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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) -- Possible downref: Non-RFC (?) normative reference: ref. 'VC2' Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Payload Working Group J. Weaver 3 Internet-Draft BBC 4 Intended status: Standards Track January 7, 2018 5 Expires: July 11, 2018 7 RTP Payload Format for VC-2 HQ Profile Video 8 draft-ietf-payload-rtp-vc2hq-04 10 Abstract 12 This memo describes an RTP Payload format for the High Quality (HQ) 13 profile of SMPTE Standard ST 2042-1 known as VC-2. This document 14 describes the transport of HQ Profile VC-2 in RTP packets and has 15 applications for low-complexity, high-bandwidth streaming of both 16 lossless and lossy compressed video. 18 The HQ profile of VC-2 is intended for low latency video compression 19 (with latency potentially on the order of lines of video) at high 20 data rates (with compression ratios on the order of 2:1 or 4:1). 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on July 11, 2018. 39 Copyright Notice 41 Copyright (c) 2018 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (https://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 2. Conventions, Definitions and Acronyms . . . . . . . . . . . . 3 58 3. Media Format Description . . . . . . . . . . . . . . . . . . 3 59 4. Payload format . . . . . . . . . . . . . . . . . . . . . . . 4 60 4.1. RTP Header Usage . . . . . . . . . . . . . . . . . . . . 9 61 4.2. Payload Header . . . . . . . . . . . . . . . . . . . . . 10 62 4.3. The Choice of Parse Codes (Informative) . . . . . . . . . 12 63 4.4. Stream Constraints . . . . . . . . . . . . . . . . . . . 12 64 4.5. Payload Data . . . . . . . . . . . . . . . . . . . . . . 13 65 4.5.1. Reassembling the Data . . . . . . . . . . . . . . . . 14 66 5. Congestion Control Considerations . . . . . . . . . . . . . . 16 67 6. Payload Format Parameters . . . . . . . . . . . . . . . . . . 16 68 6.1. Media Type Definition . . . . . . . . . . . . . . . . . . 16 69 6.2. Mapping to SDP . . . . . . . . . . . . . . . . . . . . . 18 70 6.3. Offer/Answer Considerations . . . . . . . . . . . . . . . 18 71 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 72 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 73 9. RFC Editor Considerations . . . . . . . . . . . . . . . . . . 19 74 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 75 10.1. Normative References . . . . . . . . . . . . . . . . . . 19 76 10.2. Informative References . . . . . . . . . . . . . . . . . 20 77 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21 79 1. Introduction 81 This memo specifies an RTP payload format for the video coding 82 standard SMPTE ST 2042-1:2017 [VC2] also known as VC-2 84 The VC-2 codec is a wavelet-based codec intended primarily for 85 professional video use with high bit-rates and only low levels of 86 compression. It has been designed to be low-complexity, and 87 potentially have a very low latency through both encoder and decoder: 88 with some choices of parameters this latency may be as low as a few 89 lines of video. 91 The low level of complexity in the VC-2 codec allows for this low 92 latency operation but also means that it lacks many of the more 93 powerful compression techniques used in other codecs. As such it is 94 suitable for low compression ratios that produce coded data rates 95 around half to a quarter of that of uncompressed video, at a similar 96 visual quality. 98 The primary use for VC-2 is likely to be in professional video 99 production environments. 101 2. Conventions, Definitions and Acronyms 103 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 104 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 105 document are to be interpreted as described in RFC 2119 [RFC2119]. 107 3. Media Format Description 109 The VC-2 specification defines a VC-2 stream as being composed of one 110 or more Sequences. Each Sequence is independently decodable, 111 containing all of the needed parameters and metadata for configuring 112 the decoder. 114 Each Sequence consists of a series of 13-octet Parse Info headers and 115 variable length Data Units. The Sequence begins and ends with a 116 Parse Info header and each Data Unit is preceded by a Parse Info 117 Header. Data Units come in a variety of types, the most important 118 being the Sequence Header, which contains configuration data needed 119 by the decoder, and several types of Coded Picture, which contain the 120 coded data for the pictures themselves. Each picture represents a 121 frame in a progressively scanned video Sequence or a field in an 122 interlaced video Sequence. 