idnits 2.17.1 draft-ietf-payload-rtp-vc2hq-07.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The exact meaning of the all-uppercase expression 'MAY NOT' is not defined in RFC 2119. If it is intended as a requirements expression, it should be rewritten using one of the combinations defined in RFC 2119; otherwise it should not be all-uppercase. == The expression 'MAY NOT', while looking like RFC 2119 requirements text, is not defined in RFC 2119, and should not be used. Consider using 'MUST NOT' instead (if that is what you mean). Found 'MAY NOT' in this paragraph: In this specification each RTP packet is used to carry data corresponding to a single Parse Info Header and its following data unit (if it has one). A single packet MAY NOT contain data from more than one Parse Info header or data unit. A single Parse Info Header and Data Unit pair MUST NOT be split accross more than one packet, the sole exception to this rule is that an Auxiliary Data Unit MAY be split between multiple packets, using the B and E flags to indicate start and end. -- The document date (August 13, 2018) is 2055 days in the past. Is this intentional? 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 (~~), 2 warnings (==), 3 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 August 13, 2018 5 Expires: February 14, 2019 7 RTP Payload Format for VC-2 HQ Profile Video 8 draft-ietf-payload-rtp-vc2hq-07 10 Abstract 12 This memo describes an RTP Payload format for the High Quality (HQ) 13 profile of Society of Motion Picture and Television Engineers 14 Standard ST 2042-1 known as VC-2. This document describes the 15 transport of HQ Profile VC-2 in RTP packets and has applications for 16 low-complexity, high-bandwidth streaming of both lossless and lossy 17 compressed video. 19 The HQ profile of VC-2 is intended for low latency video compression 20 (with latency potentially on the order of lines of video) at high 21 data rates (with compression ratios on the order of 2:1 or 4:1). 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at https://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on February 14, 2019. 40 Copyright Notice 42 Copyright (c) 2018 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (https://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 2. Conventions, Definitions and Acronyms . . . . . . . . . . . . 3 59 3. Media Format Description . . . . . . . . . . . . . . . . . . 3 60 4. Payload format . . . . . . . . . . . . . . . . . . . . . . . 4 61 4.1. RTP Header Usage . . . . . . . . . . . . . . . . . . . . 10 62 4.2. Payload Header . . . . . . . . . . . . . . . . . . . . . 11 63 4.3. The Choice of Parse Codes (Informative) . . . . . . . . . 13 64 4.4. Stream Constraints . . . . . . . . . . . . . . . . . . . 13 65 4.5. Payload Data . . . . . . . . . . . . . . . . . . . . . . 15 66 4.5.1. Reassembling the Data . . . . . . . . . . . . . . . . 15 67 5. Congestion Control Considerations . . . . . . . . . . . . . . 17 68 6. Payload Format Parameters . . . . . . . . . . . . . . . . . . 18 69 6.1. Media Type Definition . . . . . . . . . . . . . . . . . . 18 70 6.2. Mapping to SDP . . . . . . . . . . . . . . . . . . . . . 19 71 6.3. Offer/Answer Considerations . . . . . . . . . . . . . . . 20 72 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 73 8. Security Considerations . . . . . . . . . . . . . . . . . . . 20 74 9. RFC Editor Considerations . . . . . . . . . . . . . . . . . . 21 75 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 76 10.1. Normative References . . . . . . . . . . . . . . . . . . 21 77 10.2. Informative References . . . . . . . . . . . . . . . . . 22 78 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 23 80 1. Introduction 82 This memo specifies an RTP payload format for the video coding 83 standard Society of Motion Picture and Television Engineers ST 84 2042-1:2017 [VC2] also known as VC-2 86 The VC-2 codec is a wavelet-based codec intended primarily for 87 professional video use with high bit-rates and only low levels of 88 compression. It has been designed to be low-complexity, and 89 potentially have a very low latency through both encoder and decoder: 90 with some choices of parameters this latency may be as low as a few 91 lines of video. 93 The low level of complexity in the VC-2 codec allows for this low 94 latency operation but also means that it lacks many of the more 95 powerful compression techniques used in other codecs. As such it is 96 suitable for low compression ratios that produce coded data rates 97 around half to a quarter of that of uncompressed video, at a similar 98 visual quality. 100 The primary use for VC-2 is likely to be in professional video 101 production environments. 