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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '1' on line 7654 -- Looks like a reference, but probably isn't: '2' on line 7663 -- Looks like a reference, but probably isn't: '3' on line 7672 -- Looks like a reference, but probably isn't: '4' on line 7742 -- Looks like a reference, but probably isn't: '5' on line 7741 -- Looks like a reference, but probably isn't: '6' on line 7735 -- Looks like a reference, but probably isn't: '7' on line 7744 -- Possible downref: Non-RFC (?) normative reference: ref. 'MIDI' -- Possible downref: Non-RFC (?) normative reference: ref. 'MPEGSA' ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) -- Possible downref: Non-RFC (?) normative reference: ref. 'MPEGAUDIO' -- Possible downref: Non-RFC (?) normative reference: ref. 'DLS2' ** Obsolete normative reference: RFC 4234 (Obsoleted by RFC 5234) ** 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 normative reference: RFC 3555 (Obsoleted by RFC 4855, RFC 4856) -- 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: 7 errors (**), 0 flaws (~~), 3 warnings (==), 22 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT J. Lazzaro 3 February 28, 2007 J. Wawrzynek 4 Expires: August 28, 2007 UC Berkeley 6 RTP Payload Format for MIDI 8 10 Status of This Memo 12 By submitting this Internet-Draft, each author represents that any 13 applicable patent or other IPR claims of which he or she is aware have 14 been or will be disclosed, and any of which he or she becomes aware 15 will be disclosed, in accordance with Section 6 of BCP 79. 17 Internet-Drafts are working documents of the Internet Engineering Task 18 Force (IETF), its areas, and its working groups. Note that other 19 groups may also distribute working documents as Internet-Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference material 24 or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/1id-abstracts.html 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html 32 This Internet-Draft will expire on August 28, 2007. 34 Copyright (C) The IETF Trust (2007). 36 Abstract 38 This memo describes a Real-time Transport Protocol (RTP) payload 39 format for the MIDI (Musical Instrument Digital Interface) command 40 language. The format encodes all commands that may legally appear on 41 a MIDI 1.0 DIN cable. The format is suitable for interactive 42 applications (such as network musical performance) and content- 43 delivery applications (such as file streaming). The format may be 44 used over unicast and multicast UDP and TCP, and it defines tools for 45 graceful recovery from packet loss. Stream behavior, including the 46 MIDI rendering method, may be customized during session setup. The 47 format also serves as a mode for the mpeg4-generic format, to support 48 the MPEG 4 Audio Object Types for General MIDI, Downloadable Sounds 49 Level 2, and Structured Audio. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 5 54 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 55 1.2. Bitfield Conventions . . . . . . . . . . . . . . . . . . . 6 56 2. Packet Format . . . . . . . . . . . . . . . . . . . . . . . . . . 7 57 2.1. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 7 58 2.2. MIDI Payload . . . . . . . . . . . . . . . . . . . . . . . 12 59 3. MIDI Command Section . . . . . . . . . . . . . . . . . . . . . . 14 60 3.1. Timestamps . . . . . . . . . . . . . . . . . . . . . . . . 15 61 3.2. Command Coding . . . . . . . . . . . . . . . . . . . . . . 17 62 4. The Recovery Journal System . . . . . . . . . . . . . . . . . . . 24 63 5. Recovery Journal Format . . . . . . . . . . . . . . . . . . . . . 26 64 6. Session Description Protocol . . . . . . . . . . . . . . . . . . 30 65 6.1. Session Descriptions for Native Streams . . . . . . . . . 31 66 6.2. Session Descriptions for mpeg4-generic Streams . . . . . . 33 67 6.3. Parameters . . . . . . . . . . . . . . . . . . . . . . . . 35 68 7. Extensibility . . . . . . . . . . . . . . . . . . . . . . . . . . 37 69 8. Congestion Control . . . . . . . . . . . . . . . . . . . . . . . 38 70 9. Security Considerations . . . . . . . . . . . . . . . . . . . . . 39 71 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 40 72 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 40 73 11.1. rtp-midi Media Type Registration . . . . . . . . . . . . 41 74 11.1.1. Repository Request for "audio/rtp-midi" . . . . . 43 75 11.2. mpeg4-generic Media Type Registration . . . . . . . . . . 45 76 11.2.1. Repository Request for Mode rtp-midi for 77 mpeg4-generic . . . . . . . . . . . . . . . . . . 48 78 11.3. asc Media Type Registration . . . . . . . . . . . . . . . 49 79 A. The Recovery Journal Channel Chapters . . . . . . . . . . . . . . 52 80 A.1. Recovery Journal Definitions . . . . . . . . . . . . . . . 52 81 A.2. Chapter P: MIDI Program Change . . . . . . . . . . . . . . 57 82 A.3. Chapter C: MIDI Control Change . . . . . . . . . . . . . . 58 83 A.3.1. Log Inclusion Rules . . . . . . . . . . . . . . . . 58 84 A.3.2. Controller Log Format . . . . . . . . . . . . . . . 60 85 A.3.3. Log List Coding Rules . . . . . . . . . . . . . . . 62 86 A.3.4. The Parameter System . . . . . . . . . . . . . . . 65 87 A.4. Chapter M: MIDI Parameter System . . . . . . . . . . . . . 67 88 A.4.1. Log Inclusion Rules . . . . . . . . . . . . . . . . 68 89 A.4.2. Log Coding Rules . . . . . . . . . . . . . . . . . 70 90 A.4.2.1. The Value Tool . . . . . . . . . . . . . . . 71 91 A.4.2.2. The Count Tool . . . . . . . . . . . . . . . 75 92 A.5. Chapter W: MIDI Pitch Wheel . . . . . . . . . . . . . . . 76 93 A.6. Chapter N: MIDI NoteOff and NoteOn . . . . . . . . . . . . 77 94 A.6.1. Header Structure . . . . . . . . . . . . . . . . . 78 95 A.6.2. Note Structures . . . . . . . . . . . . . . . . . . 79 96 A.7. Chapter E: MIDI Note Command Extras . . . . . . . . . . . 81 97 A.7.1. Note Log Format . . . . . . . . . . . . . . . . . . 82 98 A.7.2. Log Inclusion Rules . . . . . . . . . . . . . . . . 82 99 A.8. Chapter T: MIDI Channel Aftertouch . . . . . . . . . . . . 83 100 A.9. Chapter A: MIDI Poly Aftertouch . . . . . . . . . . . . . 84 101 B. The Recovery Journal System Chapters . . . . . . . . . . . . . . 86 102 B.1. System Chapter D: Simple System Commands . . . . . . . . . 86 103 B.1.1. Undefined System Commands . . . . . . . . . . 87 104 B.2. System Chapter V: Active Sense Command . . . . . . . . . . 90 105 B.3. System Chapter Q: Sequencer State Commands . . . . . . . . 91 106 B.3.1. Non-compliant Sequencers . . . . . . . . . . . 93 107 B.4. System Chapter F: MIDI Time Code Tape Position . . . . . . 94 108 B.4.1. Partial Frames . . . . . . . . . . . . . . . . . . 96 109 B.5. System Chapter X: System Exclusive . . . . . . . . . . . . 98 110 B.5.1. Chapter Format . . . . . . . . . . . . . . . . 98 111 B.5.2. Log Inclusion Semantics . . . . . . . . . . . 101 112 B.5.3. TCOUNT and COUNT Fields . . . . . . . . . . . 103 113 C. Session Configuration Tools . . . . . . . . . . . . . . . . . . . 105 114 C.1. Configuration Tools: Stream Subsetting . . . . . . . . . . 106 115 C.2. Configuration Tools: The Journalling System . . . . . . . 110 116 C.2.1. The j_sec Parameter . . . . . . . . . . . . . . . . 111 117 C.2.2. The j_update Parameter . . . . . . . . . . . . . . 112 118 C.2.2.1. The anchor Sending Policy . . . . . . . . . 113 119 C.2.2.2. The closed-loop Sending Policy . . . . . . . 113 120 C.2.2.3. The open-loop Sending Policy . . . . . . . . 117 121 C.2.3. Recovery Journal Chapter Inclusion Parameters . . . 119 122 C.3. Configuration Tools: Timestamp Semantics . . . . . . . . . 124 123 C.3.1. The comex Algorithm . . . . . . . . . . . . . . . . 124 124 C.3.2. The async Algorithm . . . . . . . . . . . . . . . . 125 125 C.3.3. The buffer Algorithm . . . . . . . . . . . . . . . 126 126 C.4. Configuration Tools: Packet Timing Tools . . . . . . . . . 128 127 C.4.1. Packet Duration Tools . . . . . . . . . . . . . . . 128 128 C.4.2. The guardtime Parameter . . . . . . . . . . . . . . 129 129 C.5. Configuration Tools: Stream Description . . . . . . . . . 131 130 C.6. Configuration Tools: MIDI Rendering . . . . . . . . . . . 137 131 C.6.1. The multimode Parameter . . . . . . . . . . . . . . 138 132 C.6.2. Renderer Specification . . . . . . . . . . . . . . 138 133 C.6.3. Renderer Initialization . . . . . . . . . . . . . . 141 134 C.6.4. MIDI Channel Mapping . . . . . . . . . . . . . . . 143 135 C.6.4.1. The smf_info Parameter . . . . . . . . . . . 143 136 C.6.4.2. The smf_inline, smf_url, and smf_cid 137 Parameters . . . . . . . . . . . . . . . . . 145 138 C.6.4.3. The chanmask Parameter . . . . . . . . . . . 146 139 C.6.5. The audio/asc Media Type . . . . . . . . . . . . . 147 140 C.7. Interoperability . . . . . . . . . . . . . . . . . . . . . 149 141 C.7.1. MIDI Content Streaming Applications . . . . . . . 149 142 C.7.2. MIDI Network Musical Performance Applications . . . 152 143 D. Parameter Syntax Definitions . . . . . . . . . . . . . . . . . . 161 144 E. A MIDI Overview for Networking Specialists . . . . . . . . . . . 168 145 E.1. Commands Types . . . . . . . . . . . . . . . . . . . . . . 170 146 E.2. Running Status . . . . . . . . . . . . . . . . . . . . . . 170 147 E.3. Command Timing . . . . . . . . . . . . . . . . . . . . . . 171 148 E.4. AudioSpecificConfig Templates for MMA Renderers . . . . . 171 149 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176 150 Normative References . . . . . . . . . . . . . . . . . . . . . 176 151 Informative References . . . . . . . . . . . . . . . . . . . . 177 152 Change Log for . . . . . . . . . 181 153 1. Introduction 155 The Internet Engineering Task Force (IETF) has developed a set of 156 focused tools for multimedia networking ([RFC3550] [RFC4566] [RFC3261] 157 [RFC2326]). These tools can be combined in different ways to support a 158 variety of real-time applications over Internet Protocol (IP) networks. 160 For example, a telephony application might use the Session Initiation 161 Protocol (SIP, [RFC3261]) to set up a phone call. Call setup would 162 include negotiations to agree on a common audio codec [RFC3264]. 163 Negotiations would use the Session Description Protocol (SDP, [RFC4566]) 164 to describe candidate codecs. 166 After a call is set up, audio data would flow between the parties using 167 the Real Time Protocol (RTP, [RFC3550]) under any applicable profile 168 (for example, the Audio/Visual Profile (AVP, [RFC3551])). The tools 169 used in this telephony example (SIP, SDP, RTP) might be combined in a 170 different way to support a content streaming application, perhaps in 171 conjunction with other tools, such as the Real Time Streaming Protocol 172 (RTSP, [RFC2326]). 174 The MIDI (Musical Instrument Digital Interface) command language [MIDI] 175 is widely used in musical applications that are analogous to the 176 examples described above. On stage and in the recording studio, MIDI is 177 used for the interactive remote control of musical instruments, an 178 application similar in spirit to telephony. On web pages, Standard MIDI 179 Files (SMFs, [MIDI]) rendered using the General MIDI standard [MIDI] 180 provide a low-bandwidth substitute for audio streaming. 182 This memo is motivated by a simple premise: if MIDI performances could 183 be sent as RTP streams that are managed by IETF session tools, a 184 hybridization of the MIDI and IETF application domains may occur. 186 For example, interoperable MIDI networking may foster network music 187 performance applications, in which a group of musicians, located at 188 different physical locations, interact over a network to perform as they 189 would if they were located in the same room [NMP]. As a second example, 190 the streaming community may begin to use MIDI for low- bitrate audio 191 coding, perhaps in conjunction with normative sound synthesis methods 192 [MPEGSA]. 194 To enable MIDI applications to use RTP, this memo defines an RTP payload 195 format and its media type. Sections 2-5 and Appendices A-B define the 196 RTP payload format. Section 6 and Appendices C-D define the media types 197 identifying the payload format, the parameters needed for configuration, 198 and how the parameters are utilized in SDP. 200 Appendix C also includes interoperability guidelines for the example 201 applications described above: network musical performance using SIP 202 (Appendix C.7.2) and content-streaming using RTSP (Appendix C.7.1). 204 Another potential application area for RTP MIDI is MIDI networking for 205 professional audio equipment and electronic musical instruments. We do 206 not offer interoperability guidelines for this application in this memo. 207 However, RTP MIDI has been designed with stage and studio applications 208 in mind, and we expect that efforts to define a stage and studio 209 framework will rely on RTP MIDI for MIDI transport services. 211 Some applications may require MIDI media delivery at a certain service 212 quality level (latency, jitter, packet loss, etc). RTP itself does not 213 provide service guarantees. However, applications may use lower-layer 214 network protocols to configure the quality of the transport services 215 that RTP uses. These protocols may act to reserve network resources for 216 RTP flows [RFC2205] or may simply direct RTP traffic onto a dedicated 217 "media network" in a local installation. Note that RTP and the MIDI 218 payload format do provide tools that applications may use to achieve the 219 best possible real-time performance at a given service level. 221 This memo normatively defines the syntax and semantics of the MIDI 222 payload format. However, this memo does not define algorithms for 223 sending and receiving packets. An ancillary document [RFC4696] provides 224 informative guidance on algorithms. Supplemental information may be 225 found in related conference publications [NMP] [GRAME]. 227 Throughout this memo, the phrase "native stream" refers to a stream that 228 uses the rtp-midi media type. The phrase "mpeg4-generic stream" refers 229 to a stream that uses the mpeg4-generic media type (in mode rtp-midi) to 230 operate in an MPEG 4 environment [RFC3640]. Section 6 describes this 231 distinction in detail. 233 1.1. Terminology 235 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 236 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 237 document are to be interpreted as described in BCP 14, RFC 2119 238 [RFC2119]. 240 1.2. Bitfield Conventions 242 In this document, the packet bitfields that share a common name often 243 have identical semantics. As most of these bitfields appear in 244 Appendices A-B, we define the common bitfield names in Appendix A.1. 246 However, a few of these common names also appear in the main text of 247 this document. For convenience, we list these definitions below: 249 o R flag bit. R flag bits are reserved for future use. Senders 250 MUST set R bits to 0. Receivers MUST ignore R bit values. 252 o LENGTH field. All fields named LENGTH (as distinct from LEN) 253 code the number of octets in the structure that contains it, 254 including the header it resides in and all hierarchical levels 255 below it. If a structure contains a LENGTH field, a receiver 256 MUST use the LENGTH field value to advance past the structure 257 during parsing, rather than use knowledge about the internal 258 format of the structure. 260 2. Packet Format 262 In this section, we introduce the format of RTP MIDI packets. The 263 description includes some background information on RTP, for the benefit 264 of MIDI implementors new to IETF tools. Implementors should consult 265 [RFC3550] for an authoritative description of RTP. 267 This memo assumes that the reader is familiar with MIDI syntax and 268 semantics. Appendix E provides a MIDI overview, at a level of detail 269 sufficient to understand most of this memo. Implementors should consult 270 [MIDI] for an authoritative description of MIDI. 272 The MIDI payload format maps a MIDI command stream (16 voice channels + 273 systems) onto an RTP stream. An RTP media stream is a sequence of 274 logical packets that share a common format. Each packet consists of two 275 parts: the RTP header and the MIDI payload. Figure 1 shows this format 276 (vertical space delineates the header and payload). 278 We describe RTP packets as "logical" packets to highlight the fact that 279 RTP itself is not a network-layer protocol. Instead, RTP packets are 280 mapped onto network protocols (such as unicast UDP, multicast UDP, or 281 TCP) by an application [ALF]. The interleaved mode of the Real Time 282 Streaming Protocol (RTSP, [RFC2326]) is an example of an RTP mapping to 283 TCP transport, as is [RFC4571]. 285 2.1. RTP Header 287 [RFC3550] provides a complete description of the RTP header fields. In 288 this section, we clarify the role of a few RTP header fields for MIDI 289 applications. All fields are coded in network byte order (big- endian). 291 0 1 2 3 292 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 1 293 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 294 | V |P|X| CC |M| PT | Sequence number | 295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 296 | Timestamp | 297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 298 | SSRC | 299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 301 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 302 | MIDI command section ... | 303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 304 | Journal section ... | 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 307 Figure 1 -- Packet format 309 The behavior of the 1-bit M field depends on the media type of the 310 stream. For native streams, the M bit MUST be set to 1 if the MIDI 311 command section has a non-zero LEN field, and MUST be set to 0 312 otherwise. For mpeg4-generic streams, the M bit MUST be set to 1 for 313 all packets (to conform to [RFC3640]). 315 In an RTP MIDI stream, the 16-bit sequence number field is initialized 316 to a randomly chosen value and is incremented by one (modulo 2^16) for 317 each packet sent in the stream. A related quantity, the 32-bit extended 318 packet sequence number, may be computed by tracking rollovers of the 319 16-bit sequence number. Note that different receivers of the same 320 stream may compute different extended packet sequence numbers, depending 321 on when the receiver joined the session. 323 The 32-bit timestamp field sets the base timestamp value for the packet. 324 The payload codes MIDI command timing relative to this value. The 325 timestamp units are set by the clock rate parameter. For example, if 326 the clock rate has a value of 44100 Hz, two packets whose base timestamp 327 values differ by 2 seconds have RTP timestamp fields that differ by 328 88200. 330 Note that the clock rate parameter is not encoded within each RTP MIDI 331 packet. A receiver of an RTP MIDI stream becomes aware of the clock 332 rate as part of the session setup process. For example, if a session 333 management tool uses the Session Description Protocol (SDP, [RFC4566]) 334 to describe a media session, the clock rate parameter is set using the 335 rtpmap attribute. We show examples of session setup in Section 6. 337 For RTP MIDI streams destined to be rendered into audio, the clock rate 338 SHOULD be an audio sample rate of 32 KHz or higher. This recommendation 339 is due to the sensitivity of human musical perception to small timing 340 errors in musical note sequences, and due to the timbral changes that 341 occur when two near-simultaneous MIDI NoteOns are rendered with a 342 different timing than that desired by the content author due to clock 343 rate quantization. RTP MIDI streams that are not destined for audio 344 rendering (such as MIDI streams that control stage lighting) MAY use a 345 lower clock rate but SHOULD use a clock rate high enough to avoid timing 346 artifacts in the application. 348 For RTP MIDI streams destined to be rendered into audio, the clock rate 349 SHOULD be chosen from rates in common use in professional audio 350 applications or in consumer audio distribution. At the time of this 351 writing, these rates include 32 KHz, 44.1 KHz, 48 KHz, 64 KHz, 88.2 KHz, 352 96 KHz, 176.4 KHz, and 192 KHz. If the RTP MIDI session is a part of a 353 synchronized media session that includes another (non-MIDI) RTP audio 354 stream with a clock rate of 32 KHz or higher, the RTP MIDI stream SHOULD 355 use a clock rate that matches the clock rate of the other audio stream. 356 However, if the RTP MIDI stream is destined to be rendered into audio, 357 the RTP MIDI stream SHOULD NOT use a clock rate lower than 32 KHz, even 358 if this second stream has a clock rate less than 32 KHz. 360 Timestamps of consecutive packets do not necessarily increment at a 361 fixed rate, because RTP MIDI packets are not necessarily sent at a fixed 362 rate. The degree of packet transmission regularity reflects the 363 underlying application dynamics. Interactive applications may vary the 364 packet sending rate to track the gestural rate of a human performer, 365 whereas content-streaming applications may send packets at a fixed rate. 367 Therefore, the timestamps for two sequential RTP packets may be 368 identical, or the second packet may have a timestamp arbitrarily larger 369 than the first packet (modulo 2^32). Section 3 places additional 370 restrictions on the RTP timestamps for two sequential RTP packets, as 371 does the guardtime parameter (Appendix C.4.2). 373 We use the term "media time" to denote the temporal duration of the 374 media coded by an RTP packet. The media time coded by a packet is 375 computed by subtracting the last command timestamp in the MIDI command 376 section from the RTP timestamp (modulo 2^32). If the MIDI list of the 377 MIDI command section of a packet is empty, the media time coded by the 378 packet is 0 ms. Appendix C.4.1 discusses media time issues in detail. 380 We now define RTP session semantics, in the context of sessions 381 specified using the session description protocol [RFC4566]. A session 382 description media line ("m=") specifies an RTP session. An RTP session 383 has an independent space of 2^32 synchronization sources. 384 Synchronization source identifiers are coded in the SSRC header field of 385 RTP session packets. The payload types that may appear in the PT header 386 field of RTP session packets are listed at the end of the media line. 388 Several RTP MIDI streams may appear in an RTP session. Each stream is 389 distinguished by a unique SSRC value and has a unique sequence number 390 and RTP timestamp space. Multiple streams in the RTP session may be 391 sent by a single party. Multiple parties may send streams in the RTP 392 session. An RTP MIDI stream encodes data for a single MIDI command name 393 space (16 voice channels + Systems). 395 Streams in an RTP session may use different payload types, or they may 396 use the same payload type. However, each party may send, at most, one 397 RTP MIDI stream for each payload type mapped to an RTP MIDI payload 398 format in an RTP session. Recall that dynamic binding of payload type 399 numbers in [RFC4566] lets a party map many payload type numbers to the 400 RTP MIDI payload format; thus a party may send many RTP MIDI streams in 401 a single RTP session. Pairs of streams (unicast or multicast) that 402 communicate between two parties in an RTP session and that share a 403 payload type have the same association as a MIDI cable pair that cross- 404 connects two devices in a MIDI 1.0 DIN network. 406 The RTP session architecture described above is efficient in its use of 407 network ports, as one RTP session (using a port pair per party) supports 408 the transport of many MIDI name spaces (16 MIDI channels + systems). We 409 define tools for grouping and labelling MIDI name spaces across streams 410 and sessions in Appendix C.5 of this memo. 412 The RTP header timestamps for each stream in an RTP session have 413 separately and randomly chosen initialization values. Receivers use the 414 timing fields encoded in the RTP control protocol (RTCP, [RFC3550]) 415 sender reports to synchronize the streams sent by a party. The SSRC 416 values for each stream in an RTP session are also separately and 417 randomly chosen, as described in [RFC3550]. Receivers use the CNAME 418 field encoded in RTCP sender reports to verify that streams were sent by 419 the same party, and to detect SSRC collisions, as described in 420 [RFC3550]. 422 In some applications, a receiver renders MIDI commands into audio (or 423 into control actions, such as the rewind of a tape deck or the dimming 424 of stage lights). In other applications, a receiver presents a MIDI 425 stream to software programs via an Application Programmer Interface 426 (API). Appendix C.6 defines session configuration tools to specify what 427 receivers should do with a MIDI command stream. 429 If a multimedia session uses different RTP MIDI streams to send 430 different classes of media, the streams MUST be sent over different RTP 431 sessions. For example, if a multimedia session uses one MIDI stream for 432 audio and a second MIDI stream to control a lighting system, the audio 433 and lighting streams MUST be sent over different RTP sessions, each with 434 its own media line. 436 Session description tools defined in Appendix C.5 let a sending party 437 split a single MIDI name space (16 voice channels + systems) over 438 several RTP MIDI streams. Split transport of a MIDI command stream is a 439 delicate task, because correct command stream reconstruction by a 440 receiver depends on exact timing synchronization across the streams. 442 To support split name spaces, we define the following requirements: 444 o A party MUST NOT send several RTP MIDI streams that share a MIDI 445 name space in the same RTP session. Instead, each stream MUST 446 be sent from a different RTP session. 448 o If several RTP MIDI streams sent by a party share a MIDI name 449 space, all streams MUST use the same SSRC value and MUST use the 450 same randomly chosen RTP timestamp initialization value. 452 These rules let a receiver identify streams that share a MIDI name space 453 (by matching SSRC values) and also let a receiver accurately reconstruct 454 the source MIDI command stream (by using RTP timestamps to interleave 455 commands from the two streams). Care MUST be taken by senders to ensure 456 that SSRC changes due to collisions are reflected in both streams. 457 Receivers MUST regularly examine the RTCP CNAME fields associated with 458 the linked streams, to ensure that the assumed link is legitimate and 459 not the result of an SSRC collision by another sender. 461 Except for the special cases described above, a party may send many RTP 462 MIDI streams in the same session. However, it is sometimes advantageous 463 for two RTP MIDI streams to be sent over different RTP sessions. For 464 example, two streams may need different values for RTP session-level 465 attributes (such as the sendonly and recvonly attributes). As a second 466 example, two RTP sessions may be needed to send two unicast streams in a 467 multimedia session that originate on different computers (with different 468 IP numbers). Two RTP sessions are needed in this case because transport 469 addresses are specified on the RTP-session or multimedia-session level, 470 not on a payload type level. 472 On a final note, in some uses of MIDI, parties send bidirectional 473 traffic to conduct transactions (such as file exchange). These commands 474 were designed to work over MIDI 1.0 DIN cable networks may be configured 475 in a multicast topology, which use pure "party-line" signalling. Thus, 476 if a multimedia session ensures a multicast connection between all 477 parties, bidirectional MIDI commands will work without additional 478 support from the RTP MIDI payload format. 480 2.2. MIDI Payload 482 The payload (Figure 1) MUST begin with the MIDI command section. The 483 MIDI command section codes a (possibly empty) list of timestamped MIDI 484 commands, and provides the essential service of the payload format. 486 The payload MAY also contain a journal section. The journal section 487 provides resiliency by coding the recent history of the stream. A flag 488 in the MIDI command section codes the presence of a journal section in 489 the payload. 491 Section 3 defines the MIDI command section. Sections 4-5 and Appendices 492 A-B define the recovery journal, the default format for the journal 493 section. Here, we describe how these payload sections operate in a 494 stream in an RTP session. 496 The journalling method for a stream is set at the start of a session and 497 MUST NOT be changed thereafter. A stream may be set to use the recovery 498 journal, to use an alternative journal format (none are defined in this 499 memo), or not to use a journal. 501 The default journalling method of a stream is inferred from its 502 transport type. Streams that use unreliable transport (such as UDP) 503 default to using the recovery journal. Streams that use reliable 504 transport (such as TCP) default to not using a journal. Appendix C.2.1 505 defines session configuration tools for overriding these defaults. For 506 all types of transport, a sender MUST transmit an RTP packet stream with 507 consecutive sequence numbers (modulo 2^16). 509 If a stream uses the recovery journal, every payload in the stream MUST 510 include a journal section. If a stream does not use journalling, a 511 journal section MUST NOT appear in a stream payload. If a stream uses 512 an alternative journal format, the specification for the journal format 513 defines an inclusion policy. 515 If a stream is sent over UDP transport, the Maximum Transmission Unit 516 (MTU) of the underlying network limits the practical size of the payload 517 section (for example, an Ethernet MTU is 1500 octets), for applications 518 where predictable and minimal packet transmission latency is critical. 519 A sender SHOULD NOT create RTP MIDI UDP packets whose size exceeds the 520 MTU of the underlying network. Instead, the sender SHOULD take steps to 521 keep the maximum packet size under the MTU limit. 523 These steps may take many forms. The default closed-loop recovery 524 journal sending policy (defined in Appendix C.2.2.2) uses RTP control 525 protocol (RTCP, [RFC3550]) feedback to manage the RTP MIDI packet size. 526 In addition, Section 3.2 and Appendix B.5.2 provide specific tools for 527 managing the size of packets that code MIDI System Exclusive (0xF0) 528 commands. Appendix C.5 defines session configuration tools that may be 529 used to split a dense MIDI name space into several UDP streams (each 530 sent in a different RTP session, per Section 2.1) so that the payload 531 fits comfortably into an MTU. Another option is to use TCP. Section 532 4.3 of [RFC4696] provides non-normative advice for packet size 533 management. 535 3. MIDI Command Section 537 Figure 2 shows the format of the MIDI command section. 539 0 1 2 3 540 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 1 541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 542 |B|J|Z|P|LEN... | MIDI list ... | 543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 545 Figure 2 -- MIDI command section 547 The MIDI command section begins with a variable-length header. 549 The header field LEN codes the number of octets in the MIDI list that 550 follow the header. If the header flag B is 0, the header is one octet 551 long, and LEN is a 4-bit field, supporting a maximum MIDI list length of 552 15 octets. 554 If B is 1, the header is two octets long, and LEN is a 12-bit field, 555 supporting a maximum MIDI list length of 4095 octets. LEN is coded in 556 network byte order (big-endian): the 4 bits of LEN that appear in the 557 first header octet code the most significant 4 bits of the 12-bit LEN 558 value. 560 A LEN value of 0 is legal, and it codes an empty MIDI list. 562 If the J header bit is set to 1, a journal section MUST appear after the 563 MIDI command section in the payload. If the J header bit is set to 0, 564 the payload MUST NOT contain a journal section. 566 We define the semantics of the P header bit in Section 3.2. 568 If the LEN header field is nonzero, the MIDI list has the structure 569 shown in Figure 3. 571 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 572 | Delta Time 0 (1-4 octets long, or 0 octets if Z = 1) | 573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 574 | MIDI Command 0 (1 or more octets long) | 575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 576 | Delta Time 1 (1-4 octets long) | 577 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 578 | MIDI Command 1 (1 or more octets long) | 579 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 580 | ... | 581 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 582 | Delta Time N (1-4 octets long) | 583 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 584 | MIDI Command N (0 or more octets long) | 585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 587 Figure 3 -- MIDI list structure 589 If the header flag Z is 1, the MIDI list begins with a complete MIDI 590 command (coded in the MIDI Command 0 field, in Figure 3) preceded by a 591 delta time (coded in the Delta Time 0 field). If Z is 0, the Delta Time 592 0 field is not present in the MIDI list, and the command coded in the 593 MIDI Command 0 field has an implicit delta time of 0. 595 The MIDI list structure may also optionally encode a list of N 596 additional complete MIDI commands, each coded in a MIDI Command K field. 597 Each additional command MUST be preceded by a Delta Time K field, which 598 codes the command's delta time. We discuss exceptions to the "command 599 fields code complete MIDI commands" rule in Section 3.2. 601 The final MIDI command field (i.e., the MIDI Command N field, shown in 602 Figure 3) in the MIDI list MAY be empty. Moreover, a MIDI list MAY 603 consist a single delta time (encoded in the Delta Time 0 field) without 604 an associated command (which would have been encoded in the MIDI Command 605 0 field). These rules enable MIDI coding features that are explained in 606 Section 3.1. We delay the explanations because an understanding of RTP 607 MIDI timestamps is necessary to describe the features. 609 3.1. Timestamps 611 In this section, we describe how RTP MIDI encodes a timestamp for each 612 MIDI list command. Command timestamps have the same units as RTP packet 613 header timestamps (described in Section 2.1 and [RFC3550]). Recall that 614 RTP timestamps have units of seconds, whose scaling is set during 615 session configuration (see Section 6.1 and [RFC4566]). 617 As shown in Figure 3, the MIDI list encodes time using a compact delta- 618 time format. The RTP MIDI delta time syntax is a modified form of the 619 MIDI File delta time syntax [MIDI]. RTP MIDI delta times use 1-4 octet 620 fields to encode 32-bit unsigned integers. Figure 4 shows the encoded 621 and decoded forms of delta times. Note that delta time values may be 622 legally encoded in multiple formats; for example, there are four legal 623 ways to encode the zero delta time (0x00, 0x8000, 0x808000, 0x80808000). 625 RTP MIDI uses delta times to encode a timestamp for each MIDI command. 626 The timestamp for MIDI Command K is the summation (modulo 2^32) of the 627 RTP timestamp and decoded delta times 0 through K. This cumulative 628 coding technique, borrowed from MIDI File delta time coding, is 629 efficient because it reduces the number of multi-octet delta times. 631 All command timestamps in a packet MUST be less than or equal to the RTP 632 timestamp of the next packet in the stream (modulo 2^32). 634 This restriction ensures that a particular RTP MIDI packet in a stream 635 is uniquely responsible for encoding time starting at the moment after 636 the RTP timestamp encoded in the RTP packet header, and ending at the 637 moment before the final command timestamp encoded in the MIDI list. The 638 "moment before" and "moment after" qualifiers acknowledge the "less than 639 or equal" semantics (as opposed to "strictly less than") in the sentence 640 above this paragraph. 642 Note that it is possible to "pad" the end of an RTP MIDI packet with 643 time that is guaranteed to be void of MIDI commands, by setting the 644 "Delta Time N" field of the MIDI list to the end of the void time, and 645 by omitting its corresponding "MIDI Command N" field (a syntactic 646 construction the preamble of Section 3 expressly made legal). 648 In addition, it is possible to code an RTP MIDI packet to express that a 649 period of time in the stream is void of MIDI commands. The RTP 650 timestamp in the header would code the start of the void time. The MIDI 651 list of this packet would consist of a "Delta Time 0" field that coded 652 the end of the void time. No other fields would be present in the MIDI 653 list (a syntactic construction the preamble of Section 3 also expressly 654 made legal). 656 By default, a command timestamp indicates the execution time for the 657 command. The difference between two timestamps indicates the time delay 658 between the execution of the commands. This difference may be zero, 659 coding simultaneous execution. In this memo, we refer to this 660 interpretation of timestamps as "comex" (COMmand EXecution) semantics. 661 We formally define comex semantics in Appendix C.3. 663 The comex interpretation of timestamps works well for transcoding a 664 Standard MIDI File (SMF) into an RTP MIDI stream, as SMFs code a 665 timestamp for each MIDI command stored in the file. To transcode an SMF 666 that uses metric time markers, use the SMF tempo map (encoded in the SMF 667 as meta-events) to convert metric SMF timestamp units into seconds-based 668 RTP timestamp units. 670 The comex interpretation also works well for MIDI hardware controllers 671 that are coding raw sensor data directly onto an RTP MIDI stream. Note 672 that this controller design is preferable to a design that converts raw 673 sensor data into a MIDI 1.0 cable command stream and then transcodes the 674 stream onto an RTP MIDI stream. 676 The comex interpretation of timestamps is usually not the best timestamp 677 interpretation for transcoding a MIDI source that uses implicit command 678 timing (such as MIDI 1.0 DIN cables) into an RTP MIDI stream. Appendix 679 C.3 defines alternatives to comex semantics and describes session 680 configuration tools for selecting the timestamp interpretation semantics 681 for a stream. 683 One-Octet Delta Time: 685 Encoded form: 0ddddddd 686 Decoded form: 00000000 00000000 00000000 0ddddddd 688 Two-Octet Delta Time: 690 Encoded form: 1ccccccc 0ddddddd 691 Decoded form: 00000000 00000000 00cccccc cddddddd 693 Three-Octet Delta Time: 695 Encoded form: 1bbbbbbb 1ccccccc 0ddddddd 696 Decoded form: 00000000 000bbbbb bbcccccc cddddddd 698 Four-Octet Delta Time: 700 Encoded form: 1aaaaaaa 1bbbbbbb 1ccccccc 0ddddddd 701 Decoded form: 0000aaaa aaabbbbb bbcccccc cddddddd 703 Figure 4 -- Decoding delta time formats 705 3.2. Command Coding 707 Each non-empty MIDI Command field in the MIDI list codes one of the MIDI 708 command types that may legally appear on a MIDI 1.0 DIN cable. Standard 709 MIDI File meta-events do not fit this definition and MUST NOT appear in 710 the MIDI list. As a rule, each MIDI Command field codes a complete 711 command, in the binary command format defined in [MIDI]. In the 712 remainder of this section, we describe exceptions to this rule. 714 The first MIDI channel command in the MIDI list MUST include a status 715 octet. Running status coding, as defined in [MIDI], MAY be used for all 716 subsequent MIDI channel commands in the list. As in [MIDI], System 717 Common and System Exclusive messages (0xF0 ... 0xF7) cancel the running 718 status state, but System Real-time messages (0xF8 ... 0xFF) do not 719 affect the running status state. All System commands in the MIDI list 720 MUST include a status octet. 722 As we note above, the first channel command in the MIDI list MUST 723 include a status octet. However, the corresponding command in the 724 original MIDI source data stream might not have a status octet (in this 725 case, the source would be coding the command using running status). If 726 the status octet of the first channel command in the MIDI list does not 727 appear in the source data stream, the P (phantom) header bit MUST be set 728 to 1. In all other cases, the P bit MUST be set to 0. 730 Note that the P bit describes the MIDI source data stream, not the MIDI 731 list encoding; regardless of the state of the P bit, the MIDI list MUST 732 include the status octet. 734 As receivers MUST be able to decode running status, sender implementors 735 should feel free to use running status to improve bandwidth efficiency. 736 However, senders SHOULD NOT introduce timing jitter into an existing 737 MIDI command stream through an inappropriate use or removal of running 738 status coding. This warning primarily applies to senders whose RTP MIDI 739 streams may be transcoded onto a MIDI 1.0 DIN cable [MIDI] by the 740 receiver: both the timestamps and the command coding (running status or 741 not) must comply with the physical restrictions of implicit time coding 742 over a slow serial line. 744 On a MIDI 1.0 DIN cable [MIDI], a System Real-time command may be 745 embedded inside of another "host" MIDI command. This syntactic 746 construction is not supported in the payload format: a MIDI Command 747 field in the MIDI list codes exactly one MIDI command (partially or 748 completely). 750 To encode an embedded System Real-time command, senders MUST extract the 751 command from its host and code it in the MIDI list as a separate 752 command. The host command and System Real-time command SHOULD appear in 753 the same MIDI list. The delta time of the System Real-time command 754 SHOULD result in a command timestamp that encodes the System Real-time 755 command placement in its original embedded position. 757 Two methods are provided for encoding MIDI System Exclusive (SysEx) 758 commands in the MIDI list. A SysEx command may be encoded in a MIDI 759 Command field verbatim: a 0xF0 octet, followed by an arbitrary number of 760 data octets, followed by a 0xF7 octet. 762 Alternatively, a SysEx command may be encoded as multiple segments. The 763 command is divided into two or more SysEx command segments; each segment 764 is encoded in its own MIDI Command field in the MIDI list. 766 The payload format supports segmentation in order to encode SysEx 767 commands that encode information in the temporal pattern of data octets. 768 By encoding these commands as a series of segments, each data octet may 769 be associated with a distinct delta time. Segmentation also supports 770 the coding of large SysEx commands across several packets. 772 To segment a SysEx command, first partition its data octet list into two 773 or more sublists. The last sublist MAY be empty (i.e., contain no 774 octets); all other sublists MUST contain at least one data octet. To 775 complete the segmentation, add the status octets defined in Figure 5 to 776 the head and tail of the first, last, and any "middle" sublists. Figure 777 6 shows example segmentations of a SysEx command. 779 A sender MAY cancel a segmented SysEx command transmission that is in 780 progress, by sending the "cancel" sublist shown in Figure 5. A "cancel" 781 sublist MAY follow a "first" or "middle" sublist in the transmission, 782 but MUST NOT follow a "last" sublist. The cancel MUST be empty (thus, 783 0xF7 0xF4 is the only legal cancel sublist). 785 The cancellation feature is needed because Appendix C.1 defines 786 configuration tools that let session parties exclude certain SysEx 787 commands in the stream. Senders that transcode a MIDI source onto an 788 RTP MIDI stream under these constraints have the responsibility of 789 excluding undesired commands from the RTP MIDI stream. 791 The cancellation feature lets a sender start the transmission of a 792 command before the MIDI source has sent the entire command. If a sender 793 determines that the command whose transmission is in progress should not 794 appear on the RTP stream, it cancels the command. Without a method for 795 cancelling a SysEx command transmission, senders would be forced to use 796 a high-latency store-and-forward approach to transcoding SysEx commands 797 onto RTP MIDI packets, in order to validate each SysEx command before 798 transmission. 800 The recommended receiver reaction to a cancellation depends on the 801 capabilities of the receiver. For example, a sound synthesizer that is 802 directly parsing RTP MIDI packets and rendering them to audio will be 803 aware of the fact that SysEx commands may be cancelled in RTP MIDI. 804 These receivers SHOULD detect a SysEx cancellation in the MIDI list and 805 act as if they had never received the SysEx command. 807 As a second example, a synthesizer may be receiving MIDI data from an 808 RTP MIDI stream via a MIDI DIN cable (or a software API emulation of a 809 MIDI DIN cable). In this case, an RTP-MIDI-aware system receives the 810 RTP MIDI stream and transcodes it onto the MIDI DIN cable (or its 811 emulation). Upon the receipt of the cancel sublist, the RTP-MIDI- aware 812 transcoder might have already sent the first part of the SysEx command 813 on the MIDI DIN cable to the receiver. 815 Unfortunately, the MIDI DIN cable protocol cannot directly code "cancel 816 SysEx in progress" semantics. However, MIDI DIN cable receivers begin 817 SysEx processing after the complete command arrives. The receiver 818 checks to see if it recognizes the command (coded in the first few 819 octets) and then checks to see if the command is the correct length. 820 Thus, in practice, a transcoder can cancel a SysEx command by sending an 821 0xF7 to (prematurely) end the SysEx command -- the receiver will detect 822 the incorrect command length and discard the command. 824 Appendix C.1 defines configuration tools that may be used to prohibit 825 SysEx command cancellation. 827 The relative ordering of SysEx command segments in a MIDI list must 828 match the relative ordering of the sublists in the original SysEx 829 command. By default, commands other than System Real-time MIDI commands 830 MUST NOT appear between SysEx command segments (Appendix C.1 defines 831 configuration tools to change this default, to let other commands types 832 appear between segments). If the command segments of a SysEx command 833 are placed in the MIDI lists of two or more RTP packets, the segment 834 ordering rules apply to the concatenation of all affected MIDI lists. 