124 The first Data Unit in a Sequence as produced by an encoder is always 125 a Sequence Header, but Sequences can be joined in the middle, so this 126 should not be assumed. 128 The High Quality (HQ) profile for VC-2 restricts the types of Parse 129 Info Headers which may appear in the Sequence to only: 131 o Sequence Headers, 133 o High Quality Pictures, 135 o High Quality Fragments, 137 o Auxiliary Data, 139 o Padding Data, and 141 o End of Sequence. 143 At time of writing there is currently no definition for the use of 144 Auxiliary Data in VC-2, and Padding Data is required to be ignored by 145 all receivers. 147 Each High Quality Picture data unit contains a set of parameters for 148 the picture followed by a series of coded Slices, each representing a 149 rectangular region of the transformed picture. Slices within a 150 picture may vary in coded length, but all represent the same shape 151 and size of rectangle in the picture. 153 Each High Quality Fragment data unit contains either a set of 154 parameters for a picture or a series of coded Slices. Fragments 155 carry the same data as pictures, but broken up into smaller units to 156 facilitate transmission via packet-based protocols such as RTP. 158 4. Payload format 160 This specification only covers the transport of Sequence Headers, 161 High Quality Fragments, Auxiliary Data, and (optionally) End of 162 Sequence Headers and Padding Data. 164 High Quality Pictures can be transported by converting them into an 165 equivalent set of High Quality Fragments. The size of fragments 166 should be chosen so as to fit within the MTU of the network in use. 168 For this reason this document defines six types of RTP packets in a 169 VC-2 media stream: one which carries the VC-2 Sequence Header 170 (Figure 1), one which carries the Picture Fragment containing the 171 VC-2 Transform Parameters for a Picture (Figure 2), one which carries 172 a Picture Fragment containing VC-2 Coded Slices (Figure 3) for a 173 picture, one which signals the end of a VC-2 Sequence (Figure 4), one 174 which carries the contents of an auxiliary data unit (Figure 5), and 175 one which indicates the presence of a padding data unit (Figure 6). 177 These six packet-types can be distinguished by the fact that they use 178 different codes in the "PC (Parse Code)" field, except for the two 179 types of picture fragment which both use the same value in PC but 180 have different values in the "No. of slices" field. 182 The choices of PC codes is explained in more detail in a following 183 informative section (Section 4.3). 185 0 1 2 3 186 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 1 187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 188 | V |P|X| CC |M| PT | Sequence Number | 189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 190 | Timestamp | 191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 192 | SSRC | 193 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 194 | contributing source (CSRC) identifiers | 195 | .... | 196 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 197 | Optional Extension Header | 198 | .... | 199 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 200 | Extended Sequence Number | Reserved | PC = 0x00 | 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 202 . . 203 . Variable Length Coded Sequence Header . 204 . . 205 +---------------------------------------------------------------+ 207 Figure 1: RTP Payload Format For Sequence Header 209 0 1 2 3 210 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 1 211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 212 | V |P|X| CC |M| PT | Sequence Number | 213 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 214 | Timestamp | 215 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 216 | SSRC | 217 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 218 | contributing source (CSRC) identifiers | 219 | .... | 220 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 221 | Optional Extension Header | 222 | .... | 223 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 224 | Extended Sequence Number | Reserved |I|F| PC = 0xEC | 225 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 226 | Picture Number | 227 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 228 | Slice Prefix Bytes | Slice Size Scaler | 229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 230 | Fragment Length | No. of Slices = 0 | 231 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 232 . . 