The chapter consists of a 1-octet header, followed by a variable length 2433 list of 2-octet controller logs. The list MUST contain at least one 2434 controller log. The 7-bit LEN field codes the number of controller logs 2435 in the list, minus one. We define the semantics of the controller log 2436 fields in Appendix A.3.2. 2438 A channel journal MUST contain Chapter C if the rules defined in this 2439 appendix require that one or more controller logs appear in the list. 2441 A.3.1. Log Inclusion Rules 2443 A controller log encodes information about a particular Control Change 2444 command in the session history. 2446 In the default use of the payload format, list logs MUST encode 2447 information about the most recent active command in the session history 2448 for a controller number. Logs encoding earlier commands MUST NOT appear 2449 in the list. 2451 Also, as a rule, the list MUST contain a log for the most recent active 2452 command for a controller number that appears in the checkpoint history. 2453 Below, we define exceptions to this rule: 2455 o MIDI streams may transmit 14-bit controller values using paired 2456 Most Significant Byte (MSB, controller numbers 0-31, 99, 101) and 2457 Least Significant Byte (LSB, controller numbers 32-63, 98, 100) 2458 Control Change commands [MIDI]. 2460 If the most recent active Control Change command in the session 2461 history for a 14-bit controller pair uses the MSB number, Chapter 2462 C MAY omit the controller log for the most recent active Control 2463 Change command for the associated LSB number, as the command 2464 ordering makes this LSB value irrelevant. However, this exception 2465 MUST NOT be applied if the sender is not certain that the MIDI 2466 source uses 14-bit semantics for the controller number pair. Note 2467 that some MIDI sources ignore 14-bit controller semantics and use 2468 the LSB controller numbers as independent 7-bit controllers. 2470 o If active Control Change commands for controller numbers 0 (Bank 2471 Select MSB) or 32 (Bank Select LSB) appear in the checkpoint 2472 history, and if the command instances are also coded in the 2473 BANK-MSB and BANK-LSB fields of the Chapter P (Appendix A.2), 2474 Chapter C MAY omit the controller logs for the commands. 2476 o Several controller number pairs are defined to be mutually 2477 exclusive. Controller numbers 124 (Omni Off) and 125 (Omni On) 2478 form a mutually exclusive pair, as do controller numbers 126 2479 (Mono) and 127 (Poly). 2481 If active Control Change commands for one or both members of 2482 a mutually exclusive pair appear in the checkpoint history, a 2483 log for the controller number of the most recent command for the 2484 pair in the checkpoint history MUST appear in the controller list. 2485 However, the list MAY omit the controller log for the most recent 2486 active command for the other number in the pair. 2488 If active Control Change commands for one or both members of a 2489 mutually exclusive pair appear in the session history, and if a 2490 log for the controller number of the most recent command for the 2491 pair does not appear in the controller list, a log for the most 2492 recent command for the other number of the pair MUST NOT appear 2493 in the controller list. 2495 o If an active Control Change command for controller number 121 2496 (Reset All Controllers) appears in the session history, the 2497 controller list MAY omit logs for Control Change commands that 2498 precede the Reset All Controllers command in the session history, 2499 under certain conditions. 2501 Namely, a log MAY be omitted if the sender is certain that a 2502 command stream follows the Reset All Controllers semantics 2503 defined in [RP015], and if the log codes a controller number 2504 for which [RP015] specifies a reset value. 2506 For example, [RP015] specifies that controller number 1 2507 (Modulation Wheel) is reset to the value 0, and thus 2508 a controller log for Modulation Wheel MAY be omitted 2509 from the controller log list. In contrast, [RP015] specifies 2510 that controller number 7 (Channel Volume) is not reset, 2511 and thus a controller log for Channel Volume MUST NOT 2512 be omitted from the controller log list. 2514 o Appendix A.3.4 defines exception rules for the MIDI Parameter 2515 System controller numbers 6, 38, and 96-101. 2517 A.3.2. Controller Log Format 2519 Figure A.3.2 shows the controller log structure of Chapter C. 2521 0 1 2522 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2524 |S| NUMBER |A| VALUE/ALT | 2525 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2527 Figure A.3.2 -- Chapter C controller log 2529 The 7-bit NUMBER field identifies the controller number of the coded 2530 command. The 7-bit VALUE/ALT field codes recovery information for the 2531 command. The A bit sets the format of the VALUE/ALT field. 2533 A log encodes recovery information using one of the following tools: the 2534 value tool, the toggle tool, or the count tool. 2536 A log uses the value tool if the A bit is set to 0. The value tool 2537 codes the 7-bit data value of a command in the VALUE/ALT field. The 2538 value tool works best for controllers that code a continuous quantity, 2539 such as number 1 (Modulation Wheel). 2541 The A bit is set to 1 to code the toggle or count tool. These tools 2542 work best for controllers that code discrete actions. Figure A.3.3 2543 shows the controller log for these tools. 2545 0 1 2546 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2548 |S| NUMBER |1|T| ALT | 2549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2551 Figure A.3.3 -- Controller log for ALT tools 2553 A log uses the toggle tool if the T bit is set to 0. A log uses the 2554 count tool if the T bit is set to 1. Both methods use the 6-bit ALT 2555 field as an unsigned integer. 2557 The toggle tool works best for controllers that act as on/off switches, 2558 such as 64 (Damper Pedal (Sustain)). These controllers code the "off" 2559 state with control values 0-63 and the "on" state with 64-127. 2561 For the toggle tool, the ALT field codes the total number of toggles 2562 (off->on and on->off) due to Control Change commands in the session 2563 history, up to and including a toggle caused by the command coded by the 2564 log. The toggle count includes toggles caused by Control Change 2565 commands for controller number 121 (Reset All Controllers). 2567 Toggle counting is performed modulo 64. The toggle count is reset at 2568 the start of a session, and whenever a Reset State command (Appendix 2569 A.1) appears in the session history. When these reset events occur, the 2570 toggle count for a controller is set to 0 (for controllers whose default 2571 value is 0-63) or 1 (for controllers whose default value is 64-127). 2573 The Damper Pedal (Sustain) controller illustrates the benefits of the 2574 toggle tool over the value tool for switch controllers. As often used 2575 in piano applications, the "on" state of the controller lets notes 2576 resonate, while the "off" state immediately damps notes to silence. The 2577 loss of the "off" command in an "on->off->on" sequence results in 2578 ringing notes that should have been damped silent. The toggle tool lets 2579 receivers detect this lost "off" command, but the value tool does not. 2581 The count tool is conceptually similar to the toggle tool. For the 2582 count tool, the ALT field codes the total number of Control Change 2583 commands in the session history, up to and including the command coded 2584 by the log. Command counting is performed modulo 64. The command count 2585 is set to 0 at the start of the session and is reset to 0 whenever a 2586 Reset State command (Appendix A.1) appears in the session history. 2588 Because the count tool ignores the data value, it is a good match for 2589 controllers whose controller value is ignored, such as number 123 (All 2590 Notes Off). More generally, the count tool may be used to code a 2591 (modulo 64) identification number for a command. 2593 A.3.3. Log List Coding Rules 2595 In this section, we describe the organization of controller logs in the 2596 Chapter C log list. 2598 A log encodes information about a particular Control Change command in 2599 the session history. In most cases, a command SHOULD be coded by a 2600 single tool (and, thus, a single log). If a number is coded with a 2601 single tool and this tool is the count tool, recovery Control Change 2602 commands generated by a receiver SHOULD use the default control value 2603 for the controller. 2605 However, a command MAY be coded by several tool types (and, thus, 2606 several logs, each using a different tool). This technique may improve 2607 recovery performance for controllers with complex semantics, such as 2608 controller number 84 (Portamento Control) or controller number 121 2609 (Reset All Controllers) when used with a non-zero data octet (with the 2610 semantics described in [DLS2]). 2612 If a command is encoded by multiple tools, the logs MUST be placed in 2613 the list in the following order: count tool log (if any), followed by 2614 value tool log (if any), followed by toggle tool log (if any). 2616 The Chapter C log list MUST obey the oldest-first ordering rule (defined 2617 in Appendix A.1). Note that this ordering preserves the information 2618 necessary for the recovery of 14-bit controller values, without 2619 precluding the use of MSB and LSB controller pairs as independent 7-bit 2620 controllers. 2622 In the default use of the payload format, all logs that appear in the 2623 list for a controller number encode information about one Control Change 2624 command -- namely, the most recent active Control Change command in the 2625 session history for the number. 2627 This coding scheme provides good recovery performance for the standard 2628 uses of Control Change commands defined in [MIDI]. However, not all 2629 MIDI applications restrict the use of Control Change commands to those 2630 defined in [MIDI]. 2632 For example, consider the common MIDI encoding of rotary encoders 2633 ("infinite" rotation knobs). The mixing console MIDI convention defined 2634 in [LCP] codes the position of rotary encoders as a series of Control 2635 Change commands. Each command encodes a relative change of knob 2636 position from the last update (expressed as a clockwise or counter- 2637 clockwise knob turning angle). 2639 As the knob position is encoded incrementally over a series of Control 2640 Change commands, the best recovery performance is obtained if the log 2641 list encodes all Control Change commands for encoder controller numbers 2642 that appear in the checkpoint history, not only the most recent command. 2644 To support application areas that use Control Change commands in this 2645 way, Chapter C may be configured to encode information about several 2646 Control Change commands for a controller number. We use the term 2647 "enhanced" to describe this encoding method, which we describe below. 2649 In Appendix C.2.3, we show how to configure a stream to use enhanced 2650 Chapter C encoding for specific controller numbers. In Section 5 in the 2651 main text, we show how the H bits in the recovery journal header (Figure 2652 8) and in the channel journal header (Figure 9) indicate the use of 2653 enhanced Chapter C encoding. 2655 Here, we define how to encode a Chapter C log list that uses the 2656 enhanced encoding method. 2658 Senders that use the enhanced encoding method for a controller number 2659 MUST obey the rules below. These rules let a receiver determine which 2660 logs in the list correspond to lost commands. Note that these rules 2661 override the exceptions listed in Appendix A.3.1. 2663 o If N commands for a controller number are encoded in the list, 2664 the commands MUST be the N most recent commands for the controller 2665 number in the session history. For example, for N = 2, the sender 2666 MUST encode the most recent command and the second most recent 2667 command, not the most recent command and the third most recent 2668 command. 2670 o If a controller number uses enhanced encoding, the encoding 2671 of the least-recent command for the controller number in the 2672 log list MUST include a count tool log. In addition, if 2673 commands are encoded for the controller number whose logs 2674 have S bits set to 0, the encoding of the least-recent 2675 command with S = 0 logs MUST include a count tool log. 2677 The count tool is OPTIONAL for the other commands for the 2678 controller number encoded in the list, as a receiver is 2679 able to efficiently deduce the count tool value for these 2680 commands, for both single-packet and multi-packet loss events. 2682 o The use of the value and toggle tools MUST be identical for all 2683 commands for a controller number encoded in the list. For 2684 example, a value tool log either MUST appear for all commands 2685 for the controller number coded in the list, or alternatively, 2686 value tool logs for the controller number MUST NOT appear in 2687 the list. Likewise, a toggle tool log either MUST appear for 2688 all commands for the controller number coded in the list, or 2689 alternatively, toggle tool logs for the controller number MUST 2690 NOT appear in the list. 2692 o If a command is encoded by multiple tools, the logs MUST be 2693 placed in the list in the following order: count tool log 2694 (if any), followed by value tool log (if any), followed by 2695 toggle tool log (if any). 2697 These rules permit a receiver recovering from a packet loss to use the 2698 count tool log to match the commands encoded in the list with its own 2699 history of the stream, as we describe below. Note that the text below 2700 describes a non-normative algorithm; receivers are free to use any 2701 algorithm to match its history with the log list. 2703 In a typical implementation of the enhanced encoding method, a receiver 2704 computes and stores count, value, and toggle tool data field values for 2705 the most recent Control Change command it has received for a controller 2706 number. 2708 After a loss event, a receiver parses the Chapter C list and processes 2709 list logs for a controller number that uses enhanced encoding as 2710 follows. 2712 The receiver compares the count tool ALT field for the least-recent 2713 command for the controller number in the list against its stored count 2714 data for the controller number, to determine if recovery is necessary 2715 for the command coded in the list. The value and toggle tool logs (if 2716 any) that directly follow the count tool log are associated with this 2717 least-recent command. 2719 To check more-recent commands for the controller, the receiver detects 2720 additional value and/or toggle tool logs for the controller number in 2721 the list and infers count tool data for the command coded by these logs. 2722 This inferred data is used to determine if recovery is necessary for the 2723 command coded by the value and/or toggle tool logs. 2725 In this way, a receiver is able to execute only lost commands, without 2726 executing a command twice. While recovering from a single packet loss, 2727 a receiver may skip through S = 1 logs in the list, as the first S = 0 2728 log for an enhanced controller number is always a count tool log. 2730 Note that the requirements in Appendix C.2.2.2 for protective sender and 2731 receiver actions during session startup for multicast operation are of 2732 particular importance for enhanced encoding, as receivers need to 2733 initialize its count tool data structures with recovery journal data in 2734 order to match commands correctly after a loss event. 2736 Finally, we note in passing that in some applications of rotary 2737 encoders, a good user experience may be possible without the use of 2738 enhanced encoding. These applications are distinguished by visual 2739 feedback of encoding position that is driven by the post-recovery rotary 2740 encoding stream, and relatively low packet loss. In these domains, 2741 recovery performance may be acceptable for rotary encoders if the log 2742 list encodes only the most recent command, if both count and value logs 2743 appear for the command. 2745 A.3.4. The Parameter System 2747 Readers may wish to review the Appendix A.1 definitions of "parameter 2748 system", "parameter system transaction", and "initiated parameter system 2749 transaction" before reading this section. 2751 Parameter system transactions update a MIDI Registered Parameter Number 2752 (RPN) or Non-Registered Parameter Number (NRPN) value. A parameter 2753 system transaction is a sequence of Control Change commands that may use 2754 the following controllers numbers: 2756 o Data Entry MSB (6) 2757 o Data Entry LSB (38) 2758 o Data Increment (96) 2759 o Data Decrement (97) 2760 o Non-Registered Parameter Number (NRPN) LSB (98) 2761 o Non-Registered Parameter Number (NRPN) MSB (99) 2762 o Registered Parameter Number (RPN) LSB (100) 2763 o Registered Parameter Number (RPN) MSB (101) 2765 Control Change commands that are a part of a parameter system 2766 transaction MUST NOT be coded in Chapter C controller logs. Instead, 2767 these commands are coded in Chapter M, the MIDI Parameter chapter 2768 defined in Appendix A.4. 2770 However, Control Change commands that use the listed controllers as 2771 general-purpose controllers (i.e., outside of a parameter system 2772 transaction) MUST NOT be coded in Chapter M. 2774 Instead, the controllers are coded in Chapter C controller logs. The 2775 controller logs follow the coding rules stated in Appendix A.3.2 and 2776 A.3.3. The rules for coding paired LSB and MSB controllers, as defined 2777 in Appendix A.3.1, apply to the pairs (6, 38), (99, 98), and (101, 100) 2778 when coded in Chapter C. 2780 If active Control Change commands for controller numbers 6, 38, or 2781 96-101 appear in the checkpoint history, and these commands are used as 2782 general-purpose controllers, the most recent general-purpose command 2783 instance for these controller numbers MUST appear as entries in the 2784 Chapter C controller list. 2786 MIDI syntax permits a source to use controllers 6, 38, 96, and 97 as 2787 parameter-system controllers and general-purpose controllers in the same 2788 stream. An RTP MIDI sender MUST deduce the role of each Control Change 2789 command for these controller numbers by noting the placement of the 2790 command in the stream and MUST use this information to code the command 2791 in Chapter C or Chapter M, as appropriate. 2793 Specifically, active Control Change commands for controllers 6, 38, 96, 2794 and 97 act in a general-purpose way when 2796 o no active Control Change commands that set an RPN or 2797 NRPN parameter number appear in the session history, or 2799 o the most recent active Control Change commands in the session 2800 history that set an RPN or NRPN parameter number code the null 2801 parameter (MSB value 0x7F, LSB value 0x7F), or 2803 o a Control Change command for controller number 121 (Reset 2804 All Controllers) appears more recently in the session history 2805 than all active Control Change commands that set an RPN or 2806 NRPN parameter number (see [RP015] for details). 2808 Finally, we note that a MIDI source that follows the recommendations of 2809 [MIDI] exclusively uses numbers 98-101 as parameter system controllers. 2810 Alternatively, a MIDI source may exclusively use 98-101 as general- 2811 purpose controllers and lose the ability to perform parameter system 2812 transactions in a stream. 2814 In the language of [MIDI], the general-purpose use of controllers 98-101 2815 constitutes a non-standard controller assignment. As most real-world 2816 MIDI sources use the standard controller assignment for controller 2817 numbers 98-101, an RTP MIDI sender SHOULD assume these controllers act 2818 as parameter system controllers, unless it knows that a MIDI source uses 2819 controller numbers 98-101 in a general-purpose way. 2821 A.4. Chapter M: MIDI Parameter System 2823 Readers may wish to review the Appendix A.1 definitions for "C-active", 2824 "parameter system", "parameter system transaction", and "initiated 2825 parameter system transaction" before reading this appendix. 2827 Chapter M protects parameter system transactions for Registered 2828 Parameter Number (RPN) and Non-Registered Parameter Number (NRPN) 2829 values. Figure A.4.1 shows the format for Chapter M. 2831 0 1 2 3 2832 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 2833 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2834 |S|P|E|U|W|Z| LENGTH |Q| PENDING | Log list ... | 2835 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2837 Figure A.4.1 -- Top-level Chapter M format 2839 Chapter M begins with a 2-octet header. If the P header bit is set to 2840 1, a 1-octet field follows the header, coding the 7-bit PENDING value 2841 and its associated Q bit. 2843 The 10-bit LENGTH field codes the size of Chapter M and conforms to 2844 semantics described in Appendix A.1. 2846 Chapter M ends with a list of zero or more variable-length parameter 2847 logs. Appendix A.4.2 defines the bitfield format of a parameter log. 2848 Appendix A.4.1 defines the inclusion semantics of the log list. 2850 A channel journal MUST contain Chapter M if the rules defined in 2851 Appendix A.4.1 require that one or more parameter logs appear in the 2852 list. 2854 A channel journal also MUST contain Chapter M if the most recent C- 2855 active Control Change command involved in a parameter system transaction 2856 in the checkpoint history is 2858 o an RPN MSB (101) or NRPN MSB (99) controller, or 2860 o an RPN LSB (100) or NRPN LSB (98) controller that completes the 2861 coding of the null parameter (MSB value 0x7F, LSB value 0x7F). 2863 This rule provides loss protection for partially transmitted parameter 2864 numbers and for the null parameter numbers. 2866 If the most recent C-active Control Change command involved in a 2867 parameter system transaction in the session history is for the RPN MSB 2868 or NRPN MSB controller, the P header bit MUST be set to 1, and the 2869 PENDING field (and its associated Q bit) MUST follow the Chapter M 2870 header. Otherwise, the P header bit MUST be set to 0, and the PENDING 2871 field and Q bit MUST NOT appear in Chapter M. 2873 If PENDING codes an NRPN MSB, the Q bit MUST be set to 1. If PENDING 2874 codes an RPN MSB, the Q bit MUST be set to 0. 2876 The E header bit codes the current transaction state of the MIDI stream. 2877 If E = 1, an initiated transaction is in progress. Below, we define the 2878 rules for setting the E header bit: 2880 o If no C-active parameter system transaction Control Change 2881 commands appear in the session history, the E bit MUST be 2882 set to 0. 2884 o If the P header bit is set to 1, the E bit MUST be set to 0. 2886 o If the most recent C-active parameter system transaction 2887 Control Change command in the session history is for the 2888 NRPN LSB or RPN LSB controller number, and if this command 2889 acts to complete the coding of the null parameter (MSB 2890 value 0x7F, LSB value 0x7F), the E bit MUST be set to 0. 2892 o Otherwise, an initiated transaction is in progress, and the 2893 E bit MUST be set to 1. 2895 The U, W, and Z header bits code properties that are shared by all 2896 parameter logs in the list. If these properties are set, parameter logs 2897 may be coded with improved efficiency (we explain how in A.4.1). 2899 By default, the U, W, and Z bits MUST be set to 0. If all parameter 2900 logs in the list code RPN parameters, the U bit MAY be set to 1. If all 2901 parameter logs in the list code NRPN parameters, the W bit MAY be set to 2902 1. If the parameter numbers of all RPN and NRPN logs in the list lie in 2903 the range 0-127 (and thus have an MSB value of 0), the Z bit MAY be set 2904 to 1. 2906 Note that C-active semantics appear in the preceding paragraphs because 2907 [RP015] specifies that pending Parameter System transactions are closed 2908 by a Control Change command for controller number 121 (Reset All 2909 Controllers). 2911 A.4.1. Log Inclusion Rules 2913 Parameter logs code recovery information for a specific RPN or NRPN 2914 parameter. 2916 A parameter log MUST appear in the list if an active Control Change 2917 command that forms a part of an initiated transaction for the parameter 2918 appears in the checkpoint history. 2920 An exception to this rule applies if the checkpoint history only 2921 contains transaction Control Change commands for controller numbers 2922 98-101 that act to terminate the transaction. In this case, a log for 2923 the parameter MAY be omitted from the list. 2925 A log MAY appear in the list if an active Control Change command that 2926 forms a part of an initiated transaction for the parameter appears in 2927 the session history. Otherwise, a log for the parameter MUST NOT appear 2928 in the list. 2930 Multiple logs for the same RPN or NRPN parameter MUST NOT appear in the 2931 log list. 2933 The parameter log list MUST obey the oldest-first ordering rule (defined 2934 in Appendix A.1), with the phrase "parameter transaction" replacing the 2935 word "command" in the rule definition. 2937 Parameter logs associated with the RPN or NRPN null parameter (LSB = 2938 0x7F, MSB = 0x7F) MUST NOT appear in the log list. Chapter M uses the E 2939 header bit (Figure A.4.1) and the log list ordering rules to code null 2940 parameter semantics. 2942 Note that "active" semantics (rather than "C-active" semantics) appear 2943 in the preceding paragraphs because [RP015] specifies that pending 2944 Parameter System transactions are not reset by a Control Change command 2945 for controller number 121 (Reset All Controllers). However, the rule 2946 that follows uses C-active semantics, because it concerns the protection 2947 of the transaction system itself, and [RP015] specifies that Reset All 2948 Controllers acts to close a transaction in progress. 2950 In most cases, parameter logs for RPN and NRPN parameters that are 2951 assigned to the ch_never parameter (Appendix C.2.3) MAY be omitted from 2952 the list. An exception applies if 2954 o the log codes the most recent initiated transaction 2955 in the session history, and 2957 o a C-active command that forms a part of the transaction 2958 appears in the checkpoint history, and 2960 o the E header bit for the top-level Chapter M header (Figure 2961 A.4.1) is set to 1. 2963 In this case, a log for the parameter MUST appear in the list. This log 2964 informs receivers recovering from a loss that a transaction is in 2965 progress, so that the receiver is able to correctly interpret RPN or 2966 NRPN Control Change commands that follow the loss event. 2968 A.4.2. Log Coding Rules 2970 Figure A.4.2 shows the parameter log structure of Chapter M. 2972 0 1 2 3 2973 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 2974 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2975 |S| PNUM-LSB |Q| PNUM-MSB |J|K|L|M|N|T|V|R| Fields ... | 2976 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2978 Figure A.4.2 -- Parameter log format 2980 The log begins with a header, whose default size (as shown in Figure 2981 A.4.2) is 3 octets. If the Q header bit is set to 0, the log encodes an 2982 RPN parameter. If Q = 1, the log encodes an NRPN parameter. The 7-bit 2983 PNUM-MSB and PNUM-LSB fields code the parameter number and reflect the 2984 Control Change command data values for controllers 99 and 98 (for NRPNs) 2985 or 101 and 100 (for RPNs). 2987 The J, K, L, M, and N header bits form a Table of Contents (TOC) for the 2988 log and signal the presence of fixed-sized fields that follow the 2989 header. A header bit that is set to 1 codes the presence of a field in 2990 the log. The ordering of fields in the log follows the ordering of the 2991 header bits in the TOC. Appendices A.4.2.1-2 define the fields 2992 associated with each TOC header bit. 2994 The T and V header bits code information about the parameter log but are 2995 not part of the TOC. A set T or V bit does not signal the presence of 2996 any parameter log field. 2998 If the rules in Appendix A.4.1 state that a log for a given parameter 2999 MUST appear in Chapter M, the log MUST code sufficient information to 3000 protect the parameter from the loss of active parameter transaction 3001 Control Change commands in the checkpoint history. 3003 This rule does not apply if the parameter coded by the log is assigned 3004 to the ch_never parameter (Appendix C.2.3). In this case, senders MAY 3005 choose to set the J, K, L, M, and N TOC bits to 0, coding a parameter 3006 log with no fields. 3008 Note that logs to protect parameters that are assigned to ch_never are 3009 REQUIRED under certain conditions (see Appendix A.4.1). The purpose of 3010 the log is to inform receivers recovering from a loss that a transaction 3011 is in progress, so that the receiver is able to correctly interpret RPN 3012 or NRPN Control Change commands that follow the loss event. 3014 Parameter logs provide two tools for parameter protection: the value 3015 tool and the count tool. Depending on the semantics of the parameter, 3016 senders may use either tool, both tools, or neither tool to protect a 3017 given parameter. 3019 The value tool codes information a receiver may use to determine the 3020 current value of an RPN or NRPN parameter. If a parameter log uses the 3021 value tool, the V header bit MUST be set to 1, and the semantics defined 3022 in Appendices A.4.2.1 for setting the J, K, L, and M TOC bits MUST be 3023 followed. If a parameter log does not use the value tool, the V bit 3024 MUST be set to 0, and the J, K, L, and M TOC bits MUST also be set to 0. 3026 The count tool codes the number of transactions for an RPN or NRPN 3027 parameter. If a parameter log uses the count tool, the T header bit 3028 MUST be set to 1, and the semantics defined in Appendices A.4.2.2 for 3029 setting the N TOC bit MUST be followed. If a parameter log does not use 3030 the count tool, the T bit and the N TOC bit MUST be set to 0. 3032 Note that V and T are set if the sender uses value (V) or count (T) tool 3033 for the log on an ongoing basis. Thus, V may be set even if J = K = L = 3034 M = 0, and T may be set even if N = 0. 3036 In many cases, all parameters coded in the log list are of one type (RPN 3037 and NRPN), and all parameter numbers lie in the range 0-127. As 3038 described in Appendix A.4.1, senders MAY signal this condition by 3039 setting the top-level Chapter M header bit Z to 1 (to code the 3040 restricted range) and by setting the U or W bit to 1 (to code the 3041 parameter type). 3043 If the top-level Chapter M header codes Z = 1 and either U = 1 or W = 1, 3044 all logs in the parameter log list MUST use a modified header format. 3045 This modification deletes bits 8-15 of the bitfield shown in Figure 3046 A.4.2, to yield a 2-octet header. The values of the deleted PNUM-MSB 3047 and Q fields may be inferred from the U, W, and Z bit values. 3049 A.4.2.1. The Value Tool 3051 The value tool uses several fields to track the value of an RPN or NRPN 3052 parameter. 3054 The J TOC bit codes the presence of the octet shown in Figure A.4.3 in 3055 the field list. 3057 0 3058 0 1 2 3 4 5 6 7 3059 +-+-+-+-+-+-+-+-+ 3060 |X| ENTRY-MSB | 3061 +-+-+-+-+-+-+-+-+ 3063 Figure A.4.3 -- ENTRY-MSB field 3065 The 7-bit ENTRY-MSB field codes the data value of the most recent active 3066 Control Change command for controller number 6 (Data Entry MSB) in the 3067 session history that appears in a transaction for the log parameter. 3069 The X bit MUST be set to 1 if the command coded by ENTRY-MSB precedes 3070 the most recent Control Change command for controller 121 (Reset All 3071 Controllers) in the session history. Otherwise, the X bit MUST be set 3072 to 0. 