836 ----------------------------------------------------------- 837 | Sublist Position | Head Status Octet | Tail Status Octet | 838 |-----------------------------------------------------------| 839 | first | 0xF0 | 0xF0 | 840 |-----------------------------------------------------------| 841 | middle | 0xF7 | 0xF0 | 842 |-----------------------------------------------------------| 843 | last | 0xF7 | 0xF7 | 844 |-----------------------------------------------------------| 845 | cancel | 0xF7 | 0xF4 | 846 ----------------------------------------------------------- 848 Figure 5 -- Command segmentation status octets 850 [MIDI] permits 0xF7 octets that are not part of a (0xF0, 0xF7) pair to 851 appear on a MIDI 1.0 DIN cable. Unpaired 0xF7 octets have no semantic 852 meaning in MIDI, apart from cancelling running status. 854 Unpaired 0xF7 octets MUST NOT appear in the MIDI list of the MIDI 855 Command section. We impose this restriction to avoid interference with 856 the command segmentation coding defined in Figure 5. 858 SysEx commands carried on a MIDI 1.0 DIN cable may use the "dropped 859 0xF7" construction [MIDI]. In this coding method, the 0xF7 octet is 860 dropped from the end of the SysEx command, and the status octet of the 861 next MIDI command acts both to terminate the SysEx command and start the 862 next command. To encode this construction in the payload format, follow 863 these steps: 865 o Determine the appropriate delta times for the SysEx command and 866 the command that follows the SysEx command. 868 o Insert the "dropped" 0xF7 octet at the end of the SysEx command, 869 to form the standard SysEx syntax. 871 o Code both commands into the MIDI list using the rules above. 873 o Replace the 0xF7 octet that terminates the verbatim SysEx 874 encoding or the last segment of the segmented SysEx encoding 875 with a 0xF5 octet. This substitution informs the receiver 876 of the original dropped 0xF7 coding. 878 [MIDI] reserves the undefined System Common commands 0xF4 and 0xF5 and 879 the undefined System Real-time commands 0xF9 and 0xFD for future use. 880 By default, undefined commands MUST NOT appear in a MIDI Command field 881 in the MIDI list, with the exception of the 0xF5 octets used to code the 882 "dropped 0xF7" construction and the 0xF4 octets used by SysEx "cancel" 883 sublists. 885 During session configuration, a stream may be customized to transport 886 undefined commands (Appendix C.1). For this case, we now define how 887 senders encode undefined commands in the MIDI list. 889 An undefined System Real-time command MUST be coded using the System 890 Real-time rules. 892 If the undefined System Common commands are put to use in a future 893 version of [MIDI], the command will begin with an 0xF4 or 0xF5 status 894 octet, followed by an arbitrary number of data octets (i.e., zero or 895 more data bytes). To encode these commands, senders MUST terminate the 896 command with an 0xF7 octet and place the modified command into the MIDI 897 Command field. 899 Unfortunately, non-compliant uses of the undefined System Common 900 commands may appear in MIDI implementations. To model these commands, 901 we assume that the command begins with an 0xF4 or 0xF5 status octet, 902 followed by zero or more data octets, followed by zero or more trailing 903 0xF7 status octets. To encode the command, senders MUST first remove 904 all trailing 0xF7 status octets from the command. Then, senders MUST 905 terminate the command with an 0xF7 octet and place the modified command 906 into the MIDI Command field. 908 Note that we include the trailing octets in our model as a cautionary 909 measure: if such commands appeared in a non-compliant use of an 910 undefined System Common command, an RTP MIDI encoding of the command 911 that did not remove trailing octets could be mistaken for an encoding of 912 "middle" or "last" sublist of a segmented SysEx commands (Figure 5) 913 under certain packet loss conditions. 915 Original SysEx command: 917 0xF0 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0xF7 919 A two-segment segmentation: 921 0xF0 0x01 0x02 0x03 0x04 0xF0 923 0xF7 0x05 0x06 0x07 0x08 0xF7 925 A different two-segment segmentation: 927 0xF0 0x01 0xF0 929 0xF7 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0xF7 931 A three-segment segmentation: 933 0xF0 0x01 0x02 0xF0 935 0xF7 0x03 0x04 0xF0 937 0xF7 0x05 0x06 0x07 0x08 0xF7 939 The segmentation with the largest number of segments: 941 0xF0 0x01 0xF0 943 0xF7 0x02 0xF0 945 0xF7 0x03 0xF0 947 0xF7 0x04 0xF0 949 0xF7 0x05 0xF0 951 0xF7 0x06 0xF0 953 0xF7 0x07 0xF0 955 0xF7 0x08 0xF0 957 0xF7 0xF7 959 Figure 6 -- Example segmentations 961 4. The Recovery Journal System 963 The recovery journal is the default resiliency tool for unreliable 964 transport. In this section, we normatively define the roles that 965 senders and receivers play in the recovery journal system. 967 MIDI is a fragile code. A single lost command in a MIDI command stream 968 may produce an artifact in the rendered performance. We normatively 969 classify rendering artifacts into two categories: 971 o Transient artifacts. Transient artifacts produce immediate 972 but short-term glitches in the performance. For example, a lost 973 NoteOn (0x9) command produces a transient artifact: one note 974 fails to play, but the artifact does not extend beyond the end 975 of that note. 977 o Indefinite artifacts. Indefinite artifacts produce long-lasting 978 errors in the rendered performance. For example, a lost NoteOff 979 (0x8) command may produce an indefinite artifact: the note that 980 should have been ended by the lost NoteOff command may sustain 981 indefinitely. As a second example, the loss of a Control Change 982 (0xB) command for controller number 7 (Channel Volume) may 983 produce an indefinite artifact: after the loss, all notes on 984 the channel may play too softly or too loudly. 986 The purpose of the recovery journal system is to satisfy the recovery 987 journal mandate: the MIDI performance rendered from an RTP MIDI stream 988 sent over unreliable transport MUST NOT contain indefinite artifacts. 990 The recovery journal system does not use packet retransmission to 991 satisfy this mandate. Instead, each packet includes a special section, 992 called the recovery journal. 994 The recovery journal codes the history of the stream, back to an earlier 995 packet called the checkpoint packet. The range of coverage for the 996 journal is called the checkpoint history. The recovery journal codes 997 the information necessary to recover from the loss of an arbitrary 998 number of packets in the checkpoint history. Appendix A.1 normatively 999 defines the checkpoint packet and the checkpoint history. 1001 When a receiver detects a packet loss, it compares its own knowledge 1002 about the history of the stream with the history information coded in 1003 the recovery journal of the packet that ends the loss event. By noting 1004 the differences in these two versions of the past, a receiver is able to 1005 transform all indefinite artifacts in the rendered performance into 1006 transient artifacts, by executing MIDI commands to repair the stream. 1008 We now state the normative role for senders in the recovery journal 1009 system. 1011 Senders prepare a recovery journal for every packet in the stream. In 1012 doing so, senders choose the checkpoint packet identity for the journal. 1013 Senders make this choice by applying a sending policy. Appendix C.2.2 1014 normatively defines three sending policies: "closed- loop", "open-loop", 1015 and "anchor". 1017 By default, senders MUST use the closed-loop sending policy. If the 1018 session description overrides this default policy, by using the 1019 parameter j_update defined in Appendix C.2.2, senders MUST use the 1020 specified policy. 1022 After choosing the checkpoint packet identity for a packet, the sender 1023 creates the recovery journal. By default, this journal MUST conform to 1024 the normative semantics in Section 5 and Appendices A-B in this memo. 1025 In Appendix C.2.3, we define parameters that modify the normative 1026 semantics for recovery journals. If the session description uses these 1027 parameters, the journal created by the sender MUST conform to the 1028 modified semantics. 1030 Next, we state the normative role for receivers in the recovery journal 1031 system. 1033 A receiver MUST detect each RTP sequence number break in a stream. If 1034 the sequence number break is due to a packet loss event (as defined in 1035 [RFC3550]), the receiver MUST repair all indefinite artifacts in the 1036 rendered MIDI performance caused by the loss. If the sequence number 1037 break is due to an out-of-order packet (as defined in [RFC3550]), the 1038 receiver MUST NOT take actions that introduce indefinite artifacts 1039 (ignoring the out-of-order packet is a safe option). 1041 Receivers take special precautions when entering or exiting a session. 1042 A receiver MUST process the first received packet in a stream as if it 1043 were a packet that ends a loss event. Upon exiting a session, a 1044 receiver MUST ensure that the rendered MIDI performance does not end 1045 with indefinite artifacts. 1047 Receivers are under no obligation to perform indefinite artifact repairs 1048 at the moment a packet arrives. A receiver that uses a playout buffer 1049 may choose to wait until the moment of rendering before processing the 1050 recovery journal, as the "lost" packet may be a late packet that arrives 1051 in time to use. 1053 Next, we state the normative role for the creator of the session 1054 description in the recovery journal system. Depending on the 1055 application, the sender, the receivers, and other parties may take part 1056 in creating or approving the session description. 1058 A session description that specifies the default closed-loop sending 1059 policy and the default recovery journal semantics satisfies the recovery 1060 journal mandate. However, these default behaviors may not be 1061 appropriate for all sessions. If the creators of a session description 1062 use the parameters defined in Appendix C.2 to override these defaults, 1063 the creators MUST ensure that the parameters define a system that 1064 satisfies the recovery journal mandate. 1066 Finally, we note that this memo does not specify sender or receiver 1067 recovery journal algorithms. Implementations are free to use any 1068 algorithm that conforms to the requirements in this section. The non- 1069 normative [RFC4696] discusses sender and receiver algorithm design. 1071 5. Recovery Journal Format 1073 This section introduces the structure of the recovery journal and 1074 defines the bitfields of recovery journal headers. Appendices A-B 1075 complete the bitfield definition of the recovery journal. 1077 The recovery journal has a three-level structure: 1079 o Top-level header. 1081 o Channel and system journal headers. These headers encode 1082 recovery information for a single voice channel (channel 1083 journal) or for all systems commands (system journal). 1085 o Chapters. Chapters describe recovery information for a 1086 single MIDI command type. 1088 Figure 7 shows the top-level structure of the recovery journal. The 1089 recovery journals consists of a 3-octet header, followed by an optional 1090 system journal (labeled S-journal in Figure 7) and an optional list of 1091 channel journals. Figure 8 shows the recovery journal header format. 1093 0 1 2 3 1094 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 1095 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1096 | Recovery journal header | S-journal ... | 1097 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1098 | Channel journals ... | 1099 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1101 Figure 7 -- Top-level recovery journal format 1103 0 1 2 1104 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 1105 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1106 |S|Y|A|H|TOTCHAN| Checkpoint Packet Seqnum | 1107 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1109 Figure 8 -- Recovery journal header 1111 If the Y header bit is set to 1, the system journal appears in the 1112 recovery journal, directly following the recovery journal header. 1114 If the A header bit is set to 1, the recovery journal ends with a list 1115 of (TOTCHAN + 1) channel journals (the 4-bit TOTCHAN header field is 1116 interpreted as an unsigned integer). 1118 A MIDI channel MAY be represented by (at most) one channel journal in a 1119 recovery journal. Channel journals MUST appear in the recovery journal 1120 in ascending channel-number order. 1122 If A and Y are both zero, the recovery journal only contains its 3- 1123 octet header and is considered to be an "empty" journal. 1125 The S (single-packet loss) bit appears in most recovery journal 1126 structures, including the recovery journal header. The S bit helps 1127 receivers efficiently parse the recovery journal in the common case of 1128 the loss of a single packet. Appendix A.1 defines S bit semantics. 1130 The H bit indicates if MIDI channels in the stream have been configured 1131 to use the enhanced Chapter C encoding (Appendix A.3.3). 1133 By default, the payload format does not use enhanced Chapter C encoding. 1134 In this default case, the H bit MUST be set to 0 for all packets in the 1135 stream. 1137 If the stream has been configured so that controller numbers for one or 1138 more MIDI channels use enhanced Chapter C encoding, the H bit MUST be 1139 set to 1 in all packets in the stream. In Appendix C.2.3, we show how 1140 to configure a stream to use enhanced Chapter C encoding. 1142 The 16-bit Checkpoint Packet Seqnum header field codes the sequence 1143 number of the checkpoint packet for this journal, in network byte order 1144 (big-endian). The choice of the checkpoint packet sets the depth of the 1145 checkpoint history for the journal (defined in Appendix A.1). 1147 Receivers may use the Checkpoint Packet Seqnum field of the packet that 1148 ends a loss event to verify that the journal checkpoint history covers 1149 the entire loss event. The checkpoint history covers the loss event if 1150 the Checkpoint Packet Seqnum field is less than or equal to one plus the 1151 highest RTP sequence number previously received on the stream (modulo 1152 2^16). 1154 0 1 2 3 1155 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 1156 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1157 |S| CHAN |H| LENGTH |P|C|M|W|N|E|T|A| Chapters ... | 1158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1160 Figure 9 -- Channel journal format 1162 Figure 9 shows the structure of a channel journal: a 3-octet header, 1163 followed by a list of leaf elements called channel chapters. A channel 1164 journal encodes information about MIDI commands on the MIDI channel 1165 coded by the 4-bit CHAN header field. Note that CHAN uses the same bit 1166 encoding as the channel nibble in MIDI Channel Messages (the cccc field 1167 in Figure E.1 of Appendix E). 1169 The 10-bit LENGTH field codes the length of the channel journal. The 1170 semantics for LENGTH fields are uniform throughout the recovery journal, 1171 and are defined in Appendix A.1. 1173 The third octet of the channel journal header is the Table of Contents 1174 (TOC) of the channel journal. The TOC is a set of bits that encode the 1175 presence of a chapter in the journal. Each chapter contains information 1176 about a certain class of MIDI channel command: 1178 o Chapter P: MIDI Program Change (0xC) 1179 o Chapter C: MIDI Control Change (0xB) 1180 o Chapter M: MIDI Parameter System (part of 0xB) 1181 o Chapter W: MIDI Pitch Wheel (0xE) 1182 o Chapter N: MIDI NoteOff (0x8), NoteOn (0x9) 1183 o Chapter E: MIDI Note Command Extras (0x8, 0x9) 1184 o Chapter T: MIDI Channel Aftertouch (0xD) 1185 o Chapter A: MIDI Poly Aftertouch (0xA) 1187 Chapters appear in a list following the header, in order of their 1188 appearance in the TOC. Appendices A.2-9 describe the bitfield format 1189 for each chapter, and define the conditions under which a chapter type 1190 MUST appear in the recovery journal. If any chapter types are required 1191 for a channel, an associated channel journal MUST appear in the recovery 1192 journal. 1194 The H bit indicates if controller numbers on a MIDI channel have been 1195 configured to use the enhanced Chapter C encoding (Appendix A.3.3). 1197 By default, controller numbers on a MIDI channel do not use enhanced 1198 Chapter C encoding. In this default case, the H bit MUST be set to 0 1199 for all channel journal headers for the channel in the recovery journal, 1200 for all packets in the stream. 1202 However, if at least one controller number for a MIDI channel has been 1203 configured to use the enhanced Chapter C encoding, the H bit for its 1204 channel journal MUST be set to 1, for all packets in the stream. 1206 In Appendix C.2.3, we show how to configure a controller number to use 1207 enhanced Chapter C encoding. 1209 0 1 2 3 1210 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 1211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1212 |S|D|V|Q|F|X| LENGTH | System chapters ... | 1213 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1215 Figure 10 -- System journal format 1217 Figure 10 shows the structure of the system journal: a 2-octet header, 1218 followed by a list of system chapters. Each chapter codes information 1219 about a specific class of MIDI Systems command: 1221 o Chapter D: Song Select (0xF3), Tune Request (0xF6), Reset (0xFF), 1222 undefined System commands (0xF4, 0xF5, 0xF9, 0xFD) 1223 o Chapter V: Active Sense (0xFE) 1224 o Chapter Q: Sequencer State (0xF2, 0xF8, 0xF9, 0xFA, 0xFB, 0xFC) 1225 o Chapter F: MTC Tape Position (0xF1, 0xF0 0x7F 0xcc 0x01 0x01) 1226 o Chapter X: System Exclusive (all other 0xF0) 1228 The 10-bit LENGTH field codes the size of the system journal and 1229 conforms to semantics described in Appendix A.1. 1231 The D, V, Q, F, and X header bits form a Table of Contents (TOC) for the 1232 system journal. A TOC bit that is set to 1 codes the presence of a 1233 chapter in the journal. Chapters appear in a list following the header, 1234 in the order of their appearance in the TOC. 1236 Appendix B describes the bitfield format for the system chapters and 1237 defines the conditions under which a chapter type MUST appear in the 1238 recovery journal. If any system chapter type is required to appear in 1239 the recovery journal, the system journal MUST appear in the recovery 1240 journal. 1242 6. Session Description Protocol 1244 RTP does not perform session management. Instead, RTP works together 1245 with session management tools, such as the Session Initiation Protocol 1246 (SIP, [RFC3261]) and the Real Time Streaming Protocol (RTSP, [RFC2326]). 1248 RTP payload formats define media type parameters for use in session 1249 management (for example, this memo defines "rtp-midi" as the media type 1250 for native RTP MIDI streams). 1252 In most cases, session management tools use the media type parameters 1253 via another standard, the Session Description Protocol (SDP, [RFC4566]). 1255 SDP is a textual format for specifying session descriptions. Session 1256 descriptions specify the network transport and media encoding for RTP 1257 sessions. Session management tools coordinate the exchange of session 1258 descriptions between participants ("parties"). 1260 Some session management tools use SDP to negotiate details of media 1261 transport (network addresses, ports, etc.). We refer to this use of SDP 1262 as "negotiated usage". One example of negotiated usage is the 1263 Offer/Answer protocol ([RFC3264] and Appendix C.7.2 in this memo) as 1264 used by SIP. 1266 Other session management tools use SDP to declare the media encoding for 1267 the session but use other techniques to negotiate network transport. We 1268 refer to this use of SDP as "declarative usage". One example of 1269 declarative usage is RTSP ([RFC2326] and Appendix C.7.1 in this memo). 1271 Below, we show session description examples for native (Section 6.1) and 1272 mpeg4-generic (Section 6.2) streams. In Section 6.3, we introduce 1273 session configuration tools that may be used to customize streams. 1275 6.1. Session Descriptions for Native Streams 1277 The session description below defines a unicast UDP RTP session (via a 1278 media ("m=") line) whose sole payload type (96) is mapped to a minimal 1279 native RTP MIDI stream. 1281 v=0 1282 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 1283 s=Example 1284 t=0 0 1285 m=audio 5004 RTP/AVP 96 1286 c=IN IP4 192.0.2.94 1287 a=rtpmap:96 rtp-midi/44100 1289 The rtpmap attribute line uses the "rtp-midi" media type to specify an 1290 RTP MIDI native stream. The clock rate specified on the rtpmap line (in 1291 the example above, 44100 Hz) sets the scaling for the RTP timestamp 1292 header field (see Section 2.1, and also [RFC3550]). 1294 Note that this document does not specify a default clock rate value for 1295 RTP MIDI. When RTP MIDI is used with SDP, parties MUST use the rtpmap 1296 line to communicate the clock rate. Guidance for selecting the RTP MIDI 1297 clock rate value appears in Section 2.1. 1299 We consider the RTP MIDI stream shown above to be "minimal" because the 1300 session description does not customize the stream with parameters. 1301 Without such customization, a native RTP MIDI stream has these 1302 characteristics: 1304 1. If the stream uses unreliable transport (unicast UDP, multicast 1305 UDP, etc.), the recovery journal system is in use, and the RTP 1306 payload contains both the MIDI command section and the journal 1307 section. If the stream uses reliable transport (such as TCP), 1308 the stream does not use journalling, and the payload contains 1309 only the MIDI command section (Section 2.2). 1311 2. If the stream uses the recovery journal system, the recovery 1312 journal system uses the default sending policy and the default 1313 journal semantics (Section 4). 1315 3. In the MIDI command section of the payload, command timestamps 1316 use the default "comex" semantics (Section 3). 1318 4. The recommended temporal duration ("media time") of an RTP 1319 packet ranges from 0 to 200 ms, and the RTP timestamp 1320 difference between sequential packets in the stream may be 1321 arbitrarily large (Section 2.1). 1323 5. If more than one minimal rtp-midi stream appears in a session, 1324 the MIDI name spaces for these streams are independent: channel 1325 1 in the first stream does not reference the same MIDI channel 1326 as channel 1 in the second stream (see Appendix C.5 for a 1327 discussion of the independence of minimal rtp-midi streams). 1329 6. The rendering method for the stream is not specified. What the 1330 receiver "does" with a minimal native MIDI stream is "out of 1331 scope" of this memo. For example, in content creation 1332 environments, a user may manually configure client software to 1333 render the stream with a specific software package. 1335 As in standard in RTP, RTP sessions managed by SIP are sendrecv by 1336 default (parties send and receive MIDI), and RTP sessions managed by 1337 RTSP are recvonly by default (server sends and client receives). 1339 In sendrecv RTP MIDI sessions for the session description shown above, 1340 the 16 voice channel + systems MIDI name space is unique for each 1341 sender. Thus, in a two-party session, the voice channel 0 sent by one 1342 party is distinct from the voice channel 0 sent by the other party. 1344 This behavior corresponds to what occurs when two MIDI 1.0 DIN devices 1345 are cross-connected with two MIDI cables (one cable routing MIDI Out 1346 from the first device into MIDI In of the second device, a second cable 1347 routing MIDI In from the first device into MIDI Out of the second 1348 device). We define this "association" formally in Section 2.1. 1350 MIDI 1.0 DIN networks may be configured in a "party-line" multicast 1351 topology. For these networks, the MIDI protocol itself provides tools 1352 for addressing specific devices in transactions on a multicast network, 1353 and for device discovery. Thus, apart from providing a 1- to-many 1354 forward path and a many-to-1 reverse path, IETF protocols do not need to 1355 provide any special support for MIDI multicast networking. 1357 6.2. Session Descriptions for mpeg4-generic Streams 1359 An mpeg4-generic [RFC3640] RTP MIDI stream uses an MPEG 4 Audio Object 1360 Type to render MIDI into audio. Three Audio Object Types accept MIDI 1361 input: 1363 o General MIDI (Audio Object Type ID 15), based on the General 1364 MIDI rendering standard [MIDI]. 1366 o Wavetable Synthesis (Audio Object Type ID 14), based on the 1367 Downloadable Sounds Level 2 (DLS 2) rendering standard [DLS2]. 1369 o Main Synthetic (Audio Object Type ID 13), based on Structured 1370 Audio and the programming language SAOL [MPEGSA]. 1372 The primary service of an mpeg4-generic stream is to code Access Units 1373 (AUs). We define the mpeg4-generic RTP MIDI AU as the MIDI payload 1374 shown in Figure 1 of Section 2.1 of this memo: a MIDI command section 1375 optionally followed by a journal section. 1377 Exactly one RTP MIDI AU MUST be mapped to one mpeg4-generic RTP MIDI 1378 packet. The mpeg4-generic options for placing several AUs in an RTP 1379 packet MUST NOT be used with RTP MIDI. The mpeg4-generic options for 1380 fragmenting and interleaving AUs MUST NOT be used with RTP MIDI. The 1381 mpeg4-generic RTP packet payload (Figure 1 in [RFC3640]) MUST contain 1382 empty AU Header and Auxiliary sections. These rules yield mpeg4-generic 1383 packets that are structurally identical to native RTP MIDI packets, an 1384 essential property for the correct operation of the payload format. 1386 The session description that follows defines a unicast UDP RTP session 1387 (via a media ("m=") line) whose sole payload type (96) is mapped to a 1388 minimal mpeg4-generic RTP MIDI stream. This example uses the General 1389 MIDI Audio Object Type under Synthesis Profile @ Level 2. 1391 v=0 1392 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 1393 s=Example 1394 t=0 0 1395 m=audio 5004 RTP/AVP 96 1396 c=IN IP6 2001:DB80::7F2E:172A:1E24 1397 a=rtpmap:96 mpeg4-generic/44100 1398 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 1399 config=7A0A0000001A4D546864000000060000000100604D54726B0000 1400 000600FF2F000 1402 (The a=fmtp line has been wrapped to fit the page to accommodate memo 1403 formatting restrictions; it comprises a single line in SDP.) 1405 The fmtp attribute line codes the four parameters (streamtype, mode, 1406 profile-level-id, and config) that are required in all mpeg4-generic 1407 session descriptions [RFC3640]. For RTP MIDI streams, the streamtype 1408 parameter MUST be set to 5, the "mode" parameter MUST be set to "rtp- 1409 midi", and the "profile-level-id" parameter MUST be set to the MPEG-4 1410 Profile Level for the stream. For the Synthesis Profile, legal profile- 1411 level-id values are 11, 12, and 13, coding low (11), medium (12), or 1412 high (13) decoder computational complexity, as defined by MPEG 1413 conformance tests. 1415 In a minimal RTP MIDI session description, the config value MUST be a 1416 hexadecimal encoding [RFC3640] of the AudioSpecificConfig data block 1417 [MPEGAUDIO] for the stream. AudioSpecificConfig encodes the Audio 1418 Object Type for the stream and also encodes initialization data (SAOL 1419 programs, DLS 2 wave tables, etc.). Standard MIDI Files encoded in 1420 AudioSpecificConfig in a minimal session description MUST be ignored by 1421 the receiver. 1423 Receivers determine the rendering algorithm for the session by 1424 interpreting the first 5 bits of AudioSpecificConfig as an unsigned 1425 integer that codes the Audio Object Type. In our example above, the 1426 leading config string nibbles "7A" yield the Audio Object Type 15 1427 (General MIDI). In Appendix E.4, we derive the config string value in 1428 the session description shown above; the starting point of the 1429 derivation is the MPEG bitstreams defined in [MPEGSA] and [MPEGAUDIO]. 1431 We consider the stream to be "minimal" because the session description 1432 does not customize the stream through the use of parameters, other than 1433 the 4 required mpeg4-generic parameters described above. In Section 1434 6.1, we describe the behavior of a minimal native stream, as a numbered 1435 list of characteristics. Items 1-4 on that list also describe the 1436 minimal mpeg4-generic stream, but items 5 and 6 require restatements, as 1437 listed below: 1439 5. If more than one minimal mpeg4-generic stream appears in 1440 a session, each stream uses an independent instance of the 1441 Audio Object Type coded in the config parameter value. 1443 6. A minimal mpeg4-generic stream encodes the AudioSpecificConfig 1444 as an inline hexadecimal constant. If a session description 1445 is sent over UDP, it may be impossible to transport large 1446 AudioSpecificConfig blocks within the Maximum Transmission Size 1447 (MTU) of the underlying network (for Ethernet, the MTU is 1500 1448 octets). In some cases, the AudioSpecificConfig block may 1449 exceed the maximum size of the UDP packet itself. 1451 The comments in Section 6.1 on SIP and RTSP stream directional defaults, 1452 sendrecv MIDI channel usage, and MIDI 1.0 DIN multicast networks also 1453 apply to mpeg4-generic RTP MIDI sessions. 1455 In sendrecv sessions, each party's session description MUST use 1456 identical values for the mpeg4-generic parameters (including the 1457 required streamtype, mode, profile-level-id, and config parameters). As 1458 a consequence, each party uses an identically configured MPEG 4 Audio 1459 Object Type to render MIDI commands into audio. The preamble to 1460 Appendix C discusses a way to create "virtual sendrecv" sessions that do 1461 not have this restriction. 1463 6.3. Parameters 1465 This section introduces parameters for session configuration for RTP 1466 MIDI streams. In session descriptions, parameters modify the semantics 1467 of a payload type. Parameters are specified on an fmtp attribute line. 1468 See the session description example in Section 6.2 for an example of a 1469 fmtp attribute line. 1471 The parameters add features to the minimal streams described in Sections 1472 6.1-2, and support several types of services: 1474 o Stream subsetting. By default, all MIDI commands that 1475 are legal to appear on a MIDI 1.0 DIN cable may appear 1476 in an RTP MIDI stream. The cm_unused parameter overrides 1477 this default by prohibiting certain commands from appearing 1478 in the stream. The cm_used parameter is used in conjunction 1479 with cm_unused, to simplify the specification of complex 1480 exclusion rules. We describe cm_unused and cm_used in 1481 Appendix C.1. 1483 o Journal customization. The j_sec and j_update parameters 1484 configure the use of the journal section. The ch_default, 1485 ch_never, and ch_anchor parameters configure the semantics 1486 of the recovery journal chapters. These parameters are 1487 described in Appendix C.2 and override the default stream 1488 behaviors 1 and 2, listed in Section 6.1 and referenced in 1489 Section 6.2. 1491 o MIDI command timestamp semantics. The tsmode, octpos, 1492 mperiod, and linerate parameters customize the semantics 1493 of timestamps in the MIDI command section. These parameters 1494 let RTP MIDI accurately encode the implicit time coding of 1495 MIDI 1.0 DIN cables. These parameters are described in 1496 Appendix C.3 and override default stream behavior 3, 1497 listed in Section 6.1 and referenced in Section 6.2 1499 o Media time. The rtp_ptime and rtp_maxptime parameters define 1500 the temporal duration ("media time") of an RTP MIDI packet. 1501 The guardtime parameter sets the minimum sending rate of stream 1502 packets. These parameters are described in Appendix C.4 1503 and override default stream behavior 4, listed in Section 6.1 1504 and referenced in Section 6.2. 1506 o Stream description. The musicport parameter labels the 1507 MIDI name space of RTP streams in a multimedia session. 1508 Musicport is described in Appendix C.5. The musicport 1509 parameter overrides default stream behavior 5, in Sections 1510 6.1 and 6.2. 1512 o MIDI rendering. Several parameters specify the MIDI 1513 rendering method of a stream. These parameters are described 1514 in Appendix C.6 and override default stream behavior 6, in 1515 Sections 6.1 and 6.2. 1517 In Appendix C.7, we specify interoperability guidelines for two RTP MIDI 1518 application areas: content-streaming using RTSP (Appendix C.7.1) and 1519 network musical performance using SIP (Appendix C.7.2). 1521 7. Extensibility 1523 The payload format defined in this memo exclusively encodes all commands 1524 that may legally appear on a MIDI 1.0 DIN cable. 1526 Many worthy uses of MIDI over RTP do not fall within the narrow scope of 1527 the payload format. For example, the payload format does not support 1528 the direct transport of Standard MIDI File (SMF) meta-event and metric 1529 timing data. As a second example, the payload format does not define 1530 transport tools for user-defined commands (apart from tools to support 1531 System Exclusive commands [MIDI]). 1533 The payload format does not provide an extension mechanism to support 1534 new features of this nature, by design. Instead, we encourage the 1535 development of new payload formats for specialized musical applications. 1536 The IETF session management tools [RFC3264] [RFC2326] support codec 1537 negotiation, to facilitate the use of new payload formats in a backward- 1538 compatible way. 1540 However, the payload format does provide several extensibility tools, 1541 which we list below: 1543 o Journalling. As described in Appendix C.2, new token 1544 values for the j_sec and j_update parameters may 1545 be defined in IETF standards-track documents. This 1546 mechanism supports the design of new journal formats 1547 and the definition of new journal sending policies. 1549 o Rendering. The payload format may be extended to support 1550 new MIDI renderers (Appendix C.6.2). Certain general aspects 1551 of the RTP MIDI rendering process may also be extended, via 1552 the definition of new token values for the render (Appendix C.6) 1553 and smf_info (Appendix C.6.4.1) parameters. 1555 o Undefined commands. [MIDI] reserves 4 MIDI System commands 1556 for future use (0xF4, 0xF5, 0xF9, 0xFD). If updates 1557 to [MIDI] define the reserved commands, IETF standards-track 1558 documents may be defined to provide resiliency support for 1559 the commands. Opaque LEGAL fields appear in System Chapter 1560 D for this purpose (Appendix B.1.1). 1562 A final form of extensibility involves the inclusion of the payload 1563 format in framework documents. Framework documents describe how to 1564 combine protocols to form a platform for interoperable applications. 1565 For example, a stage and studio framework might define how to use SIP 1566 [RFC3261], RTSP [RFC2326], SDP [RFC4566], and RTP [RFC3550] to support 1567 media networking for professional audio equipment and electronic musical 1568 instruments. 1570 8. Congestion Control 1572 The RTP congestion control requirements defined in [RFC3550] apply to 1573 RTP MIDI sessions, and implementors should carefully read the congestion 1574 control section in [RFC3550]. As noted in [RFC3550], all transport 1575 protocols used on the Internet need to address congestion control in 1576 some way, and RTP is not an exception. 1578 In addition, the congestion control requirements defined in [RFC3551] 1579 applies to RTP MIDI sessions run under applicable profiles. The basic 1580 congestion control requirement defined in [RFC3551] is that RTP sessions 1581 that use UDP transport should monitor packet loss (via RTCP or other 1582 means) to ensure that the RTP stream competes fairly with TCP flows that 1583 share the network. 1585 Finally, RTP MIDI has congestion control issues that are unique for an 1586 audio RTP payload format. In applications such as network musical 1587 performance [NMP], the packet rate is linked to the gestural rate of a 1588 human performer. Senders MUST monitor the MIDI command source for 1589 patterns that result in excessive packet rates and take actions during 1590 RTP transcoding to reduce the RTP packet rate. [RFC4696] offers 1591 implementation guidance on this issue. 1593 9. Security Considerations 1595 Implementors should carefully read the Security Considerations sections 1596 of the RTP [RFC3550], AVP [RFC3551], and other RTP profile documents, as 1597 the issues discussed in these sections directly apply to RTP MIDI 1598 streams. Implementors should also review the Secure Real-time Transport 1599 Protocol (SRTP, [RFC3711]), an RTP profile that addresses the security 1600 issues discussed in [RFC3550] and [RFC3551]. 1602 Here, we discuss security issues that are unique to the RTP MIDI payload 1603 format. 1605 When using RTP MIDI, authentication of incoming RTP and RTCP packets is 1606 RECOMMENDED. Per-packet authentication may be provided by SRTP or by 1607 other means. Without the use of authentication, attackers could forge 1608 MIDI commands into an ongoing stream, damaging speakers and eardrums. 1609 An attacker could also craft RTP and RTCP packets to exploit known bugs 1610 in the client and take effective control of a client machine. 1612 Session management tools (such as SIP [RFC3261]) SHOULD use 1613 authentication during the transport of all session descriptions 1614 containing RTP MIDI media streams. For SIP, the Security Considerations 1615 section in [RFC3261] provides an overview of possible authentication 1616 mechanisms. RTP MIDI session descriptions should use authentication 1617 because the session descriptions may code initialization data using the 1618 parameters described in Appendix C. If an attacker inserts bogus 1619 initialization data into a session description, he can corrupt the 1620 session or forge an client attack. 1622 Session descriptions may also code renderer initialization data by 1623 reference, via the url (Appendix C.6.3) and smf_url (Appendix C.6.4.2) 1624 parameters. If the coded URL is spoofed, both session and client are 1625 open to attack, even if the session description itself is authenticated. 1626 Therefore, URLs specified in url and smf_url parameters SHOULD use 1627 [RFC2818]. 1629 Section 2.1 allows streams sent by a party in two RTP sessions to have 1630 the same SSRC value and the same RTP timestamp initialization value, 1631 under certain circumstances. Normally, these values are randomly chosen 1632 for each stream in a session, to make plaintext guessing harder to do if 1633 the payloads are encrypted. Thus, Section 2.1 weakens this aspect of 1634 RTP security. 1636 10. Acknowledgements 1638 We thank the networking, media compression, and computer music community 1639 members who have commented or contributed to the effort, including Kurt 1640 B, Cynthia Bruyns, Steve Casner, Paul Davis, Robin Davies, Joanne Dow, 1641 Tobias Erichsen, Nicolas Falquet, Dominique Fober, Philippe Gentric, 1642 Michael Godfrey, Chris Grigg, Todd Hager, Alfred Hoenes, Michel Jullian, 1643 Phil Kerr, Young-Kwon Lim, Jessica Little, Jan van der Meer, Colin 1644 Perkins, Charlie Richmond, Herbie Robinson, Larry Rowe, Eric Scheirer, 1645 Dave Singer, Martijn Sipkema, William Stewart, Kent Terry, Magnus 1646 Westerlund, Tom White, Jim Wright, Doug Wyatt, and Giorgio Zoia. We 1647 also thank the members of the San Francisco Bay Area music and audio 1648 community for creating the context for the work, including Don Buchla, 1649 Chris Chafe, Richard Duda, Dan Ellis, Adrian Freed, Ben Gold, Jaron 1650 Lanier, Roger Linn, Richard Lyon, Dana Massie, Max Mathews, Keith 1651 McMillen, Carver Mead, Nelson Morgan, Tom Oberheim, Malcolm Slaney, Dave 1652 Smith, Julius Smith, David Wessel, and Matt Wright. 1654 11. IANA Considerations 1656 This section makes a series of requests to IANA. The IANA has completed 1657 registration/assignments of the below requests. 1659 The sub-sections that follow hold the actual, detailed requests. All 1660 registrations in this section are in the IETF tree and follow the rules 1661 of [RFC4288] and [RFC3555], as appropriate. 1663 In Section 11.1, we request the registration of a new media type: 1664 "audio/rtp-midi". Paired with this request is a request for a 1665 repository for new values for several parameters associated with 1666 "audio/rtp-midi". We request this repository in Section 11.1.1. 1668 In Section 11.2, we request the registration of a new value ("rtp- 1669 midi") for the "mode" parameter of the "mpeg4-generic" media type. The 1670 "mpeg4-generic" media type is defined in [RFC3640], and [RFC3640] 1671 defines a repository for the "mode" parameter. However, we believe we 1672 are the first to request the registration of a "mode" value, so we 1673 believe the registry for "mode" has not yet been created by IANA. 1675 Paired with our "mode" parameter value request for "mpeg4-generic" is a 1676 request for a repository for new values for several parameters we have 1677 defined for use with the "rtp-midi" mode value. We request this 1678 repository in Section 11.2.1. 1680 In Section 11.3, we request the registration of a new media type: 1681 "audio/asc". No repository request is associated with this request. 1683 11.1. rtp-midi Media Type Registration 1685 This section requests the registration of the "rtp-midi" subtype for the 1686 "audio" media type. We request the registration of the parameters 1687 listed in the "optional parameters" section below (both the "non- 1688 extensible parameters" and the "extensible parameters" lists). We also 1689 request the creation of repositories for the "extensible parameters"; 1690 the details of this request appear in Section 11.1.1, below. 1692 Media type name: 1694 audio 1696 Subtype name: 1698 rtp-midi 1700 Required parameters: 1702 rate: The RTP timestamp clock rate. See Sections 2.1 and 6.1 1703 for usage details. 1705 Optional parameters: 1707 Non-extensible parameters: 1709 ch_anchor: See Appendix C.2.3 for usage details. 1710 ch_default: See Appendix C.2.3 for usage details. 1711 ch_never: See Appendix C.2.3 for usage details. 1712 cm_unused: See Appendix C.1 for usage details. 1713 cm_used: See Appendix C.1 for usage details. 1714 chanmask: See Appendix C.6.4.3 for usage details. 1715 cid: See Appendix C.6.3 for usage details. 1716 guardtime: See Appendix C.4.2 for usage details. 1717 inline: See Appendix C.6.3 for usage details. 1718 linerate: See Appendix C.3 for usage details. 1719 mperiod: See Appendix C.3 for usage details. 1720 multimode: See Appendix C.6.1 for usage details. 1721 musicport: See Appendix C.5 for usage details. 1722 octpos: See Appendix C.3 for usage details. 1723 rinit: See Appendix C.6.3 for usage details. 1724 rtp_maxptime: See Appendix C.4.1 for usage details. 1725 rtp_ptime: See Appendix C.4.1 for usage details. 1727 smf_cid: See Appendix C.6.4.2 for usage details. 1728 smf_inline: See Appendix C.6.4.2 for usage details. 1729 smf_url: See Appendix C.6.4.2 for usage details. 1730 tsmode: See Appendix C.3 for usage details. 1731 url: See Appendix C.6.3 for usage details. 1733 Extensible parameters: 1735 j_sec: See Appendix C.2.1 for usage details. See 1736 Section 11.1.1 for repository details. 1737 j_update: See Appendix C.2.2 for usage details. See 1738 Section 11.1.1 for repository details. 1739 render: See Appendix C.6 for usage details. See 1740 Section 11.1.1 for repository details. 1741 subrender: See Appendix C.6.2 for usage details. See 1742 Section 11.1.1 for repository details. 1743 smf_info: See Appendix C.6.4.1 for usage details. See 1744 Section 11.1.1 for repository details. 1746 Encoding considerations: 1748 The format for this type is framed and binary. 1750 Restrictions on usage: 1752 This type is only defined for real-time transfers of MIDI 1753 streams via RTP. Stored-file semantics for rtp-midi may 1754 be defined in the future. 1756 Security considerations: 1758 See Section 9 of this memo. 1760 Interoperability considerations: 1762 None. 1764 Published specification: 1766 This memo and [MIDI] serve as the normative specification. In 1767 addition, references [NMP], [GRAME], and [RFC4696] provide 1768 non-normative implementation guidance. 1770 Applications that use this media type: 1772 Audio content-creation hardware, such as MIDI controller piano 1773 keyboards and MIDI audio synthesizers. Audio content-creation 1774 software, such as music sequencers, digital audio workstations, 1775 and soft synthesizers. Computer operating systems, for network 1776 support of MIDI Application Programmer Interfaces. Content 1777 distribution servers and terminals may use this media type for 1778 low bit-rate music coding. 1780 Additional information: 1782 None. 1784 Person & email address to contact for further information: 1786 John Lazzaro 1788 Intended usage: 1790 COMMON. 1792 Author: 1794 John Lazzaro 1796 Change controller: 1798 IETF Audio/Video Transport Working Group delegated 1799 from the IESG. 1801 11.1.1. Repository Request for "audio/rtp-midi" 1803 For the "rtp-midi" subtype, we request the creation of repositories for 1804 extensions to the following parameters (which are those listed as 1805 "extensible parameters" in Section 11.1). 1807 j_sec: 1809 Registrations for this repository may only occur 1810 via an IETF standards-track document. Appendix C.2.1 1811 of this memo describes appropriate registrations for this 1812 repository. 1814 Initial values for this repository appear below: 1816 "none": Defined in Appendix C.2.1 of this memo. 1817 "recj": Defined in Appendix C.2.1 of this memo. 1819 j_update: 1821 Registrations for this repository may only occur 1822 via an IETF standards-track document. Appendix C.2.2 1823 of this memo describes appropriate registrations for this 1824 repository. 1826 Initial values for this repository appear below: 1828 "anchor": Defined in Appendix C.2.2 of this memo. 1829 "open-loop": Defined in Appendix C.2.2 of this memo. 1830 "closed-loop": Defined in Appendix C.2.2 of this memo. 1832 render: 1834 Registrations for this repository MUST include a 1835 specification of the usage of the proposed value. 1836 See text in the preamble of Appendix C.6 for details 1837 (the paragraph that begins "Other render token ..."). 