103 2. Conventions, Definitions and Acronyms 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 107 "OPTIONAL" in this document are to be interpreted as described in BCP 108 14 [RFC2119] [RFC8174] when, and only when, they appear in all 109 capitals, as shown here. 111 3. Media Format Description 113 The VC-2 specification defines a VC-2 stream as being composed of one 114 or more Sequences. Each Sequence is independently decodable, 115 containing all of the needed parameters and metadata for configuring 116 the decoder. 118 Each Sequence consists of a series of 13-octet Parse Info headers and 119 variable length Data Units. The Sequence begins and ends with a 120 Parse Info header and each Data Unit is preceded by a Parse Info 121 Header. Data Units come in a variety of types, and the type of a 122 Data Unit is signaled in the proceding Parse Info Header. The most 123 important types are the Sequence Header, which contains configuration 124 data needed by the decoder, and several types of Coded Picture, which 125 contain the coded data for the pictures themselves. Each picture 126 represents a frame in a progressively scanned video Sequence or a 127 field in an interlaced video Sequence. 129 The first Data Unit in a Sequence as produced by an encoder is always 130 a Sequence Header, but Sequences can be joined in the middle, so this 131 should not be assumed. 133 The High Quality (HQ) profile for VC-2 restricts the types of Parse 134 Info Headers which may appear in the Sequence (and hence also the 135 types of Data Unit) to only: 137 o Sequence Headers (which are always followed by a Data Unit), 139 o High Quality Pictures (which are always followed by a Data Unit), 141 o High Quality Fragments (which are always followed by a Data Unit), 143 o Auxiliary Data (which are always followed by a Data Unit), 144 o Padding Data (which are always followed by a Data Unit), and 146 o End of Sequence (which are never followed by a Data Unit). 148 At time of writing there is currently no definition for the use of 149 Auxiliary Data in VC-2, and Padding Data is required to be ignored by 150 all receivers. 152 Each High Quality Picture data unit contains a set of parameters for 153 the picture followed by a series of coded Slices, each representing a 154 rectangular region of the transformed picture. Slices within a 155 picture may vary in coded length, but all represent the same shape 156 and size of rectangle in the picture. 158 Each High Quality Fragment data unit contains either a set of 159 parameters for a picture or it contains a series of coded Slices. 160 Fragments carry the same data as pictures, but broken up into smaller 161 units to facilitate transmission via packet-based protocols such as 162 RTP. 164 This payload format only makes use of fragments, not pictures. 166 4. Payload format 168 In this specification each RTP packet is used to carry data 169 corresponding to a single Parse Info Header and its following data 170 unit (if it has one). A single packet MAY NOT contain data from more 171 than one Parse Info header or data unit. A single Parse Info Header 172 and Data Unit pair MUST NOT be split accross more than one packet, 173 the sole exception to this rule is that an Auxiliary Data Unit MAY be 174 split between multiple packets, using the B and E flags to indicate 175 start and end. 177 This specification only covers the transport of Sequence Headers 178 (together with their accompanying data unit), High Quality Fragments 179 (together with their accompanying data unit), Auxiliary Data 180 (together with their accompanying data unit), and (optionally) End 181 Sequence Headers and Padding Data (for which no data unit it 182 carried). 184 High Quality Pictures can be transported by converting them into an 185 equivalent set of High Quality Fragments. The size of fragments 186 should be chosen so as to fit within the MTU of the network in use. 188 For this reason this document defines six types of RTP packets in a 189 VC-2 media stream: 191 o A VC-2 Sequence Header (Figure 1) (see Section 11 of the VC-2 192 specification [VC2]), 194 o A Picture Fragment containing the VC-2 Transform Parameters for a 195 Picture (Figure 2) (see Section 14 of the VC-2 specification 196 [VC2]), 198 o A Picture Fragment containing VC-2 Coded Slices (Figure 3) for a 199 picture (see Section 14 of the VC-2 specification [VC2]), 201 o The end of a VC-2 Sequence (Figure 4)(see Section 10.5.2 of the 202 VC-2 specification [VC2]), 204 o The contents of an auxiliary data unit (Figure 5)(see 205 Section 10.4.4 of the VC-2 specification [VC2]), and 207 o An indication of the presence of a padding data unit (Figure 6) 208 (see Section 10.4.5 of the VC-2 specification [VC2]). 210 These six packet-types can be distinguished by the fact that they use 211 different codes in the "PC (Parse Code)" field, except for the two 212 types of picture fragment which both use the same value in PC but 213 have different values in the "No. of slices" field. 