233 . Variable Length Coded Transform Parameters . 234 . . 235 +---------------------------------------------------------------+ 237 Figure 2: RTP Payload Format For Transform Parameters 239 0 1 2 3 240 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 1 241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 242 | V |P|X| CC |M| PT | Sequence Number | 243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 244 | Timestamp | 245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 246 | SSRC | 247 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 248 | contributing source (CSRC) identifiers | 249 | .... | 250 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 251 | Optional Extension Header | 252 | .... | 253 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 254 | Extended Sequence Number | Reserved |I|F| PC = 0xEC | 255 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 256 | Picture Number | 257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 258 | Slice Prefix Bytes | Slice Size Scaler | 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 260 | Fragment Length | No. of Slices | 261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 262 | Slice Offset X | Slice Offset Y | 263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 264 . . 265 . Coded Slices . 266 . . 267 +---------------------------------------------------------------+ 269 Figure 3: RTP Payload Format For Slices 271 0 1 2 3 272 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 1 273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 274 | V |P|X| CC |M| PT | Sequence Number | 275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 276 | Timestamp | 277 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 278 | SSRC | 279 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 280 | contributing source (CSRC) identifiers | 281 | .... | 282 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 283 | Optional Extension Header | 284 | .... | 285 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 286 | Extended Sequence Number | Reserved | PC = 0x10 | 287 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 289 Figure 4: RTP Payload Format For End of Sequence 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 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 300 | contributing source (CSRC) identifiers | 301 | .... | 302 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 303 | Optional Extension Header | 304 | .... | 305 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 306 | Extended Sequence Number |B|E| Reserved | PC = 0x20 | 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 | Data Length | 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 . . 311 . Uncoded Payload Data . 312 . . 313 +---------------------------------------------------------------+ 315 Figure 5: RTP Payload Format For Auxiliary Data 317 0 1 2 3 318 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 1 319 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 320 | V |P|X| CC |M| PT | Sequence Number | 321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 322 | Timestamp | 323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 324 | SSRC | 325 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 326 | contributing source (CSRC) identifiers | 327 | .... | 328 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 329 | Optional Extension Header | 330 | .... | 331 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 332 | Extended Sequence Number |B|E| Reserved | PC = 0x30 | 333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 334 | Data Length | 335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 336 . . 337 . Optional Payload Data . 338 . . 339 +---------------------------------------------------------------+ 341 Figure 6: RTP Payload Format For Padding Data 343 4.1. RTP Header Usage 345 The fields of the RTP header have the following additional notes on 346 their useage: 348 Marker Bit (M): 1 bit The marker bit MUST be set on any packet which 349 contains the final slice in a coded picture and MUST NOT be set 350 otherwise. 352 Payload Type (PT): 7 bits A dynamically allocated payload type field 353 that designates the payload as VC-2 coded video. 