3074 A parameter log that uses the value tool MUST include the ENTRY-MSB 3075 field if an active Control Change command for controller number 6 3076 appears in the checkpoint history. 3078 Note that [RP015] specifies that Control Change commands for controller 3079 121 (Reset All Controllers) do not reset RPN and NRPN values, and thus 3080 the X bit would not play a recovery role for MIDI systems that comply 3081 with [RP015]. 3083 However, certain renderers (such as DLS 2 [DLS2]) specify that certain 3084 RPN values are reset for some uses of Reset All Controllers. The X bit 3085 (and other bitfield features of this nature in this appendix) plays a 3086 role in recovery for renderers of this type. 3088 The K TOC bit codes the presence of the octet shown in Figure A.4.4 in 3089 the field list. 3091 0 3092 0 1 2 3 4 5 6 7 3093 +-+-+-+-+-+-+-+-+ 3094 |X| ENTRY-LSB | 3095 +-+-+-+-+-+-+-+-+ 3097 Figure A.4.4 -- ENTRY-LSB field 3099 The 7-bit ENTRY-LSB field codes the data value of the most recent active 3100 Control Change command for controller number 38 (Data Entry LSB) in the 3101 session history that appears in a transaction for the log parameter. 3103 The X bit MUST be set to 1 if the command coded by ENTRY-LSB precedes 3104 the most recent Control Change command for controller 121 (Reset All 3105 Controllers) in the session history. Otherwise, the X bit MUST be set 3106 to 0. 3108 As a rule, a parameter log that uses the value tool MUST include the 3109 ENTRY-LSB field if an active Control Change command for controller 3110 number 38 appears in the checkpoint history. However, the ENTRY-LSB 3111 field MUST NOT appear in a parameter log if the Control Change command 3112 associated with the ENTRY-LSB precedes a Control Change command for 3113 controller number 6 (Data Entry MSB) that appears in a transaction for 3114 the log parameter in the session history. 3116 The L TOC bit codes the presence of the octets shown in Figure A.4.5 in 3117 the field list. 3119 0 1 3120 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3122 |G|X| A-BUTTON | 3123 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3125 Figure A.4.5 -- A-BUTTON field 3127 The 14-bit A-BUTTON field codes a count of the number of active Control 3128 Change commands for controller numbers 96 and 97 (Data Increment and 3129 Data Decrement) in the session history that appear in a transaction for 3130 the log parameter. 3132 The M TOC bit codes the presence of the octets shown in Figure A.4.6 in 3133 the field list. 3135 0 1 3136 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3137 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3138 |G|R| C-BUTTON | 3139 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3141 Figure A.4.6 -- C-BUTTON field 3143 The 14-bit C-BUTTON field has semantics identical to A-BUTTON, except 3144 that Data Increment and Data Decrement Control Change commands that 3145 precede the most recent Control Change command for controller 121 (Reset 3146 All Controllers) in the session history are not counted. 3148 For both A-BUTTON and C-BUTTON, Data Increment and Data Decrement 3149 Control Change commands are not counted if they precede Control Changes 3150 commands for controller numbers 6 (Data Entry MSB) or 38 (Data Entry 3151 LSB) that appear in a transaction for the log parameter in the session 3152 history. 3154 The A-BUTTON and C-BUTTON fields are interpreted as unsigned integers, 3155 and the G bit associated with the field codes the sign of the integer (G 3156 = 0 for positive or zero, G = 1 for negative). 3158 To compute and code the count value, initialize the count value to 0, 3159 add 1 for each qualifying Data Increment command, and subtract 1 for 3160 each qualifying Data Decrement command. After each add or subtract, 3161 limit the count magnitude to 16383. The G bit codes the sign of the 3162 count, and the A-BUTTON or C-BUTTON field codes the count magnitude. 3164 For the A-BUTTON field, if the most recent qualified Data Increment or 3165 Data Decrement command precedes the most recent Control Change command 3166 for controller 121 (Reset All Controllers) in the session history, the X 3167 bit associated with A-BUTTON field MUST be set to 1. Otherwise, the X 3168 bit MUST be set to 0. 3170 A parameter log that uses the value tool MUST include the A-BUTTON and 3171 C-BUTTON fields if an active Control Change command for controller 3172 numbers 96 or 97 appears in the checkpoint history. However, to improve 3173 coding efficiency, this rule has several exceptions: 3175 o If the log includes the A-BUTTON field, and if the X bit of 3176 the A-BUTTON field is set to 1, the C-BUTTON field (and its 3177 associated R and G bits) MAY be omitted from the log. 3179 o If the log includes the A-BUTTON field, and if the A-BUTTON 3180 and C-BUTTON fields (and their associated G bits) code identical 3181 values, the C-BUTTON field (and its associated R and G bits) 3182 MAY be omitted from the log. 3184 A.4.2.2. The Count Tool 3186 The count tool tracks the number of transactions for an RPN or NRPN 3187 parameter. The N TOC bit codes the presence of the octet shown in 3188 Figure A.4.7 in the field list. 3190 0 3191 0 1 2 3 4 5 6 7 3192 +-+-+-+-+-+-+-+-+ 3193 |X| COUNT | 3194 +-+-+-+-+-+-+-+-+ 3196 Figure A.4.7 -- COUNT field 3198 The 7-bit COUNT codes the number of initiated transactions for the log 3199 parameter that appear in the session history. Initiated transactions 3200 are counted if they contain one or more active Control Change commands, 3201 including commands for controllers 98-101 that initiate the parameter 3202 transaction. 3204 If the most recent counted transaction precedes the most recent Control 3205 Change command for controller 121 (Reset All Controllers) in the session 3206 history, the X bit associated with the COUNT field MUST be set to 1. 3207 Otherwise, the X bit MUST be set to 0. 3209 Transaction counting is performed modulo 128. The transaction count is 3210 set to 0 at the start of a session and is reset to 0 whenever a Reset 3211 State command (Appendix A.1) appears in the session history. 3213 A parameter log that uses the count tool MUST include the COUNT field if 3214 an active command that increments the transaction count (modulo 128) 3215 appears in the checkpoint history. 3217 A.5. Chapter W: MIDI Pitch Wheel 3219 A channel journal MUST contain Chapter W if a C-active MIDI Pitch Wheel 3220 (0xE) command appears in the checkpoint history. Figure A.5.1 shows the 3221 format for Chapter W. 3223 0 1 3224 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3226 |S| FIRST |R| SECOND | 3227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3229 Figure A.5.1 -- Chapter W format 3231 The chapter has a fixed size of 16 bits. The FIRST and SECOND fields 3232 are the 7-bit values of the first and second data octets of the most 3233 recent active Pitch Wheel command in the session history. 3235 Note that Chapter W encodes C-active commands and thus does not encode 3236 active commands that are not C-active (see the second-to-last paragraph 3237 of Appendix A.1 for an explanation of chapter inclusion text in this 3238 regard). 3240 Chapter W does not encode "active but not C-active" commands because 3241 [RP015] declares that Control Change commands for controller number 121 3242 (Reset All Controllers) act to reset the Pitch Wheel value to 0. If 3243 Chapter W encoded "active but not C-active" commands, a repair operation 3244 following a Reset All Controllers command could incorrectly repair the 3245 stream with a stale Pitch Wheel value. 3247 A.6. Chapter N: MIDI NoteOff and NoteOn 3249 In this appendix, we consider NoteOn commands with zero velocity to be 3250 NoteOff commands. Readers may wish to review the Appendix A.1 3251 definition of "N-active commands" before reading this appendix. 3253 Chapter N completely protects note commands in streams that alternate 3254 between NoteOn and NoteOff commands for a particular note number. 3255 However, in rare applications, multiple overlapping NoteOn commands may 3256 appear for a note number. Chapter E, described in Appendix A.7, 3257 augments Chapter N to completely protect these streams. 3259 A channel journal MUST contain Chapter N if an N-active MIDI NoteOn 3260 (0x9) or NoteOff (0x8) command appears in the checkpoint history. 3261 Figure A.6.1 shows the format for Chapter N. 3263 0 1 2 3 3264 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 3265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3266 |B| LEN | LOW | HIGH |S| NOTENUM |Y| VELOCITY | 3267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3268 |S| NOTENUM |Y| VELOCITY | .... | 3269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3270 | OFFBITS | OFFBITS | .... | OFFBITS | 3271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3273 Figure A.6.1 -- Chapter N format 3275 Chapter N consists of a 2-octet header, followed by at least one of the 3276 following data structures: 3278 o A list of note logs to code NoteOn commands. 3279 o A NoteOff bitfield structure to code NoteOff commands. 3281 We define the header bitfield semantics in Appendix A.6.1. We define 3282 the note log semantics and the NoteOff bitfield semantics in Appendix 3283 A.6.2. 3285 If one or more N-active NoteOn or NoteOff commands in the checkpoint 3286 history reference a note number, the note number MUST be coded in either 3287 the note log list or the NoteOff bitfield structure. 3289 The note log list MUST contain an entry for all note numbers whose most 3290 recent checkpoint history appearance is in an N-active NoteOn command. 3291 The NoteOff bitfield structure MUST contain a set bit for all note 3292 numbers whose most recent checkpoint history appearance is in an N- 3293 active NoteOff command. 3295 A note number MUST NOT be coded in both structures. 3297 All note logs and NoteOff bitfield set bits MUST code the most recent N- 3298 active NoteOn or NoteOff reference to a note number in the session 3299 history. 3301 The note log list MUST obey the oldest-first ordering rule (defined in 3302 Appendix A.1). 3304 A.6.1. Header Structure 3306 The header for Chapter N, shown in Figure A.6.2, codes the size of the 3307 note list and bitfield structures. 3309 0 1 3310 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3312 |B| LEN | LOW | HIGH | 3313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3315 Figure A.6.2 -- Chapter N header 3317 The LEN field, a 7-bit integer value, codes the number of 2-octet note 3318 logs in the note list. Zero is a valid value for LEN and codes an empty 3319 note list. 3321 The 4-bit LOW and HIGH fields code the number of OFFBITS octets that 3322 follow the note log list. LOW and HIGH are unsigned integer values. If 3323 LOW <= HIGH, there are (HIGH - LOW + 1) OFFBITS octets in the chapter. 3324 The value pairs (LOW = 15, HIGH = 0) and (LOW = 15, HIGH = 1) code an 3325 empty NoteOff bitfield structure (i.e., no OFFBITS octets). Other (LOW 3326 > HIGH) value pairs MUST NOT appear in the header. 3328 The B bit provides S-bit functionality (Appendix A.1) for the NoteOff 3329 bitfield structure. By default, the B bit MUST be set to 1. However, 3330 if the MIDI command section of the previous packet (packet I - 1, with I 3331 as defined in Appendix A.1) includes a NoteOff command for the channel, 3332 the B bit MUST be set to 0. If the B bit is set to 0, the higher-level 3333 recovery journal elements that contain Chapter N MUST have S bits that 3334 are set to 0, including the top-level journal header. 3336 The LEN value of 127 codes a note list length of 127 or 128 note logs, 3337 depending on the values of LOW and HIGH. If LEN = 127, LOW = 15, and 3338 HIGH = 0, the note list holds 128 note logs, and the NoteOff bitfield 3339 structure is empty. For other values of LOW and HIGH, LEN = 127 codes 3340 that the note list contains 127 note logs. In this case, the chapter 3341 has (HIGH - LOW + 1) NoteOff OFFBITS octets if LOW <= HIGH and has no 3342 OFFBITS octets if LOW = 15 and HIGH = 1. 3344 A.6.2. Note Structures 3346 Figure A.6.3 shows the 2-octet note log structure. 3348 0 1 3349 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3351 |S| NOTENUM |Y| VELOCITY | 3352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3354 Figure A.6.3 -- Chapter N note log 3356 The 7-bit NOTENUM field codes the note number for the log. A note 3357 number MUST NOT be represented by multiple note logs in the note list. 3359 The 7-bit VELOCITY field codes the velocity value for the most recent N- 3360 active NoteOn command for the note number in the session history. 3361 Multiple overlapping NoteOns for a given note number may be coded using 3362 Chapter E, as discussed in Appendix A.7. 3364 VELOCITY is never zero; NoteOn commands with zero velocity are coded as 3365 NoteOff commands in the NoteOff bitfield structure. 3367 The note log does not code the execution time of the NoteOn command. 3368 However, the Y bit codes a hint from the sender about the NoteOn 3369 execution time. The Y bit codes a recommendation to play (Y = 1) or 3370 skip (Y = 0) the NoteOn command recovered from the note log. See 3371 Section 4.2 of [RFC4696] for non-normative guidance on the use of the Y 3372 bit. 3374 Figure A.6.1 shows the NoteOff bitfield structure, as the list of 3375 OFFBITS octets at the end of the chapter. A NoteOff OFFBITS octet codes 3376 NoteOff information for eight consecutive MIDI note numbers, with the 3377 most-significant bit representing the lowest note number. The most- 3378 significant bit of the first OFFBITS octet codes the note number 8*LOW; 3379 the most-significant bit of the last OFFBITS octet codes the note number 3380 8*HIGH. 3382 A set bit codes a NoteOff command for the note number. In the most 3383 efficient coding for the NoteOff bitfield structure, the first and last 3384 octets of the structure contain at least one set bit. Note that Chapter 3385 N does not code NoteOff velocity data. 3387 Note that in the general case, the recovery journal does not code the 3388 relative placement of a NoteOff command and a Change Control command for 3389 controller 64 (Damper Pedal (Sustain)). In many cases, a receiver 3390 processing a loss event may deduce this relative placement from the 3391 history of the stream and thus determine if a NoteOff note is sustained 3392 by the pedal. If such a determination is not possible, receivers SHOULD 3393 err on the side of silencing pedal sustains, as erroneously sustained 3394 notes may produce unpleasant (albeit transient) artifacts. 3396 A.7. Chapter E: MIDI Note Command Extras 3398 Readers may wish to review the Appendix A.1 definition of "N-active 3399 commands" before reading this appendix. In this appendix, a NoteOn 3400 command with a velocity of 0 is considered to be a NoteOff command with 3401 a release velocity value of 64. 3403 Chapter E encodes recovery information about MIDI NoteOn (0x9) and 3404 NoteOff (0x8) command features that rarely appear in MIDI streams. 3405 Receivers use Chapter E to reduce transient artifacts for streams where 3406 several NoteOn commands appear for a note number without an intervening 3407 NoteOff. Receivers also use Chapter E to reduce transient artifacts for 3408 streams that use NoteOff release velocity. Chapter E supplements the 3409 note information coded in Chapter N (Appendix A.6). 3411 Figure A.7.1 shows the format for Chapter E. 3413 0 1 2 3 3414 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 3415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3416 |S| LEN |S| NOTENUM |V| COUNT/VEL |S| NOTENUM | 3417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3418 |V| COUNT/VEL | .... | 3419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3421 Figure A.7.1 -- Chapter E format 3423 The chapter consists of a 1-octet header, followed by a variable-length 3424 list of 2-octet note logs. Appendix A.7.1 defines the bitfield format 3425 for a note log. 3427 The log list MUST contain at least one note log. The 7-bit LEN header 3428 field codes the number of note logs in the list, minus one. A channel 3429 journal MUST contain Chapter E if the rules defined in this appendix 3430 require that one or more note logs appear in the list. The note log 3431 list MUST obey the oldest-first ordering rule (defined in Appendix A.1). 3433 A.7.1. Note Log Format 3435 Figure A.7.2 reproduces the note log structure of Chapter E. 3437 0 1 3438 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3440 |S| NOTENUM |V| COUNT/VEL | 3441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3443 Figure A.7.2 -- Chapter E note log 3445 A note log codes information about the MIDI note number coded by the 3446 7-bit NOTENUM field. The nature of the information depends on the value 3447 of the V flag bit. 3449 If the V bit is set to 1, the COUNT/VEL field codes the release velocity 3450 value for the most recent N-active NoteOff command for the note number 3451 that appears in the session history. 3453 If the V bit is set to 0, the COUNT/VEL field codes a reference count of 3454 the number of NoteOn and NoteOff commands for the note number that 3455 appear in the session history. 3457 The reference count is set to 0 at the start of the session. NoteOn 3458 commands increment the count by 1. NoteOff commands decrement the count 3459 by 1. However, a decrement that generates a negative count value is not 3460 performed. 3462 If the reference count is in the range 0-126, the 7-bit COUNT/VEL field 3463 codes an unsigned integer representation of the count. If the count is 3464 greater than or equal to 127, COUNT/VEL is set to 127. 3466 By default, the count is reset to 0 whenever a Reset State command 3467 (Appendix A.1) appears in the session history, and whenever MIDI Control 3468 Change commands for controller numbers 123-127 (numbers with All Notes 3469 Off semantics) or 120 (All Sound Off) appear in the session history. 3471 A.7.2. Log Inclusion Rules 3473 If the most recent N-active NoteOn or NoteOff command for a note number 3474 in the checkpoint history is a NoteOff command with a release velocity 3475 value other than 64, a note log whose V bit is set to 1 MUST appear in 3476 Chapter E for the note number. 3478 If the most recent N-active NoteOn or NoteOff command for a note number 3479 in the checkpoint history is a NoteOff command, and if the reference 3480 count for the note number is greater than 0, a note log whose V bit is 3481 set to 0 MUST appear in Chapter E for the note number. 3483 If the most recent N-active NoteOn or NoteOff command for a note number 3484 in the checkpoint history is a NoteOn command, and if the reference 3485 count for the note number is greater than 1, a note log whose V bit is 3486 set to 0 MUST appear in Chapter E for the note number. 3488 At most, two note logs MAY appear in Chapter E for a note number: one 3489 log whose V bit is set to 0, and one log whose V bit is set to 1. 3491 Chapter E codes a maximum of 128 note logs. If the log inclusion rules 3492 yield more than 128 REQUIRED logs, note logs whose V bit is set to 1 3493 MUST be dropped from Chapter E in order to reach the 128-log limit. 3494 Note logs whose V bit is set to 0 MUST NOT be dropped. 3496 Most MIDI streams do not use NoteOn and NoteOff commands in ways that 3497 would trigger the log inclusion rules. For these streams, Chapter E 3498 would never be REQUIRED to appear in a channel journal. 3500 The ch_never parameter (Appendix C.2.3) may be used to configure the log 3501 inclusion rules for Chapter E. 3503 A.8. Chapter T: MIDI Channel Aftertouch 3505 A channel journal MUST contain Chapter T if an N-active and C-active 3506 MIDI Channel Aftertouch (0xD) command appears in the checkpoint history. 3507 Figure A.8.1 shows the format for Chapter T. 3509 0 3510 0 1 2 3 4 5 6 7 3511 +-+-+-+-+-+-+-+-+ 3512 |S| PRESSURE | 3513 +-+-+-+-+-+-+-+-+ 3515 Figure A.8.1 -- Chapter T format 3517 The chapter has a fixed size of 8 bits. The 7-bit PRESSURE field holds 3518 the pressure value of the most recent N-active and C-active Channel 3519 Aftertouch command in the session history. 3521 Chapter T only encodes commands that are C-active and N-active. We 3522 define a C-active restriction because [RP015] declares that a Control 3523 Change command for controller 121 (Reset All Controllers) acts to reset 3524 the channel pressure to 0 (see the discussion at the end of Appendix A.5 3525 for a more complete rationale). 3527 We define an N-active restriction on the assumption that aftertouch 3528 commands are linked to note activity, and thus Channel Aftertouch 3529 commands that are not N-active are stale and should not be used to 3530 repair a stream. 3532 A.9. Chapter A: MIDI Poly Aftertouch 3534 A channel journal MUST contain Chapter A if a C-active Poly Aftertouch 3535 (0xA) command appears in the checkpoint history. Figure A.9.1 shows the 3536 format for Chapter A. 3538 0 1 2 3 3539 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 3540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3541 |S| LEN |S| NOTENUM |X| PRESSURE |S| NOTENUM | 3542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3543 |X| PRESSURE | .... | 3544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3546 Figure A.9.1 -- Chapter A format 3548 The chapter consists of a 1-octet header, followed by a variable-length 3549 list of 2-octet note logs. A note log MUST appear for a note number if 3550 a C-active Poly Aftertouch command for the note number appears in the 3551 checkpoint history. A note number MUST NOT be represented by multiple 3552 note logs in the note list. The note log list MUST obey the oldest- 3553 first ordering rule (defined in Appendix A.1). 3555 The 7-bit LEN field codes the number of note logs in the list, minus 3556 one. Figure A.9.2 reproduces the note log structure of Chapter A. 3558 0 1 3559 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3560 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3561 |S| NOTENUM |X| PRESSURE | 3562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3564 Figure A.9.2 -- Chapter A note log 3566 The 7-bit PRESSURE field codes the pressure value of the most recent C- 3567 active Poly Aftertouch command in the session history for the MIDI note 3568 number coded in the 7-bit NOTENUM field. 3570 As a rule, the X bit MUST be set to 0. However, the X bit MUST be set 3571 to 1 if the command coded by the log appears before one of the following 3572 commands in the session history: MIDI Control Change numbers 123-127 3573 (numbers with All Notes Off semantics) or 120 (All Sound Off). 3575 We define C-active restrictions for Chapter A because [RP015] declares 3576 that a Control Change command for controller 121 (Reset All Controllers) 3577 acts to reset the polyphonic pressure to 0 (see the discussion at the 3578 end of Appendix A.5 for a more complete rationale). 3580 B. The Recovery Journal System Chapters 3582 B.1. System Chapter D: Simple System Commands 3584 The system journal MUST contain Chapter D if an active MIDI Reset 3585 (0xFF), MIDI Tune Request (0xF6), MIDI Song Select (0xF3), undefined 3586 MIDI System Common (0xF4 and 0xF5), or undefined MIDI System Real-time 3587 (0xF9 and 0xFD) command appears in the checkpoint history. 3589 Figure B.1.1 shows the variable-length format for Chapter D. 3591 0 1 2 3 3592 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 3593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3594 |S|B|G|H|J|K|Y|Z| Command logs ... | 3595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3597 Figure B.1.1 -- System Chapter D format 3599 The chapter consists of a 1-octet header, followed by one or more 3600 command logs. Header flag bits indicate the presence of command logs 3601 for the Reset (B = 1), Tune Request (G = 1), Song Select (H = 1), 3602 undefined System Common 0xF4 (J = 1), undefined System Common 0xF5 (K = 3603 1), undefined System Real-time 0xF9 (Y = 1), or undefined System Real- 3604 time 0xFD (Z = 1) commands. 3606 Command logs appear in a list following the header, in the order that 3607 the flag bits appear in the header. 3609 Figure B.1.2 shows the 1-octet command log format for the Reset and Tune 3610 Request commands. 3612 0 3613 0 1 2 3 4 5 6 7 3614 +-+-+-+-+-+-+-+-+ 3615 |S| COUNT | 3616 +-+-+-+-+-+-+-+-+ 3618 Figure B.1.2 -- Command log for Reset and Tune Request 3620 Chapter D MUST contain the Reset command log if an active Reset command 3621 appears in the checkpoint history. The 7-bit COUNT field codes the 3622 total number of Reset commands (modulo 128) present in the session 3623 history. 3625 Chapter D MUST contain the Tune Request command log if an active Tune 3626 Request command appears in the checkpoint history. The 7-bit COUNT 3627 field codes the total number of Tune Request commands (modulo 128) 3628 present in the session history. 3630 For these commands, the COUNT field acts as a reference count. See the 3631 definition of "session history reference counts" in Appendix A.1 for 3632 more information. 3634 Figure B.1.3 shows the 1-octet command log format for the Song Select 3635 command. 3637 0 3638 0 1 2 3 4 5 6 7 3639 +-+-+-+-+-+-+-+-+ 3640 |S| VALUE | 3641 +-+-+-+-+-+-+-+-+ 3643 Figure B.1.3 -- Song Select command log format 3645 Chapter D MUST contain the Song Select command log if an active Song 3646 Select command appears in the checkpoint history. The 7-bit VALUE field 3647 codes the song number of the most recent active Song Select command in 3648 the session history. 3650 B.1.1. Undefined System Commands 3652 In this section, we define the Chapter D command logs for the undefined 3653 System commands. [MIDI] reserves the undefined System commands 0xF4, 3654 0xF5, 0xF9, and 0xFD for future use. At the time of this writing, any 3655 MIDI command stream that uses these commands is non-compliant with 3656 [MIDI]. However, future versions of [MIDI] may define these commands, 3657 and a few products do use these commands in a non-compliant manner. 3659 Figure B.1.4 shows the variable-length command log format for the 3660 undefined System Common commands (0xF4 and 0xF5). 3662 0 1 2 3 3663 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 3664 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3665 |S|C|V|L|DSZ| LENGTH | COUNT | VALUE ... | 3666 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3667 | LEGAL ... | 3668 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3670 Figure B.1.4 -- Undefined System Common command log format 3672 The command log codes a single command type (0xF4 or 0xF5, not both). 3673 Chapter D MUST contain a command log if an active 0xF4 command appears 3674 in the checkpoint history and MUST contain an independent command log if 3675 an active 0xF5 command appears in the checkpoint history. 3677 A Chapter D Undefined System Common command log consists of a two-octet 3678 header followed by a variable number of data fields. Header flag bits 3679 indicate the presence of the COUNT field (C = 1), the VALUE field (V = 3680 1), and the LEGAL field (L = 1). The 10-bit LENGTH field codes the size 3681 of the command log and conforms to semantics described in Appendix A.1. 3683 The 2-bit DSZ field codes the number of data octets in the command 3684 instance that appears most recently in the session history. If DSZ = 3685 0-2, the command has 0-2 data octets. If DSZ = 3, the command has 3 or 3686 more command data octets. 3688 We now define the default rules for the use of the COUNT, VALUE, and 3689 LEGAL fields. The session configuration tools defined in Appendix C.2.3 3690 may be used to override this behavior. 3692 By default, if the DSZ field is set to 0, the command log MUST include 3693 the COUNT field. The 8-bit COUNT field codes the total number of 3694 commands of the type coded by the log (0xF4 or 0xF5) present in the 3695 session history, modulo 256. 3697 By default, if the DSZ field is set to 1-3, the command log MUST include 3698 the VALUE field. The variable-length VALUE field codes a verbatim copy 3699 the data octets for the most recent use of the command type coded by the 3700 log (0xF4 or 0xF5) in the session history. The most-significant bit of 3701 the final data octet MUST be set to 1, and the most-significant bit of 3702 all other data octets MUST be set to 0. 3704 The LEGAL field is reserved for future use. If an update to [MIDI] 3705 defines the 0xF4 or 0xF5 command, an IETF standards-track document may 3706 define the LEGAL field. Until such a document appears, senders MUST NOT 3707 use the LEGAL field, and receivers MUST use the LENGTH field to skip 3708 over the LEGAL field. The LEGAL field would be defined by the IETF if 3709 the semantics of the new 0xF4 or 0xF5 command could not be protected 3710 from packet loss via the use of the COUNT and VALUE fields. 3712 Figure B.1.5 shows the variable-length command log format for the 3713 undefined System Real-time commands (0xF9 and 0xFD). 3715 0 1 2 3 3716 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 3717 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3718 |S|C|L| LENGTH | COUNT | LEGAL ... | 3719 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3721 Figure B.1.5 -- Undefined System Real-time command log format 3723 The command log codes a single command type (0xF9 or 0xFD, not both). 3724 Chapter D MUST contain a command log if an active 0xF9 command appears 3725 in the checkpoint history and MUST contain an independent command log if 3726 an active 0xFD command appears in the checkpoint history. 3728 A Chapter D Undefined System Real-time command log consists of a one- 3729 octet header followed by a variable number of data fields. Header flag 3730 bits indicate the presence of the COUNT field (C = 1) and the LEGAL 3731 field (L = 1). The 5-bit LENGTH field codes the size of the command log 3732 and conforms to semantics described in Appendix A.1. 3734 We now define the default rules for the use of the COUNT and LEGAL 3735 fields. The session configuration tools defined in Appendix C.2.3 may 3736 be used to override this behavior. 3738 The 8-bit COUNT field codes the total number of commands of the type 3739 coded by the log present in the session history, modulo 256. By 3740 default, the COUNT field MUST be present in the command log. 3742 The LEGAL field is reserved for future use. If an update to [MIDI] 3743 defines the 0xF9 or 0xFD command, an IETF standards-track document may 3744 define the LEGAL field to protect the command. Until such a document 3745 appears, senders MUST NOT use the LEGAL field, and receivers MUST use 3746 the LENGTH field to skip over the LEGAL field. The LEGAL field would be 3747 defined by the IETF if the semantics of the new 0xF9 or 0xFD command 3748 could not be protected from packet loss via the use of the COUNT field. 3750 Finally, we note that some non-standard uses of the undefined System 3751 Real-time commands act to implement non-compliant variants of the MIDI 3752 sequencer system. In Appendix B.3.1, we describe resiliency tools for 3753 the MIDI sequencer system that provide some protection in this case. 3755 B.2. System Chapter V: Active Sense Command 3757 The system journal MUST contain Chapter V if an active MIDI Active Sense 3758 (0xFE) command appears in the checkpoint history. Figure B.2.1 shows 3759 the format for Chapter V. 3761 0 3762 0 1 2 3 4 5 6 7 3763 +-+-+-+-+-+-+-+-+ 3764 |S| COUNT | 3765 +-+-+-+-+-+-+-+-+ 3767 Figure B.2.1 -- System Chapter V format 3769 The 7-bit COUNT field codes the total number of Active Sense commands 3770 (modulo 128) present in the session history. The COUNT field acts as a 3771 reference count. See the definition of "session history reference 3772 counts" in Appendix A.1 for more information. 