1839 Initial values for this repository appear below: 1841 "unknown": Defined in Appendix C.6 of this memo. 1842 "synthetic": Defined in Appendix C.6 of this memo. 1843 "api": Defined in Appendix C.6 of this memo. 1844 "null": Defined in Appendix C.6 of this memo. 1846 subrender: 1848 Registrations for this repository MUST include a 1849 specification of the usage of the proposed value. 1850 See text Appendix C.6.2 for details (the paragraph 1851 that begins "Other subrender token ..."). 1853 Initial values for this repository appear below: 1855 "default": Defined in Appendix C.6.2 of this memo. 1857 smf_info: 1859 Registrations for this repository MUST include a 1860 specification of the usage of the proposed value. 1861 See text in Appendix C.6.4.1 for details (the 1862 paragraph that begins "Other smf_info token ..."). 1864 Initial values for this repository appear below: 1866 "ignore": Defined in Appendix C.6.4.1 of this memo. 1867 "sdp_start": Defined in Appendix C.6.4.1 of this memo. 1868 "identity": Defined in Appendix C.6.4.1 of this memo. 1870 11.2. mpeg4-generic Media Type Registration 1872 This section requests the registration of the "rtp-midi" value for the 1873 "mode" parameter of the "mpeg4-generic" media type. The "mpeg4- 1874 generic" media type is defined in [RFC3640], and [RFC3640] defines a 1875 repository for the "mode" parameter. We are registering mode rtp- midi 1876 to support the MPEG Audio codecs [MPEGSA] that use MIDI. 1878 In conjunction with this registration request, we request the 1879 registration of the parameters listed in the "optional parameters" 1880 section below (both the "non-extensible parameters" and the "extensible 1881 parameters" lists). We also request the creation of repositories for 1882 the "extensible parameters"; the details of this request appear in 1883 Appendix 11.2.1, below. 1885 Media type name: 1887 audio 1889 Subtype name: 1891 mpeg4-generic 1893 Required parameters: 1895 The "mode" parameter is required by [RFC3640]. [RFC3640] requests 1896 a repository for "mode", so that new values for mode 1897 may be added. We request that the value "rtp-midi" be 1898 added to the "mode" repository. 1900 In mode rtp-midi, the mpeg4-generic parameter rate is 1901 a required parameter. Rate specifies the RTP timestamp 1902 clock rate. See Sections 2.1 and 6.2 for usage details 1903 of rate in mode rtp-midi. 1905 Optional parameters: 1907 We request registration of the following parameters 1908 for use in mode rtp-midi for mpeg4-generic. 1910 Non-extensible parameters: 1912 ch_anchor: See Appendix C.2.3 for usage details. 1913 ch_default: See Appendix C.2.3 for usage details. 1914 ch_never: See Appendix C.2.3 for usage details. 1915 cm_unused: See Appendix C.1 for usage details. 1916 cm_used: See Appendix C.1 for usage details. 1917 chanmask: See Appendix C.6.4.3 for usage details. 1918 cid: See Appendix C.6.3 for usage details. 1919 guardtime: See Appendix C.4.2 for usage details. 1920 inline: See Appendix C.6.3 for usage details. 1921 linerate: See Appendix C.3 for usage details. 1922 mperiod: See Appendix C.3 for usage details. 1923 multimode: See Appendix C.6.1 for usage details. 1924 musicport: See Appendix C.5 for usage details. 1925 octpos: See Appendix C.3 for usage details. 1926 rinit: See Appendix C.6.3 for usage details. 1927 rtp_maxptime: See Appendix C.4.1 for usage details. 1928 rtp_ptime: See Appendix C.4.1 for usage details. 1929 smf_cid: See Appendix C.6.4.2 for usage details. 1930 smf_inline: See Appendix C.6.4.2 for usage details. 1931 smf_url: See Appendix C.6.4.2 for usage details. 1932 tsmode: See Appendix C.3 for usage details. 1933 url: See Appendix C.6.3 for usage details. 1935 Extensible parameters: 1937 j_sec: See Appendix C.2.1 for usage details. See 1938 Section 11.2.1 for repository details. 1939 j_update: See Appendix C.2.2 for usage details. See 1940 Section 11.2.1 for repository details. 1941 render: See Appendix C.6 for usage details. See 1942 Section 11.2.1 for repository details. 1943 subrender: See Appendix C.6.2 for usage details. See 1944 Section 11.2.1 for repository details. 1945 smf_info: See Appendix C.6.4.1 for usage details. See 1946 Section 11.2.1 for repository details. 1948 Encoding considerations: 1950 The format for this type is framed and binary. 1952 Restrictions on usage: 1954 Only defined for real-time transfers of audio/mpeg4-generic 1955 RTP streams with mode=rtp-midi. 1957 Security considerations: 1959 See Section 9 of this memo. 1961 Interoperability considerations: 1963 Except for the marker bit (Section 2.1), the packet formats 1964 for audio/rtp-midi and audio/mpeg4-generic (mode rtp-midi) 1965 are identical. The formats differ in use: audio/mpeg4-generic 1966 is for MPEG work, and audio/rtp-midi is for all other work. 1968 Published specification: 1970 This memo, [MIDI], and [MPEGSA] are the normative references. 1971 In addition, references [NMP], [GRAME], and [RFC4696] provide 1972 non-normative implementation guidance. 1974 Applications that use this media type: 1976 MPEG 4 servers and terminals that support [MPEGSA]. 1978 Additional information: 1980 None. 1982 Person & email address to contact for further information: 1984 John Lazzaro 1986 Intended usage: 1988 COMMON. 1990 Author: 1992 John Lazzaro 1994 Change controller: 1996 IETF Audio/Video Transport Working Group delegated 1997 from the IESG. 1999 11.2.1. Repository Request for Mode rtp-midi for mpeg4-generic 2001 For mode rtp-midi of the mpeg4-generic subtype, we request the creation 2002 of repositories for extensions to the following parameters (which are 2003 those listed as "extensible parameters" in Section 11.2). 2005 j_sec: 2007 Registrations for this repository may only occur 2008 via an IETF standards-track document. Appendix C.2.1 2009 of this memo describes appropriate registrations for this 2010 repository. 2012 Initial values for this repository appear below: 2014 "none": Defined in Appendix C.2.1 of this memo. 2015 "recj": Defined in Appendix C.2.1 of this memo. 2017 j_update: 2019 Registrations for this repository may only occur 2020 via an IETF standards-track document. Appendix C.2.2 2021 of this memo describes appropriate registrations for this 2022 repository. 2024 Initial values for this repository appear below: 2026 "anchor": Defined in Appendix C.2.2 of this memo. 2027 "open-loop": Defined in Appendix C.2.2 of this memo. 2028 "closed-loop": Defined in Appendix C.2.2 of this memo. 2030 render: 2032 Registrations for this repository MUST include a 2033 specification of the usage of the proposed value. 2034 See text in the preamble of Appendix C.6 for details 2035 (the paragraph that begins "Other render token ..."). 2037 Initial values for this repository appear below: 2039 "unknown": Defined in Appendix C.6 of this memo. 2040 "synthetic": Defined in Appendix C.6 of this memo. 2041 "null": Defined in Appendix C.6 of this memo. 2043 subrender: 2045 Registrations for this repository MUST include a 2046 specification of the usage of the proposed value. 2047 See text in Appendix C.6.2 for details (the paragraph 2048 that begins "Other subrender token ..." and 2049 subsequent paragraphs). Note that the text in 2050 Appendix C.6.2 contains restrictions on subrender 2051 registrations for mpeg4-generic ("Registrations 2052 for mpeg4-generic subrender values ..."). 2054 Initial values for this repository appear below: 2056 "default": Defined in Appendix C.6.2 of this memo. 2058 smf_info: 2060 Registrations for this repository MUST include a 2061 specification of the usage of the proposed value. 2062 See text in Appendix C.6.4.1 for details (the 2063 paragraph that begins "Other smf_info token ..."). 2065 Initial values for this repository appear below: 2067 "ignore": Defined in Appendix C.6.4.1 of this memo. 2068 "sdp_start": Defined in Appendix C.6.4.1 of this memo. 2069 "identity": Defined in Appendix C.6.4.1 of this memo. 2071 11.3. asc Media Type Registration 2073 This section registers "asc" as a subtype for the "audio" media type. 2074 We register this subtype to support the remote transfer of the "config" 2075 parameter of the mpeg4-generic media type [RFC3640] when it is used with 2076 mpeg4-generic mode rtp-midi (registered in Appendix 11.2 above). We 2077 explain the mechanics of using "audio/asc" to set the config parameter 2078 in Section 6.2 and Appendix C.6.5 of this document. 2080 Note that this registration is a new subtype registration and is not an 2081 addition to a repository defined by MPEG-related memos (such as 2082 [RFC3640]). Also note that this request for "audio/asc" does not 2083 register parameters, and does not request the creation of a repository. 2085 Media type name: 2087 audio 2089 Subtype name: 2091 asc 2093 Required parameters: 2095 None. 2097 Optional parameters: 2099 None. 2101 Encoding considerations: 2103 The native form of the data object is binary data, 2104 zero-padded to an octet boundary. 2106 Restrictions on usage: 2108 This type is only defined for data object (stored file) 2109 transfer. The most common transports for the type are 2110 HTTP and SMTP. 2112 Security considerations: 2114 See Section 9 of this memo. 2116 Interoperability considerations: 2118 None. 2120 Published specification: 2122 The audio/asc data object is the AudioSpecificConfig 2123 binary data structure, which is normatively defined in [MPEGAUDIO]. 2125 Applications that use this media type: 2127 MPEG 4 Audio servers and terminals that support 2128 audio/mpeg4-generic RTP streams for mode rtp-midi. 2130 Additional information: 2132 None. 2134 Person & email address to contact for further information: 2136 John Lazzaro 2138 Intended usage: 2140 COMMON. 2142 Author: 2144 John Lazzaro 2146 Change controller: 2148 IETF Audio/Video Transport Working Group delegated 2149 from the IESG. 2151 A. The Recovery Journal Channel Chapters 2153 A.1. Recovery Journal Definitions 2155 This appendix defines the terminology and the coding idioms that are 2156 used in the recovery journal bitfield descriptions in Section 5 (journal 2157 header structure), Appendices A.2 to A.9 (channel journal chapters) and 2158 Appendices B.1 to B.5 (system journal chapters). 2160 We assume that the recovery journal resides in the journal section of an 2161 RTP packet with sequence number I ("packet I") and that the Checkpoint 2162 Packet Seqnum field in the top-level recovery journal header refers to a 2163 previous packet with sequence number C (an exception is the self- 2164 referential C = I case). Unless stated otherwise, algorithms are 2165 assumed to use modulo 2^16 arithmetic for calculations on 16-bit 2166 sequence numbers and modulo 2^32 arithmetic for calculations on 32-bit 2167 extended sequence numbers. 2169 Several bitfield coding idioms appear throughout the recovery journal 2170 system, with consistent semantics. Most recovery journal elements begin 2171 with an "S" (Single-packet loss) bit. S bits are designed to help 2172 receivers efficiently parse through the recovery journal hierarchy in 2173 the common case of the loss of a single packet. 2175 As a rule, S bits MUST be set to 1. However, an exception applies if a 2176 recovery journal element in packet I encodes data about a command stored 2177 in the MIDI command section of packet I - 1. In this case, the S bit of 2178 the recovery journal element MUST be set to 0. If a recovery journal 2179 element has its S bit set to 0, all higher-level recovery journal 2180 elements that contain it MUST also have S bits that are set to 0, 2181 including the top-level recovery journal header. 2183 Other consistent bitfield coding idioms are described below: 2185 o R flag bit. R flag bits are reserved for future use. Senders 2186 MUST set R bits to 0. Receivers MUST ignore R bit values. 2188 o LENGTH field. All fields named LENGTH (as distinct from LEN) 2189 code the number of octets in the structure that contains it, 2190 including the header it resides in and all hierarchical levels 2191 below it. If a structure contains a LENGTH field, a receiver 2192 MUST use the LENGTH field value to advance past the structure 2193 during parsing, rather than use knowledge about the internal 2194 format of the structure. 2196 We now define normative terms used to describe recovery journal 2197 semantics. 2199 o Checkpoint history. The checkpoint history of a recovery journal 2200 is the concatenation of the MIDI command sections of packets C 2201 through I - 1. The final command in the MIDI command section for 2202 packet I - 1 is considered the most recent command; the first 2203 command in the MIDI command section for packet C is the oldest 2204 command. If command X is less recent than command Y, X is 2205 considered to be "before Y". A checkpoint history with no 2206 commands is considered to be empty. The checkpoint history 2207 never contains the MIDI command section of packet I (the 2208 packet containing the recovery journal), so if C == I, the 2209 checkpoint history is empty by definition. 2211 o Session history. The session history of a recovery journal is 2212 the concatenation of MIDI command sections from the first 2213 packet of the session up to packet I - 1. The definitions of 2214 command recency and history emptiness follow those in the 2215 checkpoint history. The session history never contains the 2216 MIDI command section of packet I, and so the session history of 2217 the first packet in the session is empty by definition. 2219 o Finished/unfinished commands. If all octets of a MIDI command 2220 appear in the session history, the command is defined as being 2221 finished. If some but not all octets of a command appear 2222 in the session history, the command is defined as being unfinished. 2223 Unfinished commands occur if segments of a SysEx command appear 2224 in several RTP packets. For example, if a SysEx command is coded 2225 as 3 segments, with segment 1 in packet K, segment 2 in packet 2226 K + 1, and segment 3 in packet K + 2, the session histories for 2227 packets K + 1 and K + 2 contain unfinished versions of the command. 2228 A session history contains a finished version of a cancelled SysEx 2229 command if the history contains the cancel sublist for the command. 2231 o Reset State commands. Reset State (RS) commands reset 2232 renderers to an initialized "powerup" condition. The 2233 RS commands are: System Reset (0xFF), General MIDI System Enable 2234 (0xF0 0x7E 0xcc 0x09 0x01 0xF7), General MIDI 2 System Enable 2235 (0xF0 0x7E 0xcc 0x09 0x03 0xF7), General MIDI System Disable 2236 (0xF0 0x7E 0xcc 0x09 0x00 0xF7), Turn DLS On (0xF0 0x7E 0xcc 0x0A 2237 0x01 0xF7), and Turn DLS Off (0xF0 0x7E 0xcc 0x0A 0x02 0xF7). 2238 Registrations of subrender parameter token values (Appendix C.6.2) 2239 and IETF standards-track documents MAY specify additional 2240 RS commands. 2242 o Active commands. Active command are MIDI commands that do not 2243 appear before a Reset State command in the session history. 2245 o N-active commands. N-active commands are MIDI commands that do 2246 not appear before one of the following commands in the session 2247 history: MIDI Control Change numbers 123-127 (numbers with All 2248 Notes Off semantics) or 120 (All Sound Off), and any Reset 2249 State command. 2251 o C-active commands. C-active commands are MIDI commands that do 2252 not appear before one of the following commands in the session 2253 history: MIDI Control Change number 121 (Reset All Controllers) 2254 and any Reset State command. 2256 o Oldest-first ordering rule. Several recovery journal chapters 2257 contain a list of elements, where each element is associated 2258 with a MIDI command that appears in the session history. In 2259 most cases, the chapter definition requires that list elements 2260 be ordered in accordance with the "oldest-first ordering rule". 2261 Below, we normatively define this rule: 2263 Elements associated with the most recent command in the session 2264 history coded in the list MUST appear at the end of the list. 2266 Elements associated with the oldest command in the session 2267 history coded in the list MUST appear at the start of the list. 2269 All other list elements MUST be arranged with respect to these 2270 boundary elements, to produce a list ordering that strictly 2271 reflects the relative session history recency of the commands 2272 coded by the elements in the list. 2274 o Parameter system. A MIDI feature that provides two sets of 2275 16,384 parameters to expand the 0-127 controller number space. 2276 The Registered Parameter Names (RPN) system and the Non-Registered 2277 Parameter Names (NRPN) system each provides 16,384 parameters. 2279 o Parameter system transaction. The value of RPNs and NRPNs are 2280 changed by a series of Control Change commands that form a 2281 parameter system transaction. A canonical transaction begins 2282 with two Control Change commands to set the parameter number 2283 (controller numbers 99 and 98 for NRPNs, controller numbers 101 2284 and 100 for RPNs). The transaction continues with an arbitrary 2285 number of Data Entry (controller numbers 6 and 38), Data Increment 2286 (controller number 96), and Data Decrement (controller number 2287 97) Control Change commands to set the parameter value. The 2288 transaction ends with a second pair of (99, 98) or (101, 100) 2289 Control Change commands that specify the null parameter (MSB 2290 value 0x7F, LSB value 0x7F). 2292 Several variants of the canonical transaction sequence are 2293 possible. Most commonly, the terminal pair of (99, 98) or 2294 (101, 100) Control Change commands may specify a parameter 2295 other than the null parameter. In this case, the command 2296 pair terminates the first transaction and starts a second 2297 transaction. The command pair is considered to be a part 2298 of both transactions. This variant is legal and recommended 2299 in [MIDI]. We refer to this variant as a "type 1 variant". 2301 Less commonly, the MSB (99 or 101) or LSB (98 or 100) command 2302 of a (99, 98) or (101, 100) Control Change pair may be omitted. 2304 If the MSB command is omitted, the transaction uses the MSB value 2305 of the most recent C-active Control Change command for controller 2306 number 99 or 101 that appears in the session history. We refer to 2307 this variant as a "type 2 variant". 2309 If the LSB command is omitted, the LSB value 0x00 is assumed. We 2310 refer to this variant as a "type 3 variant". The type 2 and type 3 2311 variants are defined as legal, but are not recommended, in [MIDI]. 2313 System real-time commands may appear at any point during 2314 a transaction (even between octets of individual commands 2315 in the transaction). More generally, [MIDI] does not forbid 2316 the appearance of unrelated MIDI commands during an open 2317 transaction. As a rule, these commands are considered to 2318 be "outside" the transaction and do not affect the status 2319 of the transaction in any way. Exceptions to this rule are 2320 commands whose semantics act to terminate transactions: 2321 Reset State commands, and Control Change (0xB) for controller 2322 number 121 (Reset All Controllers) [RP015]. 2324 o Initiated parameter system transaction. A canonical parameter 2325 system transaction whose (99, 98) or (101, 100) initial Control 2326 Change command pair appears in the session history is considered 2327 to be an initiated parameter system transaction. This definition 2328 also holds for type 1 variants. For type 2 variants (dropped MSB), 2329 a transaction whose initial LSB Control Change command appears in 2330 the session history is an initiated transaction. For type 3 2331 variants (dropped LSB), a transaction is considered to be 2332 initiated if at least one transaction command follows the initial 2333 MSB (99 or 101) Control Change command in the session history. 2334 The completion of a transaction does not nullify its "initiated" 2335 status. 2337 o Session history reference counts. Several recovery journal 2338 chapters include a reference count field, which codes the 2339 total number of commands of a type that appear in the session 2340 history. Examples include the Reset and Tune Request command 2341 logs (Chapter D, Appendix B.1) and the Active Sense command 2342 (Chapter V, Appendix B.2). Upon the detection of a loss event, 2343 reference count fields let a receiver deduce if any instances of 2344 the command have been lost, by comparing the journal reference 2345 count with its own reference count. Thus, a reference count 2346 field makes sense, even for command types in which knowing the 2347 NUMBER of lost commands is irrelevant (as is true with all of 2348 the example commands mentioned above). 2350 The chapter definitions in Appendices A.2 to A.9 and B.1 to B.5 reflect 2351 the default recovery journal behavior. The ch_default, ch_never, and 2352 ch_anchor parameters modify these definitions, as described in Appendix 2353 C.2.3. 2355 The chapter definitions specify if data MUST be present in the journal. 2356 Senders MAY also include non-required data in the journal. This 2357 optional data MUST comply with the normative chapter definition. For 2358 example, if a chapter definition states that a field codes data from the 2359 most recent active command in the session history, the sender MUST NOT 2360 code inactive commands or older commands in the field. 2362 Finally, we note that a channel journal only encodes information about 2363 MIDI commands appearing on the MIDI channel the journal protects. All 2364 references to MIDI commands in Appendices A.2 to A.9 should be read as 2365 "MIDI commands appearing on this channel." 2366 A.2. Chapter P: MIDI Program Change 2368 A channel journal MUST contain Chapter P if an active Program Change 2369 (0xC) command appears in the checkpoint history. Figure A.2.1 shows the 2370 format for Chapter P. 2372 0 1 2 2373 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 2374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2375 |S| PROGRAM |B| BANK-MSB |X| BANK-LSB | 2376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2378 Figure A.2.1 -- Chapter P format 2380 The chapter has a fixed size of 24 bits. The PROGRAM field indicates 2381 the data value of the most recent active Program Change command in the 2382 session history. By default, the B, BANK-MSB, X, and BANK-LSB fields 2383 MUST be set to 0. Below, we define exceptions to this default 2384 condition. 2386 If an active Control Change (0xB) command for controller number 0 (Bank 2387 Select MSB) appears before the Program Change command in the session 2388 history, the B bit MUST be set to 1, and the BANK-MSB field MUST code 2389 the data value of the Control Change command. 2391 If B is set to 1, the BANK-LSB field MUST code the data value of the 2392 most recent Control Change command for controller number 32 (Bank Select 2393 LSB) that preceded the Program Change command coded in the PROGRAM field 2394 and followed the Control Change command coded in the BANK-MSB field. If 2395 no such Control Change command exists, the BANK-LSB field MUST be set to 2396 0. 2398 If B is set to 1, and if a Control Change command for controller number 2399 121 (Reset All Controllers) appears in the MIDI stream between the 2400 Control Change command coded by the BANK-MSB field and the Program 2401 Change command coded by the PROGRAM field, the X bit MUST be set to 1. 2403 Note that [RP015] specifies that Reset All Controllers does not reset 2404 the values of controller numbers 0 (Bank Select MSB) and 32 (Bank Select 2405 LSB). Thus, the X bit does not effect how receivers will use the BANK- 2406 LSB and BANK-MSB values when recovering from a lost Program Change 2407 command. The X bit serves to aid recovery in MIDI applications where 2408 controller numbers 0 and 32 are used in a non-standard way. 2410 A.3. Chapter C: MIDI Control Change 2412 Figure A.3.1 shows the format for Chapter C. 2414 0 1 2 3 2415 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 2416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2417 |S| LEN |S| NUMBER |A| VALUE/ALT |S| NUMBER | 2418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2419 |A| VALUE/ALT | .... | 2420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2422 Figure A.3.1 -- Chapter C format 2424 The chapter consists of a 1-octet header, followed by a variable length 2425 list of 2-octet controller logs. The list MUST contain at least one 2426 controller log. The 7-bit LEN field codes the number of controller logs 2427 in the list, minus one. We define the semantics of the controller log 2428 fields in Appendix A.3.2. 2430 A channel journal MUST contain Chapter C if the rules defined in this 2431 appendix require that one or more controller logs appear in the list. 2433 A.3.1. Log Inclusion Rules 2435 A controller log encodes information about a particular Control Change 2436 command in the session history. 2438 In the default use of the payload format, list logs MUST encode 2439 information about the most recent active command in the session history 2440 for a controller number. Logs encoding earlier commands MUST NOT appear 2441 in the list. 2443 Also, as a rule, the list MUST contain a log for the most recent active 2444 command for a controller number that appears in the checkpoint history. 2445 Below, we define exceptions to this rule: 2447 o MIDI streams may transmit 14-bit controller values using paired 2448 Most Significant Byte (MSB, controller numbers 0-31, 99, 101) and 2449 Least Significant Byte (LSB, controller numbers 32-63, 98, 100) 2450 Control Change commands [MIDI]. 2452 If the most recent active Control Change command in the session 2453 history for a 14-bit controller pair uses the MSB number, Chapter 2454 C MAY omit the controller log for the most recent active Control 2455 Change command for the associated LSB number, as the command 2456 ordering makes this LSB value irrelevant. However, this exception 2457 MUST NOT be applied if the sender is not certain that the MIDI 2458 source uses 14-bit semantics for the controller number pair. Note 2459 that some MIDI sources ignore 14-bit controller semantics and use 2460 the LSB controller numbers as independent 7-bit controllers. 2462 o If active Control Change commands for controller numbers 0 (Bank 2463 Select MSB) or 32 (Bank Select LSB) appear in the checkpoint 2464 history, and if the command instances are also coded in the 2465 BANK-MSB and BANK-LSB fields of the Chapter P (Appendix A.2), 2466 Chapter C MAY omit the controller logs for the commands. 2468 o Several controller number pairs are defined to be mutually 2469 exclusive. Controller numbers 124 (Omni Off) and 125 (Omni On) 2470 form a mutually exclusive pair, as do controller numbers 126 2471 (Mono) and 127 (Poly). 2473 If active Control Change commands for one or both members of 2474 a mutually exclusive pair appear in the checkpoint history, a 2475 log for the controller number of the most recent command for the 2476 pair in the checkpoint history MUST appear in the controller list. 2477 However, the list MAY omit the controller log for the most recent 2478 active command for the other number in the pair. 2480 If active Control Change commands for one or both members of a 2481 mutually exclusive pair appear in the session history, and if a 2482 log for the controller number of the most recent command for the 2483 pair does not appear in the controller list, a log for the most 2484 recent command for the other number of the pair MUST NOT appear 2485 in the controller list. 2487 o If an active Control Change command for controller number 121 2488 (Reset All Controllers) appears in the session history, the 2489 controller list MAY omit logs for Control Change commands that 2490 precede the Reset All Controllers command in the session history, 2491 under certain conditions. 2493 Namely, a log MAY be omitted if the sender is certain that a 2494 command stream follows the Reset All Controllers semantics 2495 defined in [RP015], and if the log codes a controller number 2496 for which [RP015] specifies a reset value. 2498 For example, [RP015] specifies that controller number 1 2499 (Modulation Wheel) is reset to the value 0, and thus 2500 a controller log for Modulation Wheel MAY be omitted 2501 from the controller log list. In contrast, [RP015] specifies 2502 that controller number 7 (Channel Volume) is not reset, 2503 and thus a controller log for Channel Volume MUST NOT 2504 be omitted from the controller log list. 2506 o Appendix A.3.4 defines exception rules for the MIDI Parameter 2507 System controller numbers 6, 38, and 96-101. 2509 A.3.2. Controller Log Format 2511 Figure A.3.2 shows the controller log structure of Chapter C. 2513 0 1 2514 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2516 |S| NUMBER |A| VALUE/ALT | 2517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2519 Figure A.3.2 -- Chapter C controller log 2521 The 7-bit NUMBER field identifies the controller number of the coded 2522 command. The 7-bit VALUE/ALT field codes recovery information for the 2523 command. The A bit sets the format of the VALUE/ALT field. 2525 A log encodes recovery information using one of the following tools: the 2526 value tool, the toggle tool, or the count tool. 2528 A log uses the value tool if the A bit is set to 0. The value tool 2529 codes the 7-bit data value of a command in the VALUE/ALT field. The 2530 value tool works best for controllers that code a continuous quantity, 2531 such as number 1 (Modulation Wheel). 2533 The A bit is set to 1 to code the toggle or count tool. These tools 2534 work best for controllers that code discrete actions. Figure A.3.3 2535 shows the controller log for these tools. 2537 0 1 2538 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 2539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2540 |S| NUMBER |1|T| ALT | 2541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2543 Figure A.3.3 -- Controller log for ALT tools 2545 A log uses the toggle tool if the T bit is set to 0. A log uses the 2546 count tool if the T bit is set to 1. Both methods use the 6-bit ALT 2547 field as an unsigned integer. 2549 The toggle tool works best for controllers that act as on/off switches, 2550 such as 64 (Damper Pedal (Sustain)). These controllers code the "off" 2551 state with control values 0-63 and the "on" state with 64-127. 2553 For the toggle tool, the ALT field codes the total number of toggles 2554 (off->on and on->off) due to Control Change commands in the session 2555 history, up to and including a toggle caused by the command coded by the 2556 log. The toggle count includes toggles caused by Control Change 2557 commands for controller number 121 (Reset All Controllers). 2559 Toggle counting is performed modulo 64. The toggle count is reset at 2560 the start of a session, and whenever a Reset State command (Appendix 2561 A.1) appears in the session history. When these reset events occur, the 2562 toggle count for a controller is set to 0 (for controllers whose default 2563 value is 0-63) or 1 (for controllers whose default value is 64-127). 2565 The Damper Pedal (Sustain) controller illustrates the benefits of the 2566 toggle tool over the value tool for switch controllers. As often used 2567 in piano applications, the "on" state of the controller lets notes 2568 resonate, while the "off" state immediately damps notes to silence. The 2569 loss of the "off" command in an "on->off->on" sequence results in 2570 ringing notes that should have been damped silent. The toggle tool lets 2571 receivers detect this lost "off" command, but the value tool does not. 2573 The count tool is conceptually similar to the toggle tool. For the 2574 count tool, the ALT field codes the total number of Control Change 2575 commands in the session history, up to and including the command coded 2576 by the log. Command counting is performed modulo 64. The command count 2577 is set to 0 at the start of the session and is reset to 0 whenever a 2578 Reset State command (Appendix A.1) appears in the session history. 2580 Because the count tool ignores the data value, it is a good match for 2581 controllers whose controller value is ignored, such as number 123 (All 2582 Notes Off). More generally, the count tool may be used to code a 2583 (modulo 64) identification number for a command. 2585 A.3.3. Log List Coding Rules 2587 In this section, we describe the organization of controller logs in the 2588 Chapter C log list. 2590 A log encodes information about a particular Control Change command in 2591 the session history. In most cases, a command SHOULD be coded by a 2592 single tool (and, thus, a single log). If a number is coded with a 2593 single tool and this tool is the count tool, recovery Control Change 2594 commands generated by a receiver SHOULD use the default control value 2595 for the controller. 2597 However, a command MAY be coded by several tool types (and, thus, 2598 several logs, each using a different tool). This technique may improve 2599 recovery performance for controllers with complex semantics, such as 2600 controller number 84 (Portamento Control) or controller number 121 2601 (Reset All Controllers) when used with a non-zero data octet (with the 2602 semantics described in [DLS2]). 2604 If a command is encoded by multiple tools, the logs MUST be placed in 2605 the list in the following order: count tool log (if any), followed by 2606 value tool log (if any), followed by toggle tool log (if any). 2608 The Chapter C log list MUST obey the oldest-first ordering rule (defined 2609 in Appendix A.1). Note that this ordering preserves the information 2610 necessary for the recovery of 14-bit controller values, without 2611 precluding the use of MSB and LSB controller pairs as independent 7-bit 2612 controllers. 2614 In the default use of the payload format, all logs that appear in the 2615 list for a controller number encode information about one Control Change 2616 command -- namely, the most recent active Control Change command in the 2617 session history for the number. 2619 This coding scheme provides good recovery performance for the standard 2620 uses of Control Change commands defined in [MIDI]. However, not all 2621 MIDI applications restrict the use of Control Change commands to those 2622 defined in [MIDI]. 2624 For example, consider the common MIDI encoding of rotary encoders 2625 ("infinite" rotation knobs). The mixing console MIDI convention defined 2626 in [LCP] codes the position of rotary encoders as a series of Control 2627 Change commands. Each command encodes a relative change of knob 2628 position from the last update (expressed as a clockwise or counter- 2629 clockwise knob turning angle). 2631 As the knob position is encoded incrementally over a series of Control 2632 Change commands, the best recovery performance is obtained if the log 2633 list encodes all Control Change commands for encoder controller numbers 2634 that appear in the checkpoint history, not only the most recent command. 2636 To support application areas that use Control Change commands in this 2637 way, Chapter C may be configured to encode information about several 2638 Control Change commands for a controller number. We use the term 2639 "enhanced" to describe this encoding method, which we describe below. 2641 In Appendix C.2.3, we show how to configure a stream to use enhanced 2642 Chapter C encoding for specific controller numbers. In Section 5 in the 2643 main text, we show how the H bits in the recovery journal header (Figure 2644 8) and in the channel journal header (Figure 9) indicate the use of 2645 enhanced Chapter C encoding. 2647 Here, we define how to encode a Chapter C log list that uses the 2648 enhanced encoding method. 2650 Senders that use the enhanced encoding method for a controller number 2651 MUST obey the rules below. These rules let a receiver determine which 2652 logs in the list correspond to lost commands. Note that these rules 2653 override the exceptions listed in Appendix A.3.1. 2655 o If N commands for a controller number are encoded in the list, 2656 the commands MUST be the N most recent commands for the controller 2657 number in the session history. For example, for N = 2, the sender 2658 MUST encode the most recent command and the second most recent 2659 command, not the most recent command and the third most recent 2660 command. 2662 o If a controller number uses enhanced encoding, the encoding 2663 of the least-recent command for the controller number in the 2664 log list MUST include a count tool log. In addition, if 2665 commands are encoded for the controller number whose logs 2666 have S bits set to 0, the encoding of the least-recent 2667 command with S = 0 logs MUST include a count tool log. 2669 The count tool is OPTIONAL for the other commands for the 2670 controller number encoded in the list, as a receiver is 2671 able to efficiently deduce the count tool value for these 2672 commands, for both single-packet and multi-packet loss events. 2674 o The use of the value and toggle tools MUST be identical for all 2675 commands for a controller number encoded in the list. For 2676 example, a value tool log either MUST appear for all commands 2677 for the controller number coded in the list, or alternatively, 2678 value tool logs for the controller number MUST NOT appear in 2679 the list. Likewise, a toggle tool log either MUST appear for 2680 all commands for the controller number coded in the list, or 2681 alternatively, toggle tool logs for the controller number MUST 2682 NOT appear in the list. 2684 o If a command is encoded by multiple tools, the logs MUST be 2685 placed in the list in the following order: count tool log 2686 (if any), followed by value tool log (if any), followed by 2687 toggle tool log (if any). 2689 These rules permit a receiver recovering from a packet loss to use the 2690 count tool log to match the commands encoded in the list with its own 2691 history of the stream, as we describe below. Note that the text below 2692 describes a non-normative algorithm; receivers are free to use any 2693 algorithm to match its history with the log list. 2695 In a typical implementation of the enhanced encoding method, a receiver 2696 computes and stores count, value, and toggle tool data field values for 2697 the most recent Control Change command it has received for a controller 2698 number. 2700 After a loss event, a receiver parses the Chapter C list and processes 2701 list logs for a controller number that uses enhanced encoding as 2702 follows. 2704 The receiver compares the count tool ALT field for the least-recent 2705 command for the controller number in the list against its stored count 2706 data for the controller number, to determine if recovery is necessary 2707 for the command coded in the list. The value and toggle tool logs (if 2708 any) that directly follow the count tool log are associated with this 2709 least-recent command. 2711 To check more-recent commands for the controller, the receiver detects 2712 additional value and/or toggle tool logs for the controller number in 2713 the list and infers count tool data for the command coded by these logs. 2714 This inferred data is used to determine if recovery is necessary for the 2715 command coded by the value and/or toggle tool logs. 2717 In this way, a receiver is able to execute only lost commands, without 2718 executing a command twice. While recovering from a single packet loss, 2719 a receiver may skip through S = 1 logs in the list, as the first S = 0 2720 log for an enhanced controller number is always a count tool log. 2722 Note that the requirements in Appendix C.2.2.2 for protective sender and 2723 receiver actions during session startup for multicast operation are of 2724 particular importance for enhanced encoding, as receivers need to 2725 initialize its count tool data structures with recovery journal data in 2726 order to match commands correctly after a loss event. 2728 Finally, we note in passing that in some applications of rotary 2729 encoders, a good user experience may be possible without the use of 2730 enhanced encoding. These applications are distinguished by visual 2731 feedback of encoding position that is driven by the post-recovery rotary 2732 encoding stream, and relatively low packet loss. In these domains, 2733 recovery performance may be acceptable for rotary encoders if the log 2734 list encodes only the most recent command, if both count and value logs 2735 appear for the command. 2737 A.3.4. The Parameter System 2739 Readers may wish to review the Appendix A.1 definitions of "parameter 2740 system", "parameter system transaction", and "initiated parameter system 2741 transaction" before reading this section. 2743 Parameter system transactions update a MIDI Registered Parameter Number 2744 (RPN) or Non-Registered Parameter Number (NRPN) value. A parameter 2745 system transaction is a sequence of Control Change commands that may use 2746 the following controllers numbers: 2748 o Data Entry MSB (6) 2749 o Data Entry LSB (38) 2750 o Data Increment (96) 2751 o Data Decrement (97) 2752 o Non-Registered Parameter Number (NRPN) LSB (98) 2753 o Non-Registered Parameter Number (NRPN) MSB (99) 2754 o Registered Parameter Number (RPN) LSB (100) 2755 o Registered Parameter Number (RPN) MSB (101) 2757 Control Change commands that are a part of a parameter system 2758 transaction MUST NOT be coded in Chapter C controller logs. Instead, 2759 these commands are coded in Chapter M, the MIDI Parameter chapter 2760 defined in Appendix A.4. 2762 However, Control Change commands that use the listed controllers as 2763 general-purpose controllers (i.e., outside of a parameter system 2764 transaction) MUST NOT be coded in Chapter M. 2766 Instead, the controllers are coded in Chapter C controller logs. The 2767 controller logs follow the coding rules stated in Appendix A.3.2 and 2768 A.3.3. The rules for coding paired LSB and MSB controllers, as defined 2769 in Appendix A.3.1, apply to the pairs (6, 38), (99, 98), and (101, 100) 2770 when coded in Chapter C. 2772 If active Control Change commands for controller numbers 6, 38, or 2773 96-101 appear in the checkpoint history, and these commands are used as 2774 general-purpose controllers, the most recent general-purpose command 2775 instance for these controller numbers MUST appear as entries in the 2776 Chapter C controller list. 2778 MIDI syntax permits a source to use controllers 6, 38, 96, and 97 as 2779 parameter-system controllers and general-purpose controllers in the same 2780 stream. An RTP MIDI sender MUST deduce the role of each Control Change 2781 command for these controller numbers by noting the placement of the 2782 command in the stream and MUST use this information to code the command 2783 in Chapter C or Chapter M, as appropriate. 2785 Specifically, active Control Change commands for controllers 6, 38, 96, 2786 and 97 act in a general-purpose way when 2788 o no active Control Change commands that set an RPN or 2789 NRPN parameter number appear in the session history, or 2791 o the most recent active Control Change commands in the session 2792 history that set an RPN or NRPN parameter number code the null 2793 parameter (MSB value 0x7F, LSB value 0x7F), or 2795 o a Control Change command for controller number 121 (Reset 2796 All Controllers) appears more recently in the session history 2797 than all active Control Change commands that set an RPN or 2798 NRPN parameter number (see [RP015] for details). 2800 Finally, we note that a MIDI source that follows the recommendations of 2801 [MIDI] exclusively uses numbers 98-101 as parameter system controllers. 2802 Alternatively, a MIDI source may exclusively use 98-101 as general- 2803 purpose controllers and lose the ability to perform parameter system 2804 transactions in a stream. 2806 In the language of [MIDI], the general-purpose use of controllers 98-101 2807 constitutes a non-standard controller assignment. As most real-world 2808 MIDI sources use the standard controller assignment for controller 2809 numbers 98-101, an RTP MIDI sender SHOULD assume these controllers act 2810 as parameter system controllers, unless it knows that a MIDI source uses 2811 controller numbers 98-101 in a general-purpose way. 2813 A.4. Chapter M: MIDI Parameter System 2815 Readers may wish to review the Appendix A.1 definitions for "C-active", 2816 "parameter system", "parameter system transaction", and "initiated 2817 parameter system transaction" before reading this appendix. 2819 Chapter M protects parameter system transactions for Registered 2820 Parameter Number (RPN) and Non-Registered Parameter Number (NRPN) 2821 values. Figure A.4.1 shows the format for Chapter M. 2823 0 1 2 3 2824 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 2825 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2826 |S|P|E|U|W|Z| LENGTH |Q| PENDING | Log list ... | 2827 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2829 Figure A.4.1 -- Top-level Chapter M format 2831 Chapter M begins with a 2-octet header. If the P header bit is set to 2832 1, a 1-octet field follows the header, coding the 7-bit PENDING value 2833 and its associated Q bit. 2835 The 10-bit LENGTH field codes the size of Chapter M and conforms to 2836 semantics described in Appendix A.1. 2838 Chapter M ends with a list of zero or more variable-length parameter 2839 logs. Appendix A.4.2 defines the bitfield format of a parameter log. 2840 Appendix A.4.1 defines the inclusion semantics of the log list. 2842 A channel journal MUST contain Chapter M if the rules defined in 2843 Appendix A.4.1 require that one or more parameter logs appear in the 2844 list. 2846 A channel journal also MUST contain Chapter M if the most recent C- 2847 active Control Change command involved in a parameter system transaction 2848 in the checkpoint history is 2850 o an RPN MSB (101) or NRPN MSB (99) controller, or 2852 o an RPN LSB (100) or NRPN LSB (98) controller that completes the 2853 coding of the null parameter (MSB value 0x7F, LSB value 0x7F). 2855 This rule provides loss protection for partially transmitted parameter 2856 numbers and for the null parameter numbers. 2858 If the most recent C-active Control Change command involved in a 2859 parameter system transaction in the session history is for the RPN MSB 2860 or NRPN MSB controller, the P header bit MUST be set to 1, and the 2861 PENDING field (and its associated Q bit) MUST follow the Chapter M 2862 header. Otherwise, the P header bit MUST be set to 0, and the PENDING 2863 field and Q bit MUST NOT appear in Chapter M. 2865 If PENDING codes an NRPN MSB, the Q bit MUST be set to 1. If PENDING 2866 codes an RPN MSB, the Q bit MUST be set to 0. 