355 Sequence Number: 16 bits Because the data rate of VC-2 coded streams 356 can often be very high, in the order of gigabits rather than 357 megabits per second, the standard 16-bit RTP sequence number 358 can cycle very quickly. For this reason the sequence number is 359 extneded to 32-bits, and this field MUST hold the low-order 360 16-bits of this value. 362 Timestamp: 32 bits If the packet contains transform parameters or 363 coded slice data for a coded picture then the timestamp 364 corresponds to the sampling instant of the coded picture. A 365 90kHz clock SHOULD be used. A single RTP packet MUST NOT 366 contain coded data for more than one coded picture, so there is 367 no ambiguity here. 369 A Sequence Header packet SHOULD have the same timestamp as the 370 next picture which will follow it in the stream. An End of 371 Sequence packet SHOULD have the same timestamp as the previous 372 picture which appeared in the stream. 374 The remaining RTP header fields are used as specified in RTP 375 [RFC3550]. 377 4.2. Payload Header 379 The fields of the extended headers are defined as follows: 381 Extended Sequence Number: 16 bits MUST Contain the high-order 382 16-bits of the 32-bit packet sequence number, a number which 383 increments with each packet. This is needed since the high 384 data rates of VC2 Sequences mean that it is highly likely that 385 the 16-bit sequence number will roll-over too frequently to be 386 of use for stream synchronisation. 388 B: 1 bit MUST be set to 1 if the packet contains the first byte of 389 an Auxiliary Data or Padded Data Unit. 391 E: 1 bit MUST be set to 1 if the packet contains the final byte of 392 an Auxiliary Data or Padded Data Unit. 394 I: 1 bit SHOULD be set to 1 if the packet contains coded picture 395 paramaters or slice data from a field in an interlaced frame, 396 and to 0 if the packet contains data from any part of a 397 progressive frame. 399 F: 1 bit SHOULD be set to 1 if the packet contains coded picture 400 paramaters or slice data from the second field of an interlaced 401 frame, and to 0 if the packet contains data from the first 402 field of an interlaced frame or any part of a progressive 403 frame. 405 Parse Code (PC): 8 bits Contains a Parse Code which MUST be the 406 value indicated for the type of data in the packet. 408 Data Length: 32 bits For an auxiliary data unit this contains the 409 number of bytes of data contained in the uncoded payload 410 section of this packet. For a Padding Data Unit this field may 411 have any value and simply indicates the size of the recommended 412 padding. 414 Picture Number: 32 bits MUST contain the Picture Number for the 415 coded picture this packet contains data for, as described in 416 Section 12.1 of the VC-2 specification [VC2]. 418 The sender MUST send at least one transform parameters packet 419 for each coded picture and MAY include more than one as long as 420 they contain identical data. The sender MUST NOT send a packet 421 from a new picture until all the coded data from the current 422 picture has been sent. 424 If the receiver does not receive a transform parameters packet 425 for a picture then it MAY assume that the parameters are 426 unchanged since the last picture, or MAY discard the picture. 428 Slice Prefix Bytes: 16 bits MUST contain the Slice Prefix Bytes 429 value for the coded picture this packet contains data for, as 430 described in Section 12.3.4 of the VC-2 specification [VC2]. 432 In the VC-2 specification this value is not restricted to 16 433 bits, but in practice this is unlikely to ever be too large. 435 Slice Size Scaler: 16 bits MUST contain the Slice Size Scaler value 436 for the coded picture this packet contains data for, as 437 described in Section 12.3.4 of the VC-2 specification [VC2]. 439 In the VC-2 specification this value is not restricted to 16 440 bits, but in practice this is unlikely to ever be too large. 442 Fragment Length: 16 bits Contains the number of bytes of data 443 contained in the coded payload section of this packet. 445 No. of Slices: 16 bits Contains the number of coded slices contained 446 in this packet, which MUST be 0 for a packet containing 447 transform parameters. In a packet containing coded slices this 448 number MUST be the number of whole slices contained in the 449 packet, and the packet MUST NOT contain any partial slices. 451 Slice Offset X: 16 bits Indicates the X coordinate of the first 452 slice in this packet, in slices, starting from the top left 453 corner of the picture. 