215 The choices of PC codes is explained in more detail in a following 216 informative section (Section 4.3). 218 0 1 2 3 219 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 1 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 221 | V |P|X| CC |M| PT | Sequence Number | 222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 223 | Timestamp | 224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 225 | SSRC | 226 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 227 | contributing source (CSRC) identifiers | 228 | .... | 229 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 230 | Optional Extension Header | 231 | .... | 232 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 233 | Extended Sequence Number | Reserved | PC = 0x00 | 234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 235 . . 236 . Variable Length Coded Sequence Header . 237 . . 238 +---------------------------------------------------------------+ 240 Figure 1: RTP Payload Format For Sequence Header 242 0 1 2 3 243 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 1 244 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 245 | V |P|X| CC |M| PT | Sequence Number | 246 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 247 | Timestamp | 248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 249 | SSRC | 250 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 251 | contributing source (CSRC) identifiers | 252 | .... | 253 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 254 | Optional Extension Header | 255 | .... | 256 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 257 | Extended Sequence Number | Reserved |I|F| PC = 0xEC | 258 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 259 | Picture Number | 260 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 261 | Slice Prefix Bytes | Slice Size Scaler | 262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 263 | Fragment Length | No. of Slices = 0 | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 265 . . 266 . Variable Length Coded Transform Parameters . 267 . . 268 +---------------------------------------------------------------+ 270 Figure 2: RTP Payload Format For Transform Parameters Fragment 272 0 1 2 3 273 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 1 274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 275 | V |P|X| CC |M| PT | Sequence Number | 276 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 277 | Timestamp | 278 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 279 | SSRC | 280 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 281 | contributing source (CSRC) identifiers | 282 | .... | 283 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 284 | Optional Extension Header | 285 | .... | 286 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 287 | Extended Sequence Number | Reserved |I|F| PC = 0xEC | 288 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 289 | Picture Number | 290 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 291 | Slice Prefix Bytes | Slice Size Scaler | 292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 293 | Fragment Length | No. of Slices | 294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 295 | Slice Offset X | Slice Offset Y | 296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 297 . . 298 . Coded Slices . 299 . . 300 +---------------------------------------------------------------+ 302 Figure 3: RTP Payload Format For Fragment Containing Slices 304 0 1 2 3 305 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 1 306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 307 | V |P|X| CC |M| PT | Sequence Number | 308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 309 | Timestamp | 310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 311 | SSRC | 312 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 313 | contributing source (CSRC) identifiers | 314 | .... | 315 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 316 | Optional Extension Header | 317 | .... | 318 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 319 | Extended Sequence Number | Reserved | PC = 0x10 | 320 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 322 Figure 4: RTP Payload Format For End of Sequence 324 0 1 2 3 325 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 1 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 | V |P|X| CC |M| PT | Sequence Number | 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 | Timestamp | 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 | SSRC | 332 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 333 | contributing source (CSRC) identifiers | 334 | .... | 335 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 336 | Optional Extension Header | 337 | .... | 338 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 339 | Extended Sequence Number |B|E| Reserved | PC = 0x20 | 340 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 341 | Data Length | 342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 343 . . 