3774 B.3. System Chapter Q: Sequencer State Commands 3776 This appendix describes Chapter Q, the system chapter for the MIDI 3777 sequencer commands. 3779 The system journal MUST contain Chapter Q if an active MIDI Song 3780 Position Pointer (0xF2), MIDI Clock (0xF8), MIDI Start (0xFA), MIDI 3781 Continue (0xFB), or MIDI Stop (0xFC) command appears in the checkpoint 3782 history, and if the rules defined in this appendix require a change in 3783 the Chapter Q bitfield contents because of the command appearance. 3785 Figure B.3.1 shows the variable-length format for Chapter Q. 3787 0 1 2 3 3788 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 3789 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3790 |S|N|D|C|T| TOP | CLOCK | TIMETOOLS ... | 3791 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3792 | ... | 3793 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3795 Figure B.3.1 -- System Chapter Q format 3797 Chapter Q consists of a 1-octet header followed by several optional 3798 fields, in the order shown in Figure B.3.1. 3800 Header flag bits signal the presence of the 16-bit CLOCK field (C = 1) 3801 and the 24-bit TIMETOOLS field (T = 1). The 3-bit TOP header field is 3802 interpreted as an unsigned integer, as are CLOCK and TIMETOOLS. We 3803 describe the TIMETOOLS field in Appendix B.3.1. 3805 Chapter Q encodes the most recent state of the sequencer system. 3806 Receivers use the chapter to re-synchronize the sequencer after a packet 3807 loss episode. Chapter fields encode the on/off state of the sequencer, 3808 the current position in the song, and the downbeat. 3810 The N header bit encodes the relative occurrence of the Start, Stop, and 3811 Continue commands in the session history. If an active Start or 3812 Continue command appears most recently, the N bit MUST be set to 1. If 3813 an active Stop appears most recently, or if no active Start, Stop, or 3814 Continue commands appear in the session history, the N bit MUST be set 3815 to 0. 3817 The C header flag, the TOP header field, and the CLOCK field act to code 3818 the current position in the sequence: 3820 o If C = 1, the 3-bit TOP header field and the 16-bit 3821 CLOCK field are combined to form the 19-bit unsigned quantity 3822 65536*TOP + CLOCK. This value encodes the song position 3823 in units of MIDI Clocks (24 clocks per quarter note), 3824 modulo 524288. Note that the maximum song position value 3825 that may be coded by the Song Position Pointer command is 3826 98303 clocks (which may be coded with 17 bits), and that 3827 MIDI-coded songs are generally constructed to avoid durations 3828 longer than this value. However, the 19-bit size may be useful 3829 for real-time applications, such as a drum machine MIDI output 3830 that is sending clock commands for long periods of time. 3832 o If C = 0, the song position is the start of the song. 3833 The C = 0 position is identical to the position coded 3834 by C = 1, TOP = 0, and CLOCK = 0, for the case where 3835 the song position is less than 524288 MIDI clocks. 3836 In certain situations (defined later in this section), 3837 normative text may require the C = 0 or the C = 1, 3838 TOP = 0, CLOCK = 0 encoding of the start of the song. 3840 The C, TOP, and CLOCK fields MUST be set to code the current song 3841 position, for both N = 0 and N = 1 conditions. If C = 0, the TOP field 3842 MUST be set to 0. See [MIDI] for a precise definition of a song 3843 position. 3845 The D header bit encodes information about the downbeat and acts to 3846 qualify the song position coded by the C, TOP, and CLOCK fields. 3848 If the D bit is set to 1, the song position represents the most recent 3849 position in the sequence that has played. If D = 1, the next Clock 3850 command (if N = 1) or the next (Continue, Clock) pair (if N = 0) acts to 3851 increment the song position by one clock, and to play the updated 3852 position. 3854 If the D bit is set to 0, the song position represents a position in the 3855 sequence that has not yet been played. If D = 0, the next Clock command 3856 (if N = 1) or the next (Continue, Clock) pair (if N = 0) acts to play 3857 the point in the song coded by the song position. The song position is 3858 not incremented. 3860 An example of a stream that uses D = 0 coding is one whose most recent 3861 sequence command is a Start or Song Position Pointer command (both N = 1 3862 conditions). However, it is also possible to construct examples where D 3863 = 0 and N = 0. A Start command immediately followed by a Stop command 3864 is coded in Chapter Q by setting C = 0, D = 0, N = 0, TOP = 0. 3866 If N = 1 (coding Start or Continue), D = 0 (coding that the downbeat has 3867 yet to be played), and the song position is at the start of the song, 3868 the C = 0 song position encoding MUST be used if a Start command occurs 3869 more recently than a Continue command in the session history, and the C 3870 = 1, TOP = 0, CLOCK = 0 song position encoding MUST be used if a 3871 Continue command occurs more recently than a Start command in the 3872 session history. 3874 B.3.1. Non-compliant Sequencers 3876 The Chapter Q description in this appendix assumes that the sequencer 3877 system counts off time with Clock commands, as mandated in [MIDI]. 3878 However, a few non-compliant products do not use Clock commands to count 3879 off time, but instead use non-standard methods. 3881 Chapter Q uses the TIMETOOLS field to provide resiliency support for 3882 these non-standard products. By default, the TIMETOOLS field MUST NOT 3883 appear in Chapter Q, and the T header bit MUST be set to 0. The session 3884 configuration tools described in Appendix C.2.3 may be used to select 3885 TIMETOOLS coding. 3887 Figure B.3.2 shows the format of the 24-bit TIMETOOLS field. 3889 0 1 2 3890 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 3891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3892 | TIME | 3893 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3895 Figure B.3.2 -- TIMETOOLS format 3897 The TIME field is a 24-bit unsigned integer quantity, with units of 3898 milliseconds. TIME codes an additive correction term for the song 3899 position coded by the TOP, CLOCK, and C fields. TIME is coded in 3900 network byte order (big-endian). 3902 A receiver computes the correct song position by converting TIME into 3903 units of MIDI clocks and adding it to 65536*TOP + CLOCK (assuming C = 3904 1). Alternatively, a receiver may convert 65536*TOP + CLOCK into 3905 milliseconds (assuming C = 1) and add it to TIME. The downbeat (D 3906 header bit) semantics defined in Appendix B.3 apply to the corrected 3907 song position. 3909 B.4. System Chapter F: MIDI Time Code Tape Position 3911 This appendix describes Chapter F, the system chapter for the MIDI Time 3912 Code (MTC) commands. Readers may wish to review the Appendix A.1 3913 definition of "finished/unfinished commands" before reading this 3914 appendix. 3916 The system journal MUST contain Chapter F if an active System Common 3917 Quarter Frame command (0xF1) or an active finished System Exclusive 3918 (Universal Real Time) MTC Full Frame command (F0 7F cc 01 01 hr mn sc fr 3919 F7) appears in the checkpoint history. Otherwise, the system journal 3920 MUST NOT contain Chapter F. 3922 Figure B.4.1 shows the variable-length format for Chapter F. 3924 0 1 2 3 3925 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 3926 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3927 |S|C|P|Q|D|POINT| COMPLETE ... | 3928 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3929 | ... | PARTIAL ... | 3930 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3931 | ... | 3932 +-+-+-+-+-+-+-+-+ 3934 Figure B.4.1 -- System Chapter F format 3936 Chapter F holds information about recent MTC tape positions coded in the 3937 session history. Receivers use Chapter F to re-synchronize the MTC 3938 system after a packet loss episode. 3940 Chapter F consists of a 1-octet header followed by several optional 3941 fields, in the order shown in Figure B.4.1. The C and P header bits 3942 form a Table of Contents (TOC) and signal the presence of the 32-bit 3943 COMPLETE field (C = 1) and the 32-bit PARTIAL field (P = 1). 3945 The Q header bit codes information about the COMPLETE field format. If 3946 Chapter F does not contain a COMPLETE field, Q MUST be set to 0. 3948 The D header bit codes the tape movement direction. If the tape is 3949 moving forward, or if the tape direction is indeterminate, the D bit 3950 MUST be set to 0. If the tape is moving in the reverse direction, the D 3951 bit MUST be set to 1. In most cases, the ordering of commands in the 3952 session history clearly defines the tape direction. However, a few 3953 command sequences have an indeterminate direction (such as a session 3954 history consisting of one Full Frame command). 3956 The 3-bit POINT header field is interpreted as an unsigned integer. 3957 Appendix B.4.1 defines how the POINT field codes information about the 3958 contents of the PARTIAL field. If Chapter F does not contain a PARTIAL 3959 field, POINT MUST be set to 7 (if D = 0) or 0 (if D = 1). 3961 Chapter F MUST include the COMPLETE field if an active finished Full 3962 Frame command appears in the checkpoint history, or if an active Quarter 3963 Frame command that completes the encoding of a frame value appears in 3964 the checkpoint history. 3966 The COMPLETE field encodes the most recent active complete MTC frame 3967 value that appears in the session history. This frame value may take 3968 the form of a series of 8 active Quarter Frame commands (0xF1 0x0n 3969 through 0xF1 0x7n for forward tape movement, 0xF1 0x7n through 0xF1 0x0n 3970 for reverse tape movement) or may take the form of an active finished 3971 Full Frame command. 3973 If the COMPLETE field encodes a Quarter Frame command series, the Q 3974 header bit MUST be set to 1, and the COMPLETE field MUST have the format 3975 shown in Figure B.4.2. The 4-bit fields MT0 through MT7 code the data 3976 (lower) nibble for the Quarter Frame commands for Message Type 0 through 3977 Message Type 7 [MIDI]. These nibbles encode a complete frame value, in 3978 addition to fields reserved for future use by [MIDI]. 3980 0 1 2 3 3981 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 3982 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3983 | MT0 | MT1 | MT2 | MT3 | MT4 | MT5 | MT6 | MT7 | 3984 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3986 Figure B.4.2 -- COMPLETE field format, Q = 1 3988 In this usage, the frame value encoded in the COMPLETE field MUST be 3989 offset by 2 frames (relative to the frame value encoded in the Quarter 3990 Frame commands) if the frame value codes a 0xF1 0x0n through 0xF1 0x7n 3991 command sequence. This offset compensates for the two-frame latency of 3992 the Quarter Frame encoding for forward tape movement. No offset is 3993 applied if the frame value codes a 0xF1 0x7n through 0xF1 0x0n Quarter 3994 Frame command sequence. 3996 The most recent active complete MTC frame value may alternatively be 3997 encoded by an active finished Full Frame command. In this case, the Q 3998 header bit MUST be set to 0, and the COMPLETE field MUST have format 3999 shown in Figure B.4.3. The HR, MN, SC, and FR fields correspond to the 4000 hr, mn, sc, and fr data octets of the Full Frame command. 4002 0 1 2 3 4003 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 4004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4005 | HR | MN | SC | FR | 4006 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4008 Figure B.4.3 -- COMPLETE field format, Q = 0 4010 B.4.1. Partial Frames 4012 The most recent active session history command that encodes MTC frame 4013 value data may be a Quarter Frame command other than a forward-moving 4014 0xF1 0x7n command (which completes a frame value for forward tape 4015 movement) or a reverse-moving 0xF1 0x1n command (which completes a frame 4016 value for reverse tape movement). 4018 We consider this type of Quarter Frame command to be associated with a 4019 partial frame value. The Quarter Frame sequence that defines a partial 4020 frame value MUST either start at Message Type 0 and increment 4021 contiguously to an intermediate Message Type less than 7, or start at 4022 Message Type 7 and decrement contiguously to an intermediate Message 4023 type greater than 0. A Quarter Frame command sequence that does not 4024 follow this pattern is not associated with a partial frame value. 4026 Chapter F MUST include a PARTIAL field if the most recent active command 4027 in the checkpoint history that encodes MTC frame value data is a Quarter 4028 Frame command that is associated with a partial frame value. Otherwise, 4029 Chapter F MUST NOT include a PARTIAL field. 4031 The partial frame value consists of the data (lower) nibbles of the 4032 Quarter Frame command sequence. The PARTIAL field codes the partial 4033 frame value, using the format shown in Figure B.4.2. Message Type 4034 fields that are not associated with a Quarter Frame command MUST be set 4035 to 0. 4037 The POINT header field identifies the Message Type fields in the PARTIAL 4038 field that code valid data. If P = 1, the POINT field MUST encode the 4039 unsigned integer value formed by the lower 3 bits of the upper nibble of 4040 the data value of the most recent active Quarter Frame command in the 4041 session history. If D = 0 and P = 1, POINT MUST take on a value in the 4042 range 0-6. If D = 1 and P = 1, POINT MUST take on a value in the range 4043 1-7. 4045 If D = 0, MT fields (Figure B.4.2) in the inclusive range from 0 up to 4046 and including the POINT value encode the partial frame value. If D = 1, 4047 MT fields in the inclusive range from 7 down to and including the POINT 4048 value encode the partial frame value. Note that, unlike the COMPLETE 4049 field encoding, senders MUST NOT add a 2-frame offset to the partial 4050 frame value encoded in PARTIAL. 4052 For the default semantics, if a recovery journal contains Chapter F, and 4053 if the session history codes a legal [MIDI] series of Quarter Frame and 4054 Full Frame commands, the chapter always contains a COMPLETE or a PARTIAL 4055 field (and may contain both fields). Thus, a one-octet Chapter F (C = P 4056 = 0) always codes the presence of an illegal command sequence in the 4057 session history (under some conditions, the C = 1, P = 0 condition may 4058 also code the presence of an illegal command sequence). The illegal 4059 command sequence conditions are transient in nature and usually indicate 4060 that a Quarter Frame command sequence began with an intermediate Message 4061 Type. 4063 B.5. System Chapter X: System Exclusive 4065 This appendix describes Chapter X, the system chapter for MIDI System 4066 Exclusive (SysEx) commands (0xF0). Readers may wish to review the 4067 Appendix A.1 definition of "finished/unfinished commands" before reading 4068 this appendix. 4070 Chapter X consists of a list of one or more command logs. Each log in 4071 the list codes information about a specific finished or unfinished SysEx 4072 command that appears in the session history. The system journal MUST 4073 contain Chapter X if the rules defined in Appendix B.5.2 require that 4074 one or more logs appear in the list. 4076 The log list is not preceded by a header. Instead, each log implicitly 4077 encodes its own length. Given the length of the N'th list log, the 4078 presence of the (N+1)'th list log may be inferred from the LENGTH field 4079 of the system journal header (Figure 10 in Section 5 of the main text). 4080 The log list MUST obey the oldest-first ordering rule (defined in 4081 Appendix A.1). 4083 B.5.1. Chapter Format 4085 Figure B.5.1 shows the bitfield format for the Chapter X command logs. 4087 0 1 2 3 4088 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 4089 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4090 |S|T|C|F|D|L|STA| TCOUNT | COUNT | FIRST ... | 4091 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4092 | DATA ... | 4093 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4095 Figure B.5.1 -- Chapter X command log format 4097 A Chapter X command log consists of a 1-octet header, followed by the 4098 optional TCOUNT, COUNT, FIRST, and DATA fields. 4100 The T, C, F, and D header bits act as a Table of Contents (TOC) for the 4101 log. If T is set to 1, the 1-octet TCOUNT field appears in the log. If 4102 C is set to 1, the 1-octet COUNT field appears in the log. If F is set 4103 to 1, the variable-length FIRST field appears in the log. If D is set 4104 to 1, the variable-length DATA field appears in the log. 4106 The L header bit sets the coding tool for the log. We define the log 4107 coding tools in Appendix B.5.2. 4109 The STA field codes the status of the command coded by the log. The 4110 2-bit STA value is interpreted as an unsigned integer. If STA is 0, the 4111 log codes an unfinished command. Non-zero STA values code different 4112 classes of finished commands. An STA value of 1 codes a cancelled 4113 command, an STA value of 2 codes a command that uses the "dropped F7" 4114 construction, and an STA value of 3 codes all other finished commands. 4115 Section 3.2 in the main text describes cancelled and "dropped F7" 4116 commands. 4118 The S bit (Appendix A.1) of the first log in the list acts as the S bit 4119 for Chapter X. For the other logs in the list, the S bit refers to the 4120 log itself. The value of the "phantom" S bit associated with the first 4121 log is defined by the following rules: 4123 o If the list codes one log, the phantom S-bit value is 4124 the same as the Chapter X S-bit value. 4126 o If the list codes multiple logs, the phantom S-bit value is 4127 the logical OR of the S-bit value of the first and second 4128 command logs in the list. 4130 In all other respects, the S bit follows the semantics defined in 4131 Appendix A.1. 4133 The FIRST field (present if F = 1) encodes a variable-length unsigned 4134 integer value that sets the coverage of the DATA field. 4136 The FIRST field (present if F = 1) encodes a variable-length unsigned 4137 integer value that specifies which SysEx data bytes are encoded in the 4138 DATA field of the log. The FIRST field consists of an octet whose most- 4139 significant bit is set to 0, optionally preceded by one or more octets 4140 whose most-significant bit is set to 1. The algorithm shown in Figure 4141 B.5.2 decodes this format into an unsigned integer, to yield the value 4142 dec(FIRST). FIRST uses a variable-length encoding because dec(FIRST) 4143 references a data octet in a SysEx command, and a SysEx command may 4144 contain an arbitrary number of data octets. 4146 One-Octet FIRST value: 4148 Encoded form: 0ddddddd 4149 Decoded form: 00000000 00000000 00000000 0ddddddd 4151 Two-Octet FIRST value: 4153 Encoded form: 1ccccccc 0ddddddd 4154 Decoded form: 00000000 00000000 00cccccc cddddddd 4156 Three-Octet FIRST value: 4158 Encoded form: 1bbbbbbb 1ccccccc 0ddddddd 4159 Decoded form: 00000000 000bbbbb bbcccccc cddddddd 4161 Four-Octet FIRST value: 4163 Encoded form: 1aaaaaaa 1bbbbbbb 1ccccccc 0ddddddd 4164 Decoded form: 0000aaaa aaabbbbb bbcccccc cddddddd 4166 Figure B.5.2 -- Decoding FIRST field formats 4168 The DATA field (present if D = 1) encodes a modified version of the data 4169 octets of the SysEx command coded by the log. Status octets MUST NOT be 4170 coded in the DATA field. 4172 If F = 0, the DATA field begins with the first data octet of the SysEx 4173 command and includes all subsequent data octets for the command that 4174 appear in the session history. If F = 1, the DATA field begins with the 4175 (dec(FIRST) + 1)'th data octet of the SysEx command and includes all 4176 subsequent data octets for the command that appear in the session 4177 history. Note that the word "command" in the descriptions above refers 4178 to the original SysEx command as it appears in the source MIDI data 4179 stream, not to a particular MIDI list SysEx command segment. 4181 The length of the DATA field is coded implicitly, using the most- 4182 significant bit of each octet. The most-significant bit of the final 4183 octet of the DATA field MUST be set to 1. The most-significant bit of 4184 all other DATA octets MUST be set to 0. This coding method relies on 4185 the fact that the most-significant bit of a MIDI data octet is 0 by 4186 definition. Apart from this length-coding modification, the DATA field 4187 encodes a verbatim copy of all data octets it encodes. 4189 B.5.2. Log Inclusion Semantics 4191 Chapter X offers two tools to protect SysEx commands: the "recency" tool 4192 and the "list" tool. The tool definitions use the concept of the "SysEx 4193 type" of a command, which we now define. 4195 Each SysEx command instance in a session, excepting MTC Full Frame 4196 commands, is said to have a "SysEx type". Types are used in equality 4197 comparisons: two SysEx commands in a session are said to have "the same 4198 SysEx type" or "different SysEx types". 4200 If efficiency is not a concern, a sender may follow a simple typing 4201 rule: every SysEx command in the session history has a different SysEx 4202 type, and thus no two commands in the session have the same type. 4204 To improve efficiency, senders MAY implement exceptions to this rule. 4205 These exceptions declare that certain sets of SysEx command instances 4206 have the same SysEx type. Any command not covered by an exception 4207 follows the simple rule. We list exceptions below: 4209 o All commands with identical data octet fields (same number of 4210 data octets, same value for each data octet) have the same type. 4211 This rule MUST be applied to all SysEx commands in the session, 4212 or not at all. Note that the implementation of this exception 4213 requires no sender knowledge of the format and semantics of 4214 the SysEx commands in the stream, merely the ability to count 4215 and compare octets. 4217 o Two instances of the same command whose semantics set or report 4218 the value of the same "parameter" have the same type. The 4219 implementation of this exception requires specific knowledge of 4220 the format and semantics of SysEx commands. In practice, a 4221 sender implementation chooses to support this exception for 4222 certain classes of commands (such as the Universal System 4223 Exclusive commands defined in [MIDI]). If a sender supports 4224 this exception for a particular command in a class (for 4225 example, the Universal Real Time System Exclusive message 4226 for Master Volume, F0 F7 cc 04 01 vv vv F7, defined in [MIDI]), 4227 it MUST support the exception to all instances of this 4228 particular command in the session. 4230 We now use this definition of "SysEx type" to define the "recency" tool 4231 and the "list" tool for Chapter X. 4233 By default, the Chapter X log list MUST code sufficient information to 4234 protect the rendered MIDI performance from indefinite artifacts caused 4235 by the loss of all finished or unfinished active SysEx commands that 4236 appear in the checkpoint history (excluding finished MTC Full Frame 4237 commands, which are coded in Chapter F (Appendix B.4)). 4239 To protect a command of a specific SysEx type with the recency tool, 4240 senders MUST code a log in the log list for the most recent finished 4241 active instance of the SysEx type that appears in the checkpoint 4242 history. Additionally, if an unfinished active instance of the SysEx 4243 type appears in the checkpoint history, senders MUST code a log in the 4244 log list for the unfinished command instance. The L header bit of both 4245 command logs MUST be set to 0. 4247 To protect a command of a specific SysEx type with the list tool, 4248 senders MUST code a log in the Chapter X log list for each finished or 4249 unfinished active instance of the SysEx type that appears in the 4250 checkpoint history. The L header bit of list tool command logs MUST be 4251 set to 1. 4253 As a rule, a log REQUIRED by the list or recency tool MUST include a 4254 DATA field that codes all data octets that appear in the checkpoint 4255 history for the SysEx command instance associated with the log. The 4256 FIRST field MAY be used to configure a DATA field that minimally meets 4257 this requirement. 4259 An exception to this rule applies to cancelled commands (defined in 4260 Section 3.2). REQUIRED command logs associated with cancelled commands 4261 MAY be coded with no DATA field. However, if DATA appears in the log, 4262 DATA MUST code all data octets that appear in the checkpoint history for 4263 the command associated with the log. 4265 As defined by the preceding text in this section, by default all 4266 finished or unfinished active SysEx commands that appear in the 4267 checkpoint history (excluding finished MTC Full Frame commands) MUST be 4268 protected by the list tool or the recency tool. 4270 For some MIDI source streams, this default yields a Chapter X whose size 4271 is too large. For example, imagine that a sender begins to transcode a 4272 SysEx command with 10,000 data octets onto a UDP RTP stream "on the 4273 fly", by sending SysEx command segments as soon as data octets are 4274 delivered by the MIDI source. After 1000 octets have been sent, the 4275 expansion of Chapter X yields an RTP packet that is too large to fit in 4276 the Maximum Transmission Unit (MTU) for the stream. 4278 In this situation, if a sender uses the closed-loop sending policy for 4279 SysEx commands, the RTP packet size may always be capped by stalling the 4280 stream. In a stream stall, once the packet reaches a maximum size, the 4281 sender refrains from sending new packets with non-empty MIDI Command 4282 Sections until receiver feedback permits the trimming of Chapter X. If 4283 the stream permits arbitrary commands to appear between SysEx segments 4284 (selectable during configuration using the tools defined in Appendix 4285 C.1), the sender may stall the SysEx segment stream but continue to code 4286 other commands in the MIDI list. 4288 Stalls are a workable but sub-optimal solution to Chapter X size issues. 4289 As an alternative to stalls, senders SHOULD take preemptive action 4290 during session configuration to reduce the anticipated size of Chapter 4291 X, using the methods described below: 4293 o Partitioned transport. Appendix C.5 provides tools 4294 for sending a MIDI name space over several RTP streams. 4295 Senders may use these tools to map a MIDI source 4296 into a low-latency UDP RTP stream (for channel commands 4297 and short SysEx commands) and a reliable [RFC4571] TCP stream 4298 (for bulk-data SysEx commands). The cm_unused and 4299 cm_used parameters (Appendix C.1) may be used to 4300 communicate the nature of the SysEx command partition. 4301 As TCP is reliable, the RTP MIDI TCP stream would not 4302 use the recovery journal. To minimize transmission 4303 latency for short SysEx commands, senders may begin 4304 segmental transmission for all SysEx commands over the 4305 UDP stream and then cancel the UDP transmission of long 4306 commands (using tools described in Section 3.2) and 4307 resend the commands over the TCP stream. 4309 o Selective protection. Journal protection may not be 4310 necessary for all SysEx commands in a stream. The 4311 ch_never parameter (Appendix C.2) may be used to 4312 communicate which SysEx commands are excluded from 4313 Chapter X. 4315 B.5.3. TCOUNT and COUNT Fields 4317 If the T header bit is set to 1, the 8-bit TCOUNT field appears in the 4318 command log. If the C header bit is set to 1, the 8-bit COUNT field 4319 appears in the command log. TCOUNT and COUNT are interpreted as 4320 unsigned integers. 4322 The TCOUNT field codes the total number of SysEx commands of the SysEx 4323 type coded by the log that appear in the session history, at the moment 4324 after the (finished or unfinished) command coded by the log enters the 4325 session history. 4327 The COUNT field codes the total number of SysEx commands that appear in 4328 the session history, excluding commands that are excluded from Chapter X 4329 via the ch_never parameter (Appendix C.2), at the moment after the 4330 (finished or unfinished) command coded by the log enters the session 4331 history. 4333 Command counting for TCOUNT and COUNT uses modulo-256 arithmetic. MTC 4334 Full Frame command instances (Appendix B.4) are included in command 4335 counting if the TCOUNT and COUNT definitions warrant their inclusion, as 4336 are cancelled commands (Section 3.2). 4338 Senders use the TCOUNT and COUNT fields to track the identity and (for 4339 TCOUNT) the sequence position of a command instance. Senders MUST use 4340 the TCOUNT or COUNT fields if identity or sequence information is 4341 necessary to protect the command type coded by the log. 4343 If a sender uses the COUNT field in a session, the final command log in 4344 every Chapter X in the stream MUST code the COUNT field. This rule lets 4345 receivers resynchronize the COUNT value after a packet loss. 4347 C. Session Configuration Tools 4349 In Sections 6.1-2 of the main text, we show session descriptions for 4350 minimal native and mpeg4-generic RTP MIDI streams. Minimal streams lack 4351 the flexibility to support some applications. In this appendix, we 4352 describe how to customize stream behavior through the use of the payload 4353 format parameters. 4355 The appendix begins with 6 sections, each devoted to parameters that 4356 affect a particular aspect of stream behavior: 4358 o Appendix C.1 describes the stream subsetting system 4359 (cm_unused and cm_used). 4361 o Appendix C.2 describes the journalling system (ch_anchor, 4362 ch_default, ch_never, j_sec, j_update). 4364 o Appendix C.3 describes MIDI command timestamp semantics 4365 (linerate, mperiod, octpos, tsmode). 4367 o Appendix C.4 describes the temporal duration ("media time") 4368 of an RTP MIDI packet (guardtime, rtp_maxptime, rtp_ptime). 4370 o Appendix C.5 concerns stream description (musicport). 4372 o Appendix C.6 describes MIDI rendering (chanmask, cid, 4373 inline, multimode, render, rinit, subrender, smf_cid, 4374 smf_info, smf_inline, smf_url, url). 4376 The parameters listed above may optionally appear in session 4377 descriptions of RTP MIDI streams. If these parameters are used in an 4378 SDP session description, the parameters appear on an fmtp attribute 4379 line. This attribute line applies to the payload type associated with 4380 the fmtp line. 4382 The parameters listed above add extra functionality ("features") to 4383 minimal RTP MIDI streams. In Appendix C.7, we show how to use these 4384 features to support two classes of applications: content-streaming using 4385 RTSP (Appendix C.7.1) and network musical performance using SIP 4386 (Appendix C.7.2). 4388 The participants in a multimedia session MUST share a common view of all 4389 of the RTP MIDI streams that appear in an RTP session, as defined by a 4390 single media (m=) line. In some RTP MIDI applications, the "common 4391 view" restriction makes it difficult to use sendrecv streams (all 4392 parties send and receive), as each party has its own requirements. For 4393 example, a two-party network musical performance application may wish to 4394 customize the renderer on each host to match the CPU performance of the 4395 host [NMP]. 4397 We solve this problem by using two RTP MIDI streams -- one sendonly, one 4398 recvonly -- in lieu of one sendrecv stream. The data flows in the two 4399 streams travel in opposite directions, to control receivers configured 4400 to use different renderers. In the third example in Appendix C.5, we 4401 show how the musicport parameter may be used to define virtual sendrecv 4402 streams. 