455 Slice Offset Y: 16 bits Indicates the Y coordinate of the first 456 slice in this packet, in slices, starting from the top left 457 corner of the picture. 459 4.3. The Choice of Parse Codes (Informative) 461 The "PC" field in the packets is used to carry the Parse Code which 462 identifies the type of content in the packet. This code matches the 463 value of the Parse Code used to identify each data unit in a VC-2 464 stream, as defined in the VC-2 specification, and each packet 465 contains the entire data unit. 467 The table below lists all of the parse codes currently allowed in a 468 VC-2 Sequence. The final column indicates whether the code in 469 question can be present in a stream transmitted using this 470 specification. 472 +----------+-----------+---------------------+---------------+ 473 | PC (hex) | Binary | Description | Valid | 474 +----------+-----------+---------------------+---------------+ 475 | 0x00 | 0000 0000 | Sequence Header | Yes | 476 | 0x10 | 0001 0000 | End of Sequence | Yes | 477 | 0x20 | 0010 0000 | Auxiliary Data | Yes | 478 | 0x30 | 0011 0000 | Padding Data | Yes | 479 +----------+-----------+---------------------+---------------+ 480 | 0xC8 | 1100 1000 | LD Picture | No | 481 | 0xE8 | 1110 1000 | HQ Picture | No | 482 | 0xEC | 1110 1100 | HQ Picture Fragment | Yes | 483 +----------+-----------+---------------------+---------------+ 485 Figure 7: Parse Codes and Meanings 487 4.4. Stream Constraints 489 There are some constraints which a Sequence needs to conform to in 490 order to be transmissible with this specification. 492 o The sequence MUST NOT contain Parse Info Headers with a Parse Code 493 which is not 0x00 (Sequence Header), 0x10 (End of Sequence), 0x20 494 (Auxiliary Data), 0x30 (Padding Data) and 0xEC (High Quality 495 Picture Fragment). Some other streams MAY be convertible to meet 496 this restriction (see below). 498 o Every High Quality Picture Fragment MUST contain no more than 499 65535 slices. This can be ensured by splitting large fragments 500 into several smaller fragments. 502 o Every High Quality Picture Fragment MUST be no longer than 65535 503 bytes. This can usually be ensured by splitting large fragments 504 into several smaller fragments, except in the case where an 505 individual slice is too large, in which case see the notes below 506 on conversion. 508 o Every High Quality Picture Fragment SHOULD be small enough that 509 the RTP packet carrying it will fit within the network MTU size. 510 This can usually be ensured by splitting large fragments into 511 several smaller fragments, except in the case where an individual 512 slice is too large, in which case see the notes below on 513 conversion. 515 o Every High Quality Picture Fragment MUST be encoded using values 516 for Slice Prefix Bytes and Slice Size Scaler no greater than 517 65535. 519 If a Sequence intended for tranmission does not conform to these 520 restrictions then it MAY be possible to simply convert it into a form 521 that does by splitting pictures and/or large fragments into suitably 522 sized fragments. This can be done provided that the following 523 (weaker) constraints are met: 525 o The sequence does not contain Parse Info Headers with a Parse Code 526 which is not 0x00 (Sequence Header), 0x10 (End of Sequence), 0x20 527 (Auxiliary Data), 0x30 (Padding Data), 0xE8 (High Quality 528 Picture), and 0xEC (High Quality Picture Fragment). 530 o Every High Quality Picture or High Quality Picture Fragment 531 contains no slices which are individually longer than 65535 bytes. 532 Note: When this is the case the values of Slice Prefix Bytes and 533 Slice Size Scaler will necessarily also be smaller than 65535. 535 o Every High Quality Picture or High Quality Picture Fragment 536 contains no slices which are individually so large that an RTP 537 packet carrying a Fragment containing that single slice will fit 538 within the network MTU size. 540 Sending a Stream which does not meet these requirements via this 541 mechanism is not possible unless the stream is re-encoded by a VC-2 542 Encoder so as to meet them. 544 When encoding VC-2 video intended to be transported via RTP a VC-2 545 profile and level which ensures these requirements are met SHOULD be 546 used. 548 4.5. Payload Data 550 For the Sequence Header packet type (PC = 0x00) the payload data MUST 551 be the coded Sequence Header exactly as it appears in the VC-2 552 Sequence. 