2868 The E header bit codes the current transaction state of the MIDI stream. 2869 If E = 1, an initiated transaction is in progress. Below, we define the 2870 rules for setting the E header bit: 2872 o If no C-active parameter system transaction Control Change 2873 commands appear in the session history, the E bit MUST be 2874 set to 0. 2876 o If the P header bit is set to 1, the E bit MUST be set to 0. 2878 o If the most recent C-active parameter system transaction 2879 Control Change command in the session history is for the 2880 NRPN LSB or RPN LSB controller number, and if this command 2881 acts to complete the coding of the null parameter (MSB 2882 value 0x7F, LSB value 0x7F), the E bit MUST be set to 0. 2884 o Otherwise, an initiated transaction is in progress, and the 2885 E bit MUST be set to 1. 2887 The U, W, and Z header bits code properties that are shared by all 2888 parameter logs in the list. If these properties are set, parameter logs 2889 may be coded with improved efficiency (we explain how in A.4.1). 2891 By default, the U, W, and Z bits MUST be set to 0. If all parameter 2892 logs in the list code RPN parameters, the U bit MAY be set to 1. If all 2893 parameter logs in the list code NRPN parameters, the W bit MAY be set to 2894 1. If the parameter numbers of all RPN and NRPN logs in the list lie in 2895 the range 0-127 (and thus have an MSB value of 0), the Z bit MAY be set 2896 to 1. 2898 Note that C-active semantics appear in the preceding paragraphs because 2899 [RP015] specifies that pending Parameter System transactions are closed 2900 by a Control Change command for controller number 121 (Reset All 2901 Controllers). 2903 A.4.1. Log Inclusion Rules 2905 Parameter logs code recovery information for a specific RPN or NRPN 2906 parameter. 2908 A parameter log MUST appear in the list if an active Control Change 2909 command that forms a part of an initiated transaction for the parameter 2910 appears in the checkpoint history. 2912 An exception to this rule applies if the checkpoint history only 2913 contains transaction Control Change commands for controller numbers 2914 98-101 that act to terminate the transaction. In this case, a log for 2915 the parameter MAY be omitted from the list. 2917 A log MAY appear in the list if an active Control Change command that 2918 forms a part of an initiated transaction for the parameter appears in 2919 the session history. Otherwise, a log for the parameter MUST NOT appear 2920 in the list. 2922 Multiple logs for the same RPN or NRPN parameter MUST NOT appear in the 2923 log list. 2925 The parameter log list MUST obey the oldest-first ordering rule (defined 2926 in Appendix A.1), with the phrase "parameter transaction" replacing the 2927 word "command" in the rule definition. 2929 Parameter logs associated with the RPN or NRPN null parameter (LSB = 2930 0x7F, MSB = 0x7F) MUST NOT appear in the log list. Chapter M uses the E 2931 header bit (Figure A.4.1) and the log list ordering rules to code null 2932 parameter semantics. 2934 Note that "active" semantics (rather than "C-active" semantics) appear 2935 in the preceding paragraphs because [RP015] specifies that pending 2936 Parameter System transactions are not reset by a Control Change command 2937 for controller number 121 (Reset All Controllers). However, the rule 2938 that follows uses C-active semantics, because it concerns the protection 2939 of the transaction system itself, and [RP015] specifies that Reset All 2940 Controllers acts to close a transaction in progress. 2942 In most cases, parameter logs for RPN and NRPN parameters that are 2943 assigned to the ch_never parameter (Appendix C.2.3) MAY be omitted from 2944 the list. An exception applies if 2946 o the log codes the most recent initiated transaction 2947 in the session history, and 2949 o a C-active command that forms a part of the transaction 2950 appears in the checkpoint history, and 2952 o the E header bit for the top-level Chapter M header (Figure 2953 A.4.1) is set to 1. 2955 In this case, a log for the parameter MUST appear in the list. This log 2956 informs receivers recovering from a loss that a transaction is in 2957 progress, so that the receiver is able to correctly interpret RPN or 2958 NRPN Control Change commands that follow the loss event. 2960 A.4.2. Log Coding Rules 2962 Figure A.4.2 shows the parameter log structure of Chapter M. 2964 0 1 2 3 2965 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 2966 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2967 |S| PNUM-LSB |Q| PNUM-MSB |J|K|L|M|N|T|V|R| Fields ... | 2968 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2970 Figure A.4.2 -- Parameter log format 2972 The log begins with a header, whose default size (as shown in Figure 2973 A.4.2) is 3 octets. If the Q header bit is set to 0, the log encodes an 2974 RPN parameter. If Q = 1, the log encodes an NRPN parameter. The 7-bit 2975 PNUM-MSB and PNUM-LSB fields code the parameter number and reflect the 2976 Control Change command data values for controllers 99 and 98 (for NRPNs) 2977 or 101 and 100 (for RPNs). 2979 The J, K, L, M, and N header bits form a Table of Contents (TOC) for the 2980 log and signal the presence of fixed-sized fields that follow the 2981 header. A header bit that is set to 1 codes the presence of a field in 2982 the log. The ordering of fields in the log follows the ordering of the 2983 header bits in the TOC. Appendices A.4.2.1-2 define the fields 2984 associated with each TOC header bit. 2986 The T and V header bits code information about the parameter log but are 2987 not part of the TOC. A set T or V bit does not signal the presence of 2988 any parameter log field. 2990 If the rules in Appendix A.4.1 state that a log for a given parameter 2991 MUST appear in Chapter M, the log MUST code sufficient information to 2992 protect the parameter from the loss of active parameter transaction 2993 Control Change commands in the checkpoint history. 2995 This rule does not apply if the parameter coded by the log is assigned 2996 to the ch_never parameter (Appendix C.2.3). In this case, senders MAY 2997 choose to set the J, K, L, M, and N TOC bits to 0, coding a parameter 2998 log with no fields. 3000 Note that logs to protect parameters that are assigned to ch_never are 3001 REQUIRED under certain conditions (see Appendix A.4.1). The purpose of 3002 the log is to inform receivers recovering from a loss that a transaction 3003 is in progress, so that the receiver is able to correctly interpret RPN 3004 or NRPN Control Change commands that follow the loss event. 3006 Parameter logs provide two tools for parameter protection: the value 3007 tool and the count tool. Depending on the semantics of the parameter, 3008 senders may use either tool, both tools, or neither tool to protect a 3009 given parameter. 3011 The value tool codes information a receiver may use to determine the 3012 current value of an RPN or NRPN parameter. If a parameter log uses the 3013 value tool, the V header bit MUST be set to 1, and the semantics defined 3014 in Appendices A.4.2.1 for setting the J, K, L, and M TOC bits MUST be 3015 followed. If a parameter log does not use the value tool, the V bit 3016 MUST be set to 0, and the J, K, L, and M TOC bits MUST also be set to 0. 3018 The count tool codes the number of transactions for an RPN or NRPN 3019 parameter. If a parameter log uses the count tool, the T header bit 3020 MUST be set to 1, and the semantics defined in Appendices A.4.2.2 for 3021 setting the N TOC bit MUST be followed. If a parameter log does not use 3022 the count tool, the T bit and the N TOC bit MUST be set to 0. 3024 Note that V and T are set if the sender uses value (V) or count (T) tool 3025 for the log on an ongoing basis. Thus, V may be set even if J = K = L = 3026 M = 0, and T may be set even if N = 0. 3028 In many cases, all parameters coded in the log list are of one type (RPN 3029 and NRPN), and all parameter numbers lie in the range 0-127. As 3030 described in Appendix A.4.1, senders MAY signal this condition by 3031 setting the top-level Chapter M header bit Z to 1 (to code the 3032 restricted range) and by setting the U or W bit to 1 (to code the 3033 parameter type). 3035 If the top-level Chapter M header codes Z = 1 and either U = 1 or W = 1, 3036 all logs in the parameter log list MUST use a modified header format. 3037 This modification deletes bits 8-15 of the bitfield shown in Figure 3038 A.4.2, to yield a 2-octet header. The values of the deleted PNUM-MSB 3039 and Q fields may be inferred from the U, W, and Z bit values. 3041 A.4.2.1. The Value Tool 3043 The value tool uses several fields to track the value of an RPN or NRPN 3044 parameter. 3046 The J TOC bit codes the presence of the octet shown in Figure A.4.3 in 3047 the field list. 3049 0 3050 0 1 2 3 4 5 6 7 3051 +-+-+-+-+-+-+-+-+ 3052 |X| ENTRY-MSB | 3053 +-+-+-+-+-+-+-+-+ 3055 Figure A.4.3 -- ENTRY-MSB field 3057 The 7-bit ENTRY-MSB field codes the data value of the most recent active 3058 Control Change command for controller number 6 (Data Entry MSB) in the 3059 session history that appears in a transaction for the log parameter. 3061 The X bit MUST be set to 1 if the command coded by ENTRY-MSB precedes 3062 the most recent Control Change command for controller 121 (Reset All 3063 Controllers) in the session history. Otherwise, the X bit MUST be set 3064 to 0. 3066 A parameter log that uses the value tool MUST include the ENTRY-MSB 3067 field if an active Control Change command for controller number 6 3068 appears in the checkpoint history. 3070 Note that [RP015] specifies that Control Change commands for controller 3071 121 (Reset All Controllers) do not reset RPN and NRPN values, and thus 3072 the X bit would not play a recovery role for MIDI systems that comply 3073 with [RP015]. 3075 However, certain renderers (such as DLS 2 [DLS2]) specify that certain 3076 RPN values are reset for some uses of Reset All Controllers. The X bit 3077 (and other bitfield features of this nature in this appendix) plays a 3078 role in recovery for renderers of this type. 3080 The K TOC bit codes the presence of the octet shown in Figure A.4.4 in 3081 the field list. 3083 0 3084 0 1 2 3 4 5 6 7 3085 +-+-+-+-+-+-+-+-+ 3086 |X| ENTRY-LSB | 3087 +-+-+-+-+-+-+-+-+ 3089 Figure A.4.4 -- ENTRY-LSB field 3091 The 7-bit ENTRY-LSB field codes the data value of the most recent active 3092 Control Change command for controller number 38 (Data Entry LSB) in the 3093 session history that appears in a transaction for the log parameter. 3095 The X bit MUST be set to 1 if the command coded by ENTRY-LSB precedes 3096 the most recent Control Change command for controller 121 (Reset All 3097 Controllers) in the session history. Otherwise, the X bit MUST be set 3098 to 0. 3100 As a rule, a parameter log that uses the value tool MUST include the 3101 ENTRY-LSB field if an active Control Change command for controller 3102 number 38 appears in the checkpoint history. However, the ENTRY-LSB 3103 field MUST NOT appear in a parameter log if the Control Change command 3104 associated with the ENTRY-LSB precedes a Control Change command for 3105 controller number 6 (Data Entry MSB) that appears in a transaction for 3106 the log parameter in the session history. 3108 The L TOC bit codes the presence of the octets shown in Figure A.4.5 in 3109 the field list. 3111 0 1 3112 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3113 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3114 |G|X| A-BUTTON | 3115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3117 Figure A.4.5 -- A-BUTTON field 3119 The 14-bit A-BUTTON field codes a count of the number of active Control 3120 Change commands for controller numbers 96 and 97 (Data Increment and 3121 Data Decrement) in the session history that appear in a transaction for 3122 the log parameter. 3124 The M TOC bit codes the presence of the octets shown in Figure A.4.6 in 3125 the field list. 3127 0 1 3128 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3129 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3130 |G|R| C-BUTTON | 3131 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3133 Figure A.4.6 -- C-BUTTON field 3135 The 14-bit C-BUTTON field has semantics identical to A-BUTTON, except 3136 that Data Increment and Data Decrement Control Change commands that 3137 precede the most recent Control Change command for controller 121 (Reset 3138 All Controllers) in the session history are not counted. 3140 For both A-BUTTON and C-BUTTON, Data Increment and Data Decrement 3141 Control Change commands are not counted if they precede Control Changes 3142 commands for controller numbers 6 (Data Entry MSB) or 38 (Data Entry 3143 LSB) that appear in a transaction for the log parameter in the session 3144 history. 3146 The A-BUTTON and C-BUTTON fields are interpreted as unsigned integers, 3147 and the G bit associated with the field codes the sign of the integer (G 3148 = 0 for positive or zero, G = 1 for negative). 3150 To compute and code the count value, initialize the count value to 0, 3151 add 1 for each qualifying Data Increment command, and subtract 1 for 3152 each qualifying Data Decrement command. After each add or subtract, 3153 limit the count magnitude to 16383. The G bit codes the sign of the 3154 count, and the A-BUTTON or C-BUTTON field codes the count magnitude. 3156 For the A-BUTTON field, if the most recent qualified Data Increment or 3157 Data Decrement command precedes the most recent Control Change command 3158 for controller 121 (Reset All Controllers) in the session history, the X 3159 bit associated with A-BUTTON field MUST be set to 1. Otherwise, the X 3160 bit MUST be set to 0. 3162 A parameter log that uses the value tool MUST include the A-BUTTON and 3163 C-BUTTON fields if an active Control Change command for controller 3164 numbers 96 or 97 appears in the checkpoint history. However, to improve 3165 coding efficiency, this rule has several exceptions: 3167 o If the log includes the A-BUTTON field, and if the X bit of 3168 the A-BUTTON field is set to 1, the C-BUTTON field (and its 3169 associated R and G bits) MAY be omitted from the log. 3171 o If the log includes the A-BUTTON field, and if the A-BUTTON 3172 and C-BUTTON fields (and their associated G bits) code identical 3173 values, the C-BUTTON field (and its associated R and G bits) 3174 MAY be omitted from the log. 3176 A.4.2.2. The Count Tool 3178 The count tool tracks the number of transactions for an RPN or NRPN 3179 parameter. The N TOC bit codes the presence of the octet shown in 3180 Figure A.4.7 in the field list. 3182 0 3183 0 1 2 3 4 5 6 7 3184 +-+-+-+-+-+-+-+-+ 3185 |X| COUNT | 3186 +-+-+-+-+-+-+-+-+ 3188 Figure A.4.7 -- COUNT field 3190 The 7-bit COUNT codes the number of initiated transactions for the log 3191 parameter that appear in the session history. Initiated transactions 3192 are counted if they contain one or more active Control Change commands, 3193 including commands for controllers 98-101 that initiate the parameter 3194 transaction. 3196 If the most recent counted transaction precedes the most recent Control 3197 Change command for controller 121 (Reset All Controllers) in the session 3198 history, the X bit associated with the COUNT field MUST be set to 1. 3199 Otherwise, the X bit MUST be set to 0. 3201 Transaction counting is performed modulo 128. The transaction count is 3202 set to 0 at the start of a session and is reset to 0 whenever a Reset 3203 State command (Appendix A.1) appears in the session history. 3205 A parameter log that uses the count tool MUST include the COUNT field if 3206 an active command that increments the transaction count (modulo 128) 3207 appears in the checkpoint history. 3209 A.5. Chapter W: MIDI Pitch Wheel 3211 A channel journal MUST contain Chapter W if a C-active MIDI Pitch Wheel 3212 (0xE) command appears in the checkpoint history. Figure A.5.1 shows the 3213 format for Chapter W. 3215 0 1 3216 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3218 |S| FIRST |R| SECOND | 3219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3221 Figure A.5.1 -- Chapter W format 3223 The chapter has a fixed size of 16 bits. The FIRST and SECOND fields 3224 are the 7-bit values of the first and second data octets of the most 3225 recent active Pitch Wheel command in the session history. 3227 Note that Chapter W encodes C-active commands and thus does not encode 3228 active commands that are not C-active (see the second-to-last paragraph 3229 of Appendix A.1 for an explanation of chapter inclusion text in this 3230 regard). 3232 Chapter W does not encode "active but not C-active" commands because 3233 [RP015] declares that Control Change commands for controller number 121 3234 (Reset All Controllers) act to reset the Pitch Wheel value to 0. If 3235 Chapter W encoded "active but not C-active" commands, a repair operation 3236 following a Reset All Controllers command could incorrectly repair the 3237 stream with a stale Pitch Wheel value. 3239 A.6. Chapter N: MIDI NoteOff and NoteOn 3241 In this appendix, we consider NoteOn commands with zero velocity to be 3242 NoteOff commands. Readers may wish to review the Appendix A.1 3243 definition of "N-active commands" before reading this appendix. 3245 Chapter N completely protects note commands in streams that alternate 3246 between NoteOn and NoteOff commands for a particular note number. 3247 However, in rare applications, multiple overlapping NoteOn commands may 3248 appear for a note number. Chapter E, described in Appendix A.7, 3249 augments Chapter N to completely protect these streams. 3251 A channel journal MUST contain Chapter N if an N-active MIDI NoteOn 3252 (0x9) or NoteOff (0x8) command appears in the checkpoint history. 3253 Figure A.6.1 shows the format for Chapter N. 3255 0 1 2 3 3256 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 3257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3258 |B| LEN | LOW | HIGH |S| NOTENUM |Y| VELOCITY | 3259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3260 |S| NOTENUM |Y| VELOCITY | .... | 3261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3262 | OFFBITS | OFFBITS | .... | OFFBITS | 3263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3265 Figure A.6.1 -- Chapter N format 3267 Chapter N consists of a 2-octet header, followed by at least one of the 3268 following data structures: 3270 o A list of note logs to code NoteOn commands. 3271 o A NoteOff bitfield structure to code NoteOff commands. 3273 We define the header bitfield semantics in Appendix A.6.1. We define 3274 the note log semantics and the NoteOff bitfield semantics in Appendix 3275 A.6.2. 3277 If one or more N-active NoteOn or NoteOff commands in the checkpoint 3278 history reference a note number, the note number MUST be coded in either 3279 the note log list or the NoteOff bitfield structure. 3281 The note log list MUST contain an entry for all note numbers whose most 3282 recent checkpoint history appearance is in an N-active NoteOn command. 3283 The NoteOff bitfield structure MUST contain a set bit for all note 3284 numbers whose most recent checkpoint history appearance is in an N- 3285 active NoteOff command. 3287 A note number MUST NOT be coded in both structures. 3289 All note logs and NoteOff bitfield set bits MUST code the most recent N- 3290 active NoteOn or NoteOff reference to a note number in the session 3291 history. 3293 The note log list MUST obey the oldest-first ordering rule (defined in 3294 Appendix A.1). 3296 A.6.1. Header Structure 3298 The header for Chapter N, shown in Figure A.6.2, codes the size of the 3299 note list and bitfield structures. 3301 0 1 3302 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3304 |B| LEN | LOW | HIGH | 3305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3307 Figure A.6.2 -- Chapter N header 3309 The LEN field, a 7-bit integer value, codes the number of 2-octet note 3310 logs in the note list. Zero is a valid value for LEN and codes an empty 3311 note list. 3313 The 4-bit LOW and HIGH fields code the number of OFFBITS octets that 3314 follow the note log list. LOW and HIGH are unsigned integer values. If 3315 LOW <= HIGH, there are (HIGH - LOW + 1) OFFBITS octets in the chapter. 3316 The value pairs (LOW = 15, HIGH = 0) and (LOW = 15, HIGH = 1) code an 3317 empty NoteOff bitfield structure (i.e., no OFFBITS octets). Other (LOW 3318 > HIGH) value pairs MUST NOT appear in the header. 3320 The B bit provides S-bit functionality (Appendix A.1) for the NoteOff 3321 bitfield structure. By default, the B bit MUST be set to 1. However, 3322 if the MIDI command section of the previous packet (packet I - 1, with I 3323 as defined in Appendix A.1) includes a NoteOff command for the channel, 3324 the B bit MUST be set to 0. If the B bit is set to 0, the higher-level 3325 recovery journal elements that contain Chapter N MUST have S bits that 3326 are set to 0, including the top-level journal header. 3328 The LEN value of 127 codes a note list length of 127 or 128 note logs, 3329 depending on the values of LOW and HIGH. If LEN = 127, LOW = 15, and 3330 HIGH = 0, the note list holds 128 note logs, and the NoteOff bitfield 3331 structure is empty. For other values of LOW and HIGH, LEN = 127 codes 3332 that the note list contains 127 note logs. In this case, the chapter 3333 has (HIGH - LOW + 1) NoteOff OFFBITS octets if LOW <= HIGH and has no 3334 OFFBITS octets if LOW = 15 and HIGH = 1. 3336 A.6.2. Note Structures 3338 Figure A.6.3 shows the 2-octet note log structure. 3340 0 1 3341 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3343 |S| NOTENUM |Y| VELOCITY | 3344 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3346 Figure A.6.3 -- Chapter N note log 3348 The 7-bit NOTENUM field codes the note number for the log. A note 3349 number MUST NOT be represented by multiple note logs in the note list. 3351 The 7-bit VELOCITY field codes the velocity value for the most recent N- 3352 active NoteOn command for the note number in the session history. 3353 Multiple overlapping NoteOns for a given note number may be coded using 3354 Chapter E, as discussed in Appendix A.7. 3356 VELOCITY is never zero; NoteOn commands with zero velocity are coded as 3357 NoteOff commands in the NoteOff bitfield structure. 3359 The note log does not code the execution time of the NoteOn command. 3360 However, the Y bit codes a hint from the sender about the NoteOn 3361 execution time. The Y bit codes a recommendation to play (Y = 1) or 3362 skip (Y = 0) the NoteOn command recovered from the note log. See 3363 Section 4.2 of [RFC4696] for non-normative guidance on the use of the Y 3364 bit. 3366 Figure A.6.1 shows the NoteOff bitfield structure, as the list of 3367 OFFBITS octets at the end of the chapter. A NoteOff OFFBITS octet codes 3368 NoteOff information for eight consecutive MIDI note numbers, with the 3369 most-significant bit representing the lowest note number. The most- 3370 significant bit of the first OFFBITS octet codes the note number 8*LOW; 3371 the most-significant bit of the last OFFBITS octet codes the note number 3372 8*HIGH. 3374 A set bit codes a NoteOff command for the note number. In the most 3375 efficient coding for the NoteOff bitfield structure, the first and last 3376 octets of the structure contain at least one set bit. Note that Chapter 3377 N does not code NoteOff velocity data. 3379 Note that in the general case, the recovery journal does not code the 3380 relative placement of a NoteOff command and a Change Control command for 3381 controller 64 (Damper Pedal (Sustain)). In many cases, a receiver 3382 processing a loss event may deduce this relative placement from the 3383 history of the stream and thus determine if a NoteOff note is sustained 3384 by the pedal. If such a determination is not possible, receivers SHOULD 3385 err on the side of silencing pedal sustains, as erroneously sustained 3386 notes may produce unpleasant (albeit transient) artifacts. 3388 A.7. Chapter E: MIDI Note Command Extras 3390 Readers may wish to review the Appendix A.1 definition of "N-active 3391 commands" before reading this appendix. In this appendix, a NoteOn 3392 command with a velocity of 0 is considered to be a NoteOff command with 3393 a release velocity value of 64. 3395 Chapter E encodes recovery information about MIDI NoteOn (0x9) and 3396 NoteOff (0x8) command features that rarely appear in MIDI streams. 3397 Receivers use Chapter E to reduce transient artifacts for streams where 3398 several NoteOn commands appear for a note number without an intervening 3399 NoteOff. Receivers also use Chapter E to reduce transient artifacts for 3400 streams that use NoteOff release velocity. Chapter E supplements the 3401 note information coded in Chapter N (Appendix A.6). 3403 Figure A.7.1 shows the format for Chapter E. 3405 0 1 2 3 3406 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 3407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3408 |S| LEN |S| NOTENUM |V| COUNT/VEL |S| NOTENUM | 3409 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3410 |V| COUNT/VEL | .... | 3411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3413 Figure A.7.1 -- Chapter E format 3415 The chapter consists of a 1-octet header, followed by a variable-length 3416 list of 2-octet note logs. Appendix A.7.1 defines the bitfield format 3417 for a note log. 3419 The log list MUST contain at least one note log. The 7-bit LEN header 3420 field codes the number of note logs in the list, minus one. A channel 3421 journal MUST contain Chapter E if the rules defined in this appendix 3422 require that one or more note logs appear in the list. The note log 3423 list MUST obey the oldest-first ordering rule (defined in Appendix A.1). 3425 A.7.1. Note Log Format 3427 Figure A.7.2 reproduces the note log structure of Chapter E. 3429 0 1 3430 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3432 |S| NOTENUM |V| COUNT/VEL | 3433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3435 Figure A.7.2 -- Chapter E note log 3437 A note log codes information about the MIDI note number coded by the 3438 7-bit NOTENUM field. The nature of the information depends on the value 3439 of the V flag bit. 3441 If the V bit is set to 1, the COUNT/VEL field codes the release velocity 3442 value for the most recent N-active NoteOff command for the note number 3443 that appears in the session history. 3445 If the V bit is set to 0, the COUNT/VEL field codes a reference count of 3446 the number of NoteOn and NoteOff commands for the note number that 3447 appear in the session history. 3449 The reference count is set to 0 at the start of the session. NoteOn 3450 commands increment the count by 1. NoteOff commands decrement the count 3451 by 1. However, a decrement that generates a negative count value is not 3452 performed. 3454 If the reference count is in the range 0-126, the 7-bit COUNT/VEL field 3455 codes an unsigned integer representation of the count. If the count is 3456 greater than or equal to 127, COUNT/VEL is set to 127. 3458 By default, the count is reset to 0 whenever a Reset State command 3459 (Appendix A.1) appears in the session history, and whenever MIDI Control 3460 Change commands for controller numbers 123-127 (numbers with All Notes 3461 Off semantics) or 120 (All Sound Off) appear in the session history. 3463 A.7.2. Log Inclusion Rules 3465 If the most recent N-active NoteOn or NoteOff command for a note number 3466 in the checkpoint history is a NoteOff command with a release velocity 3467 value other than 64, a note log whose V bit is set to 1 MUST appear in 3468 Chapter E for the note number. 3470 If the most recent N-active NoteOn or NoteOff command for a note number 3471 in the checkpoint history is a NoteOff command, and if the reference 3472 count for the note number is greater than 0, a note log whose V bit is 3473 set to 0 MUST appear in Chapter E for the note number. 3475 If the most recent N-active NoteOn or NoteOff command for a note number 3476 in the checkpoint history is a NoteOn command, and if the reference 3477 count for the note number is greater than 1, a note log whose V bit is 3478 set to 0 MUST appear in Chapter E for the note number. 3480 At most, two note logs MAY appear in Chapter E for a note number: one 3481 log whose V bit is set to 0, and one log whose V bit is set to 1. 3483 Chapter E codes a maximum of 128 note logs. If the log inclusion rules 3484 yield more than 128 REQUIRED logs, note logs whose V bit is set to 1 3485 MUST be dropped from Chapter E in order to reach the 128-log limit. 3486 Note logs whose V bit is set to 0 MUST NOT be dropped. 3488 Most MIDI streams do not use NoteOn and NoteOff commands in ways that 3489 would trigger the log inclusion rules. For these streams, Chapter E 3490 would never be REQUIRED to appear in a channel journal. 3492 The ch_never parameter (Appendix C.2.3) may be used to configure the log 3493 inclusion rules for Chapter E. 3495 A.8. Chapter T: MIDI Channel Aftertouch 3497 A channel journal MUST contain Chapter T if an N-active and C-active 3498 MIDI Channel Aftertouch (0xD) command appears in the checkpoint history. 3499 Figure A.8.1 shows the format for Chapter T. 3501 0 3502 0 1 2 3 4 5 6 7 3503 +-+-+-+-+-+-+-+-+ 3504 |S| PRESSURE | 3505 +-+-+-+-+-+-+-+-+ 3507 Figure A.8.1 -- Chapter T format 3509 The chapter has a fixed size of 8 bits. The 7-bit PRESSURE field holds 3510 the pressure value of the most recent N-active and C-active Channel 3511 Aftertouch command in the session history. 3513 Chapter T only encodes commands that are C-active and N-active. We 3514 define a C-active restriction because [RP015] declares that a Control 3515 Change command for controller 121 (Reset All Controllers) acts to reset 3516 the channel pressure to 0 (see the discussion at the end of Appendix A.5 3517 for a more complete rationale). 3519 We define an N-active restriction on the assumption that aftertouch 3520 commands are linked to note activity, and thus Channel Aftertouch 3521 commands that are not N-active are stale and should not be used to 3522 repair a stream. 3524 A.9. Chapter A: MIDI Poly Aftertouch 3526 A channel journal MUST contain Chapter A if a C-active Poly Aftertouch 3527 (0xA) command appears in the checkpoint history. Figure A.9.1 shows the 3528 format for Chapter A. 3530 0 1 2 3 3531 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 3532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3533 |S| LEN |S| NOTENUM |X| PRESSURE |S| NOTENUM | 3534 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3535 |X| PRESSURE | .... | 3536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3538 Figure A.9.1 -- Chapter A format 3540 The chapter consists of a 1-octet header, followed by a variable-length 3541 list of 2-octet note logs. A note log MUST appear for a note number if 3542 a C-active Poly Aftertouch command for the note number appears in the 3543 checkpoint history. A note number MUST NOT be represented by multiple 3544 note logs in the note list. The note log list MUST obey the oldest- 3545 first ordering rule (defined in Appendix A.1). 3547 The 7-bit LEN field codes the number of note logs in the list, minus 3548 one. Figure A.9.2 reproduces the note log structure of Chapter A. 3550 0 1 3551 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 3552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3553 |S| NOTENUM |X| PRESSURE | 3554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3556 Figure A.9.2 -- Chapter A note log 3558 The 7-bit PRESSURE field codes the pressure value of the most recent C- 3559 active Poly Aftertouch command in the session history for the MIDI note 3560 number coded in the 7-bit NOTENUM field. 3562 As a rule, the X bit MUST be set to 0. However, the X bit MUST be set 3563 to 1 if the command coded by the log appears before one of the following 3564 commands in the session history: MIDI Control Change numbers 123-127 3565 (numbers with All Notes Off semantics) or 120 (All Sound Off). 3567 We define C-active restrictions for Chapter A because [RP015] declares 3568 that a Control Change command for controller 121 (Reset All Controllers) 3569 acts to reset the polyphonic pressure to 0 (see the discussion at the 3570 end of Appendix A.5 for a more complete rationale). 3572 B. The Recovery Journal System Chapters 3574 B.1. System Chapter D: Simple System Commands 3576 The system journal MUST contain Chapter D if an active MIDI Reset 3577 (0xFF), MIDI Tune Request (0xF6), MIDI Song Select (0xF3), undefined 3578 MIDI System Common (0xF4 and 0xF5), or undefined MIDI System Real-time 3579 (0xF9 and 0xFD) command appears in the checkpoint history. 3581 Figure B.1.1 shows the variable-length format for Chapter D. 3583 0 1 2 3 3584 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 3585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3586 |S|B|G|H|J|K|Y|Z| Command logs ... | 3587 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3589 Figure B.1.1 -- System Chapter D format 3591 The chapter consists of a 1-octet header, followed by one or more 3592 command logs. Header flag bits indicate the presence of command logs 3593 for the Reset (B = 1), Tune Request (G = 1), Song Select (H = 1), 3594 undefined System Common 0xF4 (J = 1), undefined System Common 0xF5 (K = 3595 1), undefined System Real-time 0xF9 (Y = 1), or undefined System Real- 3596 time 0xFD (Z = 1) commands. 3598 Command logs appear in a list following the header, in the order that 3599 the flag bits appear in the header. 3601 Figure B.1.2 shows the 1-octet command log format for the Reset and Tune 3602 Request commands. 3604 0 3605 0 1 2 3 4 5 6 7 3606 +-+-+-+-+-+-+-+-+ 3607 |S| COUNT | 3608 +-+-+-+-+-+-+-+-+ 3610 Figure B.1.2 -- Command log for Reset and Tune Request 3612 Chapter D MUST contain the Reset command log if an active Reset command 3613 appears in the checkpoint history. The 7-bit COUNT field codes the 3614 total number of Reset commands (modulo 128) present in the session 3615 history. 3617 Chapter D MUST contain the Tune Request command log if an active Tune 3618 Request command appears in the checkpoint history. The 7-bit COUNT 3619 field codes the total number of Tune Request commands (modulo 128) 3620 present in the session history. 3622 For these commands, the COUNT field acts as a reference count. See the 3623 definition of "session history reference counts" in Appendix A.1 for 3624 more information. 3626 Figure B.1.3 shows the 1-octet command log format for the Song Select 3627 command. 3629 0 3630 0 1 2 3 4 5 6 7 3631 +-+-+-+-+-+-+-+-+ 3632 |S| VALUE | 3633 +-+-+-+-+-+-+-+-+ 3635 Figure B.1.3 -- Song Select command log format 3637 Chapter D MUST contain the Song Select command log if an active Song 3638 Select command appears in the checkpoint history. The 7-bit VALUE field 3639 codes the song number of the most recent active Song Select command in 3640 the session history. 3642 B.1.1. Undefined System Commands 3644 In this section, we define the Chapter D command logs for the undefined 3645 System commands. [MIDI] reserves the undefined System commands 0xF4, 3646 0xF5, 0xF9, and 0xFD for future use. At the time of this writing, any 3647 MIDI command stream that uses these commands is non-compliant with 3648 [MIDI]. However, future versions of [MIDI] may define these commands, 3649 and a few products do use these commands in a non-compliant manner. 3651 Figure B.1.4 shows the variable-length command log format for the 3652 undefined System Common commands (0xF4 and 0xF5). 3654 0 1 2 3 3655 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 3656 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3657 |S|C|V|L|DSZ| LENGTH | COUNT | VALUE ... | 3658 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3659 | LEGAL ... | 3660 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3662 Figure B.1.4 -- Undefined System Common command log format 3664 The command log codes a single command type (0xF4 or 0xF5, not both). 3665 Chapter D MUST contain a command log if an active 0xF4 command appears 3666 in the checkpoint history and MUST contain an independent command log if 3667 an active 0xF5 command appears in the checkpoint history. 3669 A Chapter D Undefined System Common command log consists of a two-octet 3670 header followed by a variable number of data fields. Header flag bits 3671 indicate the presence of the COUNT field (C = 1), the VALUE field (V = 3672 1), and the LEGAL field (L = 1). The 10-bit LENGTH field codes the size 3673 of the command log and conforms to semantics described in Appendix A.1. 3675 The 2-bit DSZ field codes the number of data octets in the command 3676 instance that appears most recently in the session history. If DSZ = 3677 0-2, the command has 0-2 data octets. If DSZ = 3, the command has 3 or 3678 more command data octets. 3680 We now define the default rules for the use of the COUNT, VALUE, and 3681 LEGAL fields. The session configuration tools defined in Appendix C.2.3 3682 may be used to override this behavior. 3684 By default, if the DSZ field is set to 0, the command log MUST include 3685 the COUNT field. The 8-bit COUNT field codes the total number of 3686 commands of the type coded by the log (0xF4 or 0xF5) present in the 3687 session history, modulo 256. 3689 By default, if the DSZ field is set to 1-3, the command log MUST include 3690 the VALUE field. The variable-length VALUE field codes a verbatim copy 3691 the data octets for the most recent use of the command type coded by the 3692 log (0xF4 or 0xF5) in the session history. The most-significant bit of 3693 the final data octet MUST be set to 1, and the most-significant bit of 3694 all other data octets MUST be set to 0. 3696 The LEGAL field is reserved for future use. If an update to [MIDI] 3697 defines the 0xF4 or 0xF5 command, an IETF standards-track document may 3698 define the LEGAL field. Until such a document appears, senders MUST NOT 3699 use the LEGAL field, and receivers MUST use the LENGTH field to skip 3700 over the LEGAL field. The LEGAL field would be defined by the IETF if 3701 the semantics of the new 0xF4 or 0xF5 command could not be protected 3702 from packet loss via the use of the COUNT and VALUE fields. 3704 Figure B.1.5 shows the variable-length command log format for the 3705 undefined System Real-time commands (0xF9 and 0xFD). 3707 0 1 2 3 3708 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 3709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3710 |S|C|L| LENGTH | COUNT | LEGAL ... | 3711 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3713 Figure B.1.5 -- Undefined System Real-time command log format 3715 The command log codes a single command type (0xF9 or 0xFD, not both). 3716 Chapter D MUST contain a command log if an active 0xF9 command appears 3717 in the checkpoint history and MUST contain an independent command log if 3718 an active 0xFD command appears in the checkpoint history. 3720 A Chapter D Undefined System Real-time command log consists of a one- 3721 octet header followed by a variable number of data fields. Header flag 3722 bits indicate the presence of the COUNT field (C = 1) and the LEGAL 3723 field (L = 1). The 5-bit LENGTH field codes the size of the command log 3724 and conforms to semantics described in Appendix A.1. 3726 We now define the default rules for the use of the COUNT and LEGAL 3727 fields. The session configuration tools defined in Appendix C.2.3 may 3728 be used to override this behavior. 3730 The 8-bit COUNT field codes the total number of commands of the type 3731 coded by the log present in the session history, modulo 256. By 3732 default, the COUNT field MUST be present in the command log. 3734 The LEGAL field is reserved for future use. If an update to [MIDI] 3735 defines the 0xF9 or 0xFD command, an IETF standards-track document may 3736 define the LEGAL field to protect the command. Until such a document 3737 appears, senders MUST NOT use the LEGAL field, and receivers MUST use 3738 the LENGTH field to skip over the LEGAL field. The LEGAL field would be 3739 defined by the IETF if the semantics of the new 0xF9 or 0xFD command 3740 could not be protected from packet loss via the use of the COUNT field. 3742 Finally, we note that some non-standard uses of the undefined System 3743 Real-time commands act to implement non-compliant variants of the MIDI 3744 sequencer system. In Appendix B.3.1, we describe resiliency tools for 3745 the MIDI sequencer system that provide some protection in this case. 3747 B.2. System Chapter V: Active Sense Command 3749 The system journal MUST contain Chapter V if an active MIDI Active Sense 3750 (0xFE) command appears in the checkpoint history. Figure B.2.1 shows 3751 the format for Chapter V. 3753 0 3754 0 1 2 3 4 5 6 7 3755 +-+-+-+-+-+-+-+-+ 3756 |S| COUNT | 3757 +-+-+-+-+-+-+-+-+ 3759 Figure B.2.1 -- System Chapter V format 3761 The 7-bit COUNT field codes the total number of Active Sense commands 3762 (modulo 128) present in the session history. The COUNT field acts as a 3763 reference count. See the definition of "session history reference 3764 counts" in Appendix A.1 for more information. 3766 B.3. System Chapter Q: Sequencer State Commands 3768 This appendix describes Chapter Q, the system chapter for the MIDI 3769 sequencer commands. 3771 The system journal MUST contain Chapter Q if an active MIDI Song 3772 Position Pointer (0xF2), MIDI Clock (0xF8), MIDI Start (0xFA), MIDI 3773 Continue (0xFB), or MIDI Stop (0xFC) command appears in the checkpoint 3774 history, and if the rules defined in this appendix require a change in 3775 the Chapter Q bitfield contents because of the command appearance. 3777 Figure B.3.1 shows the variable-length format for Chapter Q. 3779 0 1 2 3 3780 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 3781 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3782 |S|N|D|C|T| TOP | CLOCK | TIMETOOLS ... | 3783 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3784 | ... | 3785 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3787 Figure B.3.1 -- System Chapter Q format 3789 Chapter Q consists of a 1-octet header followed by several optional 3790 fields, in the order shown in Figure B.3.1. 3792 Header flag bits signal the presence of the 16-bit CLOCK field (C = 1) 3793 and the 24-bit TIMETOOLS field (T = 1). The 3-bit TOP header field is 3794 interpreted as an unsigned integer, as are CLOCK and TIMETOOLS. We 3795 describe the TIMETOOLS field in Appendix B.3.1. 3797 Chapter Q encodes the most recent state of the sequencer system. 3798 Receivers use the chapter to re-synchronize the sequencer after a packet 3799 loss episode. Chapter fields encode the on/off state of the sequencer, 3800 the current position in the song, and the downbeat. 3802 The N header bit encodes the relative occurrence of the Start, Stop, and 3803 Continue commands in the session history. If an active Start or 3804 Continue command appears most recently, the N bit MUST be set to 1. If 3805 an active Stop appears most recently, or if no active Start, Stop, or 3806 Continue commands appear in the session history, the N bit MUST be set 3807 to 0. 3809 The C header flag, the TOP header field, and the CLOCK field act to code 3810 the current position in the sequence: 3812 o If C = 1, the 3-bit TOP header field and the 16-bit 3813 CLOCK field are combined to form the 19-bit unsigned quantity 3814 65536*TOP + CLOCK. This value encodes the song position 3815 in units of MIDI Clocks (24 clocks per quarter note), 3816 modulo 524288. Note that the maximum song position value 3817 that may be coded by the Song Position Pointer command is 3818 98303 clocks (which may be coded with 17 bits), and that 3819 MIDI-coded songs are generally constructed to avoid durations 3820 longer than this value. However, the 19-bit size may be useful 3821 for real-time applications, such as a drum machine MIDI output 3822 that is sending clock commands for long periods of time. 3824 o If C = 0, the song position is the start of the song. 3825 The C = 0 position is identical to the position coded 3826 by C = 1, TOP = 0, and CLOCK = 0, for the case where 3827 the song position is less than 524288 MIDI clocks. 3828 In certain situations (defined later in this section), 3829 normative text may require the C = 0 or the C = 1, 3830 TOP = 0, CLOCK = 0 encoding of the start of the song. 3832 The C, TOP, and CLOCK fields MUST be set to code the current song 3833 position, for both N = 0 and N = 1 conditions. If C = 0, the TOP field 3834 MUST be set to 0. See [MIDI] for a precise definition of a song 3835 position. 3837 The D header bit encodes information about the downbeat and acts to 3838 qualify the song position coded by the C, TOP, and CLOCK fields. 3840 If the D bit is set to 1, the song position represents the most recent 3841 position in the sequence that has played. If D = 1, the next Clock 3842 command (if N = 1) or the next (Continue, Clock) pair (if N = 0) acts to 3843 increment the song position by one clock, and to play the updated 3844 position. 3846 If the D bit is set to 0, the song position represents a position in the 3847 sequence that has not yet been played. If D = 0, the next Clock command 3848 (if N = 1) or the next (Continue, Clock) pair (if N = 0) acts to play 3849 the point in the song coded by the song position. The song position is 3850 not incremented. 3852 An example of a stream that uses D = 0 coding is one whose most recent 3853 sequence command is a Start or Song Position Pointer command (both N = 1 3854 conditions). However, it is also possible to construct examples where D 3855 = 0 and N = 0. A Start command immediately followed by a Stop command 3856 is coded in Chapter Q by setting C = 0, D = 0, N = 0, TOP = 0. 3858 If N = 1 (coding Start or Continue), D = 0 (coding that the downbeat has 3859 yet to be played), and the song position is at the start of the song, 3860 the C = 0 song position encoding MUST be used if a Start command occurs 3861 more recently than a Continue command in the session history, and the C 3862 = 1, TOP = 0, CLOCK = 0 song position encoding MUST be used if a 3863 Continue command occurs more recently than a Start command in the 3864 session history. 3866 B.3.1. Non-compliant Sequencers 3868 The Chapter Q description in this appendix assumes that the sequencer 3869 system counts off time with Clock commands, as mandated in [MIDI]. 3870 However, a few non-compliant products do not use Clock commands to count 3871 off time, but instead use non-standard methods. 