4404 As a general rule, the RTP MIDI protocol does not handle parameter 4405 changes during a session well, because the parameters describe 4406 heavyweight or stateful configuration that is not easily changed once a 4407 session has begun. Thus, parties SHOULD NOT expect that parameter 4408 change requests during a session will be accepted by other parties. 4409 However, implementors SHOULD support in-session parameter changes that 4410 are easy to handle (for example, the guardtime parameter defined in 4411 Appendix C.4) and SHOULD be capable of accepting requests for changes of 4412 those parameters, as received by its session management protocol (for 4413 example, re-offers in SIP [RFC3264]). 4415 Appendix D defines the Augmented Backus-Naur Form (ABNF, [RFC5234]) 4416 syntax for the payload parameters. Section 11 provides information to 4417 the Internet Assigned Numbers Authority (IANA) on the media types and 4418 parameters defined in this document. 4420 Appendix C.6.5 defines the media type "audio/asc", a stored object for 4421 initializing mpeg4-generic renderers. As described in Appendix C.6, the 4422 audio/asc media type is assigned to the "rinit" parameter to specify an 4423 initialization data object for the default mpeg4-generic renderer. Note 4424 that RTP stream semantics are not defined for "audio/asc". Therefore, 4425 the "asc" subtype MUST NOT appear on the rtpmap line of a session 4426 description. 4428 C.1. Configuration Tools: Stream Subsetting 4430 As defined in Section 3.2 in the main text, the MIDI list of an RTP MIDI 4431 packet may encode any MIDI command that may legally appear on a MIDI 1.0 4432 DIN cable. 4434 In this appendix, we define two parameters (cm_unused and cm_used) that 4435 modify this default condition, by excluding certain types of MIDI 4436 commands from the MIDI list of all packets in a stream. For example, if 4437 a multimedia session partitions a MIDI name space into two RTP MIDI 4438 streams, the parameters may be used to define which commands appear in 4439 each stream. 4441 In this appendix, we define a simple language for specifying MIDI 4442 command types. If a command type is assigned to cm_unused, the commands 4443 coded by the string MUST NOT appear in the MIDI list. If a command type 4444 is assigned to cm_used, the commands coded by the string MAY appear in 4445 the MIDI list. 4447 The parameter list may code multiple assignments to cm_used and 4448 cm_unused. Assignments have a cumulative effect and are applied in the 4449 order of appearance in the parameter list. A later assignment of a 4450 command type to the same parameter expands the scope of the earlier 4451 assignment. A later assignment of a command type to the opposite 4452 parameter cancels (partially or completely) the effect of an earlier 4453 assignment. 4455 To initialize the stream subsetting system, "implicit" assignments to 4456 cm_unused and cm_used are processed before processing the actual 4457 assignments that appear in the parameter list. The System Common 4458 undefined commands (0xF4, 0xF5) and the System Real-Time Undefined 4459 commands (0xF9, 0xFD) are implicitly assigned to cm_unused. All other 4460 command types are implicitly assigned to cm_used. 4462 Note that the implicit assignments code the default behavior of an RTP 4463 MIDI stream as defined in Section 3.2 in the main text (namely, that all 4464 commands that may legally appear on a MIDI 1.0 DIN cable may appear in 4465 the stream). Also note that assignments of the System Common undefined 4466 commands (0xF4, 0xF5) apply to the use of these commands in the MIDI 4467 source command stream, not the special use of 0xF4 and 0xF5 in SysEx 4468 segment encoding defined in Section 3.2 in the main text. 4470 As a rule, parameter assignments obey the following syntax (see Appendix 4471 D for ABNF): 4473 = [channel list][field list] 4475 The command-type list is mandatory; the channel and field lists are 4476 optional. 4478 The command-type list specifies the MIDI command types for which the 4479 parameter applies. The command-type list is a concatenated sequence of 4480 one or more of the letters (ABCFGHJKMNPQTVWXYZ). The letters code the 4481 following command types: 4483 o A: Poly Aftertouch (0xA) 4484 o B: System Reset (0xFF) 4485 o C: Control Change (0xB) 4486 o F: System Time Code (0xF1) 4487 o G: System Tune Request (0xF6) 4488 o H: System Song Select (0xF3) 4489 o J: System Common Undefined (0xF4) 4490 o K: System Common Undefined (0xF5) 4491 o N: NoteOff (0x8), NoteOn (0x9) 4492 o P: Program Change (0xC) 4493 o Q: System Sequencer (0xF2, 0xF8, 0xFA, 0xFB, 0xFC) 4494 o T: Channel Aftertouch (0xD) 4495 o V: System Active Sense (0xFE) 4496 o W: Pitch Wheel (0xE) 4497 o X: SysEx (0xF0, 0xF7) 4498 o Y: System Real-Time Undefined (0xF9) 4499 o Z: System Real-Time Undefined (0xFD) 4501 In addition to the letters above, the letter M may also appear in the 4502 command-type list. The letter M refers to the MIDI parameter system 4503 (see definition in Appendix A.1 and in [MIDI]). An assignment of M to 4504 cm_unused codes that no RPN or NRPN transactions may appear in the MIDI 4505 list. 4507 Note that if cm_unused is assigned the letter M, Control Change (0xB) 4508 commands for the controller numbers in the standard controller 4509 assignment might still appear in the MIDI list. For an explanation, see 4510 Appendix A.3.4 for a discussion of the "general-purpose" use of 4511 parameter system controller numbers. 4513 In the text below, rules that apply to "MIDI voice channel commands" 4514 also apply to the letter M. 4516 The letters in the command-type list MUST be uppercase and MUST appear 4517 in alphabetical order. Letters other than (ABCFGHJKMNPQTVWXYZ) that 4518 appear in the list MUST be ignored. 4520 For MIDI voice channel commands, the channel list specifies the MIDI 4521 channels for which the parameter applies. If no channel list is 4522 provided, the parameter applies to all MIDI channels (0-15). The 4523 channel list takes the form of a list of channel numbers (0 through 15) 4524 and dash-separated channel number ranges (i.e., 0-5, 8-12, etc.). Dots 4525 (i.e., "." characters) separate elements in the channel list. 4527 Recall that System commands do not have a MIDI channel associated with 4528 them. Thus, for most command-type letters that code System commands (B, 4529 F, G, H, J, K, Q, V, Y, and Z), the channel list is ignored. 4531 For the command-type letter X, the appearance of certain numbers in the 4532 channel list codes special semantics. 4534 o The digit 0 codes that SysEx "cancel" sublists (Section 4535 3.2 in the main text) MUST NOT appear in the MIDI list. 4537 o The digit 1 codes that cancel sublists MAY appear in the 4538 MIDI list (the default condition). 4540 o The digit 2 codes that commands other than System 4541 Real-time MIDI commands MUST NOT appear between SysEx 4542 command segments in the MIDI list (the default condition). 4544 o The digit 3 codes that any MIDI command type may 4545 appear between SysEx command segments in the MIDI list, 4546 with the exception of the segmented encoding of a second 4547 SysEx command (verbatim SysEx commands are OK). 4549 For command-type X, the channel list MUST NOT contain both digits 0 and 4550 1, and it MUST NOT contain both digits 2 and 3. For command-type X, 4551 channel list numbers other than the numbers defined above are ignored. 4552 If X does not have a channel list, the semantics marked "the default 4553 condition" in the list above apply. 4555 The syntax for field lists in a parameter assignment follows the syntax 4556 for channel lists. If no field list is provided, the parameter applies 4557 to all controller or note numbers. 4559 For command-type C (Control Change), the field list codes the controller 4560 numbers (0-255) for which the parameter applies. 4562 For command-type M (Parameter System), the field list codes the 4563 Registered Parameter Numbers (RPNs) and Non-Registered Parameter Numbers 4564 (NRPNs) for which the parameter applies. The number range 0-16383 4565 specifies RPNs, the number range 16384-32767 specifies NRPNs (16384 4566 corresponds to NRPN 0, 32767 corresponds to NRPN 16383). 4568 For command-types N (NoteOn and NoteOff) and A (Poly Aftertouch), the 4569 field list codes the note numbers for which the parameter applies. 4571 For command-types J and K (System Common Undefined), the field list 4572 consists of a single digit, which specifies the number of data octets 4573 that follow the command octet. 4575 For command-type X (SysEx), the field list codes the number of data 4576 octets that may appear in a SysEx command. Thus, the field list 0-255 4577 specifies SysEx commands with 255 or fewer data octets, the field list 4578 256-4294967295 specifies SysEx commands with more than 255 data octets 4579 but excludes commands with 255 or fewer data octets, and the field list 4580 0 excludes all commands. 4582 A secondary parameter assignment syntax customizes command-type X (see 4583 Appendix D for complete ABNF): 4585 = "__" *( "_" ) "__" 4587 The assignment defines the class of SysEx commands that obeys the 4588 semantics of the assigned parameter. The command class is specified by 4589 listing the permitted values of the first N data octets that follow the 4590 SysEx 0xF0 command octet. Any SysEx command whose first N data octets 4591 match the list is a member of the class. 4593 Each defines a data octet of the command, as a dot-separated 4594 (".") list of one or more hexadecimal constants (such as "7F") or dash- 4595 separated hexadecimal ranges (such as "01-1F"). Underscores ("_") 4596 separate each . Double-underscores ("__") delineate the data 4597 octet list. 4599 Using this syntax, each assignment specifies a single SysEx command 4600 class. Session descriptions may use several assignments to cm_used and 4601 cm_unused to specify complex behaviors. 4603 The example session description below illustrates the use of the stream 4604 subsetting parameters: 4606 v=0 4607 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 4608 s=Example 4609 t=0 0 4610 m=audio 5004 RTP/AVP 96 4611 c=IN IP6 2001:DB80::7F2E:172A:1E24 4612 a=rtpmap:96 rtp-midi/44100 4613 a=fmtp:96 cm_unused=ACGHJKNMPTVWXYZ; cm_used=__7F_00-7F_01_01__ 4615 The session description configures the stream for use in clock 4616 applications. All voice channels are unused, as are all System Commands 4617 except those used for MIDI Time Code (command-type F, and the Full Frame 4618 SysEx command that is matched by the string assigned to cm_used), the 4619 System Sequencer commands (command-type Q), and System Reset (command- 4620 type B). 4622 C.2. Configuration Tools: The Journalling System 4624 In this appendix, we define the payload format parameters that configure 4625 stream journalling and the recovery journal system. 4627 The j_sec parameter (Appendix C.2.1) sets the journalling method for the 4628 stream. The j_update parameter (Appendix C.2.2) sets the recovery 4629 journal sending policy for the stream. Appendix C.2.2 also defines the 4630 sending policies of the recovery journal system. 4632 Appendix C.2.3 defines several parameters that modify the recovery 4633 journal semantics. These parameters change the default recovery journal 4634 semantics as defined in Section 5 and Appendices A-B. 4636 The journalling method for a stream is set at the start of a session and 4637 MUST NOT be changed thereafter. This requirement forbids changes to the 4638 j_sec parameter once a session has begun. 4640 A related requirement, defined in the appendix sections below, forbids 4641 the acceptance of parameter values that would violate the recovery 4642 journal mandate. In many cases, a change in one of the parameters 4643 defined in this appendix during an ongoing session would result in a 4644 violation of the recovery journal mandate for an implementation; in this 4645 case, the parameter change MUST NOT be accepted. 4647 C.2.1. The j_sec Parameter 4649 Section 2.2 defines the default journalling method for a stream. 4650 Streams that use unreliable transport (such as UDP) default to using the 4651 recovery journal. Streams that use reliable transport (such as TCP) 4652 default to not using a journal. 4654 The parameter j_sec may be used to override this default. This memo 4655 defines two symbolic values for j_sec: "none", to indicate that all 4656 stream payloads MUST NOT contain a journal section, and "recj", to 4657 indicate that all stream payloads MUST contain a journal section that 4658 uses the recovery journal format. 4660 For example, the j_sec parameter might be set to "none" for a UDP stream 4661 that travels between two hosts on a local network that is known to 4662 provide reliable datagram delivery. 4664 The session description below configures a UDP stream that does not use 4665 the recovery journal: 4667 v=0 4668 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 4669 s=Example 4670 t=0 0 4671 m=audio 5004 RTP/AVP 96 4672 c=IN IP4 192.0.2.94 4673 a=rtpmap:96 rtp-midi/44100 4674 a=fmtp:96 j_sec=none 4676 Other IETF standards-track documents may define alternative journal 4677 formats. These documents MUST define new symbolic values for the j_sec 4678 parameter to signal the use of the format. 4680 Parties MUST NOT accept a j_sec value that violates the recovery journal 4681 mandate (see Section 4 for details). If a session description uses a 4682 j_sec value unknown to the recipient, the recipient MUST NOT accept the 4683 description. 4685 Special j_sec issues arise when sessions are managed by session 4686 management tools (like RTSP, [RFC2326]) that use SDP for "declarative 4687 usage" purposes (see the preamble of Section 6 for details). For these 4688 session management tools, SDP does not code transport details (such as 4689 UDP or TCP) for the session. Instead, server and client negotiate 4690 transport details via other means (for RTSP, the SETUP method). 4692 In this scenario, the use of the j_sec parameter may be ill-advised, as 4693 the creator of the session description may not yet know the transport 4694 type for the session. In this case, the session description SHOULD 4695 configure the journalling system using the parameters defined in the 4696 remainder of Appendix C.2, but it SHOULD NOT use j_sec to set the 4697 journalling status. Recall that if j_sec does not appear in the session 4698 description, the default method for choosing the journalling method is 4699 in effect (no journal for reliable transport, recovery journal for 4700 unreliable transport). 4702 However, in declarative usage situations where the creator of the 4703 session description knows that journalling is always required or never 4704 required, the session description SHOULD use the j_sec parameter. 4706 C.2.2. The j_update Parameter 4708 In Section 4, we use the term "sending policy" to describe the method a 4709 sender uses to choose the checkpoint packet identity for each recovery 4710 journal in a stream. In the sub-sections that follow, we normatively 4711 define three sending policies: anchor, closed-loop, and open-loop. 4713 As stated in Section 4, the default sending policy for a stream is the 4714 closed-loop policy. The j_update parameter may be used to override this 4715 default. 4717 We define three symbolic values for j_update: "anchor", to indicate that 4718 the stream uses the anchor sending policy, "open-loop", to indicate that 4719 the stream uses the open-loop sending policy, and "closed-loop", to 4720 indicate that the stream uses the closed-loop sending policy. See 4721 Appendix C.2.3 for examples session descriptions that use the j_update 4722 parameter. 4724 Parties MUST NOT accept a j_update value that violates the recovery 4725 journal mandate (Section 4). 4727 Other IETF standards-track documents may define additional sending 4728 policies for the recovery journal system. These documents MUST define 4729 new symbolic values for the j_update parameter to signal the use of the 4730 new policy. If a session description uses a j_update value unknown to 4731 the recipient, the recipient MUST NOT accept the description. 4733 C.2.2.1. The anchor Sending Policy 4735 In the anchor policy, the sender uses the first packet in the stream as 4736 the checkpoint packet for all packets in the stream. The anchor policy 4737 satisfies the recovery journal mandate (Section 4), as the checkpoint 4738 history always covers the entire stream. 4740 The anchor policy does not require the use of the RTP control protocol 4741 (RTCP, [RFC3550]) or other feedback from receiver to sender. Senders do 4742 not need to take special actions to ensure that received streams start 4743 up free of artifacts, as the recovery journal always covers the entire 4744 history of the stream. Receivers are relieved of the responsibility of 4745 tracking the changing identity of the checkpoint packet, because the 4746 checkpoint packet never changes. 4748 The main drawback of the anchor policy is bandwidth efficiency. Because 4749 the checkpoint history covers the entire stream, the size of the 4750 recovery journals produced by this policy usually exceeds the journal 4751 size of alternative policies. For single-channel MIDI data streams, the 4752 bandwidth overhead of the anchor policy is often acceptable (see 4753 Appendix A.4 of [NMP]). For dense streams, the closed-loop or open-loop 4754 policies may be more appropriate. 4756 C.2.2.2. The closed-loop Sending Policy 4758 The closed-loop policy is the default policy of the recovery journal 4759 system. For each packet in the stream, the policy lets senders choose 4760 the smallest possible checkpoint history that satisfies the recovery 4761 journal mandate. As smaller checkpoint histories generally yield 4762 smaller recovery journals, the closed-loop policy reduces the bandwidth 4763 of a stream, relative to the anchor policy. 4765 The closed-loop policy relies on feedback from receiver to sender. The 4766 policy assumes that a receiver periodically informs the sender of the 4767 highest sequence number it has seen so far in the stream, coded in the 4768 32-bit extension format defined in [RFC3550]. For RTCP, receivers 4769 transmit this information in the Extended Highest Sequence Number 4770 Received (EHSNR) field of Receiver Reports. RTCP Sender or Receiver 4771 Reports MUST be sent by any participant in a session with closed loop 4772 sending policy, unless another feedback mechanism has been agreed upon. 4774 The sender may safely use receiver sequence number feedback to guide 4775 checkpoint history management, because Section 4 requires that receivers 4776 repair indefinite artifacts whenever a packet loss event occur. 4778 We now normatively define the closed-loop policy. At the moment a 4779 sender prepares an RTP packet for transmission, the sender is aware of R 4780 >= 0 receivers for the stream. Senders may become aware of a receiver 4781 via RTCP traffic from the receiver, via RTP packets from a paired stream 4782 sent by the receiver to the sender, via messages from a session 4783 management tool, or by other means. As receivers join and leave a 4784 session, the value of R changes. 4786 Each known receiver k (1 <= k <= R) is associated with a 32-bit extended 4787 packet sequence number M(k), where the extension reflects the sequence 4788 number rollover count of the sender. 4790 If the sender has received at least one feedback report from receiver k, 4791 M(k) is the most recent report of the highest RTP packet sequence number 4792 seen by the receiver, normalized to reflect the rollover count of the 4793 sender. 4795 If the sender has not received a feedback report from the receiver, M(k) 4796 is the extended sequence number of the last packet the sender 4797 transmitted before it became aware of the receiver. If the sender 4798 became aware of this receiver before it sent the first packet in the 4799 stream, M(k) is the extended sequence number of the first packet in the 4800 stream. 4802 Given this definition of M(), we now state the closed-loop policy. When 4803 preparing a new packet for transmission, a sender MUST choose a 4804 checkpoint packet with extended sequence number N, such that M(k) >= (N 4805 - 1) for all k, 1 <= k <= R, where R >= 1. The policy does not restrict 4806 sender behavior in the R == 0 (no known receivers) case. 4808 Under the closed-loop policy as defined above, a sender may transmit 4809 packets whose checkpoint history is shorter than the session history (as 4810 defined in Appendix A.1). In this event, a new receiver that joins the 4811 stream may experience indefinite artifacts. 4813 For example, if a Control Change (0xB) command for Channel Volume 4814 (controller number 7) was sent early in a stream, and later a new 4815 receiver joins the session, the closed-loop policy may permit all 4816 packets sent to the new receiver to use a checkpoint history that does 4817 not include the Channel Volume Control Change command. As a result, the 4818 new receiver experiences an indefinite artifact, and plays all notes on 4819 a channel too loudly or too softly. 4821 To address this issue, the closed-loop policy states that whenever a 4822 sender becomes aware of a new receiver, the sender MUST determine if the 4823 receiver would be subject to indefinite artifacts under the closed-loop 4824 policy. If so, the sender MUST ensure that the receiver starts the 4825 session free of indefinite artifacts. For example, to solve the Channel 4826 Volume issue described above, the sender may code the current state of 4827 the Channel Volume controller numbers in the recovery journal Chapter C, 4828 until it receives the first RTCP RR report that signals that a packet 4829 containing this Chapter C has been received. 4831 In satisfying this requirement, senders MAY infer the initial MIDI state 4832 of the receiver from the session description. For example, the stream 4833 example in Section 6.2 has the initial state defined in [MIDI] for 4834 General MIDI. 4836 In a unicast RTP session, a receiver may safely assume that the sender 4837 is aware of its presence as a receiver from the first packet sent in the 4838 RTP stream. However, in other types of RTP sessions (multicast, 4839 conference focus, RTP translator/mixer), a receiver is often not able to 4840 determine if the sender is initially aware of its presence as a 4841 receiver. 4843 To address this issue, the closed-loop policy states that if a receiver 4844 participates in a session where it may have access to a stream whose 4845 sender is not aware of the receiver, the receiver MUST take actions to 4846 ensure that its rendered MIDI performance does not contain indefinite 4847 artifacts. These protections will be necessarily incomplete. For 4848 example, a receiver may monitor the Checkpoint Packet Seqnum for 4849 uncovered loss events, and "err on the side of caution" with respect to 4850 handling stuck notes due to lost MIDI NoteOff commands, but the receiver 4851 is not able to compensate for the lack of Channel Volume initialization 4852 data in the recovery journal. 4854 The receiver MUST NOT discontinue these protective actions until it is 4855 certain that the sender is aware of its presence. If a receiver is not 4856 able to ascertain sender awareness, the receiver MUST continue these 4857 protective actions for the duration of the session. 4859 Note that in a multicast session where all parties are expected to send 4860 and receive, the reception of RTCP receiver reports from the sender 4861 about the RTP stream a receiver is multicasting back is evidence of the 4862 sender's awareness that the RTP stream multicast by the sender is being 4863 monitored by the receiver. Receivers may also obtain sender awareness 4864 evidence from session management tools, or by other means. In practice, 4865 ongoing observation of the Checkpoint Packet Seqnum to determine if the 4866 sender is taking actions to prevent loss events for a receiver is a good 4867 indication of sender awareness, as is the sudden appearance of recovery 4868 journal chapters with numerous Control Change controller data that was 4869 not foreshadowed by recent commands coded in the MIDI list shortly after 4870 sending an RTCP RR. 4872 The final set of normative closed-loop policy requirements concerns how 4873 senders and receivers handle unplanned disruptions of RTCP feedback from 4874 a receiver to a sender. By "unplanned", we refer to disruptions that 4875 are not due to the signalled termination of an RTP stream, via an RTCP 4876 BYE or via session management tools. 4878 As defined earlier in this section, the closed-loop policy states that a 4879 sender MUST choose a checkpoint packet with extended sequence number N, 4880 such that M(k) >= (N - 1) for all k, 1 <= k <= R, where R >= 1. If the 4881 sender has received at least one feedback report from receiver k, M(k) 4882 is the most recent report of the highest RTP packet sequence number seen 4883 by the receiver, normalized to reflect the rollover count of the sender. 4885 If this receiver k stops sending feedback to the sender, the M(k) value 4886 used by the sender reflects the last feedback report from the receiver. 4887 As time progresses without feedback from receiver k, this fixed M(k) 4888 value forces the sender to increase the size of the checkpoint history, 4889 and thus increases the bandwidth of the stream. 4891 At some point, the sender may need to take action in order to limit the 4892 bandwidth of the stream. In most envisioned uses of RTP MIDI, long 4893 before this point is reached, the SSRC time-out mechanism defined in 4894 [RFC3550] will remove the uncooperative receiver from the session (note 4895 that the closed-loop policy does not suggest or require any special 4896 sender behavior upon an SSRC time-out, other than the sender actions 4897 related to changing R, described earlier in this section). 4899 However, in rare situations, the bandwidth of the stream (due to a lack 4900 of feedback reports from the sender) may become too large to continue 4901 sending the stream to the receiver before the SSRC time-out occurs for 4902 the receiver. In this case, the closed-loop policy states that the 4903 sender should invoke the SSRC time-out for the receiver early. 4905 We now discuss receiver responsibilities in the case of unplanned 4906 disruptions of RTCP feedback from receiver to sender. 4908 In the unicast case, if a sender invokes the SSRC time-out mechanism for 4909 a receiver, the receiver stops receiving packets from the sender. The 4910 sender behavior imposed by the guardtime parameter (Appendix C.4.2) lets 4911 the receiver conclude that an SSRC time-out has occurred in a reasonable 4912 time period. 4914 In this case of a time-out, a receiver MUST keep sending RTCP feedback, 4915 in order to re-establish the RTP flow from the sender. Unless the 4916 receiver expects a prompt recovery of the RTP flow, the receiver MUST 4917 take actions to ensure that the rendered MIDI performance does not 4918 exhibit "very long transient artifacts" (for example, by silencing 4919 NoteOns to prevent stuck notes) while awaiting reconnection of the flow. 4921 In the multicast case, if a sender invokes the SSRC time-out mechanism 4922 for a receiver, the receiver may continue to receive packets, but the 4923 sender will no longer be using the M(k) feedback from the receiver to 4924 choose each checkpoint packet. If the receiver does not have additional 4925 information that precludes an SSRC time-out (such as RTCP Receiver 4926 Reports from the sender about an RTP stream the receiver is multicasting 4927 back to the sender), the receiver MUST monitor the Checkpoint Packet 4928 Seqnum to detect an SSRC time-out. If an SSRC time-out is detected, the 4929 receiver MUST follow the instructions for SSRC time-outs described for 4930 the unicast case above. 4932 Finally, we note that the closed-loop policy is suitable for use in 4933 RTP/RTCP sessions that use multicast transport. However, aspects of the 4934 closed-loop policy do not scale well to sessions with large numbers of 4935 participants. The sender state scales linearly with the number of 4936 receivers, as the sender needs to track the identity and M(k) value for 4937 each receiver k. The average recovery journal size is not independent 4938 of the number of receivers, as the RTCP reporting interval backoff slows 4939 down the rate of a full update of M(k) values. The backoff algorithm 4940 may also increase the amount of ancillary state used by implementations 4941 of the normative sender and receiver behaviors defined in Section 4. 4943 C.2.2.3. The open-loop Sending Policy 4945 The open-loop policy is suitable for sessions that are not able to 4946 implement the receiver-to-sender feedback required by the closed-loop 4947 policy, and that are also not able to use the anchor policy because of 4948 bandwidth constraints. 4950 The open-loop policy does not place constraints on how a sender chooses 4951 the checkpoint packet for each packet in the stream. In the absence of 4952 such constraints, a receiver may find that the recovery journal in the 4953 packet that ends a loss event has a checkpoint history that does not 4954 cover the entire loss event. We refer to loss events of this type as 4955 uncovered loss events. 4957 To ensure that uncovered loss events do not compromise the recovery 4958 journal mandate, the open-loop policy assigns specific recovery tasks to 4959 senders, receivers, and the creators of session descriptions. The 4960 underlying premise of the open-loop policy is that the indefinite 4961 artifacts produced during uncovered loss events fall into two classes. 4963 One class of artifacts is recoverable indefinite artifacts. Receivers 4964 are able to repair recoverable artifacts that occur during an uncovered 4965 loss event without intervention from the sender, at the potential cost 4966 of unpleasant transient artifacts. 4968 For example, after an uncovered loss event, receivers are able to repair 4969 indefinite artifacts due to NoteOff (0x8) commands that may have 4970 occurred during the loss event, by executing NoteOff commands for all 4971 active NoteOns commands. This action causes a transient artifact (a 4972 sudden silent period in the performance), but ensures that no stuck 4973 notes sound indefinitely. We refer to MIDI commands that are amenable 4974 to repair in this fashion as recoverable MIDI commands. 4976 A second class of artifacts is unrecoverable indefinite artifacts. If 4977 this class of artifact occurs during an uncovered loss event, the 4978 receiver is not able to repair the stream. 4980 For example, after an uncovered loss event, receivers are not able to 4981 repair indefinite artifacts due to Control Change (0xB) Channel Volume 4982 (controller number 7) commands that have occurred during the loss event. 4983 A repair is impossible because the receiver has no way of determining 4984 the data value of a lost Channel Volume command. We refer to MIDI 4985 commands that are fragile in this way as unrecoverable MIDI commands. 4987 The open-loop policy does not specify how to partition the MIDI command 4988 set into recoverable and unrecoverable commands. Instead, it assumes 4989 that the creators of the session descriptions are able to come to 4990 agreement on a suitable recoverable/unrecoverable MIDI command partition 4991 for an application. 4993 Given these definitions, we now state the normative requirements for the 4994 open-loop policy. 4996 In the open-loop policy, the creators of the session description MUST 4997 use the ch_anchor parameter (defined in Appendix C.2.3) to protect all 4998 unrecoverable MIDI command types from indefinite artifacts, or 4999 alternatively MUST use the cm_unused parameter (defined in Appendix C.1) 5000 to exclude the command types from the stream. These options act to 5001 shield command types from artifacts during an uncovered loss event. 