554 For the Transform Parameters packet type (PC = 0xEC and No. Slices = 555 0) the payload data MUST be the variable length coded transform 556 parameters. This MUST NOT include the fragment header (since all 557 data in the picture header is already included in the packet header). 559 For the Auxiliary Data packet type (PC = 0x20) the payload data MUST 560 be a portion of the auxiliary data bytes contained in the Auxiliary 561 data unit being being transmitted. The B flag MUST be set on the 562 packet which contains the first byte, the E flag MUST be set on the 563 packet which contains the last byte, the bytes MUST be included in 564 order, and the packets MUST have contiguous sequence numbers. 566 For the Padding Data packet type (PC = 0x30) the payload data is 567 OPTIONAL, and if present MUST be a series of 0x00 values. 569 For the Picture Fragment packet type (PC = 0xEC and No. Slices > 0) 570 the payload data MUST be a specified number of coded slices in the 571 same order that they appear in the VC-2 stream. Which slices appear 572 in the packet is identified using the Slice Offset X and Slice Offset 573 Y fields in the payload header. 575 For the End of Sequence packet type (PC = 0x10) there is no payload 576 data. 578 4.5.1. Reassembling the Data 580 0 1 2 3 581 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 1 582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 583 | 0x42 | 0x42 | 0x43 | 0x44 | 584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 585 | Parse Code | Next Parse Offset 586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 587 | Prev Parse Offset 588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 589 | 590 +-+-+-+-+-+-+-+-+ 592 Figure 8: VC-2 Parse Info Header 594 To reassemble the data in the RTP packets into a valid VC-2 Sequence 595 the receiver SHOULD: 597 o Take the data from each packet with a Parse Code of 0x00 and 598 prepend a valid VC-2 Parse Info Header (Figure 8) with the same 599 parse code to it. The resulting Sequence Header Parse Info Header 600 and data unit MUST be included in the output stream before any 601 coded pictures which followed it in the RTP stream unless an 602 identical Sequence Header has already been included, and MAY be 603 repeated at any point that results in a valid VC-2 stream. 605 o Take the data from each packet with a Parse Code of 0xEC and No. 606 of Slices set to 0 (which together indicates that this packet 607 contains the transform parameters for a coded picture) and prepend 608 a valid VC-2 Parse Info Header (Figure 8) followed by the picture 609 number, fragment data length, and slice count (0) to it with the 610 same parse code. 612 o Take the data from each packet with a Parse Code of 0xEC and No. 613 of Slices not set to 0 (which together indicates that this packet 614 contains coded slices) and prepend a valid VC-2 Parse Info Header 615 (Figure 8) followed by the picture number, fragment data length, 616 slice count, x offset and y offset taken from the packet header to 617 it with the same parse code. 619 o A receiver MAY combine all fragment data units (with parse code 620 0xEC) and the same picture number into a single picture data unit 621 with parse code 0xE8. If the stream is required to comply with 622 major versions 1 or 2 of the VC-2 Spec then this MUST be done. 624 o Take the data from each packet with a Parse Code of 0x20 and the B 625 bit set and prepend a valid VC-2 Parse Info Header (Figure 8) with 626 the parse code 0x20 and then take each subsequent packet with 627 parse code 0x20 without the B bit set and append their payload to 628 the growing data unit. When all packets for a particular data 629 unit have been received it SHOULD be included in the output 630 stream. The final packet for a data unit will have the E bit set. 632 o Once a data unit has been assembled, whether a Sequence Header, 633 Coded Picture Fragment, Coded Picture, or Auxiliary Data Unit, the 634 next parse offset and previous parse offset values in its Parse 635 Info Header should be filled with the offset between the start of 636 the header and the start of the next or previous. 638 o An End of Sequence Parse Info Header MAY be inserted when a packet 639 with parse code set to 0x10 is encountered, or at any other time 640 that is allowed in a valid VC-2 stream. After an End of Sequence 641 Parse Info Header is included in the output stream either the 642 stream must end or it MUST be followed by a Sequence Header 643 indicating the start of a new Sequence. 