344 . Uncoded Payload Data . 345 . . 346 +---------------------------------------------------------------+ 348 Figure 5: RTP Payload Format For Auxiliary Data 350 0 1 2 3 351 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 1 352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 353 | V |P|X| CC |M| PT | Sequence Number | 354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 355 | Timestamp | 356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 357 | SSRC | 358 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 359 | contributing source (CSRC) identifiers | 360 | .... | 361 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 362 | Optional Extension Header | 363 | .... | 364 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 365 | Extended Sequence Number |B|E| Reserved | PC = 0x30 | 366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 367 | Data Length | 368 +---------------------------------------------------------------+ 370 Figure 6: RTP Payload Format For Padding Data 372 All fields in the headers longer than a single bit are interpreted as 373 unsigned integers in network byte order. 375 4.1. RTP Header Usage 377 The fields of the RTP header have the following additional notes on 378 their useage: 380 Marker Bit (M): 1 bit The marker bit MUST be set on any packet which 381 contains the final slice in a coded picture and MUST NOT be set 382 otherwise. 384 Payload Type (PT): 7 bits A dynamically allocated payload type field 385 that designates the payload as VC-2 coded video. 387 Sequence Number: 16 bits Because the data rate of VC-2 coded streams 388 can often be very high, in the order of gigabits rather than 389 megabits per second, the standard 16-bit RTP sequence number 390 can cycle very quickly. For this reason the sequence number is 391 extended to 32-bits, and this field MUST hold the low-order 392 16-bits of this value. 394 Timestamp: 32 bits If the packet contains transform parameters or 395 coded slice data for a coded picture then the timestamp 396 corresponds to the sampling instant of the coded picture. A 397 90kHz clock SHOULD be used. A single RTP packet MUST NOT 398 contain coded data for more than one coded picture, so there is 399 no ambiguity here. 401 A Sequence Header packet SHOULD have the same timestamp as the 402 next picture which will follow it in the stream. An End of 403 Sequence packet SHOULD have the same timestamp as the previous 404 picture which appeared in the stream. 406 The remaining RTP header fields are used as specified in RTP 407 [RFC3550]. 409 4.2. Payload Header 411 The fields of the extended headers are defined as follows: 413 Extended Sequence Number: 16 bits MUST Contain the high-order 414 16-bits of the 32-bit packet sequence number. This is needed 415 since the high data rates of VC2 Sequences mean that it is 416 highly likely that the 16-bit sequence number will roll-over 417 too frequently to be of use for stream synchronisation. 419 B: 1 bit MUST be set to 1 if the packet contains the first byte of 420 an Auxiliary Data Unit, and otherwise MUST be 0. If the 421 recommendations of the Stream Contraints Section of this 422 specification (Section 4.4) are followed then every Auxiliary 423 Data Unit will be small enough to fit in a single packet and so 424 this bit (where present) will always be 1. 426 E: 1 bit MUST be set to 1 if the packet contains the final byte of 427 an Auxiliary Data Unit, and otherwise MUST be 0. If the 428 recommendations of the Stream Contraints Section of this 429 specification (Section 4.4) are followed then every Auxiliary 430 Data Unit will be small enough to fit in a single packet and so 431 this bit (where present) will always be 1. 433 I: 1 bit MUST be set to 1 if the packet contains coded picture 434 paramaters or slice data from a field in an interlaced frame, 435 and to 0 if the packet contains data from any part of a 436 progressive frame. 438 F: 1 bit MUST be set to 1 if the packet contains coded picture 439 paramaters or slice data from the second field of an interlaced 440 frame, and to 0 if the packet contains data from the first 441 field of an interlaced frame or any part of a progressive 442 frame. 444 Parse Code (PC): 8 bits Contains a Parse Code which MUST be the 445 value indicated for the type of data in the packet. 447 Data Length: 32 bits For an auxiliary data unit this contains the 448 number of bytes of data contained in the payload section of 449 this packet. If the recommendations of the Stream Contraints 450 Section of this specification (Section 4.4) are followed then 451 no Auxiliary Data Unit will be large enough to cause a packet 452 to exceed the MTU of the network. 454 Picture Number: 32 bits MUST contain the Picture Number for the 455 coded picture this packet contains data for, as described in 456 Section 12.1 of the VC-2 specification [VC2]. 