5003 In the open-loop policy, receivers MUST examine the Checkpoint Packet 5004 Seqnum field of the recovery journal header after every loss event, to 5005 check if the loss event is an uncovered loss event. Section 5 shows how 5006 to perform this check. If an uncovered loss event has occurred, a 5007 receiver MUST perform indefinite artifact recovery for all MIDI command 5008 types that are not shielded by ch_anchor and cm_unused parameter 5009 assignments in the session description. 5011 The open-loop policy does not place specific constraints on the sender. 5012 However, the open-loop policy works best if the sender manages the size 5013 of the checkpoint history to ensure that uncovered losses occur 5014 infrequently, by taking into account the delay and loss characteristics 5015 of the network. Also, as each checkpoint packet change incurs the risk 5016 of an uncovered loss, senders should only move the checkpoint if it 5017 reduces the size of the journal. 5019 C.2.3. Recovery Journal Chapter Inclusion Parameters 5021 The recovery journal chapter definitions (Appendices A-B) specify under 5022 what conditions a chapter MUST appear in the recovery journal. In most 5023 cases, the definition states that if a certain command appears in the 5024 checkpoint history, a certain chapter type MUST appear in the recovery 5025 journal to protect the command. 5027 In this section, we describe the chapter inclusion parameters. These 5028 parameters modify the conditions under which a chapter appears in the 5029 journal. These parameters are essential to the use of the open-loop 5030 policy (Appendix C.2.2.3) and may also be used to simplify 5031 implementations of the closed-loop (Appendix C.2.2.2) and anchor 5032 (Appendix C.2.2.1) policies. 5034 Each parameter represents a type of chapter inclusion semantics. An 5035 assignment to a parameter declares which chapters (or chapter subsets) 5036 obey the inclusion semantics. We describe the assignment syntax for 5037 these parameters later in this section. 5039 A party MUST NOT accept chapter inclusion parameter values that violate 5040 the recovery journal mandate (Section 4). All assignments of the 5041 subsetting parameters (cm_used and cm_unused) MUST precede the first 5042 assignment of a chapter inclusion parameter in the parameter list. 5044 Below, we normatively define the semantics of the chapter inclusion 5045 parameters. For clarity, we define the action of parameters on complete 5046 chapters. If a parameter is assigned a subset of a chapter, the 5047 definition applies only to the chapter subset. 5049 o ch_never. A chapter assigned to the ch_never parameter MUST 5050 NOT appear in the recovery journal (Appendix A.4.1-2 defines 5051 exceptions to this rule for Chapter M). To signal the exclusion 5052 of a chapter from the journal, an assignment to ch_never MUST 5053 be made, even if the commands coded by the chapter are assigned 5054 to cm_unused. This rule simplifies the handling of commands 5055 types that may be coded in several chapters. 5057 o ch_default. A chapter assigned to the ch_default parameter 5058 MUST follow the default semantics for the chapter, as defined 5059 in Appendices A-B. 5061 o ch_anchor. A chapter assigned to the ch_anchor MUST obey a 5062 modified version of the default chapter semantics. In the 5063 modified semantics, all references to the checkpoint history 5064 are replaced with references to the session history, and all 5065 references to the checkpoint packet are replaced with 5066 references to the first packet sent in the stream. 5068 Parameter assignments obey the following syntax (see Appendix D for 5069 ABNF): 5071 = [channel list][field list] 5073 The chapter list is mandatory; the channel and field lists are optional. 5074 Multiple assignments to parameters have a cumulative effect and are 5075 applied in the order of parameter appearance in a media description. 5077 To determine the semantics of a list of chapter inclusion parameter 5078 assignments, we begin by assuming an implicit assignment of all channel 5079 and system chapters to the ch_default parameter, with the default values 5080 for the channel list and field list for each chapter that are defined 5081 below. 5083 We then interpret the semantics of the actual parameter assignments, 5084 using the rules below. 5086 A later assignment of a chapter to the same parameter expands the scope 5087 of the earlier assignment. In most cases, a later assignment of a 5088 chapter to a different parameter cancels (partially or completely) the 5089 effect of an earlier assignment. 5091 The chapter list specifies the channel or system chapters for which the 5092 parameter applies. The chapter list is a concatenated sequence of one 5093 or more of the letters corresponding to the chapter types 5094 (ACDEFMNPQTVWX). In addition, the list may contain one or more of the 5095 letters for the sub-chapter types (BGHJKYZ) of System Chapter D. 5097 The letters in a chapter list MUST be uppercase and MUST appear in 5098 alphabetical order. Letters other than (ABCDEFGHJKMNPQTVWXYZ) that 5099 appear in the chapter list MUST be ignored. 5101 The channel list specifies the channel journals for which this parameter 5102 applies; if no channel list is provided, the parameter applies to all 5103 channel journals. The channel list takes the form of a list of channel 5104 numbers (0 through 15) and dash-separated channel number ranges (i.e., 5105 0-5, 8-12, etc.). Dots (i.e., "." characters) separate elements in the 5106 channel list. 5108 Several of the systems chapters may be configured to have special 5109 semantics. Configuration occurs by specifying a channel list for the 5110 systems channel, using the coding described below (note that MIDI 5111 Systems commands do not have a "channel", and thus the original purpose 5112 of the channel list does not apply to systems chapters). The expression 5113 "the digit N" in the text below refers to the inclusion of N as a 5114 "channel" in the channel list for a systems chapter. 5116 For the J and K Chapter D sub-chapters (undefined System Common), the 5117 digit 0 codes that the parameter applies to the LEGAL field of the 5118 associated command log (Figure B.1.4 of Appendix B.1), the digit 1 codes 5119 that the parameter applies to the VALUE field of the command log, and 5120 the digit 2 codes that the parameter applies to the COUNT field of the 5121 command log. 5123 For the Y and Z Chapter D sub-chapters (undefined System Real-time), the 5124 digit 0 codes that the parameter applies to the LEGAL field of the 5125 associated command log (Figure B.1.5 of Appendix B.1) and the digit 1 5126 codes that the parameter applies to the COUNT field of the command log. 5128 For Chapter Q (Sequencer State Commands), the digit 0 codes that the 5129 parameter applies to the default Chapter Q definition, which forbids the 5130 TIME field. The digit 1 codes that the parameter applies to the 5131 optional Chapter Q definition, which supports the TIME field. 5133 The syntax for field lists follows the syntax for channel lists. If no 5134 field list is provided, the parameter applies to all controller or note 5135 numbers. For Chapter C, if no field list is provided, the controller 5136 numbers do not use enhanced Chapter C encoding (Appendix A.3.3). 5138 For Chapter C, the field list may take on values in the range 0 to 255. 5139 A field value X in the range 0-127 refers to a controller number X, and 5140 indicates that the controller number does not use enhanced Chapter C 5141 encoding. A field value X in the range 128-255 refers to a controller 5142 number "X minus 128" and indicates the controller number does use the 5143 enhanced Chapter C encoding. 5145 Assignments made to configure the Chapter C encoding method for a 5146 controller number MUST be made to the ch_default or ch_anchor 5147 parameters, as assignments to ch_never act to exclude the number from 5148 the recovery journal (and thus the indicated encoding method is 5149 irrelevant). 5151 A Chapter C field list MUST NOT encode conflicting information about the 5152 enhanced encoding status of a particular controller number. For 5153 example, values 0 and 128 MUST NOT both be coded by a field list. 5155 For Chapter M, the field list codes the Registered Parameter Numbers 5156 (RPNs) and Non-Registered Parameter Numbers (NRPNs) for which the 5157 parameter applies. The number range 0-16383 specifies RPNs, the number 5158 range 16384-32767 specifies NRPNs (16384 corresponds to NRPN 0, 32767 5159 corresponds to NRPN 16383). 5161 For Chapters N and A, the field list codes the note numbers for which 5162 the parameter applies. The note number range specified for Chapter N 5163 also applies to Chapter E. 5165 For Chapter E, the digit 0 codes that the parameter applies to Chapter E 5166 note logs whose V bit is set to 0, and the digit 1 codes that the 5167 parameter applies to note logs whose V bit is set to 1. 5169 For Chapter X, the field list codes the number of data octets that may 5170 appear in a SysEx command that is coded in the chapter. Thus, the field 5171 list 0-255 specifies SysEx commands with 255 or fewer data octets, the 5172 field list 256-4294967295 specifies SysEx commands with more than 255 5173 data octets but excludes commands with 255 or fewer data octets, and the 5174 field list 0 excludes all commands. 5176 A secondary parameter assignment syntax customizes Chapter X (see 5177 Appendix D for complete ABNF): 5179 = "__" *( "_" ) "__" 5181 The assignment defines a class of SysEx commands whose Chapter X coding 5182 obeys the semantics of the assigned parameter. The command class is 5183 specified by listing the permitted values of the first N data octets 5184 that follow the SysEx 0xF0 command octet. Any SysEx command whose first 5185 N data octets match the list is a member of the class. 5187 Each defines a data octet of the command, as a dot-separated 5188 (".") list of one or more hexadecimal constants (such as "7F") or dash- 5189 separated hexadecimal ranges (such as "01-1F"). Underscores ("_") 5190 separate each . Double-underscores ("__") delineate the data 5191 octet list. 5193 Using this syntax, each assignment specifies a single SysEx command 5194 class. Session descriptions may use several assignments to the same (or 5195 different) parameters to specify complex Chapter X behaviors. The 5196 ordering behavior of multiple assignments follows the guidelines for 5197 chapter parameter assignments described earlier in this section. 5199 The example session description below illustrates the use of the chapter 5200 inclusion parameters: 5202 v=0 5203 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5204 s=Example 5205 t=0 0 5206 m=audio 5004 RTP/AVP 96 5207 c=IN IP6 2001:DB80::7F2E:172A:1E24 5208 a=rtpmap:96 rtp-midi/44100 5209 a=fmtp:96 j_update=open-loop; cm_unused=ABCFGHJKMQTVWXYZ; 5210 cm_used=__7E_00-7F_09_01.02.03__; 5211 cm_used=__7F_00-7F_04_01.02__; cm_used=C7.64; 5212 ch_never=ABCDEFGHJKMQTVWXYZ; ch_never=4.11-13N; 5213 ch_anchor=P; ch_anchor=C7.64; 5214 ch_anchor=__7E_00-7F_09_01.02.03__; 5215 ch_anchor=__7F_00-7F_04_01.02__ 5217 (The a=fmtp line has been wrapped to fit the page to accommodate 5218 memo formatting restrictions; it comprises a single line in SDP.) 5220 The j_update parameter codes that the stream uses the open-loop policy. 5221 Most MIDI command-types are assigned to cm_unused and thus do not appear 5222 in the stream. As a consequence, the assignments to the first ch_never 5223 parameter reflect that most chapters are not in use. 5225 Chapter N for several MIDI channels is assigned to ch_never. Chapter N 5226 for MIDI channels other than 4, 11, 12, and 13 may appear in the 5227 recovery journal, using the (default) ch_default semantics. In 5228 practice, this assignment pattern would reflect knowledge about a 5229 resilient rendering method in use for the excluded channels. 5231 The MIDI Program Change command and several MIDI Control Change 5232 controller numbers are assigned to ch_anchor. Note that the ordering of 5233 the ch_anchor chapter C assignment after the ch_never command acts to 5234 override the ch_never assignment for the listed controller numbers (7 5235 and 64). 5237 The assignment of command-type X to cm_unused excludes most SysEx 5238 commands from the stream. Exceptions are made for General MIDI System 5239 On/Off commands and for the Master Volume and Balance commands, via the 5240 use of the secondary assignment syntax. The cm_used assignment codes 5241 the exception, and the ch_anchor assignment codes how these commands are 5242 protected in Chapter X. 5244 C.3. Configuration Tools: Timestamp Semantics 5246 The MIDI command section of the payload format consists of a list of 5247 commands, each with an associated timestamp. The semantics of command 5248 timestamps may be set during session configuration, using the parameters 5249 we describe in this section 5251 The parameter "tsmode" specifies the timestamp semantics for a stream. 5252 The parameter takes on one of three token values: "comex", "async", or 5253 "buffer". 5255 The default "comex" value specifies that timestamps code the execution 5256 time for a command (Appendix C.3.1) and supports the accurate 5257 transcoding of Standard MIDI Files (SMFs, [MIDI]). The "comex" value is 5258 also RECOMMENDED for new MIDI user-interface controller designs. The 5259 "async" value specifies an asynchronous timestamp sampling algorithm for 5260 time-of-arrival sources (Appendix C.3.2). The "buffer" value specifies 5261 a synchronous timestamp sampling algorithm (Appendix C.3.3) for time-of- 5262 arrival sources. 5264 Ancillary parameters MAY follow tsmode in a media description. We 5265 define these parameters in Appendices C.3.2-3 below. 5267 C.3.1. The comex Algorithm 5269 The default "comex" (COMmand EXecution) tsmode value specifies the 5270 execution time for the command. With comex, the difference between two 5271 timestamps indicates the time delay between the execution of the 5272 commands. This difference may be zero, coding simultaneous execution. 5274 The comex interpretation of timestamps works well for transcoding a 5275 Standard MIDI File (SMF, [MIDI]) into an RTP MIDI stream, as SMFs code a 5276 timestamp for each MIDI command stored in the file. To transcode an SMF 5277 that uses metric time markers, use the SMF tempo map (encoded in the SMF 5278 as meta-events) to convert metric SMF timestamp units into seconds-based 5279 RTP timestamp units. 5281 New MIDI controller designs (piano keyboard, drum pads, etc.) that 5282 support RTP MIDI and that have direct access to sensor data SHOULD use 5283 comex interpretation for timestamps, so that simultaneous gestural 5284 events may be accurately coded by RTP MIDI. 5286 Comex is a poor choice for transcoding MIDI 1.0 DIN cables [MIDI], for a 5287 reason that we will now explain. A MIDI DIN cable is an asynchronous 5288 serial protocol (320 microseconds per MIDI byte). MIDI commands on a 5289 DIN cable are not tagged with timestamps. Instead, MIDI DIN receivers 5290 infer command timing from the time of arrival of the bytes. Thus, two 5291 two-byte MIDI commands that occur at a source simultaneously are encoded 5292 on a MIDI 1.0 DIN cable with a 640 microsecond time offset. A MIDI DIN 5293 receiver is unable to tell if this time offset existed in the source 5294 performance or is an artifact of the serial speed of the cable. 5295 However, the RTP MIDI comex interpretation of timestamps declares that a 5296 timestamp offset between two commands reflects the timing of the source 5297 performance. 5299 This semantic mismatch is the reason that comex is a poor choice for 5300 transcoding MIDI DIN cables. Note that the choice of the RTP timestamp 5301 rate (Section 6.1-2 in the main text) cannot fix this inaccuracy issue. 5302 In the sections that follow, we describe two alternative timestamp 5303 interpretations ("async" and "buffer") that are a better match to MIDI 5304 1.0 DIN cable timing, and to other MIDI time-of-arrival sources. 5306 The "octpos", "linerate", and "mperiod" ancillary parameters (defined 5307 below) SHOULD NOT be used with comex. 5309 C.3.2. The async Algorithm 5311 The "async" tsmode value specifies the asynchronous sampling of a MIDI 5312 time-of-arrival source. In asynchronous sampling, the moment an octet 5313 is received from a source, it is labelled with a wall-clock time value. 5314 The time value has RTP timestamp units. 5316 The "octpos" ancillary parameter defines how RTP command timestamps are 5317 derived from octet time values. If octpos has the token value "first", 5318 a timestamp codes the time value of the first octet of the command. If 5319 octpos has the token value "last", a timestamp codes the time value of 5320 the last octet of the command. If the octpos parameter does not appear 5321 in the media description, the sender does not know which octet of the 5322 command the timestamp references (for example, the sender may be relying 5323 on an operating system service that does not specify this information). 5325 The octpos semantics refer to the first or last octet of a command as it 5326 appears on a time-of-arrival MIDI source, not as it appears in an RTP 5327 MIDI packet. This distinction is significant because the RTP coding may 5328 contain octets that are not present in the source. For example, the 5329 status octet of the first MIDI command in a packet may have been added 5330 to the MIDI stream during transcoding, to comply with the RTP MIDI 5331 running status requirements (Section 3.2). 5333 The "linerate" ancillary parameter defines the timespan of one MIDI 5334 octet on the transmission medium of the MIDI source to be sampled (such 5335 as a MIDI 1.0 DIN cable). The parameter has units of nanoseconds, and 5336 takes on integral values. For MIDI 1.0 DIN cables, the correct linerate 5337 value is 320000 (this value is also the default value for the 5338 parameter). 5340 We now show a session description example for the async algorithm. 5341 Consider a sender that is transcoding a MIDI 1.0 DIN cable source into 5342 RTP. The sender runs on a computing platform that assigns time values 5343 to every incoming octet of the source, and the sender uses the time 5344 values to label the first octet of each command in the RTP packet. This 5345 session description describes the transcoding: 5347 v=0 5348 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5349 s=Example 5350 t=0 0 5351 m=audio 5004 RTP/AVP 96 5352 c=IN IP4 192.0.2.94 5353 a=rtpmap:96 rtp-midi/44100 5354 a=sendonly 5355 a=fmtp:96 tsmode=async; linerate=320000; octpos=first 5357 C.3.3. The buffer Algorithm 5359 The "buffer" tsmode value specifies the synchronous sampling of a MIDI 5360 time-of-arrival source. 5362 In synchronous sampling, octets received from a source are placed in a 5363 holding buffer upon arrival. At periodic intervals, the RTP sender 5364 examines the buffer. The sender removes complete commands from the 5365 buffer and codes those commands in an RTP packet. The command timestamp 5366 codes the moment of buffer examination, expressed in RTP timestamp 5367 units. Note that several commands may have the same timestamp value. 5369 The "mperiod" ancillary parameter defines the nominal periodic sampling 5370 interval. The parameter takes on positive integral values and has RTP 5371 timestamp units. 5373 The "octpos" ancillary parameter, defined in Appendix C.3.1 for 5374 asynchronous sampling, plays a different role in synchronous sampling. 5375 In synchronous sampling, the parameter specifies the timestamp semantics 5376 of a command whose octets span several sampling periods. 5378 If octpos has the token value "first", the timestamp reflects the 5379 arrival period of the first octet of the command. If octpos has the 5380 token value "last", the timestamp reflects the arrival period of the 5381 last octet of the command. The octpos semantics refer to the first or 5382 last octet of the command as it appears on a time-of-arrival source, not 5383 as it appears in the RTP packet. 5385 If the octpos parameter does not appear in the media description, the 5386 timestamp MAY reflect the arrival period of any octet of the command; 5387 senders use this option to signal a lack of knowledge about the timing 5388 details of the buffering process at sub-command granularity. 5390 We now show a session description example for the buffer algorithm. 5391 Consider a sender that is transcoding a MIDI 1.0 DIN cable source into 5392 RTP. The sender runs on a computing platform that places source data 5393 into a buffer upon receipt. The sender polls the buffer 1000 times a 5394 second, extracts all complete commands from the buffer, and places the 5395 commands in an RTP packet. This session description describes the 5396 transcoding: 5398 v=0 5399 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5400 s=Example 5401 t=0 0 5402 m=audio 5004 RTP/AVP 96 5403 c=IN IP6 2001:DB80::7F2E:172A:1E24 5404 a=rtpmap:96 rtp-midi/44100 5405 a=sendonly 5406 a=fmtp:96 tsmode=buffer; linerate=320000; octpos=last; mperiod=44 5408 The mperiod value of 44 is derived by dividing the clock rate specified 5409 by the rtpmap attribute (44100 Hz) by the 1000 Hz buffer sampling rate 5410 and rounding to the nearest integer. Command timestamps might not 5411 increment by exact multiples of 44, as the actual sampling period might 5412 not precisely match the nominal mperiod value. 5414 C.4. Configuration Tools: Packet Timing Tools 5416 In this appendix, we describe session configuration tools for 5417 customizing the temporal behavior of MIDI stream packets. 5419 C.4.1. Packet Duration Tools 5421 Senders control the granularity of a stream by setting the temporal 5422 duration ("media time") of the packets in the stream. Short media times 5423 (20 ms or less) often imply an interactive session. Longer media times 5424 (100 ms or more) usually indicate a content streaming session. The RTP 5425 AVP profile [RFC3551] recommends audio packet media times in a range 5426 from 0 to 200 ms. 5428 By default, an RTP receiver dynamically senses the media time of packets 5429 in a stream and chooses the length of its playout buffer to match the 5430 stream. A receiver typically sizes its playout buffer to fit several 5431 audio packets and adjusts the buffer length to reflect the network 5432 jitter and the sender timing fidelity. 5434 Alternatively, the packet media time may be statically set during 5435 session configuration. Session descriptions MAY use the RTP MIDI 5436 parameter "rtp_ptime" to set the recommended media time for a packet. 5437 Session descriptions MAY also use the RTP MIDI parameter "rtp_maxptime" 5438 to set the maximum media time for a packet permitted in a stream. Both 5439 parameters MAY be used together to configure a stream. 5441 The values assigned to the rtp_ptime and rtp_maxptime parameters have 5442 the units of the RTP timestamp for the stream, as set by the rtpmap 5443 attribute (see Section 6.1). Thus, if rtpmap sets the clock rate of a 5444 stream to 44100 Hz, a maximum packet media time of 10 ms is coded by 5445 setting rtp_maxptime=441. As stated in the Appendix C preamble, the 5446 senders and receivers of a stream MUST agree on common values for 5447 rtp_ptime and rtp_maxptime if the parameters appear in the media 5448 description for the stream. 5450 0 ms is a reasonable media time value for MIDI packets and is often used 5451 in low-latency interactive applications. In a packet with a 0 ms media 5452 time, all commands execute at the instant they are coded by the packet 5453 timestamp. The session description below configures all packets in the 5454 stream to have 0 ms media time: 5456 v=0 5457 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5458 s=Example 5459 t=0 0 5460 m=audio 5004 RTP/AVP 96 5461 c=IN IP4 192.0.2.94 5462 a=rtpmap:96 rtp-midi/44100 5463 a=fmtp:96 rtp_ptime=0; rtp_maxptime=0 5465 The session attributes ptime and maxptime [RFC4566] MUST NOT be used to 5466 configure an RTP MIDI stream. Sessions MUST use rtp_ptime in lieu of 5467 ptime and MUST use rtp_maxptime in lieu of maxptime. RTP MIDI defines 5468 its own parameters for media time configuration because 0 ms values for 5469 ptime and maxptime are forbidden by [RFC3264] but are essential for 5470 certain applications of RTP MIDI. 5472 See the Appendix C.7 examples for additional discussion about using 5473 rtp_ptime and rtp_maxptime for session configuration. 5475 C.4.2. The guardtime Parameter 5477 RTP permits a sender to stop sending audio packets for an arbitrary 5478 period of time during a session. When sending resumes, the RTP sequence 5479 number series continues unbroken, and the RTP timestamp value reflects 5480 the media time silence gap. 5482 This RTP feature has its roots in telephony, but it is also well matched 5483 to interactive MIDI sessions, as players may fall silent for several 5484 seconds during (or between) songs. 5486 Certain MIDI applications benefit from a slight enhancement to this RTP 5487 feature. In interactive applications, receivers may use on-line network 5488 models to guide heuristics for handling lost and late RTP packets. 5489 These models may work poorly if a sender ceases packet transmission for 5490 long periods of time. 5492 Session descriptions may use the parameter "guardtime" to set a minimum 5493 sending rate for a media session. The value assigned to guardtime codes 5494 the maximum separation time between two sequential packets, as expressed 5495 in RTP timestamp units. 5497 Typical guardtime values are 500-2000 ms. This value range is not a 5498 normative bound, and parties SHOULD be prepared to process values 5499 outside this range. 5501 The congestion control requirements for sender implementations 5502 (described in Section 8 and [RFC3550]) take precedence over the 5503 guardtime parameter. Thus, if the guardtime parameter requests a 5504 minimum sending rate, but sending at this rate would violate the 5505 congestion control requirements, senders MUST ignore the guardtime 5506 parameter value. In this case, senders SHOULD use the lowest minimum 5507 sending rate that satisfies the congestion control requirements. 5509 Below, we show a session description that uses the guardtime parameter. 5511 v=0 5512 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5513 s=Example 5514 t=0 0 5515 m=audio 5004 RTP/AVP 96 5516 c=IN IP6 2001:DB80::7F2E:172A:1E24 5517 a=rtpmap:96 rtp-midi/44100 5518 a=fmtp:96 guardtime=44100; rtp_ptime=0; rtp_maxptime=0 5519 C.5. Configuration Tools: Stream Description 5521 As we discussed in Section 2.1, a party may send several RTP MIDI 5522 streams in the same RTP session, and several RTP sessions that carry 5523 MIDI may appear in a multimedia session. 5525 By default, the MIDI name space (16 channels + systems) of each RTP 5526 stream sent by a party in a multimedia session is independent. By 5527 independent, we mean three distinct things: 5529 o If a party sends two RTP MIDI streams (A and B), MIDI voice 5530 channel 0 in stream A is a different "channel 0" than MIDI 5531 voice channel 0 in stream B. 5533 o MIDI voice channel 0 in stream B is not considered to be 5534 "channel 16" of a 32-channel MIDI voice channel space whose 5535 "channel 0" is channel 0 of stream A. 5537 o Streams sent by different parties over different RTP sessions, 5538 or over the same RTP session but with different payload type 5539 numbers, do not share the association that is shared by a MIDI 5540 cable pair that cross-connects two devices in a MIDI 1.0 DIN 5541 network. By default, this association is only held by streams 5542 sent by different parties in the same RTP session that use the 5543 same payload type number. 5545 In this appendix, we show how to express that specific RTP MIDI streams 5546 in a multimedia session are not independent but instead are related in 5547 one of the three ways defined above. We use two tools to express these 5548 relations: 5550 o The musicport parameter. This parameter is assigned a 5551 non-negative integer value between 0 and 4294967295. It 5552 appears in the fmtp lines of payload types. 5554 o The FID grouping attribute [RFC3388] signals that several RTP 5555 sessions in a multimedia session are using the musicport 5556 parameter to express an inter-session relationship. 5558 If a multimedia session has several payload types whose musicport 5559 parameters are assigned the same integer value, streams using these 5560 payload types share an "identity relationship" (including streams that 5561 use the same payload type). Streams in an identity relationship share 5562 two properties: 5564 o Identity relationship streams sent by the same party 5565 target the same MIDI name space. Thus, if streams A 5566 and B share an identity relationship, voice channel 0 5567 in stream A is the same "channel 0" as voice channel 5568 0 in stream B. 5570 o Pairs of identity relationship streams that are sent by 5571 different parties share the association that is shared 5572 by a MIDI cable pair that cross-connects two devices in 5573 a MIDI 1.0 DIN network. 5575 A party MUST NOT send two RTP MIDI streams that share an identity 5576 relationship in the same RTP session. Instead, each stream MUST be in a 5577 separate RTP session. As explained in Section 2.1, this restriction is 5578 necessary to support the RTP MIDI method for the synchronization of 5579 streams that share a MIDI name space. 5581 If a multimedia session has several payload types whose musicport 5582 parameters are assigned sequential values (i.e., i, i+1, ... i+k), the 5583 streams using the payload types share an "ordered relationship". For 5584 example, if payload type A assigns 2 to musicport and payload type B 5585 assigns 3 to musicport, A and B are in an ordered relationship. 5587 Streams in an ordered relationship that are sent by the same party are 5588 considered by renderers to form a single larger MIDI space. For 5589 example, if stream A has a musicport value of 2 and stream B has a 5590 musicport value of 3, MIDI voice channel 0 in stream B is considered to 5591 be voice channel 16 in the larger MIDI space formed by the relationship. 5592 Note that it is possible for streams to participate in both an identity 5593 relationship and an ordered relationship. 5595 We now state several rules for using musicport: 5597 o If streams from several RTP sessions in a multimedia 5598 session use the musicport parameter, the RTP sessions 5599 MUST be grouped using the FID grouping attribute 5600 defined in [RFC3388]. 5602 o An ordered or identity relationship MUST NOT 5603 contain both native RTP MIDI streams and 5604 mpeg4-generic RTP MIDI streams. An exception applies 5605 if a relationship consists of sendonly and recvonly 5606 (but not sendrecv) streams. In this case, the sendonly 5607 streams MUST NOT contain both types of streams, and the 5608 recvonly streams MUST NOT contain both types of streams. 5610 o It is possible to construct identity relationships 5611 that violate the recovery journal mandate (for example, 5612 sending NoteOns for a voice channel on stream A and 5613 NoteOffs for the same voice channel on stream B). 5614 Parties MUST NOT generate (or accept) session 5615 descriptions that exhibit this flaw. 5617 o Other payload formats MAY define musicport media type 5618 parameters. Formats would define these parameters so that 5619 their sessions could be bundled into RTP MIDI name spaces. 5620 The parameter definitions MUST be compatible with the 5621 musicport semantics defined in this appendix. 