645 o A Padding Data Parse Info Header MAY be inserted when a packet 646 with parse code set to 0x30 and the B bit set is encountered, or 647 at any other time that is allowed in a valid VC-2 stream. The 648 length of this padding data MAY have any value, and its contents 649 MUST be set to a series of zero bytes. 651 5. Congestion Control Considerations 653 Congestion control for RTP SHALL be used in accordance with RFC 3550 654 [RFC3550], and with any applicable RTP profile; e.g., RFC 3551 655 [RFC3551]. An additional requirement if best-effort service is being 656 used is: users of this payload format MUST monitor packet loss to 657 ensure that the packet loss rate is within acceptable parameters. 658 Circuit Breakers [RFC8083] is an update to RTP [RFC3550] that defines 659 criteria for when one is required to stop sending RTP Packet Streams. 660 The circuit breakers is to be implemented and followed. 662 In particular it should be noted that the expected data rate for RTP 663 sessions which use this profile is likely to be in the range of 664 gigabits per second. If used on a closed network which has been 665 correctly provisioned for the expected data rates then profile MAY be 666 used without congestion control, but on the open internet some sort 667 of congestion control approach MUST be taken. 669 6. Payload Format Parameters 671 This RTP payload format is identified using the video/vc2 media type 672 which is registered in accordance with RFC 4855 [RFC4855] and using 673 the template of RFC 6838 [RFC6838]. 675 6.1. Media Type Definition 677 Type name: 679 video 681 Subtype name: 683 vc2 685 Required parameters: 687 rate: The RTP timestamp clock rate. Applications using this 688 payload format SHOULD use a value of 90000. 690 profile: The VC-2 profile in use, the only currently allowed value 691 is "HQ". 693 Optional parameters: 695 version: the VC-2 specification version in use. The only 696 currently allowed value is "3" since all Sequences transported 697 using this mechanism will contain HQ Picture Fragment data units, 698 which the VC-2 specification [VC2] defines as requiring version 3. 700 level: The VC-2 level in use. Any integer may be used. 702 Encoding considerations: 704 This media type is framed and binary, see section 4.8 in RFC6838 705 [RFC6838]. 707 Security considerations: 709 Please see security consideration in RFCXXXX 711 Interoperability considerations: N/A 713 Published specification: 715 "VC-2 Video Compression", SMPTE Standard ST 2042-1 [VC2] 717 Applications that use this media type: 719 Video Communication. 721 Additional information: N/A 723 Person & email address to contact for further information: 725 james.barrett@bbc.co.uk 727 Intended usage: 729 COMMON 731 Restrictions on usage: 733 This media type depends on RTP framing, and hence is only defined 734 for transfer via RTP [RFC3550]. Transport within other framing 735 protocols is not defined at this time. 737 Author: 739 Change controller: 741 IETF Payload working group delegated from the IESG. 743 Provisional registration? (standards tree only): 745 No 747 (Any other information that the author deems interesting may be added 748 below this line.) 750 6.2. Mapping to SDP 752 The mapping of the above defined payload format media type and its 753 parameters SHALL be done according to Section 3 of RFC 4855 754 [RFC4855]. 756 o The type name ("video") goes in SDP "m=" as the media name. 758 o The subtype name ("vc2") goes in SDP "a=rtpmap" as the encoding 759 name, followed by a slash ("/") and the rate parameter. 761 o The required parameter profile and the optional parameters version 762 and level, when present, are included in the "a=fmtp" attribute 763 line of SDP as a semicolon-separated list of parameter=value 764 pairs. 766 Version and level SHALL be specified in decimal when present. 768 For example, a sample SDP mapping for VC-2 could be as follows: 770 m=video 30000 RTP/AVP 112 771 a=rtpmap:112 vc2/90000 772 a=fmtp:112 profile=HQ;version=3;level=0 774 In this example, a dynamic payload type 112 is used for vc-2 data. 775 The 90 kHz RTP timestamp rate is specified in the "a=rtpmap" line 776 after the subtype. In the "a=fmtp:" line, profile HQ, version 3, and 777 level 0 (unknown or non-standard level) are specified. 779 6.3. Offer/Answer Considerations 781 All parameters are declarative. 