3873 Chapter Q uses the TIMETOOLS field to provide resiliency support for 3874 these non-standard products. By default, the TIMETOOLS field MUST NOT 3875 appear in Chapter Q, and the T header bit MUST be set to 0. The session 3876 configuration tools described in Appendix C.2.3 may be used to select 3877 TIMETOOLS coding. 3879 Figure B.3.2 shows the format of the 24-bit TIMETOOLS field. 3881 0 1 2 3882 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 3883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3884 | TIME | 3885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3887 Figure B.3.2 -- TIMETOOLS format 3889 The TIME field is a 24-bit unsigned integer quantity, with units of 3890 milliseconds. TIME codes an additive correction term for the song 3891 position coded by the TOP, CLOCK, and C fields. TIME is coded in 3892 network byte order (big-endian). 3894 A receiver computes the correct song position by converting TIME into 3895 units of MIDI clocks and adding it to 65536*TOP + CLOCK (assuming C = 3896 1). Alternatively, a receiver may convert 65536*TOP + CLOCK into 3897 milliseconds (assuming C = 1) and add it to TIME. The downbeat (D 3898 header bit) semantics defined in Appendix B.3 apply to the corrected 3899 song position. 3901 B.4. System Chapter F: MIDI Time Code Tape Position 3903 This appendix describes Chapter F, the system chapter for the MIDI Time 3904 Code (MTC) commands. Readers may wish to review the Appendix A.1 3905 definition of "finished/unfinished commands" before reading this 3906 appendix. 3908 The system journal MUST contain Chapter F if an active System Common 3909 Quarter Frame command (0xF1) or an active finished System Exclusive 3910 (Universal Real Time) MTC Full Frame command (F0 7F cc 01 01 hr mn sc fr 3911 F7) appears in the checkpoint history. Otherwise, the system journal 3912 MUST NOT contain Chapter F. 3914 Figure B.4.1 shows the variable-length format for Chapter F. 3916 0 1 2 3 3917 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 3918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3919 |S|C|P|Q|D|POINT| COMPLETE ... | 3920 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3921 | ... | PARTIAL ... | 3922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3923 | ... | 3924 +-+-+-+-+-+-+-+-+ 3926 Figure B.4.1 -- System Chapter F format 3928 Chapter F holds information about recent MTC tape positions coded in the 3929 session history. Receivers use Chapter F to re-synchronize the MTC 3930 system after a packet loss episode. 3932 Chapter F consists of a 1-octet header followed by several optional 3933 fields, in the order shown in Figure B.4.1. The C and P header bits 3934 form a Table of Contents (TOC) and signal the presence of the 32-bit 3935 COMPLETE field (C = 1) and the 32-bit PARTIAL field (P = 1). 3937 The Q header bit codes information about the COMPLETE field format. If 3938 Chapter F does not contain a COMPLETE field, Q MUST be set to 0. 3940 The D header bit codes the tape movement direction. If the tape is 3941 moving forward, or if the tape direction is indeterminate, the D bit 3942 MUST be set to 0. If the tape is moving in the reverse direction, the D 3943 bit MUST be set to 1. In most cases, the ordering of commands in the 3944 session history clearly defines the tape direction. However, a few 3945 command sequences have an indeterminate direction (such as a session 3946 history consisting of one Full Frame command). 3948 The 3-bit POINT header field is interpreted as an unsigned integer. 3949 Appendix B.4.1 defines how the POINT field codes information about the 3950 contents of the PARTIAL field. If Chapter F does not contain a PARTIAL 3951 field, POINT MUST be set to 7 (if D = 0) or 0 (if D = 1). 3953 Chapter F MUST include the COMPLETE field if an active finished Full 3954 Frame command appears in the checkpoint history, or if an active Quarter 3955 Frame command that completes the encoding of a frame value appears in 3956 the checkpoint history. 3958 The COMPLETE field encodes the most recent active complete MTC frame 3959 value that appears in the session history. This frame value may take 3960 the form of a series of 8 active Quarter Frame commands (0xF1 0x0n 3961 through 0xF1 0x7n for forward tape movement, 0xF1 0x7n through 0xF1 0x0n 3962 for reverse tape movement) or may take the form of an active finished 3963 Full Frame command. 3965 If the COMPLETE field encodes a Quarter Frame command series, the Q 3966 header bit MUST be set to 1, and the COMPLETE field MUST have the format 3967 shown in Figure B.4.2. The 4-bit fields MT0 through MT7 code the data 3968 (lower) nibble for the Quarter Frame commands for Message Type 0 through 3969 Message Type 7 [MIDI]. These nibbles encode a complete frame value, in 3970 addition to fields reserved for future use by [MIDI]. 3972 0 1 2 3 3973 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 3974 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3975 | MT0 | MT1 | MT2 | MT3 | MT4 | MT5 | MT6 | MT7 | 3976 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3978 Figure B.4.2 -- COMPLETE field format, Q = 1 3980 In this usage, the frame value encoded in the COMPLETE field MUST be 3981 offset by 2 frames (relative to the frame value encoded in the Quarter 3982 Frame commands) if the frame value codes a 0xF1 0x0n through 0xF1 0x7n 3983 command sequence. This offset compensates for the two-frame latency of 3984 the Quarter Frame encoding for forward tape movement. No offset is 3985 applied if the frame value codes a 0xF1 0x7n through 0xF1 0x0n Quarter 3986 Frame command sequence. 3988 The most recent active complete MTC frame value may alternatively be 3989 encoded by an active finished Full Frame command. In this case, the Q 3990 header bit MUST be set to 0, and the COMPLETE field MUST have format 3991 shown in Figure B.4.3. The HR, MN, SC, and FR fields correspond to the 3992 hr, mn, sc, and fr data octets of the Full Frame command. 3994 0 1 2 3 3995 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 3996 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3997 | HR | MN | SC | FR | 3998 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4000 Figure B.4.3 -- COMPLETE field format, Q = 0 4002 B.4.1. Partial Frames 4004 The most recent active session history command that encodes MTC frame 4005 value data may be a Quarter Frame command other than a forward-moving 4006 0xF1 0x7n command (which completes a frame value for forward tape 4007 movement) or a reverse-moving 0xF1 0x1n command (which completes a frame 4008 value for reverse tape movement). 4010 We consider this type of Quarter Frame command to be associated with a 4011 partial frame value. The Quarter Frame sequence that defines a partial 4012 frame value MUST either start at Message Type 0 and increment 4013 contiguously to an intermediate Message Type less than 7, or start at 4014 Message Type 7 and decrement contiguously to an intermediate Message 4015 type greater than 0. A Quarter Frame command sequence that does not 4016 follow this pattern is not associated with a partial frame value. 4018 Chapter F MUST include a PARTIAL field if the most recent active command 4019 in the checkpoint history that encodes MTC frame value data is a Quarter 4020 Frame command that is associated with a partial frame value. Otherwise, 4021 Chapter F MUST NOT include a PARTIAL field. 4023 The partial frame value consists of the data (lower) nibbles of the 4024 Quarter Frame command sequence. The PARTIAL field codes the partial 4025 frame value, using the format shown in Figure B.4.2. Message Type 4026 fields that are not associated with a Quarter Frame command MUST be set 4027 to 0. 4029 The POINT header field identifies the Message Type fields in the PARTIAL 4030 field that code valid data. If P = 1, the POINT field MUST encode the 4031 unsigned integer value formed by the lower 3 bits of the upper nibble of 4032 the data value of the most recent active Quarter Frame command in the 4033 session history. If D = 0 and P = 1, POINT MUST take on a value in the 4034 range 0-6. If D = 1 and P = 1, POINT MUST take on a value in the range 4035 1-7. 4037 If D = 0, MT fields (Figure B.4.2) in the inclusive range from 0 up to 4038 and including the POINT value encode the partial frame value. If D = 1, 4039 MT fields in the inclusive range from 7 down to and including the POINT 4040 value encode the partial frame value. Note that, unlike the COMPLETE 4041 field encoding, senders MUST NOT add a 2-frame offset to the partial 4042 frame value encoded in PARTIAL. 4044 For the default semantics, if a recovery journal contains Chapter F, and 4045 if the session history codes a legal [MIDI] series of Quarter Frame and 4046 Full Frame commands, the chapter always contains a COMPLETE or a PARTIAL 4047 field (and may contain both fields). Thus, a one-octet Chapter F (C = P 4048 = 0) always codes the presence of an illegal command sequence in the 4049 session history (under some conditions, the C = 1, P = 0 condition may 4050 also code the presence of an illegal command sequence). The illegal 4051 command sequence conditions are transient in nature and usually indicate 4052 that a Quarter Frame command sequence began with an intermediate Message 4053 Type. 4055 B.5. System Chapter X: System Exclusive 4057 This appendix describes Chapter X, the system chapter for MIDI System 4058 Exclusive (SysEx) commands (0xF0). Readers may wish to review the 4059 Appendix A.1 definition of "finished/unfinished commands" before reading 4060 this appendix. 4062 Chapter X consists of a list of one or more command logs. Each log in 4063 the list codes information about a specific finished or unfinished SysEx 4064 command that appears in the session history. The system journal MUST 4065 contain Chapter X if the rules defined in Appendix B.5.2 require that 4066 one or more logs appear in the list. 4068 The log list is not preceded by a header. Instead, each log implicitly 4069 encodes its own length. Given the length of the N'th list log, the 4070 presence of the (N+1)'th list log may be inferred from the LENGTH field 4071 of the system journal header (Figure 10 in Section 5 of the main text). 4072 The log list MUST obey the oldest-first ordering rule (defined in 4073 Appendix A.1). 4075 B.5.1. Chapter Format 4077 Figure B.5.1 shows the bitfield format for the Chapter X command logs. 4079 0 1 2 3 4080 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 4081 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4082 |S|T|C|F|D|L|STA| TCOUNT | COUNT | FIRST ... | 4083 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4084 | DATA ... | 4085 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4087 Figure B.5.1 -- Chapter X command log format 4089 A Chapter X command log consists of a 1-octet header, followed by the 4090 optional TCOUNT, COUNT, FIRST, and DATA fields. 4092 The T, C, F, and D header bits act as a Table of Contents (TOC) for the 4093 log. If T is set to 1, the 1-octet TCOUNT field appears in the log. If 4094 C is set to 1, the 1-octet COUNT field appears in the log. If F is set 4095 to 1, the variable-length FIRST field appears in the log. If D is set 4096 to 1, the variable-length DATA field appears in the log. 4098 The L header bit sets the coding tool for the log. We define the log 4099 coding tools in Appendix B.5.2. 4101 The STA field codes the status of the command coded by the log. The 4102 2-bit STA value is interpreted as an unsigned integer. If STA is 0, the 4103 log codes an unfinished command. Non-zero STA values code different 4104 classes of finished commands. An STA value of 1 codes a cancelled 4105 command, an STA value of 2 codes a command that uses the "dropped F7" 4106 construction, and an STA value of 3 codes all other finished commands. 4107 Section 3.2 in the main text describes cancelled and "dropped F7" 4108 commands. 4110 The S bit (Appendix A.1) of the first log in the list acts as the S bit 4111 for Chapter X. For the other logs in the list, the S bit refers to the 4112 log itself. The value of the "phantom" S bit associated with the first 4113 log is defined by the following rules: 4115 o If the list codes one log, the phantom S-bit value is 4116 the same as the Chapter X S-bit value. 4118 o If the list codes multiple logs, the phantom S-bit value is 4119 the logical OR of the S-bit value of the first and second 4120 command logs in the list. 4122 In all other respects, the S bit follows the semantics defined in 4123 Appendix A.1. 4125 The FIRST field (present if F = 1) encodes a variable-length unsigned 4126 integer value that sets the coverage of the DATA field. 4128 The FIRST field (present if F = 1) encodes a variable-length unsigned 4129 integer value that specifies which SysEx data bytes are encoded in the 4130 DATA field of the log. The FIRST field consists of an octet whose most- 4131 significant bit is set to 0, optionally preceded by one or more octets 4132 whose most-significant bit is set to 1. The algorithm shown in Figure 4133 B.5.2 decodes this format into an unsigned integer, to yield the value 4134 dec(FIRST). FIRST uses a variable-length encoding because dec(FIRST) 4135 references a data octet in a SysEx command, and a SysEx command may 4136 contain an arbitrary number of data octets. 4138 One-Octet FIRST value: 4140 Encoded form: 0ddddddd 4141 Decoded form: 00000000 00000000 00000000 0ddddddd 4143 Two-Octet FIRST value: 4145 Encoded form: 1ccccccc 0ddddddd 4146 Decoded form: 00000000 00000000 00cccccc cddddddd 4148 Three-Octet FIRST value: 4150 Encoded form: 1bbbbbbb 1ccccccc 0ddddddd 4151 Decoded form: 00000000 000bbbbb bbcccccc cddddddd 4153 Four-Octet FIRST value: 4155 Encoded form: 1aaaaaaa 1bbbbbbb 1ccccccc 0ddddddd 4156 Decoded form: 0000aaaa aaabbbbb bbcccccc cddddddd 4158 Figure B.5.2 -- Decoding FIRST field formats 4160 The DATA field (present if D = 1) encodes a modified version of the data 4161 octets of the SysEx command coded by the log. Status octets MUST NOT be 4162 coded in the DATA field. 4164 If F = 0, the DATA field begins with the first data octet of the SysEx 4165 command and includes all subsequent data octets for the command that 4166 appear in the session history. If F = 1, the DATA field begins with the 4167 (dec(FIRST) + 1)'th data octet of the SysEx command and includes all 4168 subsequent data octets for the command that appear in the session 4169 history. Note that the word "command" in the descriptions above refers 4170 to the original SysEx command as it appears in the source MIDI data 4171 stream, not to a particular MIDI list SysEx command segment. 4173 The length of the DATA field is coded implicitly, using the most- 4174 significant bit of each octet. The most-significant bit of the final 4175 octet of the DATA field MUST be set to 1. The most-significant bit of 4176 all other DATA octets MUST be set to 0. This coding method relies on 4177 the fact that the most-significant bit of a MIDI data octet is 0 by 4178 definition. Apart from this length-coding modification, the DATA field 4179 encodes a verbatim copy of all data octets it encodes. 4181 B.5.2. Log Inclusion Semantics 4183 Chapter X offers two tools to protect SysEx commands: the "recency" tool 4184 and the "list" tool. The tool definitions use the concept of the "SysEx 4185 type" of a command, which we now define. 4187 Each SysEx command instance in a session, excepting MTC Full Frame 4188 commands, is said to have a "SysEx type". Types are used in equality 4189 comparisons: two SysEx commands in a session are said to have "the same 4190 SysEx type" or "different SysEx types". 4192 If efficiency is not a concern, a sender may follow a simple typing 4193 rule: every SysEx command in the session history has a different SysEx 4194 type, and thus no two commands in the session have the same type. 4196 To improve efficiency, senders MAY implement exceptions to this rule. 4197 These exceptions declare that certain sets of SysEx command instances 4198 have the same SysEx type. Any command not covered by an exception 4199 follows the simple rule. We list exceptions below: 4201 o All commands with identical data octet fields (same number of 4202 data octets, same value for each data octet) have the same type. 4203 This rule MUST be applied to all SysEx commands in the session, 4204 or not at all. Note that the implementation of this exception 4205 requires no sender knowledge of the format and semantics of 4206 the SysEx commands in the stream, merely the ability to count 4207 and compare octets. 4209 o Two instances of the same command whose semantics set or report 4210 the value of the same "parameter" have the same type. The 4211 implementation of this exception requires specific knowledge of 4212 the format and semantics of SysEx commands. In practice, a 4213 sender implementation chooses to support this exception for 4214 certain classes of commands (such as the Universal System 4215 Exclusive commands defined in [MIDI]). If a sender supports 4216 this exception for a particular command in a class (for 4217 example, the Universal Real Time System Exclusive message 4218 for Master Volume, F0 F7 cc 04 01 vv vv F7, defined in [MIDI]), 4219 it MUST support the exception to all instances of this 4220 particular command in the session. 4222 We now use this definition of "SysEx type" to define the "recency" tool 4223 and the "list" tool for Chapter X. 4225 By default, the Chapter X log list MUST code sufficient information to 4226 protect the rendered MIDI performance from indefinite artifacts caused 4227 by the loss of all finished or unfinished active SysEx commands that 4228 appear in the checkpoint history (excluding finished MTC Full Frame 4229 commands, which are coded in Chapter F (Appendix B.4)). 4231 To protect a command of a specific SysEx type with the recency tool, 4232 senders MUST code a log in the log list for the most recent finished 4233 active instance of the SysEx type that appears in the checkpoint 4234 history. Additionally, if an unfinished active instance of the SysEx 4235 type appears in the checkpoint history, senders MUST code a log in the 4236 log list for the unfinished command instance. The L header bit of both 4237 command logs MUST be set to 0. 4239 To protect a command of a specific SysEx type with the list tool, 4240 senders MUST code a log in the Chapter X log list for each finished or 4241 unfinished active instance of the SysEx type that appears in the 4242 checkpoint history. The L header bit of list tool command logs MUST be 4243 set to 1. 4245 As a rule, a log REQUIRED by the list or recency tool MUST include a 4246 DATA field that codes all data octets that appear in the checkpoint 4247 history for the SysEx command instance associated with the log. The 4248 FIRST field MAY be used to configure a DATA field that minimally meets 4249 this requirement. 4251 An exception to this rule applies to cancelled commands (defined in 4252 Section 3.2). REQUIRED command logs associated with cancelled commands 4253 MAY be coded with no DATA field. However, if DATA appears in the log, 4254 DATA MUST code all data octets that appear in the checkpoint history for 4255 the command associated with the log. 4257 As defined by the preceding text in this section, by default all 4258 finished or unfinished active SysEx commands that appear in the 4259 checkpoint history (excluding finished MTC Full Frame commands) MUST be 4260 protected by the list tool or the recency tool. 4262 For some MIDI source streams, this default yields a Chapter X whose size 4263 is too large. For example, imagine that a sender begins to transcode a 4264 SysEx command with 10,000 data octets onto a UDP RTP stream "on the 4265 fly", by sending SysEx command segments as soon as data octets are 4266 delivered by the MIDI source. After 1000 octets have been sent, the 4267 expansion of Chapter X yields an RTP packet that is too large to fit in 4268 the Maximum Transmission Unit (MTU) for the stream. 4270 In this situation, if a sender uses the closed-loop sending policy for 4271 SysEx commands, the RTP packet size may always be capped by stalling the 4272 stream. In a stream stall, once the packet reaches a maximum size, the 4273 sender refrains from sending new packets with non-empty MIDI Command 4274 Sections until receiver feedback permits the trimming of Chapter X. If 4275 the stream permits arbitrary commands to appear between SysEx segments 4276 (selectable during configuration using the tools defined in Appendix 4277 C.1), the sender may stall the SysEx segment stream but continue to code 4278 other commands in the MIDI list. 4280 Stalls are a workable but sub-optimal solution to Chapter X size issues. 4281 As an alternative to stalls, senders SHOULD take preemptive action 4282 during session configuration to reduce the anticipated size of Chapter 4283 X, using the methods described below: 4285 o Partitioned transport. Appendix C.5 provides tools 4286 for sending a MIDI name space over several RTP streams. 4287 Senders may use these tools to map a MIDI source 4288 into a low-latency UDP RTP stream (for channel commands 4289 and short SysEx commands) and a reliable [RFC4571] TCP stream 4290 (for bulk-data SysEx commands). The cm_unused and 4291 cm_used parameters (Appendix C.1) may be used to 4292 communicate the nature of the SysEx command partition. 4293 As TCP is reliable, the RTP MIDI TCP stream would not 4294 use the recovery journal. To minimize transmission 4295 latency for short SysEx commands, senders may begin 4296 segmental transmission for all SysEx commands over the 4297 UDP stream and then cancel the UDP transmission of long 4298 commands (using tools described in Section 3.2) and 4299 resend the commands over the TCP stream. 4301 o Selective protection. Journal protection may not be 4302 necessary for all SysEx commands in a stream. The 4303 ch_never parameter (Appendix C.2) may be used to 4304 communicate which SysEx commands are excluded from 4305 Chapter X. 4307 B.5.3. TCOUNT and COUNT Fields 4309 If the T header bit is set to 1, the 8-bit TCOUNT field appears in the 4310 command log. If the C header bit is set to 1, the 8-bit COUNT field 4311 appears in the command log. TCOUNT and COUNT are interpreted as 4312 unsigned integers. 4314 The TCOUNT field codes the total number of SysEx commands of the SysEx 4315 type coded by the log that appear in the session history, at the moment 4316 after the (finished or unfinished) command coded by the log enters the 4317 session history. 4319 The COUNT field codes the total number of SysEx commands that appear in 4320 the session history, excluding commands that are excluded from Chapter X 4321 via the ch_never parameter (Appendix C.2), at the moment after the 4322 (finished or unfinished) command coded by the log enters the session 4323 history. 4325 Command counting for TCOUNT and COUNT uses modulo-256 arithmetic. MTC 4326 Full Frame command instances (Appendix B.4) are included in command 4327 counting if the TCOUNT and COUNT definitions warrant their inclusion, as 4328 are cancelled commands (Section 3.2). 4330 Senders use the TCOUNT and COUNT fields to track the identity and (for 4331 TCOUNT) the sequence position of a command instance. Senders MUST use 4332 the TCOUNT or COUNT fields if identity or sequence information is 4333 necessary to protect the command type coded by the log. 4335 If a sender uses the COUNT field in a session, the final command log in 4336 every Chapter X in the stream MUST code the COUNT field. This rule lets 4337 receivers resynchronize the COUNT value after a packet loss. 4339 C. Session Configuration Tools 4341 In Sections 6.1-2 of the main text, we show session descriptions for 4342 minimal native and mpeg4-generic RTP MIDI streams. Minimal streams lack 4343 the flexibility to support some applications. In this appendix, we 4344 describe how to customize stream behavior through the use of the payload 4345 format parameters. 4347 The appendix begins with 6 sections, each devoted to parameters that 4348 affect a particular aspect of stream behavior: 4350 o Appendix C.1 describes the stream subsetting system 4351 (cm_unused and cm_used). 4353 o Appendix C.2 describes the journalling system (ch_anchor, 4354 ch_default, ch_never, j_sec, j_update). 4356 o Appendix C.3 describes MIDI command timestamp semantics 4357 (linerate, mperiod, octpos, tsmode). 4359 o Appendix C.4 describes the temporal duration ("media time") 4360 of an RTP MIDI packet (guardtime, rtp_maxptime, rtp_ptime). 4362 o Appendix C.5 concerns stream description (musicport). 4364 o Appendix C.6 describes MIDI rendering (chanmask, cid, 4365 inline, multimode, render, rinit, subrender, smf_cid, 4366 smf_info, smf_inline, smf_url, url). 4368 The parameters listed above may optionally appear in session 4369 descriptions of RTP MIDI streams. If these parameters are used in an 4370 SDP session description, the parameters appear on an fmtp attribute 4371 line. This attribute line applies to the payload type associated with 4372 the fmtp line. 4374 The parameters listed above add extra functionality ("features") to 4375 minimal RTP MIDI streams. In Appendix C.7, we show how to use these 4376 features to support two classes of applications: content-streaming using 4377 RTSP (Appendix C.7.1) and network musical performance using SIP 4378 (Appendix C.7.2). 4380 The participants in a multimedia session MUST share a common view of all 4381 of the RTP MIDI streams that appear in an RTP session, as defined by a 4382 single media (m=) line. In some RTP MIDI applications, the "common 4383 view" restriction makes it difficult to use sendrecv streams (all 4384 parties send and receive), as each party has its own requirements. For 4385 example, a two-party network musical performance application may wish to 4386 customize the renderer on each host to match the CPU performance of the 4387 host [NMP]. 4389 We solve this problem by using two RTP MIDI streams -- one sendonly, one 4390 recvonly -- in lieu of one sendrecv stream. The data flows in the two 4391 streams travel in opposite directions, to control receivers configured 4392 to use different renderers. In the third example in Appendix C.5, we 4393 show how the musicport parameter may be used to define virtual sendrecv 4394 streams. 4396 As a general rule, the RTP MIDI protocol does not handle parameter 4397 changes during a session well, because the parameters describe 4398 heavyweight or stateful configuration that is not easily changed once a 4399 session has begun. Thus, parties SHOULD NOT expect that parameter 4400 change requests during a session will be accepted by other parties. 4401 However, implementors SHOULD support in-session parameter changes that 4402 are easy to handle (for example, the guardtime parameter defined in 4403 Appendix C.4) and SHOULD be capable of accepting requests for changes of 4404 those parameters, as received by its session management protocol (for 4405 example, re-offers in SIP [RFC3264]). 4407 Appendix D defines the Augmented Backus-Naur Form (ABNF, [RFC4234]) 4408 syntax for the payload parameters. Section 11 provides information to 4409 the Internet Assigned Numbers Authority (IANA) on the media types and 4410 parameters defined in this document. 4412 Appendix C.6.5 defines the media type "audio/asc", a stored object for 4413 initializing mpeg4-generic renderers. As described in Appendix C.6, the 4414 audio/asc media type is assigned to the "rinit" parameter to specify an 4415 initialization data object for the default mpeg4-generic renderer. Note 4416 that RTP stream semantics are not defined for "audio/asc". Therefore, 4417 the "asc" subtype MUST NOT appear on the rtpmap line of a session 4418 description. 4420 C.1. Configuration Tools: Stream Subsetting 4422 As defined in Section 3.2 in the main text, the MIDI list of an RTP MIDI 4423 packet may encode any MIDI command that may legally appear on a MIDI 1.0 4424 DIN cable. 4426 In this appendix, we define two parameters (cm_unused and cm_used) that 4427 modify this default condition, by excluding certain types of MIDI 4428 commands from the MIDI list of all packets in a stream. For example, if 4429 a multimedia session partitions a MIDI name space into two RTP MIDI 4430 streams, the parameters may be used to define which commands appear in 4431 each stream. 4433 In this appendix, we define a simple language for specifying MIDI 4434 command types. If a command type is assigned to cm_unused, the commands 4435 coded by the string MUST NOT appear in the MIDI list. If a command type 4436 is assigned to cm_used, the commands coded by the string MAY appear in 4437 the MIDI list. 4439 The parameter list may code multiple assignments to cm_used and 4440 cm_unused. Assignments have a cumulative effect and are applied in the 4441 order of appearance in the parameter list. A later assignment of a 4442 command type to the same parameter expands the scope of the earlier 4443 assignment. A later assignment of a command type to the opposite 4444 parameter cancels (partially or completely) the effect of an earlier 4445 assignment. 4447 To initialize the stream subsetting system, "implicit" assignments to 4448 cm_unused and cm_used are processed before processing the actual 4449 assignments that appear in the parameter list. The System Common 4450 undefined commands (0xF4, 0xF5) and the System Real-Time Undefined 4451 commands (0xF9, 0xFD) are implicitly assigned to cm_unused. All other 4452 command types are implicitly assigned to cm_used. 4454 Note that the implicit assignments code the default behavior of an RTP 4455 MIDI stream as defined in Section 3.2 in the main text (namely, that all 4456 commands that may legally appear on a MIDI 1.0 DIN cable may appear in 4457 the stream). Also note that assignments of the System Common undefined 4458 commands (0xF4, 0xF5) apply to the use of these commands in the MIDI 4459 source command stream, not the special use of 0xF4 and 0xF5 in SysEx 4460 segment encoding defined in Section 3.2 in the main text. 4462 As a rule, parameter assignments obey the following syntax (see Appendix 4463 D for ABNF): 4465 = [channel list][field list] 4467 The command-type list is mandatory; the channel and field lists are 4468 optional. 4470 The command-type list specifies the MIDI command types for which the 4471 parameter applies. The command-type list is a concatenated sequence of 4472 one or more of the letters (ABCFGHJKMNPQTVWXYZ). The letters code the 4473 following command types: 4475 o A: Poly Aftertouch (0xA) 4476 o B: System Reset (0xFF) 4477 o C: Control Change (0xB) 4478 o F: System Time Code (0xF1) 4479 o G: System Tune Request (0xF6) 4480 o H: System Song Select (0xF3) 4481 o J: System Common Undefined (0xF4) 4482 o K: System Common Undefined (0xF5) 4483 o N: NoteOff (0x8), NoteOn (0x9) 4484 o P: Program Change (0xC) 4485 o Q: System Sequencer (0xF2, 0xF8, 0xFA, 0xFB, 0xFC) 4486 o T: Channel Aftertouch (0xD) 4487 o V: System Active Sense (0xFE) 4488 o W: Pitch Wheel (0xE) 4489 o X: SysEx (0xF0, 0xF7) 4490 o Y: System Real-Time Undefined (0xF9) 4491 o Z: System Real-Time Undefined (0xFD) 4493 In addition to the letters above, the letter M may also appear in the 4494 command-type list. The letter M refers to the MIDI parameter system 4495 (see definition in Appendix A.1 and in [MIDI]). An assignment of M to 4496 cm_unused codes that no RPN or NRPN transactions may appear in the MIDI 4497 list. 4499 Note that if cm_unused is assigned the letter M, Control Change (0xB) 4500 commands for the controller numbers in the standard controller 4501 assignment might still appear in the MIDI list. For an explanation, see 4502 Appendix A.3.4 for a discussion of the "general-purpose" use of 4503 parameter system controller numbers. 4505 In the text below, rules that apply to "MIDI voice channel commands" 4506 also apply to the letter M. 4508 The letters in the command-type list MUST be uppercase and MUST appear 4509 in alphabetical order. Letters other than (ABCFGHJKMNPQTVWXYZ) that 4510 appear in the list MUST be ignored. 4512 For MIDI voice channel commands, the channel list specifies the MIDI 4513 channels for which the parameter applies. If no channel list is 4514 provided, the parameter applies to all MIDI channels (0-15). The 4515 channel list takes the form of a list of channel numbers (0 through 15) 4516 and dash-separated channel number ranges (i.e., 0-5, 8-12, etc.). Dots 4517 (i.e., "." characters) separate elements in the channel list. 4519 Recall that System commands do not have a MIDI channel associated with 4520 them. Thus, for most command-type letters that code System commands (B, 4521 F, G, H, J, K, Q, V, Y, and Z), the channel list is ignored. 4523 For the command-type letter X, the appearance of certain numbers in the 4524 channel list codes special semantics. 4526 o The digit 0 codes that SysEx "cancel" sublists (Section 4527 3.2 in the main text) MUST NOT appear in the MIDI list. 4529 o The digit 1 codes that cancel sublists MAY appear in the 4530 MIDI list (the default condition). 4532 o The digit 2 codes that commands other than System 4533 Real-time MIDI commands MUST NOT appear between SysEx 4534 command segments in the MIDI list (the default condition). 4536 o The digit 3 codes that any MIDI command type may 4537 appear between SysEx command segments in the MIDI list, 4538 with the exception of the segmented encoding of a second 4539 SysEx command (verbatim SysEx commands are OK). 4541 For command-type X, the channel list MUST NOT contain both digits 0 and 4542 1, and it MUST NOT contain both digits 2 and 3. For command-type X, 4543 channel list numbers other than the numbers defined above are ignored. 4544 If X does not have a channel list, the semantics marked "the default 4545 condition" in the list above apply. 4547 The syntax for field lists in a parameter assignment follows the syntax 4548 for channel lists. If no field list is provided, the parameter applies 4549 to all controller or note numbers. 4551 For command-type C (Control Change), the field list codes the controller 4552 numbers (0-255) for which the parameter applies. 4554 For command-type M (Parameter System), the field list codes the 4555 Registered Parameter Numbers (RPNs) and Non-Registered Parameter Numbers 4556 (NRPNs) for which the parameter applies. The number range 0-16383 4557 specifies RPNs, the number range 16384-32767 specifies NRPNs (16384 4558 corresponds to NRPN 0, 32767 corresponds to NRPN 16383). 4560 For command-types N (NoteOn and NoteOff) and A (Poly Aftertouch), the 4561 field list codes the note numbers for which the parameter applies. 4563 For command-types J and K (System Common Undefined), the field list 4564 consists of a single digit, which specifies the number of data octets 4565 that follow the command octet. 4567 For command-type X (SysEx), the field list codes the number of data 4568 octets that may appear in a SysEx command. Thus, the field list 0-255 4569 specifies SysEx commands with 255 or fewer data octets, the field list 4570 256-4294967295 specifies SysEx commands with more than 255 data octets 4571 but excludes commands with 255 or fewer data octets, and the field list 4572 0 excludes all commands. 4574 A secondary parameter assignment syntax customizes command-type X (see 4575 Appendix D for complete ABNF): 4577 = "__" *( "_" ) "__" 4579 The assignment defines the class of SysEx commands that obeys the 4580 semantics of the assigned parameter. The command class is specified by 4581 listing the permitted values of the first N data octets that follow the 4582 SysEx 0xF0 command octet. Any SysEx command whose first N data octets 4583 match the list is a member of the class. 4585 Each defines a data octet of the command, as a dot-separated 4586 (".") list of one or more hexadecimal constants (such as "7F") or dash- 4587 separated hexadecimal ranges (such as "01-1F"). Underscores ("_") 4588 separate each . Double-underscores ("__") delineate the data 4589 octet list. 4591 Using this syntax, each assignment specifies a single SysEx command 4592 class. Session descriptions may use several assignments to cm_used and 4593 cm_unused to specify complex behaviors. 4595 The example session description below illustrates the use of the stream 4596 subsetting parameters: 4598 v=0 4599 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 4600 s=Example 4601 t=0 0 4602 m=audio 5004 RTP/AVP 96 4603 c=IN IP6 2001:DB80::7F2E:172A:1E24 4604 a=rtpmap:96 rtp-midi/44100 4605 a=fmtp:96 cm_unused=ACGHJKNMPTVWXYZ; cm_used=__7F_00-7F_01_01__ 4607 The session description configures the stream for use in clock 4608 applications. All voice channels are unused, as are all System Commands 4609 except those used for MIDI Time Code (command-type F, and the Full Frame 4610 SysEx command that is matched by the string assigned to cm_used), the 4611 System Sequencer commands (command-type Q), and System Reset (command- 4612 type B). 4614 C.2. Configuration Tools: The Journalling System 4616 In this appendix, we define the payload format parameters that configure 4617 stream journalling and the recovery journal system. 4619 The j_sec parameter (Appendix C.2.1) sets the journalling method for the 4620 stream. The j_update parameter (Appendix C.2.2) sets the recovery 4621 journal sending policy for the stream. Appendix C.2.2 also defines the 4622 sending policies of the recovery journal system. 4624 Appendix C.2.3 defines several parameters that modify the recovery 4625 journal semantics. These parameters change the default recovery journal 4626 semantics as defined in Section 5 and Appendices A-B. 4628 The journalling method for a stream is set at the start of a session and 4629 MUST NOT be changed thereafter. This requirement forbids changes to the 4630 j_sec parameter once a session has begun. 4632 A related requirement, defined in the appendix sections below, forbids 4633 the acceptance of parameter values that would violate the recovery 4634 journal mandate. In many cases, a change in one of the parameters 4635 defined in this appendix during an ongoing session would result in a 4636 violation of the recovery journal mandate for an implementation; in this 4637 case, the parameter change MUST NOT be accepted. 4639 C.2.1. The j_sec Parameter 4641 Section 2.2 defines the default journalling method for a stream. 4642 Streams that use unreliable transport (such as UDP) default to using the 4643 recovery journal. Streams that use reliable transport (such as TCP) 4644 default to not using a journal. 4646 The parameter j_sec may be used to override this default. This memo 4647 defines two symbolic values for j_sec: "none", to indicate that all 4648 stream payloads MUST NOT contain a journal section, and "recj", to 4649 indicate that all stream payloads MUST contain a journal section that 4650 uses the recovery journal format. 4652 For example, the j_sec parameter might be set to "none" for a UDP stream 4653 that travels between two hosts on a local network that is known to 4654 provide reliable datagram delivery. 4656 The session description below configures a UDP stream that does not use 4657 the recovery journal: 4659 v=0 4660 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 4661 s=Example 4662 t=0 0 4663 m=audio 5004 RTP/AVP 96 4664 c=IN IP4 192.0.2.94 4665 a=rtpmap:96 rtp-midi/44100 4666 a=fmtp:96 j_sec=none 4668 Other IETF standards-track documents may define alternative journal 4669 formats. These documents MUST define new symbolic values for the j_sec 4670 parameter to signal the use of the format. 4672 Parties MUST NOT accept a j_sec value that violates the recovery journal 4673 mandate (see Section 4 for details). If a session description uses a 4674 j_sec value unknown to the recipient, the recipient MUST NOT accept the 4675 description. 4677 Special j_sec issues arise when sessions are managed by session 4678 management tools (like RTSP, [RFC2326]) that use SDP for "declarative 4679 usage" purposes (see the preamble of Section 6 for details). For these 4680 session management tools, SDP does not code transport details (such as 4681 UDP or TCP) for the session. Instead, server and client negotiate 4682 transport details via other means (for RTSP, the SETUP method). 4684 In this scenario, the use of the j_sec parameter may be ill-advised, as 4685 the creator of the session description may not yet know the transport 4686 type for the session. In this case, the session description SHOULD 4687 configure the journalling system using the parameters defined in the 4688 remainder of Appendix C.2, but it SHOULD NOT use j_sec to set the 4689 journalling status. Recall that if j_sec does not appear in the session 4690 description, the default method for choosing the journalling method is 4691 in effect (no journal for reliable transport, recovery journal for 4692 unreliable transport). 4694 However, in declarative usage situations where the creator of the 4695 session description knows that journalling is always required or never 4696 required, the session description SHOULD use the j_sec parameter. 4698 C.2.2. The j_update Parameter 4700 In Section 4, we use the term "sending policy" to describe the method a 4701 sender uses to choose the checkpoint packet identity for each recovery 4702 journal in a stream. In the sub-sections that follow, we normatively 4703 define three sending policies: anchor, closed-loop, and open-loop. 4705 As stated in Section 4, the default sending policy for a stream is the 4706 closed-loop policy. The j_update parameter may be used to override this 4707 default. 4709 We define three symbolic values for j_update: "anchor", to indicate that 4710 the stream uses the anchor sending policy, "open-loop", to indicate that 4711 the stream uses the open-loop sending policy, and "closed-loop", to 4712 indicate that the stream uses the closed-loop sending policy. See 4713 Appendix C.2.3 for examples session descriptions that use the j_update 4714 parameter. 4716 Parties MUST NOT accept a j_update value that violates the recovery 4717 journal mandate (Section 4). 4719 Other IETF standards-track documents may define additional sending 4720 policies for the recovery journal system. These documents MUST define 4721 new symbolic values for the j_update parameter to signal the use of the 4722 new policy. If a session description uses a j_update value unknown to 4723 the recipient, the recipient MUST NOT accept the description. 4725 C.2.2.1. The anchor Sending Policy 4727 In the anchor policy, the sender uses the first packet in the stream as 4728 the checkpoint packet for all packets in the stream. The anchor policy 4729 satisfies the recovery journal mandate (Section 4), as the checkpoint 4730 history always covers the entire stream. 4732 The anchor policy does not require the use of the RTP control protocol 4733 (RTCP, [RFC3550]) or other feedback from receiver to sender. Senders do 4734 not need to take special actions to ensure that received streams start 4735 up free of artifacts, as the recovery journal always covers the entire 4736 history of the stream. Receivers are relieved of the responsibility of 4737 tracking the changing identity of the checkpoint packet, because the 4738 checkpoint packet never changes. 4740 The main drawback of the anchor policy is bandwidth efficiency. Because 4741 the checkpoint history covers the entire stream, the size of the 4742 recovery journals produced by this policy usually exceeds the journal 4743 size of alternative policies. For single-channel MIDI data streams, the 4744 bandwidth overhead of the anchor policy is often acceptable (see 4745 Appendix A.4 of [NMP]). For dense streams, the closed-loop or open-loop 4746 policies may be more appropriate. 4748 C.2.2.2. The closed-loop Sending Policy 4750 The closed-loop policy is the default policy of the recovery journal 4751 system. For each packet in the stream, the policy lets senders choose 4752 the smallest possible checkpoint history that satisfies the recovery 4753 journal mandate. As smaller checkpoint histories generally yield 4754 smaller recovery journals, the closed-loop policy reduces the bandwidth 4755 of a stream, relative to the anchor policy. 4757 The closed-loop policy relies on feedback from receiver to sender. The 4758 policy assumes that a receiver periodically informs the sender of the 4759 highest sequence number it has seen so far in the stream, coded in the 4760 32-bit extension format defined in [RFC3550]. For RTCP, receivers 4761 transmit this information in the Extended Highest Sequence Number 4762 Received (EHSNR) field of Receiver Reports. RTCP Sender or Receiver 4763 Reports MUST be sent by any participant in a session with closed loop 4764 sending policy, unless another feedback mechanism has been agreed upon. 4766 The sender may safely use receiver sequence number feedback to guide 4767 checkpoint history management, because Section 4 requires that receivers 4768 repair indefinite artifacts whenever a packet loss event occur. 4770 We now normatively define the closed-loop policy. At the moment a 4771 sender prepares an RTP packet for transmission, the sender is aware of R 4772 >= 0 receivers for the stream. Senders may become aware of a receiver 4773 via RTCP traffic from the receiver, via RTP packets from a paired stream 4774 sent by the receiver to the sender, via messages from a session 4775 management tool, or by other means. As receivers join and leave a 4776 session, the value of R changes. 4778 Each known receiver k (1 <= k <= R) is associated with a 32-bit extended 4779 packet sequence number M(k), where the extension reflects the sequence 4780 number rollover count of the sender. 4782 If the sender has received at least one feedback report from receiver k, 4783 M(k) is the most recent report of the highest RTP packet sequence number 4784 seen by the receiver, normalized to reflect the rollover count of the 4785 sender. 4787 If the sender has not received a feedback report from the receiver, M(k) 4788 is the extended sequence number of the last packet the sender 4789 transmitted before it became aware of the receiver. If the sender 4790 became aware of this receiver before it sent the first packet in the 4791 stream, M(k) is the extended sequence number of the first packet in the 4792 stream. 