5623 As a rule, at most one payload type in a relationship may specify a MIDI 5624 renderer. An exception to the rule applies to relationships that 5625 contain sendonly and recvonly streams but no sendrecv streams. In this 5626 case, one sendonly session and one recvonly session may each define a 5627 renderer. 5629 Renderer specification in a relationship may be done using the tools 5630 described in Appendix C.6. These tools work for both native streams and 5631 mpeg4-generic streams. An mpeg4-generic stream that uses the Appendix 5632 C.6 tools MUST set all "config" parameters to the empty string (""). 5634 Alternatively, for mpeg4-generic streams, renderer specification may be 5635 done by setting one "config" parameter in the relationship to the 5636 renderer configuration string, and all other config parameters to the 5637 empty string (""). 5639 We now define sender and receiver rules that apply when a party sends 5640 several streams that target the same MIDI name space. 5642 Senders MAY use the subsetting parameters (Appendix C.1) to predefine 5643 the partitioning of commands between streams, or they MAY use a dynamic 5644 partitioning strategy. 5646 Receivers that merge identity relationship streams into a single MIDI 5647 command stream MUST maintain the structural integrity of the MIDI 5648 commands coded in each stream during the merging process, in the same 5649 way that software that merges traditional MIDI 1.0 DIN cable flows is 5650 responsible for creating a merged command flow compatible with [MIDI]. 5652 Senders MUST partition the name space so that the rendered MIDI 5653 performance does not contain indefinite artifacts (as defined in Section 5654 4). This responsibility holds even if all streams are sent over 5655 reliable transport, as different stream latencies may yield indefinite 5656 artifacts. For example, stuck notes may occur in a performance split 5657 over two TCP streams, if NoteOn commands are sent on one stream and 5658 NoteOff commands are sent on the other. 5660 Senders MUST NOT split a Registered Parameter Name (RPN) or Non- 5661 Registered Parameter Name (NRPN) transaction appearing on a MIDI channel 5662 across multiple identity relationship sessions. Receivers MUST assume 5663 that the RPN/NRPN transactions that appear on different identity 5664 relationship sessions are independent and MUST preserve transactional 5665 integrity during the MIDI merge. 5667 A simple way to safely partition voice channel commands is to place all 5668 MIDI commands for a particular voice channel into the same session. 5669 Safe partitioning of MIDI Systems commands may be more complicated for 5670 sessions that extensively use System Exclusive. 5672 We now show several session description examples that use the musicport 5673 parameter. 5675 Our first session description example shows two RTP MIDI streams that 5676 drive the same General MIDI decoder. The sender partitions MIDI 5677 commands between the streams dynamically. The musicport values indicate 5678 that the streams share an identity relationship. 5680 v=0 5681 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5682 s=Example 5683 t=0 0 5684 a=group:FID 1 2 5685 c=IN IP4 192.0.2.94 5686 m=audio 5004 RTP/AVP 96 5687 a=rtpmap:96 mpeg4-generic/44100 5688 a=mid:1 5689 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5690 config=7A0A0000001A4D546864000000060000000100604D54726B0 5691 000000600FF2F000; musicport=12 5692 m=audio 5006 RTP/AVP 96 5693 a=rtpmap:96 mpeg4-generic/44100 5694 a=mid:2 5695 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 5696 musicport=12 5698 (The a=fmtp lines have been wrapped to fit the page to accommodate 5699 memo formatting restrictions; they comprise single lines in SDP.) 5701 Recall that Section 2.1 defines rules for streams that target the same 5702 MIDI name space. Those rules, implemented in the example above, require 5703 that each stream resides in a separate RTP session, and that the 5704 grouping mechanisms defined in [RFC3388] signal an inter-session 5705 relationship. The "group" and "mid" attribute lines implement this 5706 grouping mechanism. 5708 A variant on this example, whose session description is not shown, would 5709 use two streams in an identity relationship driving the same MIDI 5710 renderer, each with a different transport type. One stream would use 5711 UDP and would be dedicated to real-time messages. A second stream would 5712 use TCP [RFC4571] and would be used for SysEx bulk data messages. 5714 In the next example, two mpeg4-generic streams form an ordered 5715 relationship to drive a Structured Audio decoder with 32 MIDI voice 5716 channels. Both streams reside in the same RTP session. 5718 v=0 5719 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5720 s=Example 5721 t=0 0 5722 m=audio 5006 RTP/AVP 96 97 5723 c=IN IP6 2001:DB80::7F2E:172A:1E24 5724 a=rtpmap:96 mpeg4-generic/44100 5725 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=13; 5726 musicport=5 5727 a=rtpmap:97 mpeg4-generic/44100 5728 a=fmtp:97 streamtype=5; mode=rtp-midi; config=""; profile-level-id=13; 5729 musicport=6; render=synthetic; rinit="audio/asc"; 5730 url="http://example.com/cardinal.asc"; 5731 cid="azsldkaslkdjqpwojdkmsldkfpe" 5733 (The a=fmtp lines have been wrapped to fit the page to accommodate 5734 memo formatting restrictions; they comprise single lines in SDP.) 5736 The sequential musicport values for the two sessions establish the 5737 ordered relationship. The musicport=5 session maps to Structured Audio 5738 extended channels range 0-15, the musicport=6 session maps to Structured 5739 Audio extended channels range 16-31. 5741 Both config strings are empty. The configuration data is specified by 5742 parameters that appear in the fmtp line of the second media description. 5743 We define this configuration method in Appendix C.6. 5745 The next example shows two RTP MIDI streams (one recvonly, one sendonly) 5746 that form a "virtual sendrecv" session. Each stream resides in a 5747 different RTP session (a requirement because sendonly and recvonly are 5748 RTP session attributes). 5750 v=0 5751 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5752 s=Example 5753 t=0 0 5754 a=group:FID 1 2 5755 c=IN IP4 192.0.2.94 5756 m=audio 5004 RTP/AVP 96 5757 a=sendonly 5758 a=rtpmap:96 mpeg4-generic/44100 5759 a=mid:1 5760 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5761 config=7A0A0000001A4D546864000000060000000100604D54726B0 5762 000000600FF2F000; musicport=12 5763 m=audio 5006 RTP/AVP 96 5764 a=recvonly 5765 a=rtpmap:96 mpeg4-generic/44100 5766 a=mid:2 5767 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5768 config=7A0A0000001A4D546864000000060000000100604D54726B0 5769 000000600FF2F000; musicport=12 5771 (The a=fmtp lines have been wrapped to fit the page to accommodate 5772 memo formatting restrictions; they comprise single lines in SDP.) 5774 To signal the "virtual sendrecv" semantics, the two streams assign 5775 musicport to the same value (12). As defined earlier in this section, 5776 pairs of identity relationship streams that are sent by different 5777 parties share the association that is shared by a MIDI cable pair that 5778 cross-connects two devices in a MIDI 1.0 network. We use the term 5779 "virtual sendrecv" because streams sent by different parties in a true 5780 sendrecv session also have this property. 5782 As discussed in the preamble to Appendix C, the primary advantage of the 5783 virtual sendrecv configuration is that each party can customize the 5784 property of the stream it receives. In the example above, each stream 5785 defines its own "config" string that could customize the rendering 5786 algorithm for each party (in fact, the particular strings shown in this 5787 example are identical, because General MIDI is not a configurable MPEG 4 5788 renderer). 5790 C.6. Configuration Tools: MIDI Rendering 5792 This appendix defines the session configuration tools for rendering. 5794 The "render" parameter specifies a rendering method for a stream. The 5795 parameter is assigned a token value that signals the top-level rendering 5796 class. This memo defines four token values for render: "unknown", 5797 "synthetic", "api", and "null": 5799 o An "unknown" renderer is a renderer whose nature is unspecified. 5800 It is the default renderer for native RTP MIDI streams. 5802 o A "synthetic" renderer transforms the MIDI stream into audio 5803 output (or sometimes into stage lighting changes or other 5804 actions). It is the default renderer for mpeg4-generic 5805 RTP MIDI streams. 5807 o An "api" renderer presents the command stream to applications 5808 via an Application Programmer Interface (API). 5810 o The "null" renderer discards the MIDI stream. 5812 The "null" render value plays special roles during Offer/Answer 5813 negotiations [RFC3264]. A party uses the "null" value in an answer to 5814 reject an offered renderer. Note that rejecting a renderer is 5815 independent from rejecting a payload type (coded by removing the payload 5816 type from a media line) and rejecting a media stream (coded by zeroing 5817 the port of a media line that uses the renderer). 5819 Other render token values MAY be registered with IANA. The token value 5820 MUST adhere to the ABNF for render tokens defined in Appendix D. 5821 Registrations MUST include a complete specification of parameter value 5822 usage, similar in depth to the specifications that appear throughout 5823 Appendix C.6 for "synthetic" and "api" render values. If a party is 5824 offered a session description that uses a render token value that is not 5825 known to the party, the party MUST NOT accept the renderer. Options 5826 include rejecting the renderer (using the "null" value), the payload 5827 type, the media stream, or the session description. 5829 Other parameters MAY follow a render parameter in a parameter list. The 5830 additional parameters act to define the exact nature of the renderer. 5831 For example, the "subrender" parameter (defined in Appendix C.6.2) 5832 specifies the exact nature of the renderer. 5834 Special rules apply to using the render parameter in an mpeg4-generic 5835 stream. We define these rules in Appendix C.6.5. 5837 C.6.1. The multimode Parameter 5839 A media description MAY contain several render parameters. By default, 5840 if a parameter list includes several render parameters, a receiver MUST 5841 choose exactly one renderer from the list to render the stream. The 5842 "multimode" parameter may be used to override this default. We define 5843 two token values for multimode: "one" and "all": 5845 o The default "one" value requests rendering by exactly one of 5846 the listed renderers. 5848 o The "all" value requests the synchronized rendering of the RTP 5849 MIDI stream by all listed renderers, if possible. 5851 If the multimode parameter appears in a parameter list, it MUST appear 5852 before the first render parameter assignment. 5854 Render parameters appear in the parameter list in order of decreasing 5855 priority. A receiver MAY use the priority ordering to decide which 5856 renderer(s) to retain in a session. 5858 If the "offer" in an Offer/Answer-style negotiation [RFC3264] contains a 5859 parameter list with one or more render parameters, the "answer" MUST set 5860 the render parameters of all unchosen renderers to "null". 5862 C.6.2. Renderer Specification 5864 The render parameter (Appendix C.6 preamble) specifies, in a broad 5865 sense, what a renderer does with a MIDI stream. In this appendix, we 5866 describe the "subrender" parameter. The token value assigned to 5867 subrender defines the exact nature of the renderer. Thus, "render" and 5868 "subrender" combine to define a renderer, in the same way as MIME types 5869 and MIME subtypes combine to define a type of media [RFC2045]. 5871 If the subrender parameter is used for a renderer definition, it MUST 5872 appear immediately after the render parameter in the parameter list. At 5873 most one subrender parameter may appear in a renderer definition. 5875 This document defines one value for subrender: the value "default". The 5876 "default" token specifies the use of the default renderer for the stream 5877 type (native or mpeg4-generic). The default renderer for native RTP 5878 MIDI streams is a renderer whose nature is unspecified (see point 6 in 5879 Section 6.1 for details). The default renderer for mpeg4-generic RTP 5880 MIDI streams is an MPEG 4 Audio Object Type whose ID number is 13, 14, 5881 or 15 (see Section 6.2 for details). 5883 If a renderer definition does not use the subrender parameter, the value 5884 "default" is assumed for subrender. 5886 Other subrender token values may be registered with IANA. We now 5887 discuss guidelines for registering subrender values. 5889 A subrender value is registered for a specific stream type (native or 5890 mpeg4-generic) and a specific render value (excluding "null" and 5891 "unknown"). Registrations for mpeg4-generic subrender values are 5892 restricted to new MPEG 4 Audio Object Types that accept MIDI input. The 5893 syntax of the token MUST adhere to the token definition in Appendix D. 5895 For "render=synthetic" renderers, a subrender value registration 5896 specifies an exact method for transforming the MIDI stream into audio 5897 (or sometimes into video or control actions, such as stage lighting). 5898 For standardized renderers, this specification is usually a pointer to a 5899 standards document, perhaps supplemented by RTP-MIDI-specific 5900 information. For commercial products and open-source projects, this 5901 specification usually takes the form of instructions for interfacing the 5902 RTP MIDI stream with the product or project software. A 5903 "render=synthetic" registration MAY specify additional Reset State 5904 commands for the renderer (Appendix A.1). 5906 A "render=api" subrender value registration specifies how an RTP MIDI 5907 stream interfaces with an API (Application Programmers Interface). This 5908 specification is usually a pointer to programmer's documentation for the 5909 API, perhaps supplemented by RTP-MIDI-specific information. 5911 A subrender registration MAY specify an initialization file (referred to 5912 in this document as an initialization data object) for the stream. The 5913 initialization data object MAY be encoded in the parameter list 5914 (verbatim or by reference) using the coding tools defined in Appendix 5915 C.6.3. An initialization data object MUST have a registered [RFC4288] 5916 media type and subtype [RFC2045]. 5918 For "render=synthetic" renderers, the data object usually encodes 5919 initialization data for the renderer (sample files, synthesis patch 5920 parameters, reverberation room impulse responses, etc.). 5922 For "render=api" renderers, the data object usually encodes data about 5923 the stream used by the API (for example, for an RTP MIDI stream 5924 generated by a piano keyboard controller, the manufacturer and model 5925 number of the keyboard, for use in GUI presentation). 5927 Usually, only one initialization object is encoded for a renderer. If a 5928 renderer uses multiple data objects, the correct receiver interpretation 5929 of multiple data objects MUST be defined in the subrender registration. 5931 A subrender value registration may also specify additional parameters, 5932 to appear in the parameter list immediately after subrender. These 5933 parameter names MUST begin with the subrender value, followed by an 5934 underscore ("_"), to avoid name space collisions with future RTP MIDI 5935 parameter names (for example, a parameter "foo_bar" defined for 5936 subrender value "foo"). 5938 We now specify guidelines for interpreting the subrender parameter 5939 during session configuration. 5941 If a party is offered a session description that uses a renderer whose 5942 subrender value is not known to the party, the party MUST NOT accept the 5943 renderer. Options include rejecting the renderer (using the "null" 5944 value), the payload type, the media stream, or the session description. 5946 Receivers MUST be aware of the Reset State commands (Appendix A.1) for 5947 the renderer specified by the subrender parameter and MUST insure that 5948 the renderer does not experience indefinite artifacts due to the 5949 presence (or the loss) of a Reset State command. 5951 C.6.3. Renderer Initialization 5953 If the renderer for a stream uses an initialization data object, an 5954 "rinit" parameter MUST appear in the parameter list immediately after 5955 the "subrender" parameter. If the renderer parameter list does not 5956 include a subrender parameter (recall the semantics for "default" in 5957 Appendix C.6.2), the "rinit" parameter MUST appear immediately after the 5958 "render" parameter. 5960 The value assigned to the rinit parameter MUST be the media type/subtype 5961 [RFC2045] for the initialization data object. If an initialization 5962 object type is registered with several media types, including audio, the 5963 assignment to rinit MUST use the audio media type. 5965 RTP MIDI supports several parameters for encoding initialization data 5966 objects for renderers in the parameter list: "inline", "url", and "cid". 5968 If the "inline", "url", and/or "cid" parameters are used by a renderer, 5969 these parameters MUST immediately follow the "rinit" parameter. 5971 If a "url" parameter appears for a renderer, an "inline" parameter MUST 5972 NOT appear. If an "inline" parameter appears for a renderer, a "url" 5973 parameter MUST NOT appear. However, neither "url" or "inline" is 5974 required to appear. If neither "url" or "inline" parameters follow 5975 "rinit", the "cid" parameter MUST follow "rinit". 5977 The "inline" parameter supports the inline encoding of the data object. 5978 The parameter is assigned a double-quoted Base64 [RFC2045] encoding of 5979 the binary data object, with no line breaks. Appendix E.4 shows an 5980 example that constructs an inline parameter value. 5982 The "url" parameter is assigned a double-quoted string representation of 5983 a Uniform Resource Locator (URL) for the data object. The string MUST 5984 specify either a HyperText Transport Protocol URI (HTTP, [RFC2616]) or 5985 an HTTP over TLS URI (HTTPS, [RFC2818]). The media type/subtype for the 5986 data object SHOULD be specified in the appropriate HTTP or HTTPS 5987 transport header. 5989 The "url" parameter is assigned a double-quoted string representation of 5990 a Uniform Resource Locator (URL) for the data object. The string MUST 5991 specify a HyperText Transport Protocol URL (HTTP, [RFC2616]). HTTP MAY 5992 be used over TCP or MAY be used over a secure network transport, such as 5993 the method described in [RFC2818]. The media type/subtype for the data 5994 object SHOULD be specified in the appropriate HTTP transport header. 5996 The "cid" parameter supports data object caching. The parameter is 5997 assigned a double-quoted string value that encodes a globally unique 5998 identifier for the data object. 6000 A cid parameter MAY immediately follow an inline parameter, in which 6001 case the cid identifier value MUST be associated with the inline data 6002 object. 6004 If a url parameter is present, and if the data object for the URL is 6005 expected to be unchanged for the life of the URL, a cid parameter MAY 6006 immediately follow the url parameter. The cid identifier value MUST be 6007 associated with the data object for the URL. A cid parameter assigned 6008 to the same identifier value SHOULD be specified following the data 6009 object type/subtype in the appropriate HTTP transport header. 6011 If a url parameter is present, and if the data object for the URL is 6012 expected to change during the life of the URL, a cid parameter MUST NOT 6013 follow the url parameter. A receiver interprets the presence of a cid 6014 parameter as an indication that it is safe to use a cached copy of the 6015 url data object; the absence of a cid parameter is an indication that it 6016 is not safe to use a cached copy, as it may change. 6018 Finally, the cid parameter MAY be used without the inline and url 6019 parameters. In this case, the identifier references a local or 6020 distributed catalog of data objects. 6022 In most cases, only one data object is coded in the parameter list for 6023 each renderer. For example, the default renderer for mpeg4-generic 6024 streams uses a single data object (see Appendix C.6.5 for example 6025 usage). 6027 However, a subrender registration MAY permit the use of multiple data 6028 objects for a renderer. If multiple data objects are encoded for a 6029 renderer, each object encoding begins with an "rinit" parameter, 6030 followed by "inline", "url", and/or "cid" parameters. 6032 Initialization data objects MAY encapsulate a Standard MIDI File (SMF). 6033 By default, the SMFs that are encapsulated in a data object MUST be 6034 ignored by an RTP MIDI receiver. We define parameters to override this 6035 default in Appendix C.6.4. 6037 To end this section, we offer guidelines for registering media types for 6038 initialization data objects. These guidelines are in addition to the 6039 information in [RFC4288]. 6041 Some initialization data objects are also capable of encoding MIDI note 6042 information and thus complete audio performances. These objects SHOULD 6043 be registered using the "audio" media type, so that the objects may also 6044 be used for store-and-forward rendering, and "application" media type, 6045 to support editing tools. Initialization objects without note storage, 6046 or initialization objects for non-audio renderers, SHOULD be registered 6047 only for an "application" media type. 6049 C.6.4. MIDI Channel Mapping 6051 In this appendix, we specify how to map MIDI name spaces (16 voice 6052 channels + systems) onto a renderer. 6054 In the general case: 6056 o A session may define an ordered relationship (Appendix C.5) 6057 that presents more than one MIDI name space to a renderer. 6059 o A renderer may accept an arbitrary number of MIDI name spaces, 6060 or it may expect a specific number of MIDI name spaces. 6062 A session description SHOULD provide a compatible MIDI name space to 6063 each renderer in the session. If a receiver detects that a session 6064 description has too many or too few MIDI name spaces for a renderer, 6065 MIDI data from extra stream name spaces MUST be discarded, and extra 6066 renderer name spaces MUST NOT be driven with MIDI data (except as 6067 described in Appendix C.6.4.1, below). 6069 If a parameter list defines several renderers and assigns the "all" 6070 token value to the multimode parameter, the same name space is presented 6071 to each renderer. However, the "chanmask" parameter may be used to mask 6072 out selected voice channels to each renderer. We define "chanmask" and 6073 other MIDI management parameters in the sub-sections below. 6075 C.6.4.1. The smf_info Parameter 6077 The smf_info parameter defines the use of the SMFs encapsulated in 6078 renderer data objects (if any). The smf_info parameter also defines the 6079 use of SMFs coded in the smf_inline, smf_url, and smf_cid parameters 6080 (defined in Appendix C.6.4.2). 6082 The smf_info parameter describes the "render" parameter that most 6083 recently precedes it in the parameter list. The smf_info parameter MUST 6084 NOT appear in parameter lists that do not use the "render" parameter, 6085 and MUST NOT appear before the first use of "render" in the parameter 6086 list. 6088 We define three token values for smf_info: "ignore", "sdp_start", and 6089 "identity": 6091 o The "ignore" value indicates that the SMFs MUST be discarded. 6092 This behavior is the default SMF rendering behavior. 6094 o The "sdp_start" value codes that SMFs MUST be rendered, 6095 and that the rendering MUST begin upon the acceptance of 6096 the session description. If a receiver is offered a session 6097 description with a renderer that uses an smf_info parameter 6098 set to sdp_start, and if the receiver does not support 6099 rendering SMFs, the receiver MUST NOT accept the renderer 6100 associated with the smf_info parameter. Options include 6101 rejecting the renderer (by setting the "render" parameter 6102 to "null"), the payload type, the media stream, or the 6103 entire session description. 6105 o The "identity" value indicates that the SMFs code the identity 6106 of the renderer. The value is meant for use with the 6107 "unknown" renderer (see Appendix C.6 preamble). The MIDI commands 6108 coded in the SMF are informational in nature and MUST NOT be 6109 presented to a renderer for audio presentation. In 6110 typical use, the SMF would use SysEx Identity Reply 6111 commands (F0 7E nn 06 02, as defined in [MIDI]) to identify 6112 devices, and use device-specific SysEx commands to describe 6113 current state of the devices (patch memory contents, etc.). 6115 Other smf_info token values MAY be registered with IANA. The token 6116 value MUST adhere to the ABNF for render tokens defined in Appendix D. 6117 Registrations MUST include a complete specification of parameter usage, 6118 similar in depth to the specifications that appear in this appendix for 6119 "sdp_start" and "identity". 6121 If a party is offered a session description that uses an smf_info 6122 parameter value that is not known to the party, the party MUST NOT 6123 accept the renderer associated with the smf_info parameter. Options 6124 include rejecting the renderer, the payload type, the media stream, or 6125 the entire session description. 6127 We now define the rendering semantics for the "sdp_start" token value in 6128 detail. 6130 The SMFs and RTP MIDI streams in a session description share the same 6131 MIDI name space(s). In the simple case of a single RTP MIDI stream and 6132 a single SMF, the SMF MIDI commands and RTP MIDI commands are merged 6133 into a single name space and presented to the renderer. The indefinite 6134 artifact responsibilities for merged MIDI streams defined in Appendix 6135 C.5 also apply to merging RTP and SMF MIDI data. 6137 If a payload type codes multiple SMFs, the SMF name spaces are presented 6138 as an ordered entity to the renderer. To determine the ordering of SMFs 6139 for a renderer (which SMF is "first", which is "second", etc.), use the 6140 following rules: 6142 o If the renderer uses a single data object, the order of 6143 appearance of the SMFs in the object's internal structure 6144 defines the order of the SMFs (the earliest SMF in the object 6145 is "first", the next SMF in the object is "second", etc.). 6147 o If multiple data objects are encoded for a renderer, the 6148 appearance of each data object in the parameter list 6149 sets the relative order of the SMFs encoded in each 6150 data object (SMFs encoded in parameters that appear 6151 earlier in the list are ordered before SMFs encoded 6152 in parameters that appear later in the list). 6154 o If SMFs are encoded in data objects parameters and in 6155 the parameters defined in C.6.4.2, the relative order 6156 of the data object parameters and C.6.4.2 parameters 6157 in the parameter list sets the relative order of SMFs 6158 (SMFs encoded in parameters that appear earlier in the 6159 list are ordered before SMFs in parameters that appear 6160 later in the list). 6162 Given this ordering of SMFs, we now define the mapping of SMFs to 6163 renderer name spaces. The SMF that appears first for a renderer maps to 6164 the first renderer name space. The SMF that appears second for a 6165 renderer maps to the second renderer name space, etc. If the associated 6166 RTP MIDI streams also form an ordered relationship, the first SMF is 6167 merged with the first name space of the relationship, the second SMF is 6168 merged to the second name space of the relationship, etc. 6170 Unless the streams and the SMFs both use MIDI Time Code, the time offset 6171 between SMF and stream data is unspecified. This restriction limits the 6172 use of SMFs to applications where synchronization is not critical, such 6173 as the transport of System Exclusive commands for renderer 6174 initialization, or human-SMF interactivity. 6176 Finally, we note that each SMF in the sdp_start discussion above encodes 6177 exactly one MIDI name space (16 voice channels + systems). Thus, the 6178 use of the Device Name SMF meta event to specify several MIDI name 6179 spaces in an SMF is not supported for sdp_start. 6181 C.6.4.2. The smf_inline, smf_url, and smf_cid Parameters 6183 In some applications, the renderer data object may not encapsulate SMFs, 6184 but an application may wish to use SMFs in the manner defined in 6185 Appendix C.6.4.1. 6187 The "smf_inline", "smf_url", and "smf_cid" parameters address this 6188 situation. These parameters use the syntax and semantics of the inline, 6189 url, and cid parameters defined in Appendix C.6.3, except that the 6190 encoded data object is an SMF. 6192 The "smf_inline", "smf_url", and "smf_cid" parameters belong to the 6193 "render" parameter that most recently precedes it in the session 6194 description. The "smf_inline", "smf_url", and "smf_cid" parameters MUST 6195 NOT appear in parameter lists that do not use the "render" parameter and 6196 MUST NOT appear before the first use of "render" in the parameter list. 6197 If several "smf_inline", "smf_url", or "smf_cid" parameters appear for a 6198 renderer, the order of the parameters defines the SMF name space 6199 ordering. 6201 C.6.4.3. The chanmask Parameter 6203 The chanmask parameter instructs the renderer to ignore all MIDI voice 6204 commands for certain channel numbers. The parameter value is a 6205 concatenated string of "1" and "0" digits. Each string position maps to 6206 a MIDI voice channel number (system channels may not be masked). A "1" 6207 instructs the renderer to process the voice channel; a "0" instructs the 6208 renderer to ignore the voice channel. 6210 The string length of the chanmask parameter value MUST be 16 (for a 6211 single stream or an identity relationship) or a multiple of 16 (for an 6212 ordered relationship). 6214 The chanmask parameter describes the "render" parameter that most 6215 recently precedes it in the session description; chanmask MUST NOT 6216 appear in parameter lists that do not use the "render" parameter and 6217 MUST NOT appear before the first use of "render" in the parameter list. 6219 The chanmask parameter describes the final MIDI name spaces presented to 6220 the renderer. The SMF and stream components of the MIDI name spaces may 6221 not be independently masked. 6223 If a receiver is offered a session description with a renderer that uses 6224 the chanmask parameter, and if the receiver does not implement the 6225 semantics of the chanmask parameter, the receiver MUST NOT accept the 6226 renderer unless the chanmask parameter value contains only "1"s. 6228 C.6.5. The audio/asc Media Type 6230 In Appendix 11.3, we register the audio/asc media type. The data object 6231 for audio/asc is a binary encoding of the AudioSpecificConfig data block 6232 used to initialize mpeg4-generic streams (Section 6.2 and [MPEGAUDIO]). 6234 An mpeg4-generic parameter list MAY use the render, subrender, and rinit 6235 parameters with the audio/asc media type for renderer configuration. 6236 Several restrictions apply to the use of these parameters in 6237 mpeg4-generic parameter lists: 6239 o An mpeg4-generic media description that uses the render parameter 6240 MUST assign the empty string ("") to the mpeg4-generic "config" 6241 parameter. The use of the streamtype, mode, and profile-level-id 6242 parameters MUST follow the normative text in Section 6.2. 6244 o Sessions that use identity or ordered relationships MUST follow 6245 the mpeg4-generic configuration restrictions in Appendix C.5. 