458 The sender MUST send at least one transform parameters packet 459 for each coded picture and MAY include more than one as long as 460 they contain identical data. The sender MUST NOT send a packet 461 from a new picture until all the coded data from the current 462 picture has been sent. 464 If the receiver does not receive a transform parameters packet 465 for a picture then it MAY assume that the parameters are 466 unchanged since the last picture, or MAY discard the picture. 467 Choosing between these two options is left up to the 468 implementation as it will be dependent on intended use, the 469 former may result in malformed pictures, the latter will result 470 in dropped frames. Such an occurance is an indication either 471 of packet loss, joining a stream mid-picture, or of a non- 472 compliant transmitter. 474 Slice Prefix Bytes: 16 bits MUST contain the Slice Prefix Bytes 475 value for the coded picture this packet contains data for, as 476 described in Section 12.3.4 of the VC-2 specification [VC2]. 478 In the VC-2 specification this value is not restricted to 16 479 bits, but the constraints on streams specified in this document 480 (Section 4.4) do require this. 482 Slice Size Scaler: 16 bits MUST contain the Slice Size Scaler value 483 for the coded picture this packet contains data for, as 484 described in Section 12.3.4 of the VC-2 specification [VC2]. 486 In the VC-2 specification this value is not restricted to 16 487 bits, but the constraints on streams specified in this document 488 (Section 4.4) do require this. 490 Fragment Length: 16 bits MUST contain the number of bytes of data 491 contained in the coded payload section of this packet. 493 No. of Slices: 16 bits MUST contain the number of coded slices 494 contained in this packet, which MUST be 0 for a packet 495 containing transform parameters. In a packet containing coded 496 slices this number MUST be the number of whole slices contained 497 in the packet, and the packet MUST NOT contain any partial 498 slices. 500 Slice Offset X: 16 bits MUST contain the X coordinate of the first 501 slice in this packet, in slices, starting from the top left 502 corner of the picture. 504 Slice Offset Y: 16 bits MUST contain the Y coordinate of the first 505 slice in this packet, in slices, starting from the top left 506 corner of the picture. 508 4.3. The Choice of Parse Codes (Informative) 510 The "PC" field in the packets is used to carry the Parse Code which 511 identifies the type of content in the packet. This code matches the 512 value of the Parse Code used to identify each data unit in a VC-2 513 stream, as defined in the VC-2 specification, and each packet 514 contains the entire data unit. 516 The table below lists all of the parse codes currently allowed in a 517 VC-2 Sequence. The final column indicates whether the code in 518 question can be present in a stream transmitted using this 519 specification. 521 +----------+-----------+---------------------+---------------+ 522 | PC (hex) | Binary | Description | Valid | 523 +----------+-----------+---------------------+---------------+ 524 | 0x00 | 0000 0000 | Sequence Header | Yes | 525 | 0x10 | 0001 0000 | End of Sequence | Yes | 526 | 0x20 | 0010 0000 | Auxiliary Data | Yes | 527 | 0x30 | 0011 0000 | Padding Data | Yes | 528 +----------+-----------+---------------------+---------------+ 529 | 0xC8 | 1100 1000 | LD Picture | No | 530 | 0xE8 | 1110 1000 | HQ Picture | No | 531 | 0xEC | 1110 1100 | HQ Picture Fragment | Yes | 532 +----------+-----------+---------------------+---------------+ 534 Figure 7: Parse Codes and Meanings 536 4.4. Stream Constraints 538 There are some constraints which a Sequence needs to conform to in 539 order to be transmissible with this specification. 541 o The sequence MUST NOT contain Parse Info Headers with a Parse Code 542 which is not 0x00 (Sequence Header), 0x10 (End of Sequence), 0x20 543 (Auxiliary Data), 0x30 (Padding Data) and 0xEC (High Quality 544 Picture Fragment). Some other streams MAY be convertible to meet 545 this restriction (see below). 547 o Every High Quality Picture Fragment MUST be no longer than 65535 548 bytes. This can usually be ensured by splitting large fragments 549 into several smaller fragments, except in the case where an 550 individual slice is too large, in which case see the notes below 551 on conversion. 553 o Informative note: this requirement ensures that every High Quality 554 Picture Fragment will always contain no more than 65535 slices. 556 o Every High Quality Picture Fragment SHOULD be small enough that 557 the RTP packet carrying it will fit within the network MTU size. 558 This can usually be ensured by splitting large fragments into 559 several smaller fragments, except in the case where an individual 560 slice is too large, in which case see the notes below on 561 conversion. 