4794 Given this definition of M(), we now state the closed-loop policy. When 4795 preparing a new packet for transmission, a sender MUST choose a 4796 checkpoint packet with extended sequence number N, such that M(k) >= (N 4797 - 1) for all k, 1 <= k <= R, where R >= 1. The policy does not restrict 4798 sender behavior in the R == 0 (no known receivers) case. 4800 Under the closed-loop policy as defined above, a sender may transmit 4801 packets whose checkpoint history is shorter than the session history (as 4802 defined in Appendix A.1). In this event, a new receiver that joins the 4803 stream may experience indefinite artifacts. 4805 For example, if a Control Change (0xB) command for Channel Volume 4806 (controller number 7) was sent early in a stream, and later a new 4807 receiver joins the session, the closed-loop policy may permit all 4808 packets sent to the new receiver to use a checkpoint history that does 4809 not include the Channel Volume Control Change command. As a result, the 4810 new receiver experiences an indefinite artifact, and plays all notes on 4811 a channel too loudly or too softly. 4813 To address this issue, the closed-loop policy states that whenever a 4814 sender becomes aware of a new receiver, the sender MUST determine if the 4815 receiver would be subject to indefinite artifacts under the closed-loop 4816 policy. If so, the sender MUST ensure that the receiver starts the 4817 session free of indefinite artifacts. For example, to solve the Channel 4818 Volume issue described above, the sender may code the current state of 4819 the Channel Volume controller numbers in the recovery journal Chapter C, 4820 until it receives the first RTCP RR report that signals that a packet 4821 containing this Chapter C has been received. 4823 In satisfying this requirement, senders MAY infer the initial MIDI state 4824 of the receiver from the session description. For example, the stream 4825 example in Section 6.2 has the initial state defined in [MIDI] for 4826 General MIDI. 4828 In a unicast RTP session, a receiver may safely assume that the sender 4829 is aware of its presence as a receiver from the first packet sent in the 4830 RTP stream. However, in other types of RTP sessions (multicast, 4831 conference focus, RTP translator/mixer), a receiver is often not able to 4832 determine if the sender is initially aware of its presence as a 4833 receiver. 4835 To address this issue, the closed-loop policy states that if a receiver 4836 participates in a session where it may have access to a stream whose 4837 sender is not aware of the receiver, the receiver MUST take actions to 4838 ensure that its rendered MIDI performance does not contain indefinite 4839 artifacts. These protections will be necessarily incomplete. For 4840 example, a receiver may monitor the Checkpoint Packet Seqnum for 4841 uncovered loss events, and "err on the side of caution" with respect to 4842 handling stuck notes due to lost MIDI NoteOff commands, but the receiver 4843 is not able to compensate for the lack of Channel Volume initialization 4844 data in the recovery journal. 4846 The receiver MUST NOT discontinue these protective actions until it is 4847 certain that the sender is aware of its presence. If a receiver is not 4848 able to ascertain sender awareness, the receiver MUST continue these 4849 protective actions for the duration of the session. 4851 Note that in a multicast session where all parties are expected to send 4852 and receive, the reception of RTCP receiver reports from the sender 4853 about the RTP stream a receiver is multicasting back is evidence of the 4854 sender's awareness that the RTP stream multicast by the sender is being 4855 monitored by the receiver. Receivers may also obtain sender awareness 4856 evidence from session management tools, or by other means. In practice, 4857 ongoing observation of the Checkpoint Packet Seqnum to determine if the 4858 sender is taking actions to prevent loss events for a receiver is a good 4859 indication of sender awareness, as is the sudden appearance of recovery 4860 journal chapters with numerous Control Change controller data that was 4861 not foreshadowed by recent commands coded in the MIDI list shortly after 4862 sending an RTCP RR. 4864 The final set of normative closed-loop policy requirements concerns how 4865 senders and receivers handle unplanned disruptions of RTCP feedback from 4866 a receiver to a sender. By "unplanned", we refer to disruptions that 4867 are not due to the signalled termination of an RTP stream, via an RTCP 4868 BYE or via session management tools. 4870 As defined earlier in this section, the closed-loop policy states that a 4871 sender MUST choose a checkpoint packet with extended sequence number N, 4872 such that M(k) >= (N - 1) for all k, 1 <= k <= R, where R >= 1. If the 4873 sender has received at least one feedback report from receiver k, M(k) 4874 is the most recent report of the highest RTP packet sequence number seen 4875 by the receiver, normalized to reflect the rollover count of the sender. 4877 If this receiver k stops sending feedback to the sender, the M(k) value 4878 used by the sender reflects the last feedback report from the receiver. 4879 As time progresses without feedback from receiver k, this fixed M(k) 4880 value forces the sender to increase the size of the checkpoint history, 4881 and thus increases the bandwidth of the stream. 4883 At some point, the sender may need to take action in order to limit the 4884 bandwidth of the stream. In most envisioned uses of RTP MIDI, long 4885 before this point is reached, the SSRC time-out mechanism defined in 4886 [RFC3550] will remove the uncooperative receiver from the session (note 4887 that the closed-loop policy does not suggest or require any special 4888 sender behavior upon an SSRC time-out, other than the sender actions 4889 related to changing R, described earlier in this section). 4891 However, in rare situations, the bandwidth of the stream (due to a lack 4892 of feedback reports from the sender) may become too large to continue 4893 sending the stream to the receiver before the SSRC time-out occurs for 4894 the receiver. In this case, the closed-loop policy states that the 4895 sender should invoke the SSRC time-out for the receiver early. 4897 We now discuss receiver responsibilities in the case of unplanned 4898 disruptions of RTCP feedback from receiver to sender. 4900 In the unicast case, if a sender invokes the SSRC time-out mechanism for 4901 a receiver, the receiver stops receiving packets from the sender. The 4902 sender behavior imposed by the guardtime parameter (Appendix C.4.2) lets 4903 the receiver conclude that an SSRC time-out has occurred in a reasonable 4904 time period. 4906 In this case of a time-out, a receiver MUST keep sending RTCP feedback, 4907 in order to re-establish the RTP flow from the sender. Unless the 4908 receiver expects a prompt recovery of the RTP flow, the receiver MUST 4909 take actions to ensure that the rendered MIDI performance does not 4910 exhibit "very long transient artifacts" (for example, by silencing 4911 NoteOns to prevent stuck notes) while awaiting reconnection of the flow. 4913 In the multicast case, if a sender invokes the SSRC time-out mechanism 4914 for a receiver, the receiver may continue to receive packets, but the 4915 sender will no longer be using the M(k) feedback from the receiver to 4916 choose each checkpoint packet. If the receiver does not have additional 4917 information that precludes an SSRC time-out (such as RTCP Receiver 4918 Reports from the sender about an RTP stream the receiver is multicasting 4919 back to the sender), the receiver MUST monitor the Checkpoint Packet 4920 Seqnum to detect an SSRC time-out. If an SSRC time-out is detected, the 4921 receiver MUST follow the instructions for SSRC time-outs described for 4922 the unicast case above. 4924 Finally, we note that the closed-loop policy is suitable for use in 4925 RTP/RTCP sessions that use multicast transport. However, aspects of the 4926 closed-loop policy do not scale well to sessions with large numbers of 4927 participants. The sender state scales linearly with the number of 4928 receivers, as the sender needs to track the identity and M(k) value for 4929 each receiver k. The average recovery journal size is not independent 4930 of the number of receivers, as the RTCP reporting interval backoff slows 4931 down the rate of a full update of M(k) values. The backoff algorithm 4932 may also increase the amount of ancillary state used by implementations 4933 of the normative sender and receiver behaviors defined in Section 4. 4935 C.2.2.3. The open-loop Sending Policy 4937 The open-loop policy is suitable for sessions that are not able to 4938 implement the receiver-to-sender feedback required by the closed-loop 4939 policy, and that are also not able to use the anchor policy because of 4940 bandwidth constraints. 4942 The open-loop policy does not place constraints on how a sender chooses 4943 the checkpoint packet for each packet in the stream. In the absence of 4944 such constraints, a receiver may find that the recovery journal in the 4945 packet that ends a loss event has a checkpoint history that does not 4946 cover the entire loss event. We refer to loss events of this type as 4947 uncovered loss events. 4949 To ensure that uncovered loss events do not compromise the recovery 4950 journal mandate, the open-loop policy assigns specific recovery tasks to 4951 senders, receivers, and the creators of session descriptions. The 4952 underlying premise of the open-loop policy is that the indefinite 4953 artifacts produced during uncovered loss events fall into two classes. 4955 One class of artifacts is recoverable indefinite artifacts. Receivers 4956 are able to repair recoverable artifacts that occur during an uncovered 4957 loss event without intervention from the sender, at the potential cost 4958 of unpleasant transient artifacts. 4960 For example, after an uncovered loss event, receivers are able to repair 4961 indefinite artifacts due to NoteOff (0x8) commands that may have 4962 occurred during the loss event, by executing NoteOff commands for all 4963 active NoteOns commands. This action causes a transient artifact (a 4964 sudden silent period in the performance), but ensures that no stuck 4965 notes sound indefinitely. We refer to MIDI commands that are amenable 4966 to repair in this fashion as recoverable MIDI commands. 4968 A second class of artifacts is unrecoverable indefinite artifacts. If 4969 this class of artifact occurs during an uncovered loss event, the 4970 receiver is not able to repair the stream. 4972 For example, after an uncovered loss event, receivers are not able to 4973 repair indefinite artifacts due to Control Change (0xB) Channel Volume 4974 (controller number 7) commands that have occurred during the loss event. 4975 A repair is impossible because the receiver has no way of determining 4976 the data value of a lost Channel Volume command. We refer to MIDI 4977 commands that are fragile in this way as unrecoverable MIDI commands. 4979 The open-loop policy does not specify how to partition the MIDI command 4980 set into recoverable and unrecoverable commands. Instead, it assumes 4981 that the creators of the session descriptions are able to come to 4982 agreement on a suitable recoverable/unrecoverable MIDI command partition 4983 for an application. 4985 Given these definitions, we now state the normative requirements for the 4986 open-loop policy. 4988 In the open-loop policy, the creators of the session description MUST 4989 use the ch_anchor parameter (defined in Appendix C.2.3) to protect all 4990 unrecoverable MIDI command types from indefinite artifacts, or 4991 alternatively MUST use the cm_unused parameter (defined in Appendix C.1) 4992 to exclude the command types from the stream. These options act to 4993 shield command types from artifacts during an uncovered loss event. 4995 In the open-loop policy, receivers MUST examine the Checkpoint Packet 4996 Seqnum field of the recovery journal header after every loss event, to 4997 check if the loss event is an uncovered loss event. Section 5 shows how 4998 to perform this check. If an uncovered loss event has occurred, a 4999 receiver MUST perform indefinite artifact recovery for all MIDI command 5000 types that are not shielded by ch_anchor and cm_unused parameter 5001 assignments in the session description. 5003 The open-loop policy does not place specific constraints on the sender. 5004 However, the open-loop policy works best if the sender manages the size 5005 of the checkpoint history to ensure that uncovered losses occur 5006 infrequently, by taking into account the delay and loss characteristics 5007 of the network. Also, as each checkpoint packet change incurs the risk 5008 of an uncovered loss, senders should only move the checkpoint if it 5009 reduces the size of the journal. 5011 C.2.3. Recovery Journal Chapter Inclusion Parameters 5013 The recovery journal chapter definitions (Appendices A-B) specify under 5014 what conditions a chapter MUST appear in the recovery journal. In most 5015 cases, the definition states that if a certain command appears in the 5016 checkpoint history, a certain chapter type MUST appear in the recovery 5017 journal to protect the command. 5019 In this section, we describe the chapter inclusion parameters. These 5020 parameters modify the conditions under which a chapter appears in the 5021 journal. These parameters are essential to the use of the open-loop 5022 policy (Appendix C.2.2.3) and may also be used to simplify 5023 implementations of the closed-loop (Appendix C.2.2.2) and anchor 5024 (Appendix C.2.2.1) policies. 5026 Each parameter represents a type of chapter inclusion semantics. An 5027 assignment to a parameter declares which chapters (or chapter subsets) 5028 obey the inclusion semantics. We describe the assignment syntax for 5029 these parameters later in this section. 5031 A party MUST NOT accept chapter inclusion parameter values that violate 5032 the recovery journal mandate (Section 4). All assignments of the 5033 subsetting parameters (cm_used and cm_unused) MUST precede the first 5034 assignment of a chapter inclusion parameter in the parameter list. 5036 Below, we normatively define the semantics of the chapter inclusion 5037 parameters. For clarity, we define the action of parameters on complete 5038 chapters. If a parameter is assigned a subset of a chapter, the 5039 definition applies only to the chapter subset. 5041 o ch_never. A chapter assigned to the ch_never parameter MUST 5042 NOT appear in the recovery journal (Appendix A.4.1-2 defines 5043 exceptions to this rule for Chapter M). To signal the exclusion 5044 of a chapter from the journal, an assignment to ch_never MUST 5045 be made, even if the commands coded by the chapter are assigned 5046 to cm_unused. This rule simplifies the handling of commands 5047 types that may be coded in several chapters. 5049 o ch_default. A chapter assigned to the ch_default parameter 5050 MUST follow the default semantics for the chapter, as defined 5051 in Appendices A-B. 5053 o ch_anchor. A chapter assigned to the ch_anchor MUST obey a 5054 modified version of the default chapter semantics. In the 5055 modified semantics, all references to the checkpoint history 5056 are replaced with references to the session history, and all 5057 references to the checkpoint packet are replaced with 5058 references to the first packet sent in the stream. 5060 Parameter assignments obey the following syntax (see Appendix D for 5061 ABNF): 5063 = [channel list][field list] 5065 The chapter list is mandatory; the channel and field lists are optional. 5066 Multiple assignments to parameters have a cumulative effect and are 5067 applied in the order of parameter appearance in a media description. 5069 To determine the semantics of a list of chapter inclusion parameter 5070 assignments, we begin by assuming an implicit assignment of all channel 5071 and system chapters to the ch_default parameter, with the default values 5072 for the channel list and field list for each chapter that are defined 5073 below. 5075 We then interpret the semantics of the actual parameter assignments, 5076 using the rules below. 5078 A later assignment of a chapter to the same parameter expands the scope 5079 of the earlier assignment. In most cases, a later assignment of a 5080 chapter to a different parameter cancels (partially or completely) the 5081 effect of an earlier assignment. 5083 The chapter list specifies the channel or system chapters for which the 5084 parameter applies. The chapter list is a concatenated sequence of one 5085 or more of the letters corresponding to the chapter types 5086 (ACDEFMNPQTVWX). In addition, the list may contain one or more of the 5087 letters for the sub-chapter types (BGHJKYZ) of System Chapter D. 5089 The letters in a chapter list MUST be uppercase and MUST appear in 5090 alphabetical order. Letters other than (ABCDEFGHJKMNPQTVWXYZ) that 5091 appear in the chapter list MUST be ignored. 5093 The channel list specifies the channel journals for which this parameter 5094 applies; if no channel list is provided, the parameter applies to all 5095 channel journals. The channel list takes the form of a list of channel 5096 numbers (0 through 15) and dash-separated channel number ranges (i.e., 5097 0-5, 8-12, etc.). Dots (i.e., "." characters) separate elements in the 5098 channel list. 5100 Several of the systems chapters may be configured to have special 5101 semantics. Configuration occurs by specifying a channel list for the 5102 systems channel, using the coding described below (note that MIDI 5103 Systems commands do not have a "channel", and thus the original purpose 5104 of the channel list does not apply to systems chapters). The expression 5105 "the digit N" in the text below refers to the inclusion of N as a 5106 "channel" in the channel list for a systems chapter. 5108 For the J and K Chapter D sub-chapters (undefined System Common), the 5109 digit 0 codes that the parameter applies to the LEGAL field of the 5110 associated command log (Figure B.1.4 of Appendix B.1), the digit 1 codes 5111 that the parameter applies to the VALUE field of the command log, and 5112 the digit 2 codes that the parameter applies to the COUNT field of the 5113 command log. 5115 For the Y and Z Chapter D sub-chapters (undefined System Real-time), the 5116 digit 0 codes that the parameter applies to the LEGAL field of the 5117 associated command log (Figure B.1.5 of Appendix B.1) and the digit 1 5118 codes that the parameter applies to the COUNT field of the command log. 5120 For Chapter Q (Sequencer State Commands), the digit 0 codes that the 5121 parameter applies to the default Chapter Q definition, which forbids the 5122 TIME field. The digit 1 codes that the parameter applies to the 5123 optional Chapter Q definition, which supports the TIME field. 5125 The syntax for field lists follows the syntax for channel lists. If no 5126 field list is provided, the parameter applies to all controller or note 5127 numbers. For Chapter C, if no field list is provided, the controller 5128 numbers do not use enhanced Chapter C encoding (Appendix A.3.3). 5130 For Chapter C, the field list may take on values in the range 0 to 255. 5131 A field value X in the range 0-127 refers to a controller number X, and 5132 indicates that the controller number does not use enhanced Chapter C 5133 encoding. A field value X in the range 128-255 refers to a controller 5134 number "X minus 128" and indicates the controller number does use the 5135 enhanced Chapter C encoding. 5137 Assignments made to configure the Chapter C encoding method for a 5138 controller number MUST be made to the ch_default or ch_anchor 5139 parameters, as assignments to ch_never act to exclude the number from 5140 the recovery journal (and thus the indicated encoding method is 5141 irrelevant). 5143 A Chapter C field list MUST NOT encode conflicting information about the 5144 enhanced encoding status of a particular controller number. For 5145 example, values 0 and 128 MUST NOT both be coded by a field list. 5147 For Chapter M, the field list codes the Registered Parameter Numbers 5148 (RPNs) and Non-Registered Parameter Numbers (NRPNs) for which the 5149 parameter applies. The number range 0-16383 specifies RPNs, the number 5150 range 16384-32767 specifies NRPNs (16384 corresponds to NRPN 0, 32767 5151 corresponds to NRPN 16383). 5153 For Chapters N and A, the field list codes the note numbers for which 5154 the parameter applies. The note number range specified for Chapter N 5155 also applies to Chapter E. 5157 For Chapter E, the digit 0 codes that the parameter applies to Chapter E 5158 note logs whose V bit is set to 0, and the digit 1 codes that the 5159 parameter applies to note logs whose V bit is set to 1. 5161 For Chapter X, the field list codes the number of data octets that may 5162 appear in a SysEx command that is coded in the chapter. Thus, the field 5163 list 0-255 specifies SysEx commands with 255 or fewer data octets, the 5164 field list 256-4294967295 specifies SysEx commands with more than 255 5165 data octets but excludes commands with 255 or fewer data octets, and the 5166 field list 0 excludes all commands. 5168 A secondary parameter assignment syntax customizes Chapter X (see 5169 Appendix D for complete ABNF): 5171 = "__" *( "_" ) "__" 5173 The assignment defines a class of SysEx commands whose Chapter X coding 5174 obeys the semantics of the assigned parameter. The command class is 5175 specified by listing the permitted values of the first N data octets 5176 that follow the SysEx 0xF0 command octet. Any SysEx command whose first 5177 N data octets match the list is a member of the class. 5179 Each defines a data octet of the command, as a dot-separated 5180 (".") list of one or more hexadecimal constants (such as "7F") or dash- 5181 separated hexadecimal ranges (such as "01-1F"). Underscores ("_") 5182 separate each . Double-underscores ("__") delineate the data 5183 octet list. 5185 Using this syntax, each assignment specifies a single SysEx command 5186 class. Session descriptions may use several assignments to the same (or 5187 different) parameters to specify complex Chapter X behaviors. The 5188 ordering behavior of multiple assignments follows the guidelines for 5189 chapter parameter assignments described earlier in this section. 5191 The example session description below illustrates the use of the chapter 5192 inclusion parameters: 5194 v=0 5195 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5196 s=Example 5197 t=0 0 5198 m=audio 5004 RTP/AVP 96 5199 c=IN IP6 2001:DB80::7F2E:172A:1E24 5200 a=rtpmap:96 rtp-midi/44100 5201 a=fmtp:96 j_update=open-loop; cm_unused=ABCFGHJKMQTVWXYZ; 5202 cm_used=__7E_00-7F_09_01.02.03__; 5203 cm_used=__7F_00-7F_04_01.02__; cm_used=C7.64; 5204 ch_never=ABCDEFGHJKMQTVWXYZ; ch_never=4.11-13N; 5205 ch_anchor=P; ch_anchor=C7.64; 5206 ch_anchor=__7E_00-7F_09_01.02.03__; 5207 ch_anchor=__7F_00-7F_04_01.02__ 5209 (The a=fmtp line has been wrapped to fit the page to accommodate 5210 memo formatting restrictions; it comprises a single line in SDP.) 5212 The j_update parameter codes that the stream uses the open-loop policy. 5213 Most MIDI command-types are assigned to cm_unused and thus do not appear 5214 in the stream. As a consequence, the assignments to the first ch_never 5215 parameter reflect that most chapters are not in use. 5217 Chapter N for several MIDI channels is assigned to ch_never. Chapter N 5218 for MIDI channels other than 4, 11, 12, and 13 may appear in the 5219 recovery journal, using the (default) ch_default semantics. In 5220 practice, this assignment pattern would reflect knowledge about a 5221 resilient rendering method in use for the excluded channels. 5223 The MIDI Program Change command and several MIDI Control Change 5224 controller numbers are assigned to ch_anchor. Note that the ordering of 5225 the ch_anchor chapter C assignment after the ch_never command acts to 5226 override the ch_never assignment for the listed controller numbers (7 5227 and 64). 5229 The assignment of command-type X to cm_unused excludes most SysEx 5230 commands from the stream. Exceptions are made for General MIDI System 5231 On/Off commands and for the Master Volume and Balance commands, via the 5232 use of the secondary assignment syntax. The cm_used assignment codes 5233 the exception, and the ch_anchor assignment codes how these commands are 5234 protected in Chapter X. 5236 C.3. Configuration Tools: Timestamp Semantics 5238 The MIDI command section of the payload format consists of a list of 5239 commands, each with an associated timestamp. The semantics of command 5240 timestamps may be set during session configuration, using the parameters 5241 we describe in this section 5243 The parameter "tsmode" specifies the timestamp semantics for a stream. 5244 The parameter takes on one of three token values: "comex", "async", or 5245 "buffer". 5247 The default "comex" value specifies that timestamps code the execution 5248 time for a command (Appendix C.3.1) and supports the accurate 5249 transcoding of Standard MIDI Files (SMFs, [MIDI]). The "comex" value is 5250 also RECOMMENDED for new MIDI user-interface controller designs. The 5251 "async" value specifies an asynchronous timestamp sampling algorithm for 5252 time-of-arrival sources (Appendix C.3.2). The "buffer" value specifies 5253 a synchronous timestamp sampling algorithm (Appendix C.3.3) for time-of- 5254 arrival sources. 5256 Ancillary parameters MAY follow tsmode in a media description. We 5257 define these parameters in Appendices C.3.2-3 below. 5259 C.3.1. The comex Algorithm 5261 The default "comex" (COMmand EXecution) tsmode value specifies the 5262 execution time for the command. With comex, the difference between two 5263 timestamps indicates the time delay between the execution of the 5264 commands. This difference may be zero, coding simultaneous execution. 5266 The comex interpretation of timestamps works well for transcoding a 5267 Standard MIDI File (SMF, [MIDI]) into an RTP MIDI stream, as SMFs code a 5268 timestamp for each MIDI command stored in the file. To transcode an SMF 5269 that uses metric time markers, use the SMF tempo map (encoded in the SMF 5270 as meta-events) to convert metric SMF timestamp units into seconds-based 5271 RTP timestamp units. 5273 New MIDI controller designs (piano keyboard, drum pads, etc.) that 5274 support RTP MIDI and that have direct access to sensor data SHOULD use 5275 comex interpretation for timestamps, so that simultaneous gestural 5276 events may be accurately coded by RTP MIDI. 5278 Comex is a poor choice for transcoding MIDI 1.0 DIN cables [MIDI], for a 5279 reason that we will now explain. A MIDI DIN cable is an asynchronous 5280 serial protocol (320 microseconds per MIDI byte). MIDI commands on a 5281 DIN cable are not tagged with timestamps. Instead, MIDI DIN receivers 5282 infer command timing from the time of arrival of the bytes. Thus, two 5283 two-byte MIDI commands that occur at a source simultaneously are encoded 5284 on a MIDI 1.0 DIN cable with a 640 microsecond time offset. A MIDI DIN 5285 receiver is unable to tell if this time offset existed in the source 5286 performance or is an artifact of the serial speed of the cable. 5287 However, the RTP MIDI comex interpretation of timestamps declares that a 5288 timestamp offset between two commands reflects the timing of the source 5289 performance. 5291 This semantic mismatch is the reason that comex is a poor choice for 5292 transcoding MIDI DIN cables. Note that the choice of the RTP timestamp 5293 rate (Section 6.1-2 in the main text) cannot fix this inaccuracy issue. 5294 In the sections that follow, we describe two alternative timestamp 5295 interpretations ("async" and "buffer") that are a better match to MIDI 5296 1.0 DIN cable timing, and to other MIDI time-of-arrival sources. 5298 The "octpos", "linerate", and "mperiod" ancillary parameters (defined 5299 below) SHOULD NOT be used with comex. 5301 C.3.2. The async Algorithm 5303 The "async" tsmode value specifies the asynchronous sampling of a MIDI 5304 time-of-arrival source. In asynchronous sampling, the moment an octet 5305 is received from a source, it is labelled with a wall-clock time value. 5306 The time value has RTP timestamp units. 5308 The "octpos" ancillary parameter defines how RTP command timestamps are 5309 derived from octet time values. If octpos has the token value "first", 5310 a timestamp codes the time value of the first octet of the command. If 5311 octpos has the token value "last", a timestamp codes the time value of 5312 the last octet of the command. If the octpos parameter does not appear 5313 in the media description, the sender does not know which octet of the 5314 command the timestamp references (for example, the sender may be relying 5315 on an operating system service that does not specify this information). 5317 The octpos semantics refer to the first or last octet of a command as it 5318 appears on a time-of-arrival MIDI source, not as it appears in an RTP 5319 MIDI packet. This distinction is significant because the RTP coding may 5320 contain octets that are not present in the source. For example, the 5321 status octet of the first MIDI command in a packet may have been added 5322 to the MIDI stream during transcoding, to comply with the RTP MIDI 5323 running status requirements (Section 3.2). 5325 The "linerate" ancillary parameter defines the timespan of one MIDI 5326 octet on the transmission medium of the MIDI source to be sampled (such 5327 as a MIDI 1.0 DIN cable). The parameter has units of nanoseconds, and 5328 takes on integral values. For MIDI 1.0 DIN cables, the correct linerate 5329 value is 320000 (this value is also the default value for the 5330 parameter). 5332 We now show a session description example for the async algorithm. 5333 Consider a sender that is transcoding a MIDI 1.0 DIN cable source into 5334 RTP. The sender runs on a computing platform that assigns time values 5335 to every incoming octet of the source, and the sender uses the time 5336 values to label the first octet of each command in the RTP packet. This 5337 session description describes the transcoding: 5339 v=0 5340 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5341 s=Example 5342 t=0 0 5343 m=audio 5004 RTP/AVP 96 5344 c=IN IP4 192.0.2.94 5345 a=rtpmap:96 rtp-midi/44100 5346 a=sendonly 5347 a=fmtp:96 tsmode=async; linerate=320000; octpos=first 5349 C.3.3. The buffer Algorithm 5351 The "buffer" tsmode value specifies the synchronous sampling of a MIDI 5352 time-of-arrival source. 5354 In synchronous sampling, octets received from a source are placed in a 5355 holding buffer upon arrival. At periodic intervals, the RTP sender 5356 examines the buffer. The sender removes complete commands from the 5357 buffer and codes those commands in an RTP packet. The command timestamp 5358 codes the moment of buffer examination, expressed in RTP timestamp 5359 units. Note that several commands may have the same timestamp value. 5361 The "mperiod" ancillary parameter defines the nominal periodic sampling 5362 interval. The parameter takes on positive integral values and has RTP 5363 timestamp units. 5365 The "octpos" ancillary parameter, defined in Appendix C.3.1 for 5366 asynchronous sampling, plays a different role in synchronous sampling. 5367 In synchronous sampling, the parameter specifies the timestamp semantics 5368 of a command whose octets span several sampling periods. 5370 If octpos has the token value "first", the timestamp reflects the 5371 arrival period of the first octet of the command. If octpos has the 5372 token value "last", the timestamp reflects the arrival period of the 5373 last octet of the command. The octpos semantics refer to the first or 5374 last octet of the command as it appears on a time-of-arrival source, not 5375 as it appears in the RTP packet. 5377 If the octpos parameter does not appear in the media description, the 5378 timestamp MAY reflect the arrival period of any octet of the command; 5379 senders use this option to signal a lack of knowledge about the timing 5380 details of the buffering process at sub-command granularity. 5382 We now show a session description example for the buffer algorithm. 5383 Consider a sender that is transcoding a MIDI 1.0 DIN cable source into 5384 RTP. The sender runs on a computing platform that places source data 5385 into a buffer upon receipt. The sender polls the buffer 1000 times a 5386 second, extracts all complete commands from the buffer, and places the 5387 commands in an RTP packet. This session description describes the 5388 transcoding: 5390 v=0 5391 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5392 s=Example 5393 t=0 0 5394 m=audio 5004 RTP/AVP 96 5395 c=IN IP6 2001:DB80::7F2E:172A:1E24 5396 a=rtpmap:96 rtp-midi/44100 5397 a=sendonly 5398 a=fmtp:96 tsmode=buffer; linerate=320000; octpos=last; mperiod=44 5400 The mperiod value of 44 is derived by dividing the clock rate specified 5401 by the rtpmap attribute (44100 Hz) by the 1000 Hz buffer sampling rate 5402 and rounding to the nearest integer. Command timestamps might not 5403 increment by exact multiples of 44, as the actual sampling period might 5404 not precisely match the nominal mperiod value. 5406 C.4. Configuration Tools: Packet Timing Tools 5408 In this appendix, we describe session configuration tools for 5409 customizing the temporal behavior of MIDI stream packets. 5411 C.4.1. Packet Duration Tools 5413 Senders control the granularity of a stream by setting the temporal 5414 duration ("media time") of the packets in the stream. Short media times 5415 (20 ms or less) often imply an interactive session. Longer media times 5416 (100 ms or more) usually indicate a content streaming session. The RTP 5417 AVP profile [RFC3551] recommends audio packet media times in a range 5418 from 0 to 200 ms. 5420 By default, an RTP receiver dynamically senses the media time of packets 5421 in a stream and chooses the length of its playout buffer to match the 5422 stream. A receiver typically sizes its playout buffer to fit several 5423 audio packets and adjusts the buffer length to reflect the network 5424 jitter and the sender timing fidelity. 5426 Alternatively, the packet media time may be statically set during 5427 session configuration. Session descriptions MAY use the RTP MIDI 5428 parameter "rtp_ptime" to set the recommended media time for a packet. 5429 Session descriptions MAY also use the RTP MIDI parameter "rtp_maxptime" 5430 to set the maximum media time for a packet permitted in a stream. Both 5431 parameters MAY be used together to configure a stream. 5433 The values assigned to the rtp_ptime and rtp_maxptime parameters have 5434 the units of the RTP timestamp for the stream, as set by the rtpmap 5435 attribute (see Section 6.1). Thus, if rtpmap sets the clock rate of a 5436 stream to 44100 Hz, a maximum packet media time of 10 ms is coded by 5437 setting rtp_maxptime=441. As stated in the Appendix C preamble, the 5438 senders and receivers of a stream MUST agree on common values for 5439 rtp_ptime and rtp_maxptime if the parameters appear in the media 5440 description for the stream. 5442 0 ms is a reasonable media time value for MIDI packets and is often used 5443 in low-latency interactive applications. In a packet with a 0 ms media 5444 time, all commands execute at the instant they are coded by the packet 5445 timestamp. The session description below configures all packets in the 5446 stream to have 0 ms media time: 5448 v=0 5449 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5450 s=Example 5451 t=0 0 5452 m=audio 5004 RTP/AVP 96 5453 c=IN IP4 192.0.2.94 5454 a=rtpmap:96 rtp-midi/44100 5455 a=fmtp:96 rtp_ptime=0; rtp_maxptime=0 5457 The session attributes ptime and maxptime [RFC4566] MUST NOT be used to 5458 configure an RTP MIDI stream. Sessions MUST use rtp_ptime in lieu of 5459 ptime and MUST use rtp_maxptime in lieu of maxptime. RTP MIDI defines 5460 its own parameters for media time configuration because 0 ms values for 5461 ptime and maxptime are forbidden by [RFC3264] but are essential for 5462 certain applications of RTP MIDI. 5464 See the Appendix C.7 examples for additional discussion about using 5465 rtp_ptime and rtp_maxptime for session configuration. 5467 C.4.2. The guardtime Parameter 5469 RTP permits a sender to stop sending audio packets for an arbitrary 5470 period of time during a session. When sending resumes, the RTP sequence 5471 number series continues unbroken, and the RTP timestamp value reflects 5472 the media time silence gap. 5474 This RTP feature has its roots in telephony, but it is also well matched 5475 to interactive MIDI sessions, as players may fall silent for several 5476 seconds during (or between) songs. 5478 Certain MIDI applications benefit from a slight enhancement to this RTP 5479 feature. In interactive applications, receivers may use on-line network 5480 models to guide heuristics for handling lost and late RTP packets. 5481 These models may work poorly if a sender ceases packet transmission for 5482 long periods of time. 5484 Session descriptions may use the parameter "guardtime" to set a minimum 5485 sending rate for a media session. The value assigned to guardtime codes 5486 the maximum separation time between two sequential packets, as expressed 5487 in RTP timestamp units. 5489 Typical guardtime values are 500-2000 ms. This value range is not a 5490 normative bound, and parties SHOULD be prepared to process values 5491 outside this range. 5493 The congestion control requirements for sender implementations 5494 (described in Section 8 and [RFC3550]) take precedence over the 5495 guardtime parameter. Thus, if the guardtime parameter requests a 5496 minimum sending rate, but sending at this rate would violate the 5497 congestion control requirements, senders MUST ignore the guardtime 5498 parameter value. In this case, senders SHOULD use the lowest minimum 5499 sending rate that satisfies the congestion control requirements. 5501 Below, we show a session description that uses the guardtime parameter. 5503 v=0 5504 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5505 s=Example 5506 t=0 0 5507 m=audio 5004 RTP/AVP 96 5508 c=IN IP6 2001:DB80::7F2E:172A:1E24 5509 a=rtpmap:96 rtp-midi/44100 5510 a=fmtp:96 guardtime=44100; rtp_ptime=0; rtp_maxptime=0 5511 C.5. Configuration Tools: Stream Description 5513 As we discussed in Section 2.1, a party may send several RTP MIDI 5514 streams in the same RTP session, and several RTP sessions that carry 5515 MIDI may appear in a multimedia session. 5517 By default, the MIDI name space (16 channels + systems) of each RTP 5518 stream sent by a party in a multimedia session is independent. By 5519 independent, we mean three distinct things: 5521 o If a party sends two RTP MIDI streams (A and B), MIDI voice 5522 channel 0 in stream A is a different "channel 0" than MIDI 5523 voice channel 0 in stream B. 5525 o MIDI voice channel 0 in stream B is not considered to be 5526 "channel 16" of a 32-channel MIDI voice channel space whose 5527 "channel 0" is channel 0 of stream A. 5529 o Streams sent by different parties over different RTP sessions, 5530 or over the same RTP session but with different payload type 5531 numbers, do not share the association that is shared by a MIDI 5532 cable pair that cross-connects two devices in a MIDI 1.0 DIN 5533 network. By default, this association is only held by streams 5534 sent by different parties in the same RTP session that use the 5535 same payload type number. 5537 In this appendix, we show how to express that specific RTP MIDI streams 5538 in a multimedia session are not independent but instead are related in 5539 one of the three ways defined above. We use two tools to express these 5540 relations: 5542 o The musicport parameter. This parameter is assigned a 5543 non-negative integer value between 0 and 4294967295. It 5544 appears in the fmtp lines of payload types. 5546 o The FID grouping attribute [RFC3388] signals that several RTP 5547 sessions in a multimedia session are using the musicport 5548 parameter to express an inter-session relationship. 5550 If a multimedia session has several payload types whose musicport 5551 parameters are assigned the same integer value, streams using these 5552 payload types share an "identity relationship" (including streams that 5553 use the same payload type). Streams in an identity relationship share 5554 two properties: 5556 o Identity relationship streams sent by the same party 5557 target the same MIDI name space. Thus, if streams A 5558 and B share an identity relationship, voice channel 0 5559 in stream A is the same "channel 0" as voice channel 5560 0 in stream B. 5562 o Pairs of identity relationship streams that are sent by 5563 different parties share the association that is shared 5564 by a MIDI cable pair that cross-connects two devices in 5565 a MIDI 1.0 DIN network. 5567 A party MUST NOT send two RTP MIDI streams that share an identity 5568 relationship in the same RTP session. Instead, each stream MUST be in a 5569 separate RTP session. As explained in Section 2.1, this restriction is 5570 necessary to support the RTP MIDI method for the synchronization of 5571 streams that share a MIDI name space. 5573 If a multimedia session has several payload types whose musicport 5574 parameters are assigned sequential values (i.e., i, i+1, ... i+k), the 5575 streams using the payload types share an "ordered relationship". For 5576 example, if payload type A assigns 2 to musicport and payload type B 5577 assigns 3 to musicport, A and B are in an ordered relationship. 5579 Streams in an ordered relationship that are sent by the same party are 5580 considered by renderers to form a single larger MIDI space. For 5581 example, if stream A has a musicport value of 2 and stream B has a 5582 musicport value of 3, MIDI voice channel 0 in stream B is considered to 5583 be voice channel 16 in the larger MIDI space formed by the relationship. 5584 Note that it is possible for streams to participate in both an identity 5585 relationship and an ordered relationship. 5587 We now state several rules for using musicport: 5589 o If streams from several RTP sessions in a multimedia 5590 session use the musicport parameter, the RTP sessions 5591 MUST be grouped using the FID grouping attribute 5592 defined in [RFC3388]. 5594 o An ordered or identity relationship MUST NOT 5595 contain both native RTP MIDI streams and 5596 mpeg4-generic RTP MIDI streams. An exception applies 5597 if a relationship consists of sendonly and recvonly 5598 (but not sendrecv) streams. In this case, the sendonly 5599 streams MUST NOT contain both types of streams, and the 5600 recvonly streams MUST NOT contain both types of streams. 5602 o It is possible to construct identity relationships 5603 that violate the recovery journal mandate (for example, 5604 sending NoteOns for a voice channel on stream A and 5605 NoteOffs for the same voice channel on stream B). 5606 Parties MUST NOT generate (or accept) session 5607 descriptions that exhibit this flaw. 5609 o Other payload formats MAY define musicport media type 5610 parameters. Formats would define these parameters so that 5611 their sessions could be bundled into RTP MIDI name spaces. 5612 The parameter definitions MUST be compatible with the 5613 musicport semantics defined in this appendix. 5615 As a rule, at most one payload type in a relationship may specify a MIDI 5616 renderer. An exception to the rule applies to relationships that 5617 contain sendonly and recvonly streams but no sendrecv streams. In this 5618 case, one sendonly session and one recvonly session may each define a 5619 renderer. 5621 Renderer specification in a relationship may be done using the tools 5622 described in Appendix C.6. These tools work for both native streams and 5623 mpeg4-generic streams. An mpeg4-generic stream that uses the Appendix 5624 C.6 tools MUST set all "config" parameters to the empty string (""). 5626 Alternatively, for mpeg4-generic streams, renderer specification may be 5627 done by setting one "config" parameter in the relationship to the 5628 renderer configuration string, and all other config parameters to the 5629 empty string (""). 5631 We now define sender and receiver rules that apply when a party sends 5632 several streams that target the same MIDI name space. 5634 Senders MAY use the subsetting parameters (Appendix C.1) to predefine 5635 the partitioning of commands between streams, or they MAY use a dynamic 5636 partitioning strategy. 5638 Receivers that merge identity relationship streams into a single MIDI 5639 command stream MUST maintain the structural integrity of the MIDI 5640 commands coded in each stream during the merging process, in the same 5641 way that software that merges traditional MIDI 1.0 DIN cable flows is 5642 responsible for creating a merged command flow compatible with [MIDI]. 5644 Senders MUST partition the name space so that the rendered MIDI 5645 performance does not contain indefinite artifacts (as defined in Section 5646 4). This responsibility holds even if all streams are sent over 5647 reliable transport, as different stream latencies may yield indefinite 5648 artifacts. For example, stuck notes may occur in a performance split 5649 over two TCP streams, if NoteOn commands are sent on one stream and 5650 NoteOff commands are sent on the other. 5652 Senders MUST NOT split a Registered Parameter Name (RPN) or Non- 5653 Registered Parameter Name (NRPN) transaction appearing on a MIDI channel 5654 across multiple identity relationship sessions. Receivers MUST assume 5655 that the RPN/NRPN transactions that appear on different identity 5656 relationship sessions are independent and MUST preserve transactional 5657 integrity during the MIDI merge. 5659 A simple way to safely partition voice channel commands is to place all 5660 MIDI commands for a particular voice channel into the same session. 5661 Safe partitioning of MIDI Systems commands may be more complicated for 5662 sessions that extensively use System Exclusive. 5664 We now show several session description examples that use the musicport 5665 parameter. 5667 Our first session description example shows two RTP MIDI streams that 5668 drive the same General MIDI decoder. The sender partitions MIDI 5669 commands between the streams dynamically. The musicport values indicate 5670 that the streams share an identity relationship. 