6247 o The render parameter MUST be assigned the value "synthetic", 6248 "unknown", "null", or a render value that has been added to 6249 the IANA repository for use with mpeg4-generic RTP MIDI 6250 streams. The "api" token value for render MUST NOT be used. 6252 o If a subrender parameter is present, it MUST immediately follow 6253 the render parameter, and it MUST be assigned the token value 6254 "default" or assigned a subrender value added to the IANA 6255 repository for use with mpeg4-generic RTP MIDI streams. A 6256 subrender parameter assignment may be left out of the renderer 6257 configuration, in which case the implied value of subrender 6258 is the default value of "default". 6260 o If the render parameter is assigned the value "synthetic" 6261 and the subrender parameter has the value "default" (assigned 6262 or implied), the rinit parameter MUST be assigned the value 6263 "audio/asc", and an AudioSpecificConfig data object MUST be encoded 6264 using the mechanisms defined in C.6.2-3. The AudioSpecificConfig 6265 data MUST encode one of the MPEG 4 Audio Object Types defined for 6266 use with mpeg4-generic in Section 6.2. If the subrender value is 6267 other than "default", refer to the subrender registration 6268 for information on the use of "audio/asc" with the renderer. 6270 o If the render parameter is assigned the value "null" or 6271 "unknown", the data object MAY be omitted. 6273 Several general restrictions apply to the use of the audio/asc media 6274 type in RTP MIDI: 6276 o A native stream MUST NOT assign "audio/asc" to rinit. The 6277 audio/asc media type is not intended to be a general-purpose 6278 container for rendering systems outside of MPEG usage. 6280 o The audio/asc media type defines a stored object type; it does 6281 not define semantics for RTP streams. Thus, audio/asc MUST NOT 6282 appear on an rtpmap line of a session description. 6284 Below, we show session description examples for audio/asc. The session 6285 description below uses the inline parameter to code the 6286 AudioSpecificConfig block for a mpeg4-generic General MIDI stream. We 6287 derive the value assigned to the inline parameter in Appendix E.4. The 6288 subrender token value of "default" is implied by the absence of the 6289 subrender parameter in the parameter list. 6291 v=0 6292 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 6293 s=Example 6294 t=0 0 6295 m=audio 5004 RTP/AVP 96 6296 c=IN IP4 192.0.2.94 6297 a=rtpmap:96 mpeg4-generic/44100 6298 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6299 render=synthetic; rinit="audio/asc"; 6300 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6302 (The a=fmtp line has been wrapped to fit the page to accommodate 6303 memo formatting restrictions; it comprises a single line in SDP.) 6305 The session description below uses the url parameter to code the 6306 AudioSpecificConfig block for the same General MIDI stream: 6308 v=0 6309 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 6310 s=Example 6311 t=0 0 6312 m=audio 5004 RTP/AVP 96 6313 c=IN IP4 192.0.2.94 6314 a=rtpmap:96 mpeg4-generic/44100 6315 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6316 render=synthetic; rinit="audio/asc"; url="http://example.net/oski.asc"; 6317 cid="xjflsoeiurvpa09itnvlduihgnvet98pa3w9utnuighbuk" 6319 (The a=fmtp line has been wrapped to fit the page to accommodate 6320 memo formatting restrictions; it comprises a single line in SDP.) 6322 C.7. Interoperability 6324 In this appendix, we define interoperability guidelines for two 6325 application areas: 6327 o MIDI content-streaming applications. RTP MIDI is added to 6328 RTSP-based content-streaming servers, so that viewers may 6329 experience MIDI performances (produced by a specified client- 6330 side renderer) in synchronization with other streams (video, 6331 audio). 6333 o Long-distance network musical performance applications. RTP 6334 MIDI is added to SIP-based voice chat or videoconferencing 6335 programs, as an alternative, or as an addition, to audio and/or 6336 video RTP streams. 6338 For each application, we define a core set of functionality that all 6339 implementations MUST implement. 6341 The applications we address in this section are not an exhaustive list 6342 of potential RTP MIDI uses. We expect framework documents for other 6343 applications to be developed, within the IETF or within other 6344 organizations. We discuss other potential application areas for RTP 6345 MIDI in Section 1 of the main text of this memo. 6347 C.7.1. MIDI Content Streaming Applications 6349 In content-streaming applications, a user invokes an RTSP client to 6350 initiate a request to an RTSP server to view a multimedia session. For 6351 example, clicking on a web page link for an Internet Radio channel 6352 launches an RTSP client that uses the link's RTSP URL to contact the 6353 RTSP server hosting the radio channel. 6355 The content may be pre-recorded (for example, on-demand replay of 6356 yesterday's football game) or "live" (for example, football game 6357 coverage as it occurs), but in either case the user is usually an 6358 "audience member" as opposed to a "participant" (as the user would be in 6359 telephony). 6361 Note that these examples describe the distribution of audio content to 6362 an audience member. The interoperability guidelines in this appendix 6363 address RTP MIDI applications of this nature, not applications such as 6364 the transmission of raw MIDI command streams for use in a professional 6365 environment (recording studio, performance stage, etc.). 6367 In an RTSP session, a client accesses a session description that is 6368 "declared" by the server, either via the RTSP DESCRIBE method, or via 6369 other means, such as HTTP or email. The session description defines the 6370 session from the perspective of the client. For example, if a media 6371 line in the session description contains a non-zero port number, it 6372 encodes the server's preference for the client's port numbers for RTP 6373 and RTCP reception. Once media flow begins, the server sends an RTP 6374 MIDI stream to the client, which renders it for presentation, perhaps in 6375 synchrony with video or other audio streams. 6377 We now define the interoperability text for content-streaming RTSP 6378 applications. 6380 In most cases, server interoperability responsibilities are described in 6381 terms of limits on the "reference" session description a server provides 6382 for a performance if it has no information about the capabilities of the 6383 client. The reference session is a "lowest common denominator" session 6384 that maximizes the odds that a client will be able to view the session. 6385 If a server is aware of the capabilities of the client, the server is 6386 free to provide a session description customized for the client in the 6387 DESCRIBE reply. 6389 Clients MUST support unicast UDP RTP MIDI streams that use the recovery 6390 journal with the closed-loop or the anchor sending policies. Clients 6391 MUST be able to interpret stream subsetting and chapter inclusion 6392 parameters in the session description that qualify the sending policies. 6393 Client support of enhanced Chapter C encoding is OPTIONAL. 6395 The reference session description offered by a server MUST send all RTP 6396 MIDI UDP streams as unicast streams that use the recovery journal and 6397 the closed-loop or anchor sending policies. Servers SHOULD use the 6398 stream subsetting and chapter inclusion parameters in the reference 6399 session description, to simplify the rendering task of the client. 6400 Server support of enhanced Chapter C encoding is OPTIONAL. 6402 Clients and servers MUST support the use of RTSP interleaved mode (a 6403 method for interleaving RTP onto the RTSP TCP transport). 6405 Clients MUST be able to interpret the timestamp semantics signalled by 6406 the "comex" value of the tsmode parameter (i.e., the timestamp semantics 6407 of Standard MIDI Files [MIDI]). Servers MUST use the "comex" value for 6408 the "tsmode" parameter in the reference session description. 6410 Clients MUST be able to process an RTP MIDI stream whose packets encode 6411 an arbitrary temporal duration ("media time"). Thus, in practice, 6412 clients MUST implement a MIDI playout buffer. Clients MUST NOT depend 6413 on the presence of rtp_ptime, rtp_maxtime, and guardtime parameters in 6414 the session description in order to process packets, but they SHOULD be 6415 able to use these parameters to improve packet processing. 6417 Servers SHOULD strive to send RTP MIDI streams in the same way media 6418 servers send conventional audio streams: a sequence of packets that 6419 either all code the same temporal duration (non-normative example: 50 ms 6420 packets) or that code one of an integral number of temporal durations 6421 (non-normative example: 50 ms, 100 ms, 250 ms, or 500 ms packets). 6422 Servers SHOULD encode information about the packetization method in the 6423 rtp_ptime and rtp_maxtime parameters in the session description. 6425 Clients MUST be able to examine the render and subrender parameter, to 6426 determine if a multimedia session uses a renderer it supports. Clients 6427 MUST be able to interpret the default "one" value of the "multimode" 6428 parameter, to identify supported renderers from a list of renderer 6429 descriptions. Clients MUST be able to interpret the musicport 6430 parameter, to the degree that it is relevant to the renderers it 6431 supports. Clients MUST be able to interpret the chanmask parameter. 6433 Clients supporting renderers whose data object (as encoded by a 6434 parameter value for "inline") could exceed 300 octets in size MUST 6435 support the url and cid parameters and thus must implement the HTTP 6436 protocol in addition to RTSP. HTTP over TLS [RFC2818] support for data 6437 objects is OPTIONAL. 6439 Servers MUST specify complete rendering systems for RTP MIDI streams. 6440 Note that a minimal RTP MIDI native stream does not meet this 6441 requirement (Section 6.1), as the rendering method for such streams is 6442 "not specified". 6444 At the time of this memo, the only way for servers to specify a complete 6445 rendering system is to specify an mpeg4-generic RTP MIDI stream in mode 6446 rtp-midi (Section 6.2 and C.6.5). As a consequence, the only rendering 6447 systems that may be presently used are General MIDI [MIDI], DLS 2 6448 [DLS2], or Structured Audio [MPEGSA]. Note that the maximum inline 6449 value for General MIDI is well under 300 octets (and thus clients need 6450 not support the "url" parameter), and that the maximum inline values for 6451 DLS 2 and Structured Audio may be much larger than 300 octets (and thus 6452 clients MUST support the url parameter). 6454 We anticipate that the owners of rendering systems (both standardized 6455 and proprietary) will register subrender parameters for their renderers. 6456 Once registration occurs, native RTP MIDI sessions may use render and 6457 subrender (Appendix C.6.2) to specify complete rendering systems for 6458 RTSP content-streaming multimedia sessions. 6460 Servers MUST NOT use the sdp_start value for the smf_info parameter in 6461 the reference session description, as this use would require that 6462 clients be able to parse and render Standard MIDI Files. 6464 Clients MUST support mpeg4-generic mode rtp-midi General MIDI (GM) 6465 sessions, at a polyphony limited by the hardware capabilities of the 6466 client. This requirement provides a "lowest common denominator" 6467 rendering system for content providers to target. Note that this 6468 requirement does not force implementors of a non-GM renderer (such as 6469 DLS 2 or Structured Audio) to add a second rendering engine. Instead, a 6470 client may satisfy the requirement by including a set of voice patches 6471 that implement the GM instrument set, and using this emulation for 6472 mpeg4-generic GM sessions. 6474 It is RECOMMENDED that servers use General MIDI as the renderer for the 6475 reference session description, because clients are REQUIRED to support 6476 it. We do not require General MIDI as the reference renderer, because 6477 for normative applications it is an inappropriate choice. Servers using 6478 General MIDI as a "lowest common denominator" renderer SHOULD use 6479 Universal Real-Time SysEx MIP messages [SPMIDI] to communicate the 6480 priority of voices to polyphony-limited clients. 6482 C.7.2. MIDI Network Musical Performance Applications 6484 In Internet telephony and videoconferencing applications, parties 6485 interact over an IP network as they would face-to-face. Good user 6486 experiences require low end-to-end audio latency and tight audiovisual 6487 synchronization (for "lip-sync"). The Session Initiation Protocol (SIP, 6488 [RFC3261]) is used for session management. 6490 In this appendix section, we define interoperability guidelines for 6491 using RTP MIDI streams in interactive SIP applications. Our primary 6492 interest is supporting Network Musical Performances (NMP), where 6493 musicians in different locations interact over the network as if they 6494 were in the same room. See [NMP] for background information on NMP, and 6495 see [RFC4696] for a discussion of low-latency RTP MIDI implementation 6496 techniques for NMP. 6498 Note that the goal of NMP applications is telepresence: the parties 6499 should hear audio that is close to what they would hear if they were in 6500 the same room. The interoperability guidelines in this appendix address 6501 RTP MIDI applications of this nature, not applications such as the 6502 transmission of raw MIDI command streams for use in a professional 6503 environment (recording studio, performance stage, etc.). 6505 We focus on session management for two-party unicast sessions that 6506 specify a renderer for RTP MIDI streams. Within this limited scope, the 6507 guidelines defined here are sufficient to let applications interoperate. 6508 We define the REQUIRED capabilities of RTP MIDI senders and receivers in 6509 NMP sessions and define how session descriptions exchanged are used to 6510 set up network musical performance sessions. 6512 SIP lets parties negotiate details of the session, using the 6513 Offer/Answer protocol [RFC3264]. However, RTP MIDI has so many 6514 parameters that "blind" negotiations between two parties using different 6515 applications might not yield a common session configuration. 6517 Thus, we now define a set of capabilities that NMP parties MUST support. 6518 Session description offers whose options lie outside the envelope of 6519 REQUIRED party behavior risk negotiation failure. We also define 6520 session description idioms that the RTP MIDI part of an offer MUST 6521 follow, in order to structure the offer for simpler analysis. 6523 We use the term "offerer" for the party making a SIP offer, and 6524 "answerer" for the party answering the offer. Finally, we note that 6525 unless it is qualified by the adjective "sender" or "receiver", a 6526 statement that a party MUST support X implies that it MUST support X for 6527 both sending and receiving. 6529 If an offerer wishes to define a "sendrecv" RTP MIDI stream, it may use 6530 a true sendrecv session or the "virtual sendrecv" construction described 6531 in the preamble to Appendix C and in Appendix C.5. A true sendrecv 6532 session indicates that the offerer wishes to participate in a session 6533 where both parties use identically configured renderers. A virtual 6534 sendrecv session indicates that the offerer is willing to participate in 6535 a session where the two parties may be using different renderer 6536 configurations. Thus, parties MUST be prepared to see both real and 6537 virtual sendrecv sessions in an offer. 6539 Parties MUST support unicast UDP transport of RTP MIDI streams. These 6540 streams MUST use the recovery journal with the closed-loop or anchor 6541 sending policies. These streams MUST use the stream subsetting and 6542 chapter inclusion parameters to declare the types of MIDI commands that 6543 will be sent on the stream (for sendonly streams) or will be processed 6544 (for recvonly streams), including the size limits on System Exclusive 6545 commands. Support of enhanced Chapter C encoding is OPTIONAL. 6547 Note that both TCP and multicast UDP support are OPTIONAL. We make TCP 6548 OPTIONAL because we expect NMP renderers to rely on data objects 6549 (signalled by "rinit" and associated parameters) for initialization at 6550 the start of the session, and only to use System Exclusive commands for 6551 interactive control during the session. These interactive commands are 6552 small enough to be protected via the recovery journal mechanism of RTP 6553 MIDI UDP streams. 6555 We now discuss timestamps, packet timing, and packet sending algorithms. 6557 Recall that the tsmode parameter controls the semantics of command 6558 timestamps in the MIDI list of RTP packets. 6560 Parties MUST support clock rates of 44.1 kHz, 48 kHz, 88.2 kHz, and 96 6561 kHz. Parties MUST support streams using the "comex", "async", and 6562 "buffer" tsmode values. Recvonly offers MUST offer the default "comex". 6564 Parties MUST support a wide range of packet temporal durations: from 6565 rtp_ptime and rtp_maxptime values of 0, to rtp_ptime and rtp_maxptime 6566 values that code 100 ms. Thus, receivers MUST be able to implement a 6567 playout buffer. 6569 Offers and answers MUST present rtp_ptime, rtp_maxptime, and guardtime 6570 values that support the latency that users would expect in the 6571 application, subject to bandwidth constraints. As senders MUST abide by 6572 values set for these parameters in a session description, a receiver 6573 SHOULD use these values to size its playout buffer to produce the lowest 6574 reliable latency for a session. Implementers should refer to [RFC4696] 6575 for information on packet sending algorithms for latency-sensitive 6576 applications. Parties MUST be able to implement the semantics of the 6577 guardtime parameter, for times from 5 ms to 5000 ms. 6579 We now discuss the use of the render parameter. 6581 Sessions MUST specify complete rendering systems for all RTP MIDI 6582 streams. Note that a minimal RTP MIDI native stream does not meet this 6583 requirement (Section 6.1), as the rendering method for such streams is 6584 "not specified". 6586 At the time this writing, the only way for parties to specify a complete 6587 rendering system is to specify an mpeg4-generic RTP MIDI stream in mode 6588 rtp-midi (Section 6.2 and C.6.5). We anticipate that the owners of 6589 rendering systems (both standardized and proprietary) will register 6590 subrender values for their renderers. Once IANA registration occurs, 6591 native RTP MIDI sessions may use render and subrender (Appendix C.6.2) 6592 to specify complete rendering systems for SIP network musical 6593 performance multimedia sessions. 6595 All parties MUST support General MIDI (GM) sessions, at a polyphony 6596 limited by the hardware capabilities of the party. This requirement 6597 provides a "lowest common denominator" rendering system, without which 6598 practical interoperability will be quite difficult. When using GM, 6599 parties SHOULD use Universal Real-Time SysEx MIP messages [SPMIDI] to 6600 communicate the priority of voices to polyphony-limited clients. 6602 Note that this requirement does not force implementors of a non-GM 6603 renderer (for mpeg4-generic sessions, DLS 2, or Structured Audio) to add 6604 a second rendering engine. Instead, a client may satisfy the 6605 requirement by including a set of voice patches that implement the GM 6606 instrument set, and using this emulation for mpeg4-generic GM sessions. 6607 We require GM support so that an offerer that wishes to maximize 6608 interoperability may do so by offering GM if its preferred renderer is 6609 not accepted by the answerer. 6611 Offerers MUST NOT present several renderers as options in a session 6612 description by listing several payload types on a media line, as Section 6613 2.1 uses this construct to let a party send several RTP MIDI streams in 6614 the same RTP session. 6616 Instead, an offerer wishing to present rendering options SHOULD offer a 6617 single payload type that offers several renderers. In this construct, 6618 the parameter list codes a list of render parameters (each followed by 6619 its support parameters). As discussed in Appendix C.6.1, the order of 6620 renderers in the list declares the offerer's preference. The "unknown" 6621 and "null" values MUST NOT appear in the offer. The answer MUST set all 6622 render values except the desired renderer to "null". Thus, "unknown" 6623 MUST NOT appear in the answer. 6625 We use SHOULD instead of MUST in the first sentence in the paragraph 6626 above, because this technique does not work in all situations (example: 6627 an offerer wishes to offer both mpeg4-generic renderers and native RTP 6628 MIDI renderers as options). In this case, the offerer MUST present a 6629 series of session descriptions, each offering a single renderer, until 6630 the answerer accepts a session description. 6632 Parties MUST support the musicport, chanmask, subrender, rinit, and 6633 inline parameters. Parties supporting renderers whose data object (as 6634 encoded by a parameter value for "inline") could exceed 300 octets in 6635 size MUST support the url and cid parameters and thus must implement the 6636 HTTP protocol. HTTP over TLS [RFC2818] support for data objects is 6637 OPTIONAL. Note that in mpeg4-generic, General MIDI data objects cannot 6638 exceed 300 octets, but DLS 2 and Structured Audio data objects may. 6639 Support for the other rendering parameters (smf_cif, smf_info, 6640 smf_inline, smf_url) is OPTIONAL. 6642 Thus far in this document, our discussion has assumed that the only MIDI 6643 flows that drive a renderer are the network flows described in the 6644 session description. In NMP applications, this assumption would require 6645 two rendering engines: one for local use by a party, a second for the 6646 remote party. 6648 In practice, applications may wish to have both parties share a single 6649 rendering engine. In this case, the session description MUST use a 6650 virtual sendrecv session and MUST use the stream subsetting and chapter 6651 inclusion parameters to allocate which MIDI channels are intended for 6652 use by a party. If two parties are sharing a MIDI channel, the 6653 application MUST ensure that appropriate MIDI merging occurs at the 6654 input to the renderer. 6656 We now discuss the use of (non-MIDI) audio streams in the session. 6658 Audio streams may be used for two purposes: as a "talkback" channel for 6659 parties to converse, or as a way to conduct a performance that includes 6660 MIDI and audio channels. In the latter case, offers MUST use sample 6661 rates and the packet temporal durations for the audio and MIDI streams 6662 that support low-latency synchronized rendering. 6664 We now show an example of an offer/answer exchange in a network musical 6665 performance application (next page). 6667 Below, we show an offer that complies with the interoperability text in 6668 this appendix section. 6670 v=0 6671 o=first 2520644554 2838152170 IN IP4 first.example.net 6672 s=Example 6673 t=0 0 6674 a=group:FID 1 2 6675 c=IN IP4 192.0.2.94 6676 m=audio 16112 RTP/AVP 96 6677 a=recvonly 6678 a=mid:1 6679 a=rtpmap:96 mpeg4-generic/44100 6680 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6681 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=2NPTW; 6682 cm_used=2C0.1.7.10.11.64.121.123; cm_used=2M0.1.2; 6683 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6684 ch_default=2NPTW; ch_default=2C0.1.7.10.11.64.121.123; 6685 ch_default=2M0.1.2; cm_default=X0-16; 6686 rtp_ptime=0; rtp_maxptime=0; guardtime=44100; 6687 musicport=1; render=synthetic; rinit="audio/asc"; 6688 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6689 m=audio 16114 RTP/AVP 96 6690 a=sendonly 6691 a=mid:2 6692 a=rtpmap:96 mpeg4-generic/44100 6693 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6694 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=1NPTW; 6695 cm_used=1C0.1.7.10.11.64.121.123; cm_used=1M0.1.2; 6696 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6697 ch_default=1NPTW; ch_default=1C0.1.7.10.11.64.121.123; 6698 ch_default=1M0.1.2; cm_default=X0-16; 6699 rtp_ptime=0; rtp_maxptime=0; guardtime=44100; 6700 musicport=1; render=synthetic; rinit="audio/asc"; 6701 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6703 (The a=fmtp lines have been wrapped to fit the page to accommodate 6704 memo formatting restrictions; it comprises a single line in SDP.) 6706 The owner line (o=) identifies the session owner as "first". 6708 The session description defines two MIDI streams: a recvonly stream on 6709 which "first" receives a performance, and a sendonly stream that "first" 6710 uses to send a performance. The recvonly port number encodes the ports 6711 on which "first" wishes to receive RTP (16112) and RTCP (16113) media at 6712 IP4 address 192.0.2.94. The sendonly port number encodes the port on 6713 which "first" wishes to receive RTCP for the stream (16115). 6715 The musicport parameters code that the two streams share and identity 6716 relationship and thus form a virtual sendrecv stream. 6718 Both streams are mpeg4-generic RTP MIDI streams that specify a General 6719 MIDI renderer. The stream subsetting parameters code that the recvonly 6720 stream uses MIDI channel 1 exclusively for voice commands, and that the 6721 sendonly stream uses MIDI channel 2 exclusively for voice commands. 6722 This mapping permits the application software to share a single renderer 6723 for local and remote performers. 6725 We now show the answer to the offer. 6727 v=0 6728 o=second 2520644554 2838152170 IN IP4 second.example.net 6729 s=Example 6730 t=0 0 6731 a=group:FID 1 2 6732 c=IN IP4 192.0.2.105 6733 m=audio 5004 RTP/AVP 96 6734 a=sendonly 6735 a=mid:1 6736 a=rtpmap:96 mpeg4-generic/44100 6737 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6738 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=2NPTW; 6739 cm_used=2C0.1.7.10.11.64.121.123; cm_used=2M0.1.2; 6740 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6741 ch_default=2NPTW; ch_default=2C0.1.7.10.11.64.121.123; 6742 ch_default=2M0.1.2; cm_default=X0-16; 6743 rtp_ptime=0; rtp_maxptime=882; guardtime=44100; 6744 musicport=1; render=synthetic; rinit="audio/asc"; 6745 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6746 m=audio 5006 RTP/AVP 96 6747 a=recvonly 6748 a=mid:2 6749 a=rtpmap:96 mpeg4-generic/44100 6750 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6751 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=1NPTW; 6752 cm_used=1C0.1.7.10.11.64.121.123; cm_used=1M0.1.2; 6753 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6754 ch_default=1NPTW; ch_default=1C0.1.7.10.11.64.121.123; 6755 ch_default=1M0.1.2; cm_default=X0-16; 6756 rtp_ptime=0; rtp_maxptime=0; guardtime=88200; 6757 musicport=1; render=synthetic; rinit="audio/asc"; 6758 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6760 (The a=fmtp lines have been wrapped to fit the page to accommodate 6761 memo formatting restrictions; they comprise single lines in SDP.) 6763 The owner line (o=) identifies the session owner as "second". 6765 The port numbers for both media streams are non-zero; thus, "second" has 6766 accepted the session description. The stream marked "sendonly" in the 6767 offer is marked "recvonly" in the answer, and vice versa, coding the 6768 different view of the session held by "session". The IP4 number 6769 (192.0.2.105) and the RTP (5004 and 5006) and RTCP (5005 and 5007) have 6770 been changed by "second" to match its transport wishes. 6772 In addition, "second" has made several parameter changes: rtp_maxptime 6773 for the sendonly stream has been changed to code 2 ms (441 in clock 6774 units), and the guardtime for the recvonly stream has been doubled. As 6775 these parameter modifications request capabilities that are REQUIRED to 6776 be implemented by interoperable parties, "second" can make these changes 6777 with confidence that "first" can abide by them. 6779 D. Parameter Syntax Definitions 6781 In this appendix, we define the syntax for the RTP MIDI media type 6782 parameters in Augmented Backus-Naur Form (ABNF, [RFC5234]). When using 6783 these parameters with SDP, all parameters MUST appear on a single fmtp 6784 attribute line of an RTP MIDI media description. For mpeg4-generic RTP 6785 MIDI streams, this line MUST also include any mpeg4-generic parameters 6786 (usage described in Section 6.2). An fmtp attribute line may be defined 6787 (after [RFC3640]) as: 6789 ; 6790 ; SDP fmtp line definition 6791 ; 6793 fmtp = "a=fmtp:" token SP param-assign 0*(";" SP param-assign) CRLF 6795 where codes the RTP payload type. Note that white space MUST 6796 NOT appear between the "a=fmtp:" and the RTP payload type. 6798 We now define the syntax of the parameters defined in Appendix C. The 6799 definition takes the form of the incremental assembly of the token. See [RFC3640] for the syntax of the mpeg4-generic 6801 parameters discussed in Section 6.2. 6803 ; 6804 ; 6805 ; top-level definition for all parameters 6806 ; 6807 ; 6809 ; 6810 ; Parameters defined in Appendix C.1 6812 param-assign = ("cm_unused=" (([channel-list] command-type 6813 [f-list]) / sysex-data)) 6815 param-assign =/ ("cm_used=" (([channel-list] command-type 6816 [f-list]) / sysex-data)) 6818 ; 6819 ; Parameters defined in Appendix C.2 6821 param-assign =/ ("j_sec=" ("none" / "recj" / ietf-extension)) 6823 param-assign =/ ("j_update=" ("anchor" / "closed-loop" / 6824 "open-loop" / ietf-extension)) 6826 param-assign =/ ("ch_default=" (([channel-list] chapter-list 6827 [f-list]) / sysex-data)) 6829 param-assign =/ ("ch_never=" (([channel-list] chapter-list 6830 [f-list]) / sysex-data)) 6832 param-assign =/ ("ch_anchor=" (([channel-list] chapter-list 6833 [f-list]) / sysex-data)) 6835 ; 6836 ; Parameters defined in Appendix C.3 6838 param-assign =/ ("tsmode=" ("comex" / "async" / "buffer")) 6840 param-assign =/ ("linerate=" nonzero-four-octet) 6842 param-assign =/ ("octpos=" ("first" / "last")) 6844 param-assign =/ ("mperiod=" nonzero-four-octet) 6846 ; 6847 ; Parameter defined in Appendix C.4 6849 param-assign =/ ("guardtime=" nonzero-four-octet) 6851 param-assign =/ ("rtp_ptime=" four-octet) 6853 param-assign =/ ("rtp_maxptime=" four-octet) 6855 ; 6856 ; Parameters defined in Appendix C.5 6858 param-assign =/ ("musicport=" four-octet) 6860 ; 6861 ; Parameters defined in Appendix C.6 6863 param-assign =/ ("chanmask=" 1*( 16(BIT) )) 6865 param-assign =/ ("cid=" DQUOTE cid-block DQUOTE) 6867 param-assign =/ ("inline=" DQUOTE base-64-block DQUOTE) 6869 param-assign =/ ("multimode=" ("all" / "one")) 6871 param-assign =/ ("render=" ("synthetic" / "api" / "null" / 6872 "unknown" / extension)) 6874 param-assign =/ ("rinit=" mime-type "/" mime-subtype) 6876 param-assign =/ ("smf_cid=" DQUOTE cid-block DQUOTE) 6878 param-assign =/ ("smf_info=" ("ignore" / "identity" / 6879 "sdp_start" / extension)) 6881 param-assign =/ ("smf_inline=" DQUOTE base-64-block DQUOTE) 6883 param-assign =/ ("smf_url=" DQUOTE uri-element DQUOTE) 6885 param-assign =/ ("subrender=" ("default" / extension)) 6887 param-assign =/ ("url=" DQUOTE uri-element DQUOTE) 6889 ; 6890 ; list definitions for the cm_ command-type 6891 ; 6893 command-type = [A] [B] [C] [F] [G] [H] [J] [K] [M] 6894 [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 6896 ; 6897 ; list definitions for the ch_ chapter-list 6898 ; 6900 chapter-list = [A] [B] [C] [D] [E] [F] [G] [H] [J] [K] 6901 [M] [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 6903 ; 6904 ; list definitions for the channel-list (used in ch_* / cm_* params) 6905 ; 6907 channel-list = midi-chan-element *("." midi-chan-element) 6909 midi-chan-element = midi-chan / midi-chan-range 6911 midi-chan-range = midi-chan "-" midi-chan 6912 ; 6913 ; decimal value of left midi-chan 6914 ; MUST be strictly less than 6915 ; decimal value of right midi-chan 6917 midi-chan = DIGIT / ("1" %x30-35) ; "0" .. "15" 6918 ; 6919 ; list definitions for the ch_ field list (f-list) 6920 ; 6922 f-list = midi-field-element *("." midi-field-element) 6924 midi-field-element = midi-field / midi-field-range 6926 midi-field-range = midi-field "-" midi-field 6927 ; 6928 ; decimal value of left midi-field 6929 ; MUST be strictly less than 6930 ; decimal value of right midi-field 6932 midi-field = four-octet 6933 ; 6934 ; large range accommodates Chapter M 6935 ; RPN (0-16383) and NRPN (16384-32767) 6936 ; parameters, and Chapter X octet sizes. 