563 o Every High Quality Picture Fragment MUST be encoded using values 564 for Slice Prefix Bytes and Slice Size Scaler no greater than 565 65535. 567 If a Sequence intended for tranmission does not conform to these 568 restrictions then it MAY be possible to simply convert it into a form 569 that does by splitting pictures and/or large fragments into suitably 570 sized fragments. This can be done provided that the following 571 (weaker) constraints are met: 573 o The sequence does not contain Parse Info Headers with a Parse Code 574 which is not 0x00 (Sequence Header), 0x10 (End of Sequence), 0x20 575 (Auxiliary Data), 0x30 (Padding Data), 0xE8 (High Quality 576 Picture), and 0xEC (High Quality Picture Fragment). 578 o Every High Quality Picture or High Quality Picture Fragment 579 contains no slices which are individually longer than 65535 bytes. 580 Note: When this is the case the values of Slice Prefix Bytes and 581 Slice Size Scaler will necessarily also be smaller than 65535. 583 o Every High Quality Picture or High Quality Picture Fragment 584 contains no slices which are individually so large that an RTP 585 packet carrying a Fragment containing that single slice will fit 586 within the network MTU size. 588 Sending a Stream which does not meet the above requirements via this 589 mechanism is not possible unless the stream is re-encoded by a VC-2 590 Encoder so as to meet them. 592 In addition every Auxiliary Data Unit SHOULD be small enough that a 593 single RTP packet carrying it will fit within the network MTU size. 594 Since there is currently no specification for the format of Auxiliary 595 Data in VC-2 the mechanism for ensuring this with an encoder 596 implementation that includes Auxiliary Data Units will be dependent 597 upon the implementation's use for them. 599 When encoding VC-2 video intended to be transported via RTP a VC-2 600 profile and level which ensures these requirements are met SHOULD be 601 used. 603 4.5. Payload Data 605 For the Sequence Header packet type (PC = 0x00) the payload data MUST 606 be the coded Sequence Header exactly as it appears in the VC-2 607 Sequence. 609 For the Transform Parameters packet type (PC = 0xEC and No. Slices = 610 0) the payload data MUST be the variable length coded transform 611 parameters. This MUST NOT include the fragment header (since all 612 data in the picture header is already included in the packet header). 614 For the Auxiliary Data packet type (PC = 0x20) the payload data MUST 615 be a portion of the auxiliary data bytes contained in the Auxiliary 616 data unit being being transmitted. The B flag MUST be set on the 617 packet which contains the first byte, the E flag MUST be set on the 618 packet which contains the last byte, the bytes MUST be included in 619 order, and the packets MUST have contiguous sequence numbers. 621 For the Picture Fragment packet type (PC = 0xEC and No. Slices > 0) 622 the payload data MUST be a specified number of coded slices in the 623 same order that they appear in the VC-2 stream. Which slices appear 624 in the packet is identified using the Slice Offset X and Slice Offset 625 Y fields in the payload header. 627 For the End of Sequence packet type (PC = 0x10) there is no payload 628 data. 630 4.5.1. Reassembling the Data 631 0 1 2 3 632 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 1 633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 634 | 0x42 | 0x42 | 0x43 | 0x44 | 635 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 636 | Parse Code | Next Parse Offset 637 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 638 | Prev Parse Offset 639 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 640 | 641 +-+-+-+-+-+-+-+-+ 643 Figure 8: VC-2 Parse Info Header 645 To reassemble the data in the RTP packets into a valid VC-2 Sequence 646 the receiver SHOULD: 648 o Take the data from each packet with a Parse Code of 0x00 and 649 prepend a valid VC-2 Parse Info Header (Figure 8) with the same 650 parse code to it. The resulting Sequence Header Parse Info Header 651 and data unit MUST be included in the output stream before any 652 coded pictures which followed it in the RTP stream unless an 653 identical Sequence Header has already been included, and MAY be 654 repeated (with apropriate modfifications to the next and previous 655 header oddsets) at any point that results in a valid VC-2 stream. 