783 7. IANA Considerations 785 This memo requests that IANA registers video/vc2 as specified in 786 Section 6.1. The media type is also requested to be added to the 787 IANA registry for "RTP Payload Format MIME types" 788 (http://www.iana.org/assignments/rtp-parameters). 790 8. Security Considerations 792 RTP packets using the payload format defined in this specification 793 are subject to the security considerations discussed in the RTP 794 specification [RFC3550] , and in any applicable RTP profile such as 795 RTP/AVP [RFC3551], RTP/AVPF [RFC4585], RTP/SAVP [RFC3711] or RTP/ 796 SAVPF [RFC5124]. However, as "Securing the RTP Protocol Framework: 797 Why RTP Does Not Mandate a Single Media Security Solution" [RFC7202] 798 discusses, it is not an RTP payload format's responsibility to 799 discuss or mandate what solutions are used to meet the basic security 800 goals like confidentiality, integrity and source authenticity for RTP 801 in general. This responsibility lays on anyone using RTP in an 802 application. They can find guidance on available security mechanisms 803 and important considerations in Options for Securing RTP Sessions 804 [RFC7201]. Applications SHOULD use one or more appropriate strong 805 security mechanisms. The rest of this security consideration section 806 discusses the security impacting properties of the payload format 807 itself. 809 This RTP payload format and its media decoder do not exhibit any 810 significant non-uniformity in the receiver-side computational 811 complexity for packet processing, and thus are unlikely to pose a 812 denial-of-service threat due to the receipt of pathological data. 813 Nor does the RTP payload format contain any active content. 815 To avoid buffer overruns when processing these packets the receiver 816 MUST consider both the reported fragment length and the actual 817 received size of a packet containing slice data. 819 In some cases the transmitter may need to decode variable length 820 coded headers in order to extract some data from the VC-2 bitstream 821 before assembling packets. This process is potentially subject to 822 buffer overruns if not implemented carefully. 824 9. RFC Editor Considerations 826 Note to RFC Editor: This section may be removed after carrying out 827 all the instructions of this section. 829 RFCXXXX is to be replaced by the RFC number this specification 830 receives when published. 832 10. References 834 10.1. Normative References 836 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 837 Requirement Levels", BCP 14, RFC 2119, 838 DOI 10.17487/RFC2119, March 1997, 839 . 841 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 842 Jacobson, "RTP: A Transport Protocol for Real-Time 843 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 844 July 2003, . 846 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 847 Video Conferences with Minimal Control", STD 65, RFC 3551, 848 DOI 10.17487/RFC3551, July 2003, 849 . 851 [RFC4855] Casner, S., "Media Type Registration of RTP Payload 852 Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007, 853 . 855 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 856 Specifications and Registration Procedures", BCP 13, 857 RFC 6838, DOI 10.17487/RFC6838, January 2013, 858 . 860 [RFC8083] Perkins, C. and V. Singh, "Multimedia Congestion Control: 861 Circuit Breakers for Unicast RTP Sessions", RFC 8083, 862 DOI 10.17487/RFC8083, March 2017, 863 . 865 [VC2] SMPTE, "VC-2 Video Compression", SMPTE Standard ST 2042-1, 866 2017, . 868 10.2. Informative References 870 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 871 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 872 RFC 3711, DOI 10.17487/RFC3711, March 2004, 873 . 875 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 876 "Extended RTP Profile for Real-time Transport Control 877 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 878 DOI 10.17487/RFC4585, July 2006, 879 . 881 [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for 882 Real-time Transport Control Protocol (RTCP)-Based Feedback 883 (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February 884 2008, . 886 [RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP 887 Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, 888 . 890 [RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP 891 Framework: Why RTP Does Not Mandate a Single Media 892 Security Solution", RFC 7202, DOI 10.17487/RFC7202, April 893 2014, . 895 Author's Address 897 James P. Weaver 898 BBC 900 Email: james.barrett@bbc.co.uk