6938 ; 6939 ; definitions for ch_ sysex-data 6940 ; 6942 sysex-data = "__" h-list *("_" h-list) "__" 6944 h-list = hex-field-element *("." hex-field-element) 6946 hex-field-element = hex-octet / hex-field-range 6948 hex-field-range = hex-octet "-" hex-octet 6949 ; 6950 ; hexadecimal value of left hex-octet 6951 ; MUST be strictly less than hexadecimal 6952 ; value of right hex-octet 6954 hex-octet = %x30-37 U-HEXDIG 6955 ; 6956 ; rewritten special case of hex-octet in [RFC2045] 6957 ; (page 23). 6958 ; note that a-f are not permitted, only A-F. 6959 ; hex-octet values MUST NOT exceed 0x7F. 6961 ; 6962 ; definitions for rinit parameter 6963 ; 6965 mime-type = "audio" / "application" 6966 mime-subtype = token 6967 ; 6968 ; See Appendix C.6.2 for registration 6969 ; requirements for rinit type/subtypes. 6971 ; 6972 ; definitions for base64 encoding 6973 ; copied from [RFC4566] 6974 ; changes from [RFC4566] to improve automatic syntax checking 6975 ; 6977 base-64-block = *base64-unit [base64-pad] 6979 base64-unit = 4(base64-char) 6981 base64-pad = (2(base64-char) "==") / (3(base64-char) "=") 6983 base64-char = %x41-5A / %x61-7A / %x30-39 / "+" / "/" 6984 ; A-Z, a-z, 0-9, "+" and "/" 6986 ; 6987 ; generic rules 6988 ; 6990 ietf-extension = token 6991 ; 6992 ; may only be defined in standards-track RFCs 6994 extension = token 6995 ; 6996 ; may be defined 6997 ; by filing a registration with IANA 6999 nonzero-four-octet = (NZ-DIGIT 0*8(DIGIT)) 7000 / (%x30-33 9(DIGIT)) 7001 / ("4" %x30-31 8(DIGIT)) 7002 / ("42" %x30-38 7(DIGIT)) 7003 / ("429" %x30-33 6(DIGIT)) 7004 / ("4294" %x30-38 5(DIGIT)) 7005 / ("42949" %x30-35 4(DIGIT)) 7006 / ("429496" %x30-36 3(DIGIT)) 7007 / ("4294967" %x30-31 2(DIGIT)) 7008 / ("42949672" %x30-38 (DIGIT)) 7009 / ("429496729" %x30-34) 7010 ; 7011 ; unsigned encoding of non-zero 32-bit value: 7012 ; 1 .. 4294967295 7014 four-octet = "0" / nonzero-four-octet 7015 ; 7016 ; unsigned encoding of 32-bit value: 7017 ; 0 .. 4294967295 7019 uri-element = URI-reference 7020 ; as defined in [RFC3986] 7022 token = 1*token-char 7023 ; copied from [RFC4566] 7025 token-char = %x21 / %x23-27 / %x2A-2B / %x2D-2E / 7026 %x30-39 / %x41-5A / %x5E-7E 7027 ; copied from [RFC4566] 7029 cid-block = 1*cid-char 7031 cid-char = token-char 7032 cid-char =/ "@" 7033 cid-char =/ "," 7034 cid-char =/ ";" 7035 cid-char =/ ":" 7036 cid-char =/ "\" 7037 cid-char =/ "/" 7038 cid-char =/ "[" 7039 cid-char =/ "]" 7040 cid-char =/ "?" 7041 cid-char =/ "=" 7042 ; 7043 ; - add back in the tspecials [RFC2045], except 7044 ; for DQUOTE and the non-email safe ( ) < > 7045 ; - note that the definitions above ensure that 7046 ; cid-block is always enclosed with DQUOTEs 7048 A = %x41 ; uppercase only letters used above 7049 B = %x42 7050 C = %x43 7051 D = %x44 7052 E = %x45 7053 F = %x46 7054 G = %x47 7055 H = %x48 7056 J = %x4A 7057 K = %x4B 7058 M = %x4D 7059 N = %x4E 7060 P = %x50 7061 Q = %x51 7062 T = %x54 7063 V = %x56 7064 W = %x57 7065 X = %x58 7066 Y = %x59 7067 Z = %x5A 7069 NZ-DIGIT = %x31-39 ; non-zero decimal digit 7071 U-HEXDIG = DIGIT / A / B / C / D / E / F 7072 ; variant of HEXDIG [RFC5234] : 7073 ; hexadecimal digit using uppercase A-F only 7075 ; the rules below are from the Core Rules from [RFC5234] 7077 BIT = "0" / "1" 7079 DQUOTE = %x22 ; " (Double Quote) 7081 DIGIT = %x30-39 ; 0-9 7083 ; external references 7084 ; URI-reference: from [RFC3986] 7086 ; 7087 ; End of ABNF 7089 The mpeg4-generic RTP payload [RFC3640] defines a "mode" parameter that 7090 signals the type of MPEG stream in use. We add a new mode value, "rtp- 7091 midi", using the ABNF rule below: 7093 ; 7094 ; mpeg4-generic mode parameter extension 7095 ; 7097 mode =/ "rtp-midi" 7098 ; as described in Section 6.2 of this memo 7100 E. A MIDI Overview for Networking Specialists 7102 This appendix presents an overview of the MIDI standard, for the benefit 7103 of networking specialists new to musical applications. Implementors 7104 should consult [MIDI] for a normative description of MIDI. 7106 Musicians make music by performing a controlled sequence of physical 7107 movements. For example, a pianist plays by coordinating a series of key 7108 presses, key releases, and pedal actions. MIDI represents a musical 7109 performance by encoding these physical gestures as a sequence of MIDI 7110 commands. This high-level musical representation is compact but 7111 fragile: one lost command may be catastrophic to the performance. 7113 MIDI commands have much in common with the machine instructions of a 7114 microprocessor. MIDI commands are defined as binary elements. 7115 Bitfields within a MIDI command have a regular structure and a 7116 specialized purpose. For example, the upper nibble of the first command 7117 octet (the opcode field) codes the command type. MIDI commands may 7118 consist of an arbitrary number of complete octets, but most MIDI 7119 commands are 1, 2, or 3 octets in length. 7121 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7122 | Channel Voice Messages | Bitfield Pattern | 7123 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7124 | NoteOff (end a note) | 1000cccc 0nnnnnnn 0vvvvvvv | 7125 |-------------------------------------------------------------| 7126 | NoteOn (start a note) | 1001cccc 0nnnnnnn 0vvvvvvv | 7127 |-------------------------------------------------------------| 7128 | PTouch (Polyphonic Aftertouch) | 1010cccc 0nnnnnnn 0aaaaaaa | 7129 |-------------------------------------------------------------| 7130 | CControl (Controller Change) | 1011cccc 0xxxxxxx 0yyyyyyy | 7131 |-------------------------------------------------------------| 7132 | PChange (Program Change) | 1100cccc 0ppppppp | 7133 |-------------------------------------------------------------| 7134 | CTouch (Channel Aftertouch) | 1101cccc 0aaaaaaa | 7135 |-------------------------------------------------------------| 7136 | PWheel (Pitch Wheel) | 1110cccc 0xxxxxxx 0yyyyyyy | 7137 ------------------------------------------------------------- 7139 Figure E.1 -- MIDI Channel Messages 7141 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7142 | System Common Messages | Bitfield Pattern | 7143 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7144 | System Exclusive | 11110000, followed by a | 7145 | | list of 0xxxxxx octets, | 7146 | | followed by 11110111 | 7147 |-------------------------------------------------------------| 7148 | MIDI Time Code Quarter Frame | 11110001 0xxxxxxx | 7149 |-------------------------------------------------------------| 7150 | Song Position Pointer | 11110010 0xxxxxxx 0yyyyyyy | 7151 |-------------------------------------------------------------| 7152 | Song Select | 11110011 0xxxxxxx | 7153 |-------------------------------------------------------------| 7154 | Undefined | 11110100 | 7155 |-------------------------------------------------------------| 7156 | Undefined | 11110101 | 7157 |-------------------------------------------------------------| 7158 | Tune Request | 11110110 | 7159 |-------------------------------------------------------------| 7160 | System Exclusive End Marker | 11110111 | 7161 ------------------------------------------------------------- 7163 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7164 | System Realtime Messages | Bitfield Pattern | 7165 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7166 | Clock | 11111000 | 7167 |-------------------------------------------------------------| 7168 | Undefined | 11111001 | 7169 |-------------------------------------------------------------| 7170 | Start | 11111010 | 7171 |-------------------------------------------------------------| 7172 | Continue | 11111011 | 7173 |-------------------------------------------------------------| 7174 | Stop | 11111100 | 7175 |-------------------------------------------------------------| 7176 | Undefined | 11111101 | 7177 |-------------------------------------------------------------| 7178 | Active Sense | 11111110 | 7179 |-------------------------------------------------------------| 7180 | System Reset | 11111111 | 7181 ------------------------------------------------------------- 7183 Figure E.2 -- MIDI System Messages 7185 Figure E.1 and E.2 show the MIDI command family. There are three major 7186 classes of commands: voice commands (opcode field values in the range 7187 0x8 through 0xE), system common commands (opcode field 0xF, commands 7188 0xF0 through 0xF7), and system real-time commands (opcode field 0xF, 7189 commands 0xF8 through 0xFF). Voice commands code the musical gestures 7190 for each timbre in a composition. Systems commands perform functions 7191 that usually affect all voice channels, such as System Reset (0xFF). 7193 E.1. Commands Types 7195 Voice commands execute on one of 16 MIDI channels, as coded by its 4-bit 7196 channel field (field cccc in Figure E.1). In most applications, notes 7197 for different timbres are assigned to different channels. To support 7198 applications that require more than 16 channels, MIDI systems use 7199 several MIDI command streams in parallel, to yield 32, 48, or 64 MIDI 7200 channels. 7202 As an example of a voice command, consider a NoteOn command (opcode 7203 0x9), with binary encoding 1001cccc 0nnnnnnn 0aaaaaaa. This command 7204 signals the start of a musical note on MIDI channel cccc. The note has 7205 a pitch coded by the note number nnnnnnn, and an onset amplitude coded 7206 by note velocity aaaaaaa. 7208 Other voice commands signal the end of notes (NoteOff, opcode 0x8), map 7209 a specific timbre to a MIDI channel (PChange, opcode 0xC), or set the 7210 value of parameters that modulate the timbral quality (all other voice 7211 commands). The exact meaning of most voice channel commands depends on 7212 the rendering algorithms the MIDI receiver uses to generate sound. In 7213 most applications, a MIDI sender has a model (in some sense) of the 7214 rendering method used by the receiver. 7216 System commands perform a variety of global tasks in the stream, 7217 including "sequencer" playback control of pre-recorded MIDI commands 7218 (the Song Position Pointer, Song Select, Clock, Start, Continue, and 7219 Stop messages), SMPTE time code (the MIDI Time Code Quarter Frame 7220 command), and the communication of device-specific data (the System 7221 Exclusive messages). 7223 E.2. Running Status 7225 All MIDI command bitfields share a special structure: the leading bit of 7226 the first octet is set to 1, and the leading bit of all subsequent 7227 octets is set to 0. This structure supports a data compression system, 7228 called running status [MIDI], that improves the coding efficiency of 7229 MIDI. 7231 In running status coding, the first octet of a MIDI voice command may be 7232 dropped if it is identical to the first octet of the previous MIDI voice 7233 command. This rule, in combination with a convention to consider NoteOn 7234 commands with a null third octet as NoteOff commands, supports the 7235 coding of note sequences using two octets per command. 7237 Running status coding is only used for voice commands. The presence of 7238 a system common message in the stream cancels running status mode for 7239 the next voice command. However, system real-time messages do not 7240 cancel running status mode. 7242 E.3. Command Timing 7244 The bitfield formats in Figures E.1 and E.2 do not encode the execution 7245 time for a command. Timing information is not a part of the MIDI 7246 command syntax itself; different applications of the MIDI command 7247 language use different methods to encode timing. 7249 For example, the MIDI command set acts as the transport layer for MIDI 7250 1.0 DIN cables [MIDI]. MIDI cables are short asynchronous serial lines 7251 that facilitate the remote operation of musical instruments and audio 7252 equipment. Timestamps are not sent over a MIDI 1.0 DIN cable. Instead, 7253 the standard uses an implicit "time of arrival" code. Receivers execute 7254 MIDI commands at the moment of arrival. 7256 In contrast, Standard MIDI Files (SMFs, [MIDI]), a file format for 7257 representing complete musical performances, add an explicit timestamp to 7258 each MIDI command, using a delta encoding scheme that is optimized for 7259 statistics of musical performance. SMF timestamps usually code timing 7260 using the metric notation of a musical score. SMF meta-events are used 7261 to add a tempo map to the file, so that score beats may be accurately 7262 converted into units of seconds during rendering. 7264 E.4. AudioSpecificConfig Templates for MMA Renderers 7266 In Section 6.2 and Appendix C.6.5, we describe how session descriptions 7267 include an AudioSpecificConfig data block to specify a MIDI rendering 7268 algorithm for mpeg4-generic RTP MIDI streams. 7270 The bitfield format of AudioSpecificConfig is defined in [MPEGAUDIO]. 7271 StructuredAudioSpecificConfig, a key data structure coded in 7272 AudioSpecificConfig, is defined in [MPEGSA]. 7274 For implementors wishing to specify Structured Audio renderers, a full 7275 understanding of [MPEGSA] and [MPEGAUDIO] is essential. However, many 7276 implementors will limit their rendering options to the two MIDI 7277 Manufacturers Association renderers that may be specified in 7278 AudioSpecificConfig: General MIDI (GM, [MIDI]) and Downloadable Sounds 2 7279 (DLS 2, [DLS2]). 7281 To aid these implementors, we reproduce the AudioSpecificConfig bitfield 7282 formats for a GM renderer and a DLS 2 renderer below. We have checked 7283 these bitfields carefully and believe they are correct. However, we 7284 stress that the material below is informative, and that [MPEGAUDIO] and 7285 [MPEGSA] are the normative definitions for AudioSpecificConfig. 7287 As described in Section 6.2, a minimal mpeg4-generic session description 7288 encodes the AudioSpecificConfig binary bitfield as a hexadecimal string 7289 (whose format is defined in [RFC3640]) that is assigned to the "config" 7290 parameter. As described in Appendix C.6.3, a session description that 7291 uses the render parameter encodes the AudioSpecificConfig binary 7292 bitfield as a Base64-encoded string assigned to the "inline" parameter, 7293 or in the body of an HTTP URL assigned to the "url" parameter. 7295 Below, we show a simplified binary AudioSpecificConfig bitfield format, 7296 suitable for sending and receiving GM and DLS 2 data: 7298 0 1 2 3 7299 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 7300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7301 | AOTYPE |FREQIDX|CHANNEL|SACNK| FILE_BLK 1 (required) ... | 7302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7303 |1|SACNK| FILE_BLK 2 (optional) ... | 7304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7305 | ... |1|SACNK| FILE_BLK N (optional) ... | 7306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7307 |0|0| (first "0" bit terminates FILE_BLK list) 7308 +-+-+ 7310 Figure E.3 -- Simplified AudioSpecificConfig 7312 The 5-bit AOTYPE field specifies the Audio Object Type as an unsigned 7313 integer. The legal values for use with mpeg4-generic RTP MIDI streams 7314 are "15" (General MIDI), "14" (DLS 2), and "13" (Structured Audio). 7315 Thus, receivers that do not support all three mpeg4-generic renderers 7316 may parse the first 5 bits of an AudioSpecificConfig coded in a session 7317 description and reject sessions that specify unsupported renderers. 7319 The 4-bit FREQIDX field specifies the sampling rate of the renderer. We 7320 show the mapping of FREQIDX values to sampling rates in Figure E.4. 7321 Senders MUST specify a sampling frequency that matches the RTP clock 7322 rate, if possible; if not, senders MUST specify the escape value. 7323 Receivers MUST consult the RTP clock parameter for the true sampling 7324 rate if the escape value is specified. 7326 FREQIDX Sampling Frequency 7328 0x0 96000 7329 0x1 88200 7330 0x2 64000 7331 0x3 48000 7332 0x4 44100 7333 0x5 32000 7334 0x6 24000 7335 0x7 22050 7336 0x8 16000 7337 0x9 12000 7338 0xa 11025 7339 0xb 8000 7340 0xc reserved 7341 0xd reserved 7342 0xe reserved 7343 0xf escape value 7345 Figure E.4 -- FreqIdx encoding 7347 The 4-bit CHANNEL field specifies the number of audio channels for the 7348 renderer. The values 0x1 to 0x5 specify 1 to 5 audio channels; the 7349 value 0x6 specifies 5+1 surround sound, and the value 0x7 specifies 7+1 7350 surround sound. If the rtpmap line in the session description specifies 7351 one of these formats, CHANNEL MUST be set to the corresponding value. 7352 Otherwise, CHANNEL MUST be set to 0x0. 7354 The CHANNEL field is followed by a list of one or more binary file data 7355 blocks. The 3-bit SACNK field (the chunk_type field in class 7356 StructuredAudioSpecificConfig, defined in [MPEGSA]) specifies the type 7357 of each data block. 7359 For General MIDI, only Standard MIDI Files may appear in the list (SACNK 7360 field value 2). For DLS 2, only Standard MIDI Files and DLS 2 RIFF 7361 files (SACNK field value 4) may appear. For both of these file types, 7362 the FILE_BLK field has the format shown in Figure E.5: a 32-bit unsigned 7363 integer value (FILE_LEN) coding the number of bytes in the SMF or RIFF 7364 file, followed by FILE_LEN bytes coding the file data. 7366 0 1 2 3 7367 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 7368 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7369 | FILE_LEN (32-bit, a byte count SMF file or RIFF file) | 7370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7371 | FILE_DATA (file contents, a list of FILE_LEN bytes) ... | 7372 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7374 Figure E.5 -- The FILE_BLK field format 7376 Note that several files may follow the CHANNEL field. The "1" constant 7377 fields in Figure E.3 code the presence of another file; the "0" constant 7378 field codes the end of the list. The final "0" bit in Figure E.3 codes 7379 the absence of special coding tools (see [MPEGAUDIO] for details). 7380 Senders not using these tools MUST append this "0" bit; receivers that 7381 do not understand these coding tools MUST ignore all data following a 7382 "1" in this position. 7384 The StructuredAudioSpecificConfig bitfield structure requires the 7385 presence of one FILE_BLK. For mpeg4-generic RTP MIDI use of DLS 2, 7386 FILE_BLKs MUST code RIFF files or SMF files. For mpeg4-generic RTP MIDI 7387 use of General MIDI, FILE_BLKs MUST code SMF files. By default, this 7388 SMF will be ignored (Appendix C.6.4.1). In this default case, a GM 7389 StructuredAudioSpecificConfig bitfield SHOULD code a FILE_BLK whose 7390 FILE_LEN is 0, and whose FILE_DATA is empty. 7392 To complete this appendix, we derive the StructuredAudioSpecificConfig 7393 that we use in the General MIDI session examples in this memo. 7394 Referring to Figure E.3, we note that for GM, AOTYPE = 15. Our examples 7395 use a 44,100 Hz sample rate (FREQIDX = 4) and are in mono (CHANNEL = 1). 7396 For GM, a single SMF is encoded (SACNK = 2), using the SMF shown in 7397 Figure E.6 (a 26 byte file). 7399 -------------------------------------------- 7400 | MIDI File =
| 7401 -------------------------------------------- 7403
= 7404 4D 54 68 64 00 00 00 06 00 00 00 01 00 60 7406 = 7407 4D 54 72 6B 00 00 00 04 00 FF 2F 00 7409 Figure E.6 -- SMF file encoded in the example 7411 Placing these constants in binary format into the data structure shown 7412 in Figure E.3 yields the constant shown in Figure E.7. 7414 0 1 2 3 7415 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 7416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7417 |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| 7418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7419 |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| 7420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7421 |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| 7422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7423 |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| 7424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7425 |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| 7426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7427 |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| 7428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7429 |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| 7430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7431 |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| 7432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7433 |0|0| 7434 +-+-+ 7436 Figure E.7 -- AudioSpecificConfig used in GM examples 7438 Expressing this bitfield as an ASCII hexadecimal string yields: 7440 7A0A0000001A4D546864000000060000000100604D54726B0000000600FF2F000 7442 This string is assigned to the "config" parameter in the minimal 7443 mpeg4-generic General MIDI examples in this memo (such as the example in 7444 Section 6.2). Expressing this string in Base64 [RFC2045] yields: 7446 egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA 7448 This string is assigned to the "inline" parameter in the General MIDI 7449 example shown in Appendix C.6.5. 7451 References 7453 Normative References 7455 [MIDI] MIDI Manufacturers Association. "The Complete MIDI 1.0 7456 Detailed Specification", 1996. 7458 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 7459 Jacobson, "RTP: A Transport Protocol for Real-Time 7460 Applications", STD 64, RFC 3550, July 2003. 7462 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 7463 Video Conferences with Minimal Control", STD 65, RFC 7464 3551, July 2003. 7466 [RFC3640] van der Meer, J., Mackie, D., Swaminathan, V., Singer, 7467 D., and P. Gentric, "RTP Payload Format for Transport of 7468 MPEG-4 Elementary Streams", RFC 3640, November 2003. 7470 [MPEGSA] International Standards Organization. "ISO/IEC 14496 7471 MPEG-4", Part 3 (Audio), Subpart 5 (Structured Audio), 7472 2001. 7474 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 7475 Description Protocol", RFC 4566, July 2006. 7477 [MPEGAUDIO] International Standards Organization. "ISO 14496 MPEG- 7478 4", Part 3 (Audio), 2001. 7480 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 7481 Extensions (MIME) Part One: Format of Internet Message 7482 Bodies", RFC 2045, November 1996. 7484 [DLS2] MIDI Manufacturers Association. "The MIDI Downloadable 7485 Sounds Specification", v98.2, 1998. 7487 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 7488 Specifications: ABNF", RFC 5234, January 2008. 7490 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 7491 Requirement Levels", BCP 14, RFC 2119, March 1997. 7493 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 7494 Norrman, "The Secure Real-time Transport Protocol 7495 (SRTP)", RFC 3711, March 2004. 7497 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 7498 with Session Description Protocol (SDP)", RFC 3264, June 7499 2002. 7501 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 7502 Resource Identifier (URI): Generic Syntax", STD 66, RFC 7503 3986, January 2005. 7505 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 7506 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 7507 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 7509 [RFC3388] Camarillo, G., Eriksson, G., Holler, J., and H. 7510 Schulzrinne, "Grouping of Media Lines in the Session 7511 Description Protocol (SDP)", RFC 3388, December 2002. 7513 [RP015] MIDI Manufacturers Association. "Recommended Practice 7514 015 (RP-015): Response to Reset All Controllers", 11/98. 7516 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 7517 Registration Procedures", BCP 13, RFC 4288, December 7518 2005. 7520 [RFC4855] Casner, S., "MIME Type Registration of RTP 7521 Payload Formats", RFC 4855, February 2007. 7523 Informative References 7525 [NMP] Lazzaro, J. and J. Wawrzynek. "A Case for Network 7526 Musical Performance", 11th International Workshop on 7527 Network and Operating Systems Support for Digital Audio 7528 and Video (NOSSDAV 2001) June 25-26, 2001, Port 7529 Jefferson, New York. 7531 [GRAME] Fober, D., Orlarey, Y. and S. Letz. "Real Time Musical 7532 Events Streaming over Internet", Proceedings of the 7533 International Conference on WEB Delivering of Music 2001, 7534 pages 147-154. 7536 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 7537 A., Peterson, J., Sparks, R., Handley, M., and E. 7538 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 7539 June 2002. 7541 [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time 7542 Streaming Protocol (RTSP)", RFC 2326, April 1998. 7544 [ALF] Clark, D. D. and D. L. Tennenhouse. "Architectural 7545 considerations for a new generation of protocols", 7546 SIGCOMM Symposium on Communications Architectures and 7547 Protocols , (Philadelphia, Pennsylvania), pp. 200--208, 7548 ACM, Sept. 1990. 7550 [RFC4696] Lazzaro, J. and J. Wawrzynek, "An Implementation Guide 7551 for RTP MIDI", RFC 4696, November 2006. 7553 [RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S., and S. 7554 Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 7555 Functional Specification", RFC 2205, September 1997. 7557 [RFC4571] Lazzaro, J. "Framing Real-time Transport Protocol (RTP) 7558 and RTP Control Protocol (RTCP) Packets over Connection- 7559 Oriented Transport", RFC 4571, July 2006. 7561 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 7563 [SPMIDI] MIDI Manufacturers Association. "Scalable Polyphony 7564 MIDI, Specification and Device Profiles", Document 7565 Version 1.0a, 2002. 7567 [LCP] Apple Computer. "Logic 7 Dedicated Control Surface 7568 Support", Appendix B. Product manual available from 7569 www.apple.com. 7571 Authors' Addresses 7573 John Lazzaro (corresponding author) 7574 UC Berkeley 7575 CS Division 7576 315 Soda Hall 7577 Berkeley CA 94720-1776 7578 EMail: lazzaro@cs.berkeley.edu 7580 John Wawrzynek 7581 UC Berkeley 7582 CS Division 7583 631 Soda Hall 7584 Berkeley CA 94720-1776 7585 EMail: johnw@cs.berkeley.edu 7587 Full Copyright Statement 7589 Copyright (c) 2009 IETF Trust and the persons identified as the 7590 document authors. All rights reserved. 7592 This document is subject to BCP 78 and the IETF Trust's Legal 7593 Provisions Relating to IETF Documents in effect on the date of 7594 publication of this document (http://trustee.ietf.org/license-info). 7595 Please review these documents carefully, as they describe your rights 7596 and restrictions with respect to this document. 7598 Copyright (c) 2009 IETF Trust and the persons identified as the 7599 document authors. All rights reserved. 7601 Acknowledgement 7603 Funding for the RFC Editor function is currently provided by the 7604 Internet Society. 7606 Change Log for 7608 This I-D is a modified version of RFC 4695. For every error found to 7609 date in RFC 4695, the I-D has been modified to fix the error. 7611 Below, we list the errors found in RFC 4695 that are most likely to 7612 confuse implementors. The fixes to Appendix D ABNF errors listed 7613 below are presented without comments; see Appendix D to see the 7614 commented rule in context. The list below includes the fixes for all 7615 normative errors; most fixes for other types of errors are not listed. 7616 However, the I-D itself contains fixes for all known errors. 7618 -- 7620 03-06.txt changes: 7622 No errata has been reported for RFC 4695 in the past year. 7623 Apart from updates in the document name and expiration dates, 7624 03-06.txt contains no changes from 02.txt 7626 -- 7628 02.txt changes: 7630 No errata has been reported for RFC 4695 in the past six months. 7631 Apart from updates in the document name and expiration dates, 7632 02.txt contains no changes from 01.txt 7634 -- 7636 01.txt changes: 7638 A typo was fixed in the Appendix D ABNF. P and Q are now 7639 correctly defined as: 7641 P = %x50 7642 Q = %x51 7644 Thanks to Alfred Hoenes for these changes. 7646 -- 7648 00.txt changes: 7650 Thanks to Alfred Hoenes for these changes. 7652 [1] In Appendix C.1 and Appendix C.2.3 of RFC 4695, an ABNF rule 7653 related to System Chapter X is incorrectly defined as: 7655 = "__" ["_" ] "__" 7657 The correct version of this rule is: 7659 = "__" *( "_" ) "__" 7661 [2] In Appendix C.6.3 of RFC 4695, the URIs permitted to be assigned 7662 to the "url" parameter are not stated clearly. URIs assigned to "url" 7663 MUST specify either HTTP or HTTP over TLS transport protocols. 7665 In Appendix C.7.1 and C.7.2 of RFC 4695, the transport 7666 interoperability requirements for the "url" parameter are not stated 7667 clearly. For both C.7.1 and C.7.2, HTTP is REQUIRED and HTTP over TLS 7668 is OPTIONAL. 7670 [3] Both fmtp lines in both session description examples in Appendix 7671 C.7.2 of RFC 4695 contain instances of the same syntax error (a 7672 missing ";" at a line wrap after "cm_used=2M0.1.2"). 7674 [4] In Appendix D of RFC 4695, all uses of "*ietf-extension" in rules 7675 are in error, and should be replaced with "ietf-extension". Likewise, 7676 all uses of "*extension" are in error, and should be replaced with 7677 "extension". This bug incorrectly lets the null token be assigned to 7678 the j_sec, j_update, render, smf_info, and subrender parameters. 7680 [5] In Appendix D of RFC 4695, the definitions of the 7681 and incorrectly allow lowercase letters to appear in 7682 these strings. The correct definitions of these rules appear below: 7684 command-type = [A] [B] [C] [F] [G] [H] [J] [K] [M] 7685 [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 7687 chapter-list = [A] [B] [C] [D] [E] [F] [G] [H] [J] [K] 7688 [M] [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 7690 A = %x41 7691 B = %x42 7692 C = %x43 7693 D = %x44 7694 E = %x45 7695 F = %x46 7696 G = %x47 7697 H = %x48 7698 J = %x4A 7699 K = %x4B 7700 M = %x4D 7701 N = %x4E 7702 P = %x50 ; correct as shown, these values were 7703 Q = %x51 ; incorrect in the -00.txt I-D version 7704 T = %x54 7705 V = %x56 7706 W = %x57 7707 X = %x58 7708 Y = %x59 7709 Z = %x5A 7711 [5] In Appendix D of RFC 4695, the definitions of the , 7712 , and are incorrect. The correct 7713 definitions of these rules appear below: 7715 nonzero-four-octet = (NZ-DIGIT 0*8(DIGIT)) 7716 / (%x30-33 9(DIGIT)) 7717 / ("4" %x30-31 8(DIGIT)) 7718 / ("42" %x30-38 7(DIGIT)) 7719 / ("429" %x30-33 6(DIGIT)) 7720 / ("4294" %x30-38 5(DIGIT)) 7721 / ("42949" %x30-35 4(DIGIT)) 7722 / ("429496" %x30-36 3(DIGIT)) 7723 / ("4294967" %x30-31 2(DIGIT)) 7724 / ("42949672" %x30-38 (DIGIT)) 7725 / ("429496729" %x30-34) 7727 four-octet = "0" / nonzero-four-octet 7728 midi-chan = DIGIT / ("1" %x30-35) 7730 DIGIT = %x30-39 7731 NZ-DIGIT = %x31-39 7733 [6] In Appendix D of RFC4695, the rule is 7734 incorrect. The correct definition of this rule appears below. 7736 hex-octet = %x30-37 U-HEXDIG 7737 U-HEXDIG = DIGIT / A / B / C / D / E / F 7739 ; DIGIT as defined in [5] above 7740 ; A, B, C, D, E, F as defined in [4] above 7742 [7] In Appendix D of RFC4695, the rules and 7743 are defined unclearly. The rewritten rules 7744 appear below: 7746 base64-unit = 4(base64-char) 7747 base64-pad = (2(base64-char) "==") / (3(base64-char) "=") 7749 ---