657 o Take the data from each packet with a Parse Code of 0xEC and No. 658 of Slices set to 0 (which together indicates that this packet 659 contains the transform parameters for a coded picture) and prepend 660 a valid VC-2 Parse Info Header (Figure 8) followed by the picture 661 number, fragment data length, and slice count (0) to it with the 662 same parse code. 664 o Take the data from each packet with a Parse Code of 0xEC and No. 665 of Slices not set to 0 (which together indicates that this packet 666 contains coded slices) and prepend a valid VC-2 Parse Info Header 667 (Figure 8) followed by the picture number, fragment data length, 668 slice count, x offset and y offset taken from the packet header to 669 it with the same parse code. 671 o A receiver MAY combine all fragment data units (with parse code 672 0xEC) and the same picture number into a single picture data unit 673 with parse code 0xE8. If the stream is required to comply with 674 major versions 1 or 2 of the VC-2 Spec then this MUST be done. 676 o Take the data from each packet with a Parse Code of 0x20 and the B 677 bit set and prepend a valid VC-2 Parse Info Header (Figure 8) with 678 the parse code 0x20 and then take each subsequent packet with 679 parse code 0x20 without the B bit set and append their payload to 680 the growing data unit. When all packets for a particular data 681 unit have been received it SHOULD be included in the output 682 stream. The final packet for a data unit will have the E bit set. 684 o Once a data unit has been assembled, whether a Sequence Header, 685 Coded Picture Fragment, Coded Picture, or Auxiliary Data Unit, the 686 next parse offset and previous parse offset values in its Parse 687 Info Header SHOULD be filled with the offset between the start of 688 the header and the start of the next or previous. 690 o An End of Sequence Parse Info Header MAY be inserted when a packet 691 with parse code set to 0x10 is encountered, or at any other time 692 that is allowed in a valid VC-2 stream. After an End of Sequence 693 Parse Info Header is included in the output stream either the 694 stream must end or it MUST be followed by a Sequence Header 695 indicating the start of a new Sequence. The next parse offset of 696 the End of Sequence header MUST be set t 0, and the previous parse 697 offset SHOULD be filled with the offset from the start of the 698 previous parse info header in the stream. 700 o A Padding Data Parse Info Header MAY be inserted when a packet 701 with parse code set to 0x30 and the B bit set is encountered, or 702 at any other time that is allowed in a valid VC-2 stream. The 703 length of the accompanying data unit MAY have any value, and its 704 contents MUST be set to a series of zero bytes. The next parse 705 offset and previous parse offset values in its Parse Info Header 706 SHOULD be filled with the offset between the start of the header 707 and the start of the next or previous. 709 5. Congestion Control Considerations 711 Congestion control for RTP SHALL be used in accordance with RFC 3550 712 [RFC3550], and with any applicable RTP profile; e.g., RFC 3551 713 [RFC3551]. An additional requirement if best-effort service is being 714 used is: users of this payload format MUST monitor packet loss to 715 ensure that the packet loss rate is within acceptable parameters. 716 Circuit Breakers [RFC8083] is an update to RTP [RFC3550] that defines 717 criteria for when one is required to stop sending RTP Packet Streams, 718 and applications implementing this standard MUST comply with it. RFC 719 8085 [RFC8085] provides additional information on the best practices 720 for applying congestion control to UDP streams. 722 In particular it should be noted that the expected data rate for RTP 723 sessions which use this profile is likely to be in the range of 724 gigabits per second. If used on a closed network which has been 725 correctly provisioned for the expected data rates this might not pose 726 a problem, but there is always the risk of data getting out onto the 727 open internet. 729 6. Payload Format Parameters 731 This RTP payload format is identified using the video/vc2 media type 732 which is registered in accordance with RFC 4855 [RFC4855] and using 733 the template of RFC 6838 [RFC6838]. 735 6.1. Media Type Definition 737 Type name: 739 video 741 Subtype name: 743 vc2 745 Required parameters: 747 rate: The RTP timestamp clock rate. Applications using this 748 payload format SHOULD use a value of 90000. 750 profile: The VC-2 profile in use, the only currently allowed value 751 is "HQ". 753 Optional parameters: 755 version: the VC-2 specification version in use. The only 756 currently allowed value is "3" since all Sequences transported 757 using this mechanism will contain HQ Picture Fragment data units, 758 which the VC-2 specification [VC2] defines as requiring version 3. 760 level: The VC-2 level in use. Any integer may be used. 762 Encoding considerations: 764 This media type is framed and binary, see section 4.8 in RFC6838 765 [RFC6838]. 767 Security considerations: 769 Please see security consideration in RFCXXXX 771 Interoperability considerations: N/A 773 Published specification: 775 RFC XXXX 777 Applications that use this media type: 779 Video Communication. 781 Fragment Identifier Considerations: N/A 783 