5672 v=0 5673 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5674 s=Example 5675 t=0 0 5676 a=group:FID 1 2 5677 c=IN IP4 192.0.2.94 5678 m=audio 5004 RTP/AVP 96 5679 a=rtpmap:96 mpeg4-generic/44100 5680 a=mid:1 5681 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5682 config=7A0A0000001A4D546864000000060000000100604D54726B0 5683 000000600FF2F000; musicport=12 5684 m=audio 5006 RTP/AVP 96 5685 a=rtpmap:96 mpeg4-generic/44100 5686 a=mid:2 5687 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 5688 musicport=12 5690 (The a=fmtp lines have been wrapped to fit the page to accommodate 5691 memo formatting restrictions; they comprise single lines in SDP.) 5693 Recall that Section 2.1 defines rules for streams that target the same 5694 MIDI name space. Those rules, implemented in the example above, require 5695 that each stream resides in a separate RTP session, and that the 5696 grouping mechanisms defined in [RFC3388] signal an inter-session 5697 relationship. The "group" and "mid" attribute lines implement this 5698 grouping mechanism. 5700 A variant on this example, whose session description is not shown, would 5701 use two streams in an identity relationship driving the same MIDI 5702 renderer, each with a different transport type. One stream would use 5703 UDP and would be dedicated to real-time messages. A second stream would 5704 use TCP [RFC4571] and would be used for SysEx bulk data messages. 5706 In the next example, two mpeg4-generic streams form an ordered 5707 relationship to drive a Structured Audio decoder with 32 MIDI voice 5708 channels. Both streams reside in the same RTP session. 5710 v=0 5711 o=lazzaro 2520644554 2838152170 IN IP6 first.example.net 5712 s=Example 5713 t=0 0 5714 m=audio 5006 RTP/AVP 96 97 5715 c=IN IP6 2001:DB80::7F2E:172A:1E24 5716 a=rtpmap:96 mpeg4-generic/44100 5717 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=13; 5718 musicport=5 5719 a=rtpmap:97 mpeg4-generic/44100 5720 a=fmtp:97 streamtype=5; mode=rtp-midi; config=""; profile-level-id=13; 5721 musicport=6; render=synthetic; rinit="audio/asc"; 5722 url="http://example.com/cardinal.asc"; 5723 cid="azsldkaslkdjqpwojdkmsldkfpe" 5725 (The a=fmtp lines have been wrapped to fit the page to accommodate 5726 memo formatting restrictions; they comprise single lines in SDP.) 5728 The sequential musicport values for the two sessions establish the 5729 ordered relationship. The musicport=5 session maps to Structured Audio 5730 extended channels range 0-15, the musicport=6 session maps to Structured 5731 Audio extended channels range 16-31. 5733 Both config strings are empty. The configuration data is specified by 5734 parameters that appear in the fmtp line of the second media description. 5735 We define this configuration method in Appendix C.6. 5737 The next example shows two RTP MIDI streams (one recvonly, one sendonly) 5738 that form a "virtual sendrecv" session. Each stream resides in a 5739 different RTP session (a requirement because sendonly and recvonly are 5740 RTP session attributes). 5742 v=0 5743 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 5744 s=Example 5745 t=0 0 5746 a=group:FID 1 2 5747 c=IN IP4 192.0.2.94 5748 m=audio 5004 RTP/AVP 96 5749 a=sendonly 5750 a=rtpmap:96 mpeg4-generic/44100 5751 a=mid:1 5752 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5753 config=7A0A0000001A4D546864000000060000000100604D54726B0 5754 000000600FF2F000; musicport=12 5755 m=audio 5006 RTP/AVP 96 5756 a=recvonly 5757 a=rtpmap:96 mpeg4-generic/44100 5758 a=mid:2 5759 a=fmtp:96 streamtype=5; mode=rtp-midi; profile-level-id=12; 5760 config=7A0A0000001A4D546864000000060000000100604D54726B0 5761 000000600FF2F000; musicport=12 5763 (The a=fmtp lines have been wrapped to fit the page to accommodate 5764 memo formatting restrictions; they comprise single lines in SDP.) 5766 To signal the "virtual sendrecv" semantics, the two streams assign 5767 musicport to the same value (12). As defined earlier in this section, 5768 pairs of identity relationship streams that are sent by different 5769 parties share the association that is shared by a MIDI cable pair that 5770 cross-connects two devices in a MIDI 1.0 network. We use the term 5771 "virtual sendrecv" because streams sent by different parties in a true 5772 sendrecv session also have this property. 5774 As discussed in the preamble to Appendix C, the primary advantage of the 5775 virtual sendrecv configuration is that each party can customize the 5776 property of the stream it receives. In the example above, each stream 5777 defines its own "config" string that could customize the rendering 5778 algorithm for each party (in fact, the particular strings shown in this 5779 example are identical, because General MIDI is not a configurable MPEG 4 5780 renderer). 5782 C.6. Configuration Tools: MIDI Rendering 5784 This appendix defines the session configuration tools for rendering. 5786 The "render" parameter specifies a rendering method for a stream. The 5787 parameter is assigned a token value that signals the top-level rendering 5788 class. This memo defines four token values for render: "unknown", 5789 "synthetic", "api", and "null": 5791 o An "unknown" renderer is a renderer whose nature is unspecified. 5792 It is the default renderer for native RTP MIDI streams. 5794 o A "synthetic" renderer transforms the MIDI stream into audio 5795 output (or sometimes into stage lighting changes or other 5796 actions). It is the default renderer for mpeg4-generic 5797 RTP MIDI streams. 5799 o An "api" renderer presents the command stream to applications 5800 via an Application Programmer Interface (API). 5802 o The "null" renderer discards the MIDI stream. 5804 The "null" render value plays special roles during Offer/Answer 5805 negotiations [RFC3264]. A party uses the "null" value in an answer to 5806 reject an offered renderer. Note that rejecting a renderer is 5807 independent from rejecting a payload type (coded by removing the payload 5808 type from a media line) and rejecting a media stream (coded by zeroing 5809 the port of a media line that uses the renderer). 5811 Other render token values MAY be registered with IANA. The token value 5812 MUST adhere to the ABNF for render tokens defined in Appendix D. 5813 Registrations MUST include a complete specification of parameter value 5814 usage, similar in depth to the specifications that appear throughout 5815 Appendix C.6 for "synthetic" and "api" render values. If a party is 5816 offered a session description that uses a render token value that is not 5817 known to the party, the party MUST NOT accept the renderer. Options 5818 include rejecting the renderer (using the "null" value), the payload 5819 type, the media stream, or the session description. 5821 Other parameters MAY follow a render parameter in a parameter list. The 5822 additional parameters act to define the exact nature of the renderer. 5823 For example, the "subrender" parameter (defined in Appendix C.6.2) 5824 specifies the exact nature of the renderer. 5826 Special rules apply to using the render parameter in an mpeg4-generic 5827 stream. We define these rules in Appendix C.6.5. 5829 C.6.1. The multimode Parameter 5831 A media description MAY contain several render parameters. By default, 5832 if a parameter list includes several render parameters, a receiver MUST 5833 choose exactly one renderer from the list to render the stream. The 5834 "multimode" parameter may be used to override this default. We define 5835 two token values for multimode: "one" and "all": 5837 o The default "one" value requests rendering by exactly one of 5838 the listed renderers. 5840 o The "all" value requests the synchronized rendering of the RTP 5841 MIDI stream by all listed renderers, if possible. 5843 If the multimode parameter appears in a parameter list, it MUST appear 5844 before the first render parameter assignment. 5846 Render parameters appear in the parameter list in order of decreasing 5847 priority. A receiver MAY use the priority ordering to decide which 5848 renderer(s) to retain in a session. 5850 If the "offer" in an Offer/Answer-style negotiation [RFC3264] contains a 5851 parameter list with one or more render parameters, the "answer" MUST set 5852 the render parameters of all unchosen renderers to "null". 5854 C.6.2. Renderer Specification 5856 The render parameter (Appendix C.6 preamble) specifies, in a broad 5857 sense, what a renderer does with a MIDI stream. In this appendix, we 5858 describe the "subrender" parameter. The token value assigned to 5859 subrender defines the exact nature of the renderer. Thus, "render" and 5860 "subrender" combine to define a renderer, in the same way as MIME types 5861 and MIME subtypes combine to define a type of media [RFC2045]. 5863 If the subrender parameter is used for a renderer definition, it MUST 5864 appear immediately after the render parameter in the parameter list. At 5865 most one subrender parameter may appear in a renderer definition. 5867 This document defines one value for subrender: the value "default". The 5868 "default" token specifies the use of the default renderer for the stream 5869 type (native or mpeg4-generic). The default renderer for native RTP 5870 MIDI streams is a renderer whose nature is unspecified (see point 6 in 5871 Section 6.1 for details). The default renderer for mpeg4-generic RTP 5872 MIDI streams is an MPEG 4 Audio Object Type whose ID number is 13, 14, 5873 or 15 (see Section 6.2 for details). 5875 If a renderer definition does not use the subrender parameter, the value 5876 "default" is assumed for subrender. 5878 Other subrender token values may be registered with IANA. We now 5879 discuss guidelines for registering subrender values. 5881 A subrender value is registered for a specific stream type (native or 5882 mpeg4-generic) and a specific render value (excluding "null" and 5883 "unknown"). Registrations for mpeg4-generic subrender values are 5884 restricted to new MPEG 4 Audio Object Types that accept MIDI input. The 5885 syntax of the token MUST adhere to the token definition in Appendix D. 5887 For "render=synthetic" renderers, a subrender value registration 5888 specifies an exact method for transforming the MIDI stream into audio 5889 (or sometimes into video or control actions, such as stage lighting). 5890 For standardized renderers, this specification is usually a pointer to a 5891 standards document, perhaps supplemented by RTP-MIDI-specific 5892 information. For commercial products and open-source projects, this 5893 specification usually takes the form of instructions for interfacing the 5894 RTP MIDI stream with the product or project software. A 5895 "render=synthetic" registration MAY specify additional Reset State 5896 commands for the renderer (Appendix A.1). 5898 A "render=api" subrender value registration specifies how an RTP MIDI 5899 stream interfaces with an API (Application Programmers Interface). This 5900 specification is usually a pointer to programmer's documentation for the 5901 API, perhaps supplemented by RTP-MIDI-specific information. 5903 A subrender registration MAY specify an initialization file (referred to 5904 in this document as an initialization data object) for the stream. The 5905 initialization data object MAY be encoded in the parameter list 5906 (verbatim or by reference) using the coding tools defined in Appendix 5907 C.6.3. An initialization data object MUST have a registered [RFC4288] 5908 media type and subtype [RFC2045]. 5910 For "render=synthetic" renderers, the data object usually encodes 5911 initialization data for the renderer (sample files, synthesis patch 5912 parameters, reverberation room impulse responses, etc.). 5914 For "render=api" renderers, the data object usually encodes data about 5915 the stream used by the API (for example, for an RTP MIDI stream 5916 generated by a piano keyboard controller, the manufacturer and model 5917 number of the keyboard, for use in GUI presentation). 5919 Usually, only one initialization object is encoded for a renderer. If a 5920 renderer uses multiple data objects, the correct receiver interpretation 5921 of multiple data objects MUST be defined in the subrender registration. 5923 A subrender value registration may also specify additional parameters, 5924 to appear in the parameter list immediately after subrender. These 5925 parameter names MUST begin with the subrender value, followed by an 5926 underscore ("_"), to avoid name space collisions with future RTP MIDI 5927 parameter names (for example, a parameter "foo_bar" defined for 5928 subrender value "foo"). 5930 We now specify guidelines for interpreting the subrender parameter 5931 during session configuration. 5933 If a party is offered a session description that uses a renderer whose 5934 subrender value is not known to the party, the party MUST NOT accept the 5935 renderer. Options include rejecting the renderer (using the "null" 5936 value), the payload type, the media stream, or the session description. 5938 Receivers MUST be aware of the Reset State commands (Appendix A.1) for 5939 the renderer specified by the subrender parameter and MUST insure that 5940 the renderer does not experience indefinite artifacts due to the 5941 presence (or the loss) of a Reset State command. 5943 C.6.3. Renderer Initialization 5945 If the renderer for a stream uses an initialization data object, an 5946 "rinit" parameter MUST appear in the parameter list immediately after 5947 the "subrender" parameter. If the renderer parameter list does not 5948 include a subrender parameter (recall the semantics for "default" in 5949 Appendix C.6.2), the "rinit" parameter MUST appear immediately after the 5950 "render" parameter. 5952 The value assigned to the rinit parameter MUST be the media type/subtype 5953 [RFC2045] for the initialization data object. If an initialization 5954 object type is registered with several media types, including audio, the 5955 assignment to rinit MUST use the audio media type. 5957 RTP MIDI supports several parameters for encoding initialization data 5958 objects for renderers in the parameter list: "inline", "url", and "cid". 5960 If the "inline", "url", and/or "cid" parameters are used by a renderer, 5961 these parameters MUST immediately follow the "rinit" parameter. 5963 If a "url" parameter appears for a renderer, an "inline" parameter MUST 5964 NOT appear. If an "inline" parameter appears for a renderer, a "url" 5965 parameter MUST NOT appear. However, neither "url" or "inline" is 5966 required to appear. If neither "url" or "inline" parameters follow 5967 "rinit", the "cid" parameter MUST follow "rinit". 5969 The "inline" parameter supports the inline encoding of the data object. 5970 The parameter is assigned a double-quoted Base64 [RFC2045] encoding of 5971 the binary data object, with no line breaks. Appendix E.4 shows an 5972 example that constructs an inline parameter value. 5974 The "url" parameter is assigned a double-quoted string representation of 5975 a Uniform Resource Locator (URL) for the data object. The string MUST 5976 specify either a HyperText Transport Protocol URI (HTTP, [RFC2616]) or 5977 an HTTP over TLS URI (HTTPS, [RFC2818]). The media type/subtype for the 5978 data object SHOULD be specified in the appropriate HTTP or HTTPS 5979 transport header. 5981 The "url" parameter is assigned a double-quoted string representation of 5982 a Uniform Resource Locator (URL) for the data object. The string MUST 5983 specify a HyperText Transport Protocol URL (HTTP, [RFC2616]). HTTP MAY 5984 be used over TCP or MAY be used over a secure network transport, such as 5985 the method described in [RFC2818]. The media type/subtype for the data 5986 object SHOULD be specified in the appropriate HTTP transport header. 5988 The "cid" parameter supports data object caching. The parameter is 5989 assigned a double-quoted string value that encodes a globally unique 5990 identifier for the data object. 5992 A cid parameter MAY immediately follow an inline parameter, in which 5993 case the cid identifier value MUST be associated with the inline data 5994 object. 5996 If a url parameter is present, and if the data object for the URL is 5997 expected to be unchanged for the life of the URL, a cid parameter MAY 5998 immediately follow the url parameter. The cid identifier value MUST be 5999 associated with the data object for the URL. A cid parameter assigned 6000 to the same identifier value SHOULD be specified following the data 6001 object type/subtype in the appropriate HTTP transport header. 6003 If a url parameter is present, and if the data object for the URL is 6004 expected to change during the life of the URL, a cid parameter MUST NOT 6005 follow the url parameter. A receiver interprets the presence of a cid 6006 parameter as an indication that it is safe to use a cached copy of the 6007 url data object; the absence of a cid parameter is an indication that it 6008 is not safe to use a cached copy, as it may change. 6010 Finally, the cid parameter MAY be used without the inline and url 6011 parameters. In this case, the identifier references a local or 6012 distributed catalog of data objects. 6014 In most cases, only one data object is coded in the parameter list for 6015 each renderer. For example, the default renderer for mpeg4-generic 6016 streams uses a single data object (see Appendix C.6.5 for example 6017 usage). 6019 However, a subrender registration MAY permit the use of multiple data 6020 objects for a renderer. If multiple data objects are encoded for a 6021 renderer, each object encoding begins with an "rinit" parameter, 6022 followed by "inline", "url", and/or "cid" parameters. 6024 Initialization data objects MAY encapsulate a Standard MIDI File (SMF). 6025 By default, the SMFs that are encapsulated in a data object MUST be 6026 ignored by an RTP MIDI receiver. We define parameters to override this 6027 default in Appendix C.6.4. 6029 To end this section, we offer guidelines for registering media types for 6030 initialization data objects. These guidelines are in addition to the 6031 information in [RFC4288]. 6033 Some initialization data objects are also capable of encoding MIDI note 6034 information and thus complete audio performances. These objects SHOULD 6035 be registered using the "audio" media type, so that the objects may also 6036 be used for store-and-forward rendering, and "application" media type, 6037 to support editing tools. Initialization objects without note storage, 6038 or initialization objects for non-audio renderers, SHOULD be registered 6039 only for an "application" media type. 6041 C.6.4. MIDI Channel Mapping 6043 In this appendix, we specify how to map MIDI name spaces (16 voice 6044 channels + systems) onto a renderer. 6046 In the general case: 6048 o A session may define an ordered relationship (Appendix C.5) 6049 that presents more than one MIDI name space to a renderer. 6051 o A renderer may accept an arbitrary number of MIDI name spaces, 6052 or it may expect a specific number of MIDI name spaces. 6054 A session description SHOULD provide a compatible MIDI name space to 6055 each renderer in the session. If a receiver detects that a session 6056 description has too many or too few MIDI name spaces for a renderer, 6057 MIDI data from extra stream name spaces MUST be discarded, and extra 6058 renderer name spaces MUST NOT be driven with MIDI data (except as 6059 described in Appendix C.6.4.1, below). 6061 If a parameter list defines several renderers and assigns the "all" 6062 token value to the multimode parameter, the same name space is presented 6063 to each renderer. However, the "chanmask" parameter may be used to mask 6064 out selected voice channels to each renderer. We define "chanmask" and 6065 other MIDI management parameters in the sub-sections below. 6067 C.6.4.1. The smf_info Parameter 6069 The smf_info parameter defines the use of the SMFs encapsulated in 6070 renderer data objects (if any). The smf_info parameter also defines the 6071 use of SMFs coded in the smf_inline, smf_url, and smf_cid parameters 6072 (defined in Appendix C.6.4.2). 6074 The smf_info parameter describes the "render" parameter that most 6075 recently precedes it in the parameter list. The smf_info parameter MUST 6076 NOT appear in parameter lists that do not use the "render" parameter, 6077 and MUST NOT appear before the first use of "render" in the parameter 6078 list. 6080 We define three token values for smf_info: "ignore", "sdp_start", and 6081 "identity": 6083 o The "ignore" value indicates that the SMFs MUST be discarded. 6084 This behavior is the default SMF rendering behavior. 6086 o The "sdp_start" value codes that SMFs MUST be rendered, 6087 and that the rendering MUST begin upon the acceptance of 6088 the session description. If a receiver is offered a session 6089 description with a renderer that uses an smf_info parameter 6090 set to sdp_start, and if the receiver does not support 6091 rendering SMFs, the receiver MUST NOT accept the renderer 6092 associated with the smf_info parameter. Options include 6093 rejecting the renderer (by setting the "render" parameter 6094 to "null"), the payload type, the media stream, or the 6095 entire session description. 6097 o The "identity" value indicates that the SMFs code the identity 6098 of the renderer. The value is meant for use with the 6099 "unknown" renderer (see Appendix C.6 preamble). The MIDI commands 6100 coded in the SMF are informational in nature and MUST NOT be 6101 presented to a renderer for audio presentation. In 6102 typical use, the SMF would use SysEx Identity Reply 6103 commands (F0 7E nn 06 02, as defined in [MIDI]) to identify 6104 devices, and use device-specific SysEx commands to describe 6105 current state of the devices (patch memory contents, etc.). 6107 Other smf_info token values MAY be registered with IANA. The token 6108 value MUST adhere to the ABNF for render tokens defined in Appendix D. 6109 Registrations MUST include a complete specification of parameter usage, 6110 similar in depth to the specifications that appear in this appendix for 6111 "sdp_start" and "identity". 6113 If a party is offered a session description that uses an smf_info 6114 parameter value that is not known to the party, the party MUST NOT 6115 accept the renderer associated with the smf_info parameter. Options 6116 include rejecting the renderer, the payload type, the media stream, or 6117 the entire session description. 6119 We now define the rendering semantics for the "sdp_start" token value in 6120 detail. 6122 The SMFs and RTP MIDI streams in a session description share the same 6123 MIDI name space(s). In the simple case of a single RTP MIDI stream and 6124 a single SMF, the SMF MIDI commands and RTP MIDI commands are merged 6125 into a single name space and presented to the renderer. The indefinite 6126 artifact responsibilities for merged MIDI streams defined in Appendix 6127 C.5 also apply to merging RTP and SMF MIDI data. 6129 If a payload type codes multiple SMFs, the SMF name spaces are presented 6130 as an ordered entity to the renderer. To determine the ordering of SMFs 6131 for a renderer (which SMF is "first", which is "second", etc.), use the 6132 following rules: 6134 o If the renderer uses a single data object, the order of 6135 appearance of the SMFs in the object's internal structure 6136 defines the order of the SMFs (the earliest SMF in the object 6137 is "first", the next SMF in the object is "second", etc.). 6139 o If multiple data objects are encoded for a renderer, the 6140 appearance of each data object in the parameter list 6141 sets the relative order of the SMFs encoded in each 6142 data object (SMFs encoded in parameters that appear 6143 earlier in the list are ordered before SMFs encoded 6144 in parameters that appear later in the list). 6146 o If SMFs are encoded in data objects parameters and in 6147 the parameters defined in C.6.4.2, the relative order 6148 of the data object parameters and C.6.4.2 parameters 6149 in the parameter list sets the relative order of SMFs 6150 (SMFs encoded in parameters that appear earlier in the 6151 list are ordered before SMFs in parameters that appear 6152 later in the list). 6154 Given this ordering of SMFs, we now define the mapping of SMFs to 6155 renderer name spaces. The SMF that appears first for a renderer maps to 6156 the first renderer name space. The SMF that appears second for a 6157 renderer maps to the second renderer name space, etc. If the associated 6158 RTP MIDI streams also form an ordered relationship, the first SMF is 6159 merged with the first name space of the relationship, the second SMF is 6160 merged to the second name space of the relationship, etc. 6162 Unless the streams and the SMFs both use MIDI Time Code, the time offset 6163 between SMF and stream data is unspecified. This restriction limits the 6164 use of SMFs to applications where synchronization is not critical, such 6165 as the transport of System Exclusive commands for renderer 6166 initialization, or human-SMF interactivity. 6168 Finally, we note that each SMF in the sdp_start discussion above encodes 6169 exactly one MIDI name space (16 voice channels + systems). Thus, the 6170 use of the Device Name SMF meta event to specify several MIDI name 6171 spaces in an SMF is not supported for sdp_start. 6173 C.6.4.2. The smf_inline, smf_url, and smf_cid Parameters 6175 In some applications, the renderer data object may not encapsulate SMFs, 6176 but an application may wish to use SMFs in the manner defined in 6177 Appendix C.6.4.1. 6179 The "smf_inline", "smf_url", and "smf_cid" parameters address this 6180 situation. These parameters use the syntax and semantics of the inline, 6181 url, and cid parameters defined in Appendix C.6.3, except that the 6182 encoded data object is an SMF. 6184 The "smf_inline", "smf_url", and "smf_cid" parameters belong to the 6185 "render" parameter that most recently precedes it in the session 6186 description. The "smf_inline", "smf_url", and "smf_cid" parameters MUST 6187 NOT appear in parameter lists that do not use the "render" parameter and 6188 MUST NOT appear before the first use of "render" in the parameter list. 6189 If several "smf_inline", "smf_url", or "smf_cid" parameters appear for a 6190 renderer, the order of the parameters defines the SMF name space 6191 ordering. 6193 C.6.4.3. The chanmask Parameter 6195 The chanmask parameter instructs the renderer to ignore all MIDI voice 6196 commands for certain channel numbers. The parameter value is a 6197 concatenated string of "1" and "0" digits. Each string position maps to 6198 a MIDI voice channel number (system channels may not be masked). A "1" 6199 instructs the renderer to process the voice channel; a "0" instructs the 6200 renderer to ignore the voice channel. 6202 The string length of the chanmask parameter value MUST be 16 (for a 6203 single stream or an identity relationship) or a multiple of 16 (for an 6204 ordered relationship). 6206 The chanmask parameter describes the "render" parameter that most 6207 recently precedes it in the session description; chanmask MUST NOT 6208 appear in parameter lists that do not use the "render" parameter and 6209 MUST NOT appear before the first use of "render" in the parameter list. 6211 The chanmask parameter describes the final MIDI name spaces presented to 6212 the renderer. The SMF and stream components of the MIDI name spaces may 6213 not be independently masked. 6215 If a receiver is offered a session description with a renderer that uses 6216 the chanmask parameter, and if the receiver does not implement the 6217 semantics of the chanmask parameter, the receiver MUST NOT accept the 6218 renderer unless the chanmask parameter value contains only "1"s. 6220 C.6.5. The audio/asc Media Type 6222 In Appendix 11.3, we register the audio/asc media type. The data object 6223 for audio/asc is a binary encoding of the AudioSpecificConfig data block 6224 used to initialize mpeg4-generic streams (Section 6.2 and [MPEGAUDIO]). 6226 An mpeg4-generic parameter list MAY use the render, subrender, and rinit 6227 parameters with the audio/asc media type for renderer configuration. 6228 Several restrictions apply to the use of these parameters in 6229 mpeg4-generic parameter lists: 6231 o An mpeg4-generic media description that uses the render parameter 6232 MUST assign the empty string ("") to the mpeg4-generic "config" 6233 parameter. The use of the streamtype, mode, and profile-level-id 6234 parameters MUST follow the normative text in Section 6.2. 6236 o Sessions that use identity or ordered relationships MUST follow 6237 the mpeg4-generic configuration restrictions in Appendix C.5. 6239 o The render parameter MUST be assigned the value "synthetic", 6240 "unknown", "null", or a render value that has been added to 6241 the IANA repository for use with mpeg4-generic RTP MIDI 6242 streams. The "api" token value for render MUST NOT be used. 6244 o If a subrender parameter is present, it MUST immediately follow 6245 the render parameter, and it MUST be assigned the token value 6246 "default" or assigned a subrender value added to the IANA 6247 repository for use with mpeg4-generic RTP MIDI streams. A 6248 subrender parameter assignment may be left out of the renderer 6249 configuration, in which case the implied value of subrender 6250 is the default value of "default". 6252 o If the render parameter is assigned the value "synthetic" 6253 and the subrender parameter has the value "default" (assigned 6254 or implied), the rinit parameter MUST be assigned the value 6255 "audio/asc", and an AudioSpecificConfig data object MUST be encoded 6256 using the mechanisms defined in C.6.2-3. The AudioSpecificConfig 6257 data MUST encode one of the MPEG 4 Audio Object Types defined for 6258 use with mpeg4-generic in Section 6.2. If the subrender value is 6259 other than "default", refer to the subrender registration 6260 for information on the use of "audio/asc" with the renderer. 6262 o If the render parameter is assigned the value "null" or 6263 "unknown", the data object MAY be omitted. 6265 Several general restrictions apply to the use of the audio/asc media 6266 type in RTP MIDI: 6268 o A native stream MUST NOT assign "audio/asc" to rinit. The 6269 audio/asc media type is not intended to be a general-purpose 6270 container for rendering systems outside of MPEG usage. 6272 o The audio/asc media type defines a stored object type; it does 6273 not define semantics for RTP streams. Thus, audio/asc MUST NOT 6274 appear on an rtpmap line of a session description. 6276 Below, we show session description examples for audio/asc. The session 6277 description below uses the inline parameter to code the 6278 AudioSpecificConfig block for a mpeg4-generic General MIDI stream. We 6279 derive the value assigned to the inline parameter in Appendix E.4. The 6280 subrender token value of "default" is implied by the absence of the 6281 subrender parameter in the parameter list. 6283 v=0 6284 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 6285 s=Example 6286 t=0 0 6287 m=audio 5004 RTP/AVP 96 6288 c=IN IP4 192.0.2.94 6289 a=rtpmap:96 mpeg4-generic/44100 6290 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6291 render=synthetic; rinit="audio/asc"; 6292 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6294 (The a=fmtp line has been wrapped to fit the page to accommodate 6295 memo formatting restrictions; it comprises a single line in SDP.) 6297 The session description below uses the url parameter to code the 6298 AudioSpecificConfig block for the same General MIDI stream: 6300 v=0 6301 o=lazzaro 2520644554 2838152170 IN IP4 first.example.net 6302 s=Example 6303 t=0 0 6304 m=audio 5004 RTP/AVP 96 6305 c=IN IP4 192.0.2.94 6306 a=rtpmap:96 mpeg4-generic/44100 6307 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6308 render=synthetic; rinit="audio/asc"; url="http://example.net/oski.asc"; 6309 cid="xjflsoeiurvpa09itnvlduihgnvet98pa3w9utnuighbuk" 6311 (The a=fmtp line has been wrapped to fit the page to accommodate 6312 memo formatting restrictions; it comprises a single line in SDP.) 6314 C.7. Interoperability 6316 In this appendix, we define interoperability guidelines for two 6317 application areas: 6319 o MIDI content-streaming applications. RTP MIDI is added to 6320 RTSP-based content-streaming servers, so that viewers may 6321 experience MIDI performances (produced by a specified client- 6322 side renderer) in synchronization with other streams (video, 6323 audio). 6325 o Long-distance network musical performance applications. RTP 6326 MIDI is added to SIP-based voice chat or videoconferencing 6327 programs, as an alternative, or as an addition, to audio and/or 6328 video RTP streams. 6330 For each application, we define a core set of functionality that all 6331 implementations MUST implement. 6333 The applications we address in this section are not an exhaustive list 6334 of potential RTP MIDI uses. We expect framework documents for other 6335 applications to be developed, within the IETF or within other 6336 organizations. We discuss other potential application areas for RTP 6337 MIDI in Section 1 of the main text of this memo. 6339 C.7.1. MIDI Content Streaming Applications 6341 In content-streaming applications, a user invokes an RTSP client to 6342 initiate a request to an RTSP server to view a multimedia session. For 6343 example, clicking on a web page link for an Internet Radio channel 6344 launches an RTSP client that uses the link's RTSP URL to contact the 6345 RTSP server hosting the radio channel. 6347 The content may be pre-recorded (for example, on-demand replay of 6348 yesterday's football game) or "live" (for example, football game 6349 coverage as it occurs), but in either case the user is usually an 6350 "audience member" as opposed to a "participant" (as the user would be in 6351 telephony). 6353 Note that these examples describe the distribution of audio content to 6354 an audience member. The interoperability guidelines in this appendix 6355 address RTP MIDI applications of this nature, not applications such as 6356 the transmission of raw MIDI command streams for use in a professional 6357 environment (recording studio, performance stage, etc.). 6359 In an RTSP session, a client accesses a session description that is 6360 "declared" by the server, either via the RTSP DESCRIBE method, or via 6361 other means, such as HTTP or email. The session description defines the 6362 session from the perspective of the client. For example, if a media 6363 line in the session description contains a non-zero port number, it 6364 encodes the server's preference for the client's port numbers for RTP 6365 and RTCP reception. Once media flow begins, the server sends an RTP 6366 MIDI stream to the client, which renders it for presentation, perhaps in 6367 synchrony with video or other audio streams. 6369 We now define the interoperability text for content-streaming RTSP 6370 applications. 6372 In most cases, server interoperability responsibilities are described in 6373 terms of limits on the "reference" session description a server provides 6374 for a performance if it has no information about the capabilities of the 6375 client. The reference session is a "lowest common denominator" session 6376 that maximizes the odds that a client will be able to view the session. 6377 If a server is aware of the capabilities of the client, the server is 6378 free to provide a session description customized for the client in the 6379 DESCRIBE reply. 6381 Clients MUST support unicast UDP RTP MIDI streams that use the recovery 6382 journal with the closed-loop or the anchor sending policies. Clients 6383 MUST be able to interpret stream subsetting and chapter inclusion 6384 parameters in the session description that qualify the sending policies. 6385 Client support of enhanced Chapter C encoding is OPTIONAL. 6387 The reference session description offered by a server MUST send all RTP 6388 MIDI UDP streams as unicast streams that use the recovery journal and 6389 the closed-loop or anchor sending policies. Servers SHOULD use the 6390 stream subsetting and chapter inclusion parameters in the reference 6391 session description, to simplify the rendering task of the client. 6392 Server support of enhanced Chapter C encoding is OPTIONAL. 6394 Clients and servers MUST support the use of RTSP interleaved mode (a 6395 method for interleaving RTP onto the RTSP TCP transport). 6397 Clients MUST be able to interpret the timestamp semantics signalled by 6398 the "comex" value of the tsmode parameter (i.e., the timestamp semantics 6399 of Standard MIDI Files [MIDI]). Servers MUST use the "comex" value for 6400 the "tsmode" parameter in the reference session description. 6402 Clients MUST be able to process an RTP MIDI stream whose packets encode 6403 an arbitrary temporal duration ("media time"). Thus, in practice, 6404 clients MUST implement a MIDI playout buffer. Clients MUST NOT depend 6405 on the presence of rtp_ptime, rtp_maxtime, and guardtime parameters in 6406 the session description in order to process packets, but they SHOULD be 6407 able to use these parameters to improve packet processing. 6409 Servers SHOULD strive to send RTP MIDI streams in the same way media 6410 servers send conventional audio streams: a sequence of packets that 6411 either all code the same temporal duration (non-normative example: 50 ms 6412 packets) or that code one of an integral number of temporal durations 6413 (non-normative example: 50 ms, 100 ms, 250 ms, or 500 ms packets). 6414 Servers SHOULD encode information about the packetization method in the 6415 rtp_ptime and rtp_maxtime parameters in the session description. 6417 Clients MUST be able to examine the render and subrender parameter, to 6418 determine if a multimedia session uses a renderer it supports. Clients 6419 MUST be able to interpret the default "one" value of the "multimode" 6420 parameter, to identify supported renderers from a list of renderer 6421 descriptions. Clients MUST be able to interpret the musicport 6422 parameter, to the degree that it is relevant to the renderers it 6423 supports. Clients MUST be able to interpret the chanmask parameter. 6425 Clients supporting renderers whose data object (as encoded by a 6426 parameter value for "inline") could exceed 300 octets in size MUST 6427 support the url and cid parameters and thus must implement the HTTP 6428 protocol in addition to RTSP. HTTP over TLS [RFC2818] support for data 6429 objects is OPTIONAL. 6431 Servers MUST specify complete rendering systems for RTP MIDI streams. 6432 Note that a minimal RTP MIDI native stream does not meet this 6433 requirement (Section 6.1), as the rendering method for such streams is 6434 "not specified". 6436 At the time of this memo, the only way for servers to specify a complete 6437 rendering system is to specify an mpeg4-generic RTP MIDI stream in mode 6438 rtp-midi (Section 6.2 and C.6.5). As a consequence, the only rendering 6439 systems that may be presently used are General MIDI [MIDI], DLS 2 6440 [DLS2], or Structured Audio [MPEGSA]. Note that the maximum inline 6441 value for General MIDI is well under 300 octets (and thus clients need 6442 not support the "url" parameter), and that the maximum inline values for 6443 DLS 2 and Structured Audio may be much larger than 300 octets (and thus 6444 clients MUST support the url parameter). 6446 We anticipate that the owners of rendering systems (both standardized 6447 and proprietary) will register subrender parameters for their renderers. 6448 Once registration occurs, native RTP MIDI sessions may use render and 6449 subrender (Appendix C.6.2) to specify complete rendering systems for 6450 RTSP content-streaming multimedia sessions. 6452 Servers MUST NOT use the sdp_start value for the smf_info parameter in 6453 the reference session description, as this use would require that 6454 clients be able to parse and render Standard MIDI Files. 6456 Clients MUST support mpeg4-generic mode rtp-midi General MIDI (GM) 6457 sessions, at a polyphony limited by the hardware capabilities of the 6458 client. This requirement provides a "lowest common denominator" 6459 rendering system for content providers to target. Note that this 6460 requirement does not force implementors of a non-GM renderer (such as 6461 DLS 2 or Structured Audio) to add a second rendering engine. Instead, a 6462 client may satisfy the requirement by including a set of voice patches 6463 that implement the GM instrument set, and using this emulation for 6464 mpeg4-generic GM sessions. 6466 It is RECOMMENDED that servers use General MIDI as the renderer for the 6467 reference session description, because clients are REQUIRED to support 6468 it. We do not require General MIDI as the reference renderer, because 6469 for normative applications it is an inappropriate choice. Servers using 6470 General MIDI as a "lowest common denominator" renderer SHOULD use 6471 Universal Real-Time SysEx MIP messages [SPMIDI] to communicate the 6472 priority of voices to polyphony-limited clients. 6474 C.7.2. MIDI Network Musical Performance Applications 6476 In Internet telephony and videoconferencing applications, parties 6477 interact over an IP network as they would face-to-face. Good user 6478 experiences require low end-to-end audio latency and tight audiovisual 6479 synchronization (for "lip-sync"). The Session Initiation Protocol (SIP, 6480 [RFC3261]) is used for session management. 6482 In this appendix section, we define interoperability guidelines for 6483 using RTP MIDI streams in interactive SIP applications. Our primary 6484 interest is supporting Network Musical Performances (NMP), where 6485 musicians in different locations interact over the network as if they 6486 were in the same room. See [NMP] for background information on NMP, and 6487 see [RFC4696] for a discussion of low-latency RTP MIDI implementation 6488 techniques for NMP. 6490 Note that the goal of NMP applications is telepresence: the parties 6491 should hear audio that is close to what they would hear if they were in 6492 the same room. The interoperability guidelines in this appendix address 6493 RTP MIDI applications of this nature, not applications such as the 6494 transmission of raw MIDI command streams for use in a professional 6495 environment (recording studio, performance stage, etc.). 6497 We focus on session management for two-party unicast sessions that 6498 specify a renderer for RTP MIDI streams. Within this limited scope, the 6499 guidelines defined here are sufficient to let applications interoperate. 6500 We define the REQUIRED capabilities of RTP MIDI senders and receivers in 6501 NMP sessions and define how session descriptions exchanged are used to 6502 set up network musical performance sessions. 6504 SIP lets parties negotiate details of the session, using the 6505 Offer/Answer protocol [RFC3264]. However, RTP MIDI has so many 6506 parameters that "blind" negotiations between two parties using different 6507 applications might not yield a common session configuration. 6509 Thus, we now define a set of capabilities that NMP parties MUST support. 6510 Session description offers whose options lie outside the envelope of 6511 REQUIRED party behavior risk negotiation failure. We also define 6512 session description idioms that the RTP MIDI part of an offer MUST 6513 follow, in order to structure the offer for simpler analysis. 6515 We use the term "offerer" for the party making a SIP offer, and 6516 "answerer" for the party answering the offer. Finally, we note that 6517 unless it is qualified by the adjective "sender" or "receiver", a 6518 statement that a party MUST support X implies that it MUST support X for 6519 both sending and receiving. 6521 If an offerer wishes to define a "sendrecv" RTP MIDI stream, it may use 6522 a true sendrecv session or the "virtual sendrecv" construction described 6523 in the preamble to Appendix C and in Appendix C.5. A true sendrecv 6524 session indicates that the offerer wishes to participate in a session 6525 where both parties use identically configured renderers. A virtual 6526 sendrecv session indicates that the offerer is willing to participate in 6527 a session where the two parties may be using different renderer 6528 configurations. Thus, parties MUST be prepared to see both real and 6529 virtual sendrecv sessions in an offer. 6531 Parties MUST support unicast UDP transport of RTP MIDI streams. These 6532 streams MUST use the recovery journal with the closed-loop or anchor 6533 sending policies. These streams MUST use the stream subsetting and 6534 chapter inclusion parameters to declare the types of MIDI commands that 6535 will be sent on the stream (for sendonly streams) or will be processed 6536 (for recvonly streams), including the size limits on System Exclusive 6537 commands. Support of enhanced Chapter C encoding is OPTIONAL. 6539 Note that both TCP and multicast UDP support are OPTIONAL. We make TCP 6540 OPTIONAL because we expect NMP renderers to rely on data objects 6541 (signalled by "rinit" and associated parameters) for initialization at 6542 the start of the session, and only to use System Exclusive commands for 6543 interactive control during the session. These interactive commands are 6544 small enough to be protected via the recovery journal mechanism of RTP 6545 MIDI UDP streams. 6547 We now discuss timestamps, packet timing, and packet sending algorithms. 6549 Recall that the tsmode parameter controls the semantics of command 6550 timestamps in the MIDI list of RTP packets. 6552 Parties MUST support clock rates of 44.1 kHz, 48 kHz, 88.2 kHz, and 96 6553 kHz. Parties MUST support streams using the "comex", "async", and 6554 "buffer" tsmode values. Recvonly offers MUST offer the default "comex". 6556 Parties MUST support a wide range of packet temporal durations: from 6557 rtp_ptime and rtp_maxptime values of 0, to rtp_ptime and rtp_maxptime 6558 values that code 100 ms. Thus, receivers MUST be able to implement a 6559 playout buffer. 6561 Offers and answers MUST present rtp_ptime, rtp_maxptime, and guardtime 6562 values that support the latency that users would expect in the 6563 application, subject to bandwidth constraints. As senders MUST abide by 6564 values set for these parameters in a session description, a receiver 6565 SHOULD use these values to size its playout buffer to produce the lowest 6566 reliable latency for a session. Implementers should refer to [RFC4696] 6567 for information on packet sending algorithms for latency-sensitive 6568 applications. Parties MUST be able to implement the semantics of the 6569 guardtime parameter, for times from 5 ms to 5000 ms. 6571 We now discuss the use of the render parameter. 6573 Sessions MUST specify complete rendering systems for all RTP MIDI 6574 streams. Note that a minimal RTP MIDI native stream does not meet this 6575 requirement (Section 6.1), as the rendering method for such streams is 6576 "not specified". 6578 At the time this writing, the only way for parties to specify a complete 6579 rendering system is to specify an mpeg4-generic RTP MIDI stream in mode 6580 rtp-midi (Section 6.2 and C.6.5). We anticipate that the owners of 6581 rendering systems (both standardized and proprietary) will register 6582 subrender values for their renderers. Once IANA registration occurs, 6583 native RTP MIDI sessions may use render and subrender (Appendix C.6.2) 6584 to specify complete rendering systems for SIP network musical 6585 performance multimedia sessions. 6587 All parties MUST support General MIDI (GM) sessions, at a polyphony 6588 limited by the hardware capabilities of the party. This requirement 6589 provides a "lowest common denominator" rendering system, without which 6590 practical interoperability will be quite difficult. When using GM, 6591 parties SHOULD use Universal Real-Time SysEx MIP messages [SPMIDI] to 6592 communicate the priority of voices to polyphony-limited clients. 6594 Note that this requirement does not force implementors of a non-GM 6595 renderer (for mpeg4-generic sessions, DLS 2, or Structured Audio) to add 6596 a second rendering engine. Instead, a client may satisfy the 6597 requirement by including a set of voice patches that implement the GM 6598 instrument set, and using this emulation for mpeg4-generic GM sessions. 6599 We require GM support so that an offerer that wishes to maximize 6600 interoperability may do so by offering GM if its preferred renderer is 6601 not accepted by the answerer. 6603 Offerers MUST NOT present several renderers as options in a session 6604 description by listing several payload types on a media line, as Section 6605 2.1 uses this construct to let a party send several RTP MIDI streams in 6606 the same RTP session. 6608 Instead, an offerer wishing to present rendering options SHOULD offer a 6609 single payload type that offers several renderers. In this construct, 6610 the parameter list codes a list of render parameters (each followed by 6611 its support parameters). As discussed in Appendix C.6.1, the order of 6612 renderers in the list declares the offerer's preference. The "unknown" 6613 and "null" values MUST NOT appear in the offer. The answer MUST set all 6614 render values except the desired renderer to "null". Thus, "unknown" 6615 MUST NOT appear in the answer. 6617 We use SHOULD instead of MUST in the first sentence in the paragraph 6618 above, because this technique does not work in all situations (example: 6619 an offerer wishes to offer both mpeg4-generic renderers and native RTP 6620 MIDI renderers as options). In this case, the offerer MUST present a 6621 series of session descriptions, each offering a single renderer, until 6622 the answerer accepts a session description. 6624 Parties MUST support the musicport, chanmask, subrender, rinit, and 6625 inline parameters. Parties supporting renderers whose data object (as 6626 encoded by a parameter value for "inline") could exceed 300 octets in 6627 size MUST support the url and cid parameters and thus must implement the 6628 HTTP protocol. HTTP over TLS [RFC2818] support for data objects is 6629 OPTIONAL. Note that in mpeg4-generic, General MIDI data objects cannot 6630 exceed 300 octets, but DLS 2 and Structured Audio data objects may. 6631 Support for the other rendering parameters (smf_cif, smf_info, 6632 smf_inline, smf_url) is OPTIONAL. 6634 Thus far in this document, our discussion has assumed that the only MIDI 6635 flows that drive a renderer are the network flows described in the 6636 session description. In NMP applications, this assumption would require 6637 two rendering engines: one for local use by a party, a second for the 6638 remote party. 6640 In practice, applications may wish to have both parties share a single 6641 rendering engine. In this case, the session description MUST use a 6642 virtual sendrecv session and MUST use the stream subsetting and chapter 6643 inclusion parameters to allocate which MIDI channels are intended for 6644 use by a party. If two parties are sharing a MIDI channel, the 6645 application MUST ensure that appropriate MIDI merging occurs at the 6646 input to the renderer. 6648 We now discuss the use of (non-MIDI) audio streams in the session. 6650 Audio streams may be used for two purposes: as a "talkback" channel for 6651 parties to converse, or as a way to conduct a performance that includes 6652 MIDI and audio channels. In the latter case, offers MUST use sample 6653 rates and the packet temporal durations for the audio and MIDI streams 6654 that support low-latency synchronized rendering. 6656 We now show an example of an offer/answer exchange in a network musical 6657 performance application (next page). 6659 Below, we show an offer that complies with the interoperability text in 6660 this appendix section. 6662 v=0 6663 o=first 2520644554 2838152170 IN IP4 first.example.net 6664 s=Example 6665 t=0 0 6666 a=group:FID 1 2 6667 c=IN IP4 192.0.2.94 6668 m=audio 16112 RTP/AVP 96 6669 a=recvonly 6670 a=mid:1 6671 a=rtpmap:96 mpeg4-generic/44100 6672 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6673 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=2NPTW; 6674 cm_used=2C0.1.7.10.11.64.121.123; cm_used=2M0.1.2; 6675 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6676 ch_default=2NPTW; ch_default=2C0.1.7.10.11.64.121.123; 6677 ch_default=2M0.1.2; cm_default=X0-16; 6678 rtp_ptime=0; rtp_maxptime=0; guardtime=44100; 6679 musicport=1; render=synthetic; rinit="audio/asc"; 6680 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6681 m=audio 16114 RTP/AVP 96 6682 a=sendonly 6683 a=mid:2 6684 a=rtpmap:96 mpeg4-generic/44100 6685 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6686 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=1NPTW; 6687 cm_used=1C0.1.7.10.11.64.121.123; cm_used=1M0.1.2; 6688 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6689 ch_default=1NPTW; ch_default=1C0.1.7.10.11.64.121.123; 6690 ch_default=1M0.1.2; cm_default=X0-16; 6691 rtp_ptime=0; rtp_maxptime=0; guardtime=44100; 6692 musicport=1; render=synthetic; rinit="audio/asc"; 6693 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6695 (The a=fmtp lines have been wrapped to fit the page to accommodate 6696 memo formatting restrictions; it comprises a single line in SDP.) 6698 The owner line (o=) identifies the session owner as "first". 6700 The session description defines two MIDI streams: a recvonly stream on 6701 which "first" receives a performance, and a sendonly stream that "first" 6702 uses to send a performance. The recvonly port number encodes the ports 6703 on which "first" wishes to receive RTP (16112) and RTCP (16113) media at 6704 IP4 address 192.0.2.94. The sendonly port number encodes the port on 6705 which "first" wishes to receive RTCP for the stream (16115). 6707 The musicport parameters code that the two streams share and identity 6708 relationship and thus form a virtual sendrecv stream. 6710 Both streams are mpeg4-generic RTP MIDI streams that specify a General 6711 MIDI renderer. The stream subsetting parameters code that the recvonly 6712 stream uses MIDI channel 1 exclusively for voice commands, and that the 6713 sendonly stream uses MIDI channel 2 exclusively for voice commands. 6714 This mapping permits the application software to share a single renderer 6715 for local and remote performers. 6717 We now show the answer to the offer. 6719 v=0 6720 o=second 2520644554 2838152170 IN IP4 second.example.net 6721 s=Example 6722 t=0 0 6723 a=group:FID 1 2 6724 c=IN IP4 192.0.2.105 6725 m=audio 5004 RTP/AVP 96 6726 a=sendonly 6727 a=mid:1 6728 a=rtpmap:96 mpeg4-generic/44100 6729 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6730 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=2NPTW; 6731 cm_used=2C0.1.7.10.11.64.121.123; cm_used=2M0.1.2; 6732 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6733 ch_default=2NPTW; ch_default=2C0.1.7.10.11.64.121.123; 6734 ch_default=2M0.1.2; cm_default=X0-16; 6735 rtp_ptime=0; rtp_maxptime=882; guardtime=44100; 6736 musicport=1; render=synthetic; rinit="audio/asc"; 6737 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6738 m=audio 5006 RTP/AVP 96 6739 a=recvonly 6740 a=mid:2 6741 a=rtpmap:96 mpeg4-generic/44100 6742 a=fmtp:96 streamtype=5; mode=rtp-midi; config=""; profile-level-id=12; 6743 cm_unused=ABCFGHJKMNPQTVWXYZ; cm_used=1NPTW; 6744 cm_used=1C0.1.7.10.11.64.121.123; cm_used=1M0.1.2; 6745 cm_used=X0-16; ch_never=ABCDEFGHJKMNPQTVWXYZ; 6746 ch_default=1NPTW; ch_default=1C0.1.7.10.11.64.121.123; 6747 ch_default=1M0.1.2; cm_default=X0-16; 6748 rtp_ptime=0; rtp_maxptime=0; guardtime=88200; 6749 musicport=1; render=synthetic; rinit="audio/asc"; 6750 inline="egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA" 6752 (The a=fmtp lines have been wrapped to fit the page to accommodate 6753 memo formatting restrictions; they comprise single lines in SDP.) 6755 The owner line (o=) identifies the session owner as "second". 6757 The port numbers for both media streams are non-zero; thus, "second" has 6758 accepted the session description. The stream marked "sendonly" in the 6759 offer is marked "recvonly" in the answer, and vice versa, coding the 6760 different view of the session held by "session". The IP4 number 6761 (192.0.2.105) and the RTP (5004 and 5006) and RTCP (5005 and 5007) have 6762 been changed by "second" to match its transport wishes. 6764 In addition, "second" has made several parameter changes: rtp_maxptime 6765 for the sendonly stream has been changed to code 2 ms (441 in clock 6766 units), and the guardtime for the recvonly stream has been doubled. As 6767 these parameter modifications request capabilities that are REQUIRED to 6768 be implemented by interoperable parties, "second" can make these changes 6769 with confidence that "first" can abide by them. 6771 D. Parameter Syntax Definitions 6773 In this appendix, we define the syntax for the RTP MIDI media type 6774 parameters in Augmented Backus-Naur Form (ABNF, [RFC4234]). When using 6775 these parameters with SDP, all parameters MUST appear on a single fmtp 6776 attribute line of an RTP MIDI media description. For mpeg4-generic RTP 6777 MIDI streams, this line MUST also include any mpeg4-generic parameters 6778 (usage described in Section 6.2). An fmtp attribute line may be defined 6779 (after [RFC3640]) as: 6781 ; 6782 ; SDP fmtp line definition 6783 ; 6785 fmtp = "a=fmtp:" token SP param-assign 0*(";" SP param-assign) CRLF 6787 where codes the RTP payload type. Note that white space MUST 6788 NOT appear between the "a=fmtp:" and the RTP payload type. 6790 We now define the syntax of the parameters defined in Appendix C. The 6791 definition takes the form of the incremental assembly of the token. See [RFC3640] for the syntax of the mpeg4-generic 6793 parameters discussed in Section 6.2. 6795 ; 6796 ; 6797 ; top-level definition for all parameters 6798 ; 6799 ; 6801 ; 6802 ; Parameters defined in Appendix C.1 6804 param-assign = ("cm_unused=" (([channel-list] command-type 6805 [f-list]) / sysex-data)) 6807 param-assign =/ ("cm_used=" (([channel-list] command-type 6808 [f-list]) / sysex-data)) 6810 ; 6811 ; Parameters defined in Appendix C.2 6813 param-assign =/ ("j_sec=" ("none" / "recj" / ietf-extension)) 6815 param-assign =/ ("j_update=" ("anchor" / "closed-loop" / 6816 "open-loop" / ietf-extension)) 6818 param-assign =/ ("ch_default=" (([channel-list] chapter-list 6819 [f-list]) / sysex-data)) 6821 param-assign =/ ("ch_never=" (([channel-list] chapter-list 6822 [f-list]) / sysex-data)) 6824 param-assign =/ ("ch_anchor=" (([channel-list] chapter-list 6825 [f-list]) / sysex-data)) 6827 ; 6828 ; Parameters defined in Appendix C.3 6830 param-assign =/ ("tsmode=" ("comex" / "async" / "buffer")) 6832 param-assign =/ ("linerate=" nonzero-four-octet) 6834 param-assign =/ ("octpos=" ("first" / "last")) 6836 param-assign =/ ("mperiod=" nonzero-four-octet) 6838 ; 6839 ; Parameter defined in Appendix C.4 6841 param-assign =/ ("guardtime=" nonzero-four-octet) 6843 param-assign =/ ("rtp_ptime=" four-octet) 6845 param-assign =/ ("rtp_maxptime=" four-octet) 6847 ; 6848 ; Parameters defined in Appendix C.5 6850 param-assign =/ ("musicport=" four-octet) 6852 ; 6853 ; Parameters defined in Appendix C.6 6855 param-assign =/ ("chanmask=" 1*( 16(BIT) )) 6857 param-assign =/ ("cid=" DQUOTE cid-block DQUOTE) 6859 param-assign =/ ("inline=" DQUOTE base-64-block DQUOTE) 6861 param-assign =/ ("multimode=" ("all" / "one")) 6863 param-assign =/ ("render=" ("synthetic" / "api" / "null" / 6864 "unknown" / extension)) 6866 param-assign =/ ("rinit=" mime-type "/" mime-subtype) 6868 param-assign =/ ("smf_cid=" DQUOTE cid-block DQUOTE) 6870 param-assign =/ ("smf_info=" ("ignore" / "identity" / 6871 "sdp_start" / extension)) 6873 param-assign =/ ("smf_inline=" DQUOTE base-64-block DQUOTE) 6875 param-assign =/ ("smf_url=" DQUOTE uri-element DQUOTE) 6877 param-assign =/ ("subrender=" ("default" / extension)) 6879 param-assign =/ ("url=" DQUOTE uri-element DQUOTE) 6881 ; 6882 ; list definitions for the cm_ command-type 6883 ; 6885 command-type = [A] [B] [C] [F] [G] [H] [J] [K] [M] 6886 [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 6888 ; 6889 ; list definitions for the ch_ chapter-list 6890 ; 6892 chapter-list = [A] [B] [C] [D] [E] [F] [G] [H] [J] [K] 6893 [M] [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 6895 ; 6896 ; list definitions for the channel-list (used in ch_* / cm_* params) 6897 ; 6899 channel-list = midi-chan-element *("." midi-chan-element) 6901 midi-chan-element = midi-chan / midi-chan-range 6903 midi-chan-range = midi-chan "-" midi-chan 6904 ; 6905 ; decimal value of left midi-chan 6906 ; MUST be strictly less than 6907 ; decimal value of right midi-chan 6909 midi-chan = DIGIT / ("1" %x30-35) ; "0" .. "15" 6910 ; 6911 ; list definitions for the ch_ field list (f-list) 6912 ; 6914 f-list = midi-field-element *("." midi-field-element) 6916 midi-field-element = midi-field / midi-field-range 6918 midi-field-range = midi-field "-" midi-field 6919 ; 6920 ; decimal value of left midi-field 6921 ; MUST be strictly less than 6922 ; decimal value of right midi-field 6924 midi-field = four-octet 6925 ; 6926 ; large range accommodates Chapter M 6927 ; RPN (0-16383) and NRPN (16384-32767) 6928 ; parameters, and Chapter X octet sizes. 6930 ; 6931 ; definitions for ch_ sysex-data 6932 ; 6934 sysex-data = "__" h-list *("_" h-list) "__" 6936 h-list = hex-field-element *("." hex-field-element) 6938 hex-field-element = hex-octet / hex-field-range 6940 hex-field-range = hex-octet "-" hex-octet 6941 ; 6942 ; hexadecimal value of left hex-octet 6943 ; MUST be strictly less than hexadecimal 6944 ; value of right hex-octet 6946 hex-octet = %x30-37 U-HEXDIG 6947 ; 6948 ; rewritten special case of hex-octet in [RFC2045] 6949 ; (page 23). 6950 ; note that a-f are not permitted, only A-F. 6951 ; hex-octet values MUST NOT exceed 0x7F. 6953 ; 6954 ; definitions for rinit parameter 6955 ; 6957 mime-type = "audio" / "application" 6958 mime-subtype = token 6959 ; 6960 ; See Appendix C.6.2 for registration 6961 ; requirements for rinit type/subtypes. 6963 ; 6964 ; definitions for base64 encoding 6965 ; copied from [RFC4566] 6966 ; changes from [RFC4566] to improve automatic syntax checking 6967 ; 6969 base-64-block = *base64-unit [base64-pad] 6971 base64-unit = 4(base64-char) 6973 base64-pad = (2(base64-char) "==") / (3(base64-char) "=") 6975 base64-char = %x41-5A / %x61-7A / %x30-39 / "+" / "/" 6976 ; A-Z, a-z, 0-9, "+" and "/" 6978 ; 6979 ; generic rules 6980 ; 6982 ietf-extension = token 6983 ; 6984 ; may only be defined in standards-track RFCs 6986 extension = token 6987 ; 6988 ; may be defined 6989 ; by filing a registration with IANA 6991 nonzero-four-octet = (NZ-DIGIT 0*8(DIGIT)) 6992 / (%x30-33 9(DIGIT)) 6993 / ("4" %x30-31 8(DIGIT)) 6994 / ("42" %x30-38 7(DIGIT)) 6995 / ("429" %x30-33 6(DIGIT)) 6996 / ("4294" %x30-38 5(DIGIT)) 6997 / ("42949" %x30-35 4(DIGIT)) 6998 / ("429496" %x30-36 3(DIGIT)) 6999 / ("4294967" %x30-31 2(DIGIT)) 7000 / ("42949672" %x30-38 (DIGIT)) 7001 / ("429496729" %x30-34) 7002 ; 7003 ; unsigned encoding of non-zero 32-bit value: 7004 ; 1 .. 4294967295 7006 four-octet = "0" / nonzero-four-octet 7007 ; 7008 ; unsigned encoding of 32-bit value: 7009 ; 0 .. 4294967295 7011 uri-element = URI-reference 7012 ; as defined in [RFC3986] 7014 token = 1*token-char 7015 ; copied from [RFC4566] 7017 token-char = %x21 / %x23-27 / %x2A-2B / %x2D-2E / 7018 %x30-39 / %x41-5A / %x5E-7E 7019 ; copied from [RFC4566] 7021 cid-block = 1*cid-char 7023 cid-char = token-char 7024 cid-char =/ "@" 7025 cid-char =/ "," 7026 cid-char =/ ";" 7027 cid-char =/ ":" 7028 cid-char =/ "\" 7029 cid-char =/ "/" 7030 cid-char =/ "[" 7031 cid-char =/ "]" 7032 cid-char =/ "?" 7033 cid-char =/ "=" 7034 ; 7035 ; - add back in the tspecials [RFC2045], except 7036 ; for DQUOTE and the non-email safe ( ) < > 7037 ; - note that the definitions above ensure that 7038 ; cid-block is always enclosed with DQUOTEs 7040 A = %x41 ; uppercase only letters used above 7041 B = %x42 7042 C = %x43 7043 D = %x44 7044 E = %x45 7045 F = %x46 7046 G = %x47 7047 H = %x48 7048 J = %x4A 7049 K = %x4B 7050 M = %x4D 7051 N = %x4E 7052 P = %x50 7053 Q = %x51 7054 T = %x54 7055 V = %x56 7056 W = %x57 7057 X = %x58 7058 Y = %x59 7059 Z = %x5A 7061 NZ-DIGIT = %x31-39 ; non-zero decimal digit 7063 U-HEXDIG = DIGIT / A / B / C / D / E / F 7064 ; variant of HEXDIG [RFC4234] : 7065 ; hexadecimal digit using uppercase A-F only 7067 ; the rules below are from the Core Rules from [RFC4234] 7069 BIT = "0" / "1" 7071 DQUOTE = %x22 ; " (Double Quote) 7073 DIGIT = %x30-39 ; 0-9 7075 ; external references 7076 ; URI-reference: from [RFC3986] 7078 ; 7079 ; End of ABNF 7081 The mpeg4-generic RTP payload [RFC3640] defines a "mode" parameter that 7082 signals the type of MPEG stream in use. We add a new mode value, "rtp- 7083 midi", using the ABNF rule below: 7085 ; 7086 ; mpeg4-generic mode parameter extension 7087 ; 7089 mode =/ "rtp-midi" 7090 ; as described in Section 6.2 of this memo 7092 E. A MIDI Overview for Networking Specialists 7094 This appendix presents an overview of the MIDI standard, for the benefit 7095 of networking specialists new to musical applications. Implementors 7096 should consult [MIDI] for a normative description of MIDI. 7098 Musicians make music by performing a controlled sequence of physical 7099 movements. For example, a pianist plays by coordinating a series of key 7100 presses, key releases, and pedal actions. MIDI represents a musical 7101 performance by encoding these physical gestures as a sequence of MIDI 7102 commands. This high-level musical representation is compact but 7103 fragile: one lost command may be catastrophic to the performance. 7105 MIDI commands have much in common with the machine instructions of a 7106 microprocessor. MIDI commands are defined as binary elements. 7107 Bitfields within a MIDI command have a regular structure and a 7108 specialized purpose. For example, the upper nibble of the first command 7109 octet (the opcode field) codes the command type. MIDI commands may 7110 consist of an arbitrary number of complete octets, but most MIDI 7111 commands are 1, 2, or 3 octets in length. 7113 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7114 | Channel Voice Messages | Bitfield Pattern | 7115 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7116 | NoteOff (end a note) | 1000cccc 0nnnnnnn 0vvvvvvv | 7117 |-------------------------------------------------------------| 7118 | NoteOn (start a note) | 1001cccc 0nnnnnnn 0vvvvvvv | 7119 |-------------------------------------------------------------| 7120 | PTouch (Polyphonic Aftertouch) | 1010cccc 0nnnnnnn 0aaaaaaa | 7121 |-------------------------------------------------------------| 7122 | CControl (Controller Change) | 1011cccc 0xxxxxxx 0yyyyyyy | 7123 |-------------------------------------------------------------| 7124 | PChange (Program Change) | 1100cccc 0ppppppp | 7125 |-------------------------------------------------------------| 7126 | CTouch (Channel Aftertouch) | 1101cccc 0aaaaaaa | 7127 |-------------------------------------------------------------| 7128 | PWheel (Pitch Wheel) | 1110cccc 0xxxxxxx 0yyyyyyy | 7129 ------------------------------------------------------------- 7131 Figure E.1 -- MIDI Channel Messages 7133 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7134 | System Common Messages | Bitfield Pattern | 7135 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7136 | System Exclusive | 11110000, followed by a | 7137 | | list of 0xxxxxx octets, | 7138 | | followed by 11110111 | 7139 |-------------------------------------------------------------| 7140 | MIDI Time Code Quarter Frame | 11110001 0xxxxxxx | 7141 |-------------------------------------------------------------| 7142 | Song Position Pointer | 11110010 0xxxxxxx 0yyyyyyy | 7143 |-------------------------------------------------------------| 7144 | Song Select | 11110011 0xxxxxxx | 7145 |-------------------------------------------------------------| 7146 | Undefined | 11110100 | 7147 |-------------------------------------------------------------| 7148 | Undefined | 11110101 | 7149 |-------------------------------------------------------------| 7150 | Tune Request | 11110110 | 7151 |-------------------------------------------------------------| 7152 | System Exclusive End Marker | 11110111 | 7153 ------------------------------------------------------------- 7155 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7156 | System Realtime Messages | Bitfield Pattern | 7157 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 7158 | Clock | 11111000 | 7159 |-------------------------------------------------------------| 7160 | Undefined | 11111001 | 7161 |-------------------------------------------------------------| 7162 | Start | 11111010 | 7163 |-------------------------------------------------------------| 7164 | Continue | 11111011 | 7165 |-------------------------------------------------------------| 7166 | Stop | 11111100 | 7167 |-------------------------------------------------------------| 7168 | Undefined | 11111101 | 7169 |-------------------------------------------------------------| 7170 | Active Sense | 11111110 | 7171 |-------------------------------------------------------------| 7172 | System Reset | 11111111 | 7173 ------------------------------------------------------------- 7175 Figure E.2 -- MIDI System Messages 7177 Figure E.1 and E.2 show the MIDI command family. There are three major 7178 classes of commands: voice commands (opcode field values in the range 7179 0x8 through 0xE), system common commands (opcode field 0xF, commands 7180 0xF0 through 0xF7), and system real-time commands (opcode field 0xF, 7181 commands 0xF8 through 0xFF). Voice commands code the musical gestures 7182 for each timbre in a composition. Systems commands perform functions 7183 that usually affect all voice channels, such as System Reset (0xFF). 7185 E.1. Commands Types 7187 Voice commands execute on one of 16 MIDI channels, as coded by its 4-bit 7188 channel field (field cccc in Figure E.1). In most applications, notes 7189 for different timbres are assigned to different channels. To support 7190 applications that require more than 16 channels, MIDI systems use 7191 several MIDI command streams in parallel, to yield 32, 48, or 64 MIDI 7192 channels. 7194 As an example of a voice command, consider a NoteOn command (opcode 7195 0x9), with binary encoding 1001cccc 0nnnnnnn 0aaaaaaa. This command 7196 signals the start of a musical note on MIDI channel cccc. The note has 7197 a pitch coded by the note number nnnnnnn, and an onset amplitude coded 7198 by note velocity aaaaaaa. 7200 Other voice commands signal the end of notes (NoteOff, opcode 0x8), map 7201 a specific timbre to a MIDI channel (PChange, opcode 0xC), or set the 7202 value of parameters that modulate the timbral quality (all other voice 7203 commands). The exact meaning of most voice channel commands depends on 7204 the rendering algorithms the MIDI receiver uses to generate sound. In 7205 most applications, a MIDI sender has a model (in some sense) of the 7206 rendering method used by the receiver. 7208 System commands perform a variety of global tasks in the stream, 7209 including "sequencer" playback control of pre-recorded MIDI commands 7210 (the Song Position Pointer, Song Select, Clock, Start, Continue, and 7211 Stop messages), SMPTE time code (the MIDI Time Code Quarter Frame 7212 command), and the communication of device-specific data (the System 7213 Exclusive messages). 7215 E.2. Running Status 7217 All MIDI command bitfields share a special structure: the leading bit of 7218 the first octet is set to 1, and the leading bit of all subsequent 7219 octets is set to 0. This structure supports a data compression system, 7220 called running status [MIDI], that improves the coding efficiency of 7221 MIDI. 7223 In running status coding, the first octet of a MIDI voice command may be 7224 dropped if it is identical to the first octet of the previous MIDI voice 7225 command. This rule, in combination with a convention to consider NoteOn 7226 commands with a null third octet as NoteOff commands, supports the 7227 coding of note sequences using two octets per command. 7229 Running status coding is only used for voice commands. The presence of 7230 a system common message in the stream cancels running status mode for 7231 the next voice command. However, system real-time messages do not 7232 cancel running status mode. 7234 E.3. Command Timing 7236 The bitfield formats in Figures E.1 and E.2 do not encode the execution 7237 time for a command. Timing information is not a part of the MIDI 7238 command syntax itself; different applications of the MIDI command 7239 language use different methods to encode timing. 7241 For example, the MIDI command set acts as the transport layer for MIDI 7242 1.0 DIN cables [MIDI]. MIDI cables are short asynchronous serial lines 7243 that facilitate the remote operation of musical instruments and audio 7244 equipment. Timestamps are not sent over a MIDI 1.0 DIN cable. Instead, 7245 the standard uses an implicit "time of arrival" code. Receivers execute 7246 MIDI commands at the moment of arrival. 7248 In contrast, Standard MIDI Files (SMFs, [MIDI]), a file format for 7249 representing complete musical performances, add an explicit timestamp to 7250 each MIDI command, using a delta encoding scheme that is optimized for 7251 statistics of musical performance. SMF timestamps usually code timing 7252 using the metric notation of a musical score. SMF meta-events are used 7253 to add a tempo map to the file, so that score beats may be accurately 7254 converted into units of seconds during rendering. 7256 E.4. AudioSpecificConfig Templates for MMA Renderers 7258 In Section 6.2 and Appendix C.6.5, we describe how session descriptions 7259 include an AudioSpecificConfig data block to specify a MIDI rendering 7260 algorithm for mpeg4-generic RTP MIDI streams. 7262 The bitfield format of AudioSpecificConfig is defined in [MPEGAUDIO]. 7263 StructuredAudioSpecificConfig, a key data structure coded in 7264 AudioSpecificConfig, is defined in [MPEGSA]. 7266 For implementors wishing to specify Structured Audio renderers, a full 7267 understanding of [MPEGSA] and [MPEGAUDIO] is essential. However, many 7268 implementors will limit their rendering options to the two MIDI 7269 Manufacturers Association renderers that may be specified in 7270 AudioSpecificConfig: General MIDI (GM, [MIDI]) and Downloadable Sounds 2 7271 (DLS 2, [DLS2]). 7273 To aid these implementors, we reproduce the AudioSpecificConfig bitfield 7274 formats for a GM renderer and a DLS 2 renderer below. We have checked 7275 these bitfields carefully and believe they are correct. However, we 7276 stress that the material below is informative, and that [MPEGAUDIO] and 7277 [MPEGSA] are the normative definitions for AudioSpecificConfig. 7279 As described in Section 6.2, a minimal mpeg4-generic session description 7280 encodes the AudioSpecificConfig binary bitfield as a hexadecimal string 7281 (whose format is defined in [RFC3640]) that is assigned to the "config" 7282 parameter. As described in Appendix C.6.3, a session description that 7283 uses the render parameter encodes the AudioSpecificConfig binary 7284 bitfield as a Base64-encoded string assigned to the "inline" parameter, 7285 or in the body of an HTTP URL assigned to the "url" parameter. 7287 Below, we show a simplified binary AudioSpecificConfig bitfield format, 7288 suitable for sending and receiving GM and DLS 2 data: 7290 0 1 2 3 7291 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 7292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7293 | AOTYPE |FREQIDX|CHANNEL|SACNK| FILE_BLK 1 (required) ... | 7294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7295 |1|SACNK| FILE_BLK 2 (optional) ... | 7296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7297 | ... |1|SACNK| FILE_BLK N (optional) ... | 7298 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7299 |0|0| (first "0" bit terminates FILE_BLK list) 7300 +-+-+ 7302 Figure E.3 -- Simplified AudioSpecificConfig 7304 The 5-bit AOTYPE field specifies the Audio Object Type as an unsigned 7305 integer. The legal values for use with mpeg4-generic RTP MIDI streams 7306 are "15" (General MIDI), "14" (DLS 2), and "13" (Structured Audio). 7307 Thus, receivers that do not support all three mpeg4-generic renderers 7308 may parse the first 5 bits of an AudioSpecificConfig coded in a session 7309 description and reject sessions that specify unsupported renderers. 7311 The 4-bit FREQIDX field specifies the sampling rate of the renderer. We 7312 show the mapping of FREQIDX values to sampling rates in Figure E.4. 7313 Senders MUST specify a sampling frequency that matches the RTP clock 7314 rate, if possible; if not, senders MUST specify the escape value. 7315 Receivers MUST consult the RTP clock parameter for the true sampling 7316 rate if the escape value is specified. 7318 FREQIDX Sampling Frequency 7320 0x0 96000 7321 0x1 88200 7322 0x2 64000 7323 0x3 48000 7324 0x4 44100 7325 0x5 32000 7326 0x6 24000 7327 0x7 22050 7328 0x8 16000 7329 0x9 12000 7330 0xa 11025 7331 0xb 8000 7332 0xc reserved 7333 0xd reserved 7334 0xe reserved 7335 0xf escape value 7337 Figure E.4 -- FreqIdx encoding 7339 The 4-bit CHANNEL field specifies the number of audio channels for the 7340 renderer. The values 0x1 to 0x5 specify 1 to 5 audio channels; the 7341 value 0x6 specifies 5+1 surround sound, and the value 0x7 specifies 7+1 7342 surround sound. If the rtpmap line in the session description specifies 7343 one of these formats, CHANNEL MUST be set to the corresponding value. 7344 Otherwise, CHANNEL MUST be set to 0x0. 7346 The CHANNEL field is followed by a list of one or more binary file data 7347 blocks. The 3-bit SACNK field (the chunk_type field in class 7348 StructuredAudioSpecificConfig, defined in [MPEGSA]) specifies the type 7349 of each data block. 7351 For General MIDI, only Standard MIDI Files may appear in the list (SACNK 7352 field value 2). For DLS 2, only Standard MIDI Files and DLS 2 RIFF 7353 files (SACNK field value 4) may appear. For both of these file types, 7354 the FILE_BLK field has the format shown in Figure E.5: a 32-bit unsigned 7355 integer value (FILE_LEN) coding the number of bytes in the SMF or RIFF 7356 file, followed by FILE_LEN bytes coding the file data. 7358 0 1 2 3 7359 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 7360 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7361 | FILE_LEN (32-bit, a byte count SMF file or RIFF file) | 7362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7363 | FILE_DATA (file contents, a list of FILE_LEN bytes) ... | 7364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7366 Figure E.5 -- The FILE_BLK field format 7368 Note that several files may follow the CHANNEL field. The "1" constant 7369 fields in Figure E.3 code the presence of another file; the "0" constant 7370 field codes the end of the list. The final "0" bit in Figure E.3 codes 7371 the absence of special coding tools (see [MPEGAUDIO] for details). 7372 Senders not using these tools MUST append this "0" bit; receivers that 7373 do not understand these coding tools MUST ignore all data following a 7374 "1" in this position. 7376 The StructuredAudioSpecificConfig bitfield structure requires the 7377 presence of one FILE_BLK. For mpeg4-generic RTP MIDI use of DLS 2, 7378 FILE_BLKs MUST code RIFF files or SMF files. For mpeg4-generic RTP MIDI 7379 use of General MIDI, FILE_BLKs MUST code SMF files. By default, this 7380 SMF will be ignored (Appendix C.6.4.1). In this default case, a GM 7381 StructuredAudioSpecificConfig bitfield SHOULD code a FILE_BLK whose 7382 FILE_LEN is 0, and whose FILE_DATA is empty. 7384 To complete this appendix, we derive the StructuredAudioSpecificConfig 7385 that we use in the General MIDI session examples in this memo. 7386 Referring to Figure E.3, we note that for GM, AOTYPE = 15. Our examples 7387 use a 44,100 Hz sample rate (FREQIDX = 4) and are in mono (CHANNEL = 1). 7388 For GM, a single SMF is encoded (SACNK = 2), using the SMF shown in 7389 Figure E.6 (a 26 byte file). 7391 -------------------------------------------- 7392 | MIDI File =
| 7393 -------------------------------------------- 7395
= 7396 4D 54 68 64 00 00 00 06 00 00 00 01 00 60 7398 = 7399 4D 54 72 6B 00 00 00 04 00 FF 2F 00 7401 Figure E.6 -- SMF file encoded in the example 7403 Placing these constants in binary format into the data structure shown 7404 in Figure E.3 yields the constant shown in Figure E.7. 7406 0 1 2 3 7407 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 7408 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7409 |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| 7410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7411 |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| 7412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7413 |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| 7414 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7415 |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| 7416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7417 |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| 7418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7419 |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| 7420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7421 |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| 7422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7423 |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| 7424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7425 |0|0| 7426 +-+-+ 7428 Figure E.7 -- AudioSpecificConfig used in GM examples 7430 Expressing this bitfield as an ASCII hexadecimal string yields: 7432 7A0A0000001A4D546864000000060000000100604D54726B0000000600FF2F000 7434 This string is assigned to the "config" parameter in the minimal 7435 mpeg4-generic General MIDI examples in this memo (such as the example in 7436 Section 6.2). Expressing this string in Base64 [RFC2045] yields: 7438 egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA 7440 This string is assigned to the "inline" parameter in the General MIDI 7441 example shown in Appendix C.6.5. 7443 References 7445 Normative References 7447 [MIDI] MIDI Manufacturers Association. "The Complete MIDI 1.0 7448 Detailed Specification", 1996. 7450 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 7451 Jacobson, "RTP: A Transport Protocol for Real-Time 7452 Applications", STD 64, RFC 3550, July 2003. 7454 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 7455 Video Conferences with Minimal Control", STD 65, RFC 7456 3551, July 2003. 7458 [RFC3640] van der Meer, J., Mackie, D., Swaminathan, V., Singer, 7459 D., and P. Gentric, "RTP Payload Format for Transport of 7460 MPEG-4 Elementary Streams", RFC 3640, November 2003. 7462 [MPEGSA] International Standards Organization. "ISO/IEC 14496 7463 MPEG-4", Part 3 (Audio), Subpart 5 (Structured Audio), 7464 2001. 7466 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 7467 Description Protocol", RFC 4566, July 2006. 7469 [MPEGAUDIO] International Standards Organization. "ISO 14496 MPEG- 7470 4", Part 3 (Audio), 2001. 7472 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 7473 Extensions (MIME) Part One: Format of Internet Message 7474 Bodies", RFC 2045, November 1996. 7476 [DLS2] MIDI Manufacturers Association. "The MIDI Downloadable 7477 Sounds Specification", v98.2, 1998. 7479 [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 7480 Specifications: ABNF", RFC 4234, October 2005. 7482 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 7483 Requirement Levels", BCP 14, RFC 2119, March 1997. 7485 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 7486 Norrman, "The Secure Real-time Transport Protocol 7487 (SRTP)", RFC 3711, March 2004. 7489 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 7490 with Session Description Protocol (SDP)", RFC 3264, June 7491 2002. 7493 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 7494 Resource Identifier (URI): Generic Syntax", STD 66, RFC 7495 3986, January 2005. 7497 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 7498 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 7499 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 7501 [RFC3388] Camarillo, G., Eriksson, G., Holler, J., and H. 7502 Schulzrinne, "Grouping of Media Lines in the Session 7503 Description Protocol (SDP)", RFC 3388, December 2002. 7505 [RP015] MIDI Manufacturers Association. "Recommended Practice 7506 015 (RP-015): Response to Reset All Controllers", 11/98. 7508 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 7509 Registration Procedures", BCP 13, RFC 4288, December 7510 2005. 7512 [RFC3555] Casner, S. and P. Hoschka, "MIME Type Registration of RTP 7513 Payload Formats", RFC 3555, July 2003. 7515 Informative References 7517 [NMP] Lazzaro, J. and J. Wawrzynek. "A Case for Network 7518 Musical Performance", 11th International Workshop on 7519 Network and Operating Systems Support for Digital Audio 7520 and Video (NOSSDAV 2001) June 25-26, 2001, Port 7521 Jefferson, New York. 7523 [GRAME] Fober, D., Orlarey, Y. and S. Letz. "Real Time Musical 7524 Events Streaming over Internet", Proceedings of the 7525 International Conference on WEB Delivering of Music 2001, 7526 pages 147-154. 7528 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 7529 A., Peterson, J., Sparks, R., Handley, M., and E. 7530 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 7531 June 2002. 7533 [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time 7534 Streaming Protocol (RTSP)", RFC 2326, April 1998. 7536 [ALF] Clark, D. D. and D. L. Tennenhouse. "Architectural 7537 considerations for a new generation of protocols", 7538 SIGCOMM Symposium on Communications Architectures and 7539 Protocols , (Philadelphia, Pennsylvania), pp. 200--208, 7540 ACM, Sept. 1990. 7542 [RFC4696] Lazzaro, J. and J. Wawrzynek, "An Implementation Guide 7543 for RTP MIDI", RFC 4696, November 2006. 7545 [RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S., and S. 7546 Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 7547 Functional Specification", RFC 2205, September 1997. 7549 [RFC4571] Lazzaro, J. "Framing Real-time Transport Protocol (RTP) 7550 and RTP Control Protocol (RTCP) Packets over Connection- 7551 Oriented Transport", RFC 4571, July 2006. 7553 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 7555 [SPMIDI] MIDI Manufacturers Association. "Scalable Polyphony 7556 MIDI, Specification and Device Profiles", Document 7557 Version 1.0a, 2002. 7559 [LCP] Apple Computer. "Logic 7 Dedicated Control Surface 7560 Support", Appendix B. Product manual available from 7561 www.apple.com. 7563 Authors' Addresses 7565 John Lazzaro (corresponding author) 7566 UC Berkeley 7567 CS Division 7568 315 Soda Hall 7569 Berkeley CA 94720-1776 7570 EMail: lazzaro@cs.berkeley.edu 7572 John Wawrzynek 7573 UC Berkeley 7574 CS Division 7575 631 Soda Hall 7576 Berkeley CA 94720-1776 7577 EMail: johnw@cs.berkeley.edu 7579 Full Copyright Statement 7581 Copyright (C) The IETF Trust (2007). 7583 This document is subject to the rights, licenses and restrictions 7584 contained in BCP 78, and except as set forth therein, the authors retain 7585 all their rights. 7587 This document and the information contained herein are provided on an 7588 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 7589 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 7590 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 7591 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 7592 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 7593 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 7595 Intellectual Property 7597 The IETF takes no position regarding the validity or scope of any 7598 Intellectual Property Rights or other rights that might be claimed to 7599 pertain to the implementation or use of the technology described in this 7600 document or the extent to which any license under such rights might or 7601 might not be available; nor does it represent that it has made any 7602 independent effort to identify any such rights. Information on the 7603 procedures with respect to rights in RFC documents can be found in BCP 7604 78 and BCP 79. 7606 Copies of IPR disclosures made to the IETF Secretariat and any 7607 assurances of licenses to be made available, or the result of an attempt 7608 made to obtain a general license or permission for the use of such 7609 proprietary rights by implementers or users of this specification can be 7610 obtained from the IETF on-line IPR repository at 7611 http://www.ietf.org/ipr. 7613 The IETF invites any interested party to bring to its attention any 7614 copyrights, patents or patent applications, or other proprietary rights 7615 that may cover technology that may be required to implement this 7616 standard. Please address the information to the IETF at ietf- 7617 ipr@ietf.org. 7619 Acknowledgement 7621 Funding for the RFC Editor function is currently provided by the 7622 Internet Society. 7624 Change Log for 7626 This I-D is a modified version of RFC 4695. For every error found to 7627 date in RFC 4695, the I-D has been modified to fix the error. 7629 Below, we list the errors found in RFC 4695 that are most likely to 7630 confuse implementors. The fixes to Appendix D ABNF errors listed 7631 below are presented without comments; see Appendix D to see the 7632 commented rule in context. The list below includes the fixes for all 7633 normative errors; most fixes for other types of errors are not listed. 7634 However, the I-D itself contains fixes for all known errors. 7636 -- 7638 01.txt changes: 7640 A typo was fixed in the Appendix D ABNF. P and Q are now 7641 correctly defined as: 7643 P = %x50 7644 Q = %x51 7646 Thanks to Alfred Hoenes for these changes. 7648 -- 7650 00.txt changes: 7652 Thanks to Alfred Hoenes for these changes. 7654 [1] In Appendix C.1 and Appendix C.2.3 of RFC 4695, an ABNF rule 7655 related to System Chapter X is incorrectly defined as: 7657 = "__" ["_" ] "__" 7659 The correct version of this rule is: 7661 = "__" *( "_" ) "__" 7663 [2] In Appendix C.6.3 of RFC 4695, the URIs permitted to be assigned 7664 to the "url" parameter are not stated clearly. URIs assigned to "url" 7665 MUST specify either HTTP or HTTP over TLS transport protocols. 7667 In Appendix C.7.1 and C.7.2 of RFC 4695, the transport 7668 interoperability requirements for the "url" parameter are not stated 7669 clearly. For both C.7.1 and C.7.2, HTTP is REQUIRED and HTTP over TLS 7670 is OPTIONAL. 7672 [3] Both fmtp lines in both session description examples in Appendix 7673 C.7.2 of RFC 4695 contain instances of the same syntax error (a 7674 missing ";" at a line wrap after "cm_used=2M0.1.2"). 7676 [4] In Appendix D of RFC 4695, all uses of "*ietf-extension" in rules 7677 are in error, and should be replaced with "ietf-extension". Likewise, 7678 all uses of "*extension" are in error, and should be replaced with 7679 "extension". This bug incorrectly lets the null token be assigned to 7680 the j_sec, j_update, render, smf_info, and subrender parameters. 7682 [5] In Appendix D of RFC 4695, the definitions of the 7683 and incorrectly allow lowercase letters to appear in 7684 these strings. The correct definitions of these rules appear below: 7686 command-type = [A] [B] [C] [F] [G] [H] [J] [K] [M] 7687 [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 7689 chapter-list = [A] [B] [C] [D] [E] [F] [G] [H] [J] [K] 7690 [M] [N] [P] [Q] [T] [V] [W] [X] [Y] [Z] 7692 A = %x41 7693 B = %x42 7694 C = %x43 7695 D = %x44 7696 E = %x45 7697 F = %x46 7698 G = %x47 7699 H = %x48 7700 J = %x4A 7701 K = %x4B 7702 M = %x4D 7703 N = %x4E 7704 P = %x50 ; correct as shown, these values were 7705 Q = %x51 ; incorrect in the -00.txt I-D version 7706 T = %x54 7707 V = %x56 7708 W = %x57 7709 X = %x58 7710 Y = %x59 7711 Z = %x5A 7713 [5] In Appendix D of RFC 4695, the definitions of the , 7714 , and are incorrect. The correct 7715 definitions of these rules appear below: 7717 nonzero-four-octet = (NZ-DIGIT 0*8(DIGIT)) 7718 / (%x30-33 9(DIGIT)) 7719 / ("4" %x30-31 8(DIGIT)) 7720 / ("42" %x30-38 7(DIGIT)) 7721 / ("429" %x30-33 6(DIGIT)) 7722 / ("4294" %x30-38 5(DIGIT)) 7723 / ("42949" %x30-35 4(DIGIT)) 7724 / ("429496" %x30-36 3(DIGIT)) 7725 / ("4294967" %x30-31 2(DIGIT)) 7726 / ("42949672" %x30-38 (DIGIT)) 7727 / ("429496729" %x30-34) 7729 four-octet = "0" / nonzero-four-octet 7730 midi-chan = DIGIT / ("1" %x30-35) 7732 DIGIT = %x30-39 7733 NZ-DIGIT = %x31-39 7735 [6] In Appendix D of RFC4695, the rule is 7736 incorrect. The correct definition of this rule appears below. 7738 hex-octet = %x30-37 U-HEXDIG 7739 U-HEXDIG = DIGIT / A / B / C / D / E / F 7741 ; DIGIT as defined in [5] above 7742 ; A, B, C, D, E, F as defined in [4] above 7744 [7] In Appendix D of RFC4695, the rules and 7745 are defined unclearly. The rewritten rules 7746 appear below: 7748 base64-unit = 4(base64-char) 7749 base64-pad = (2(base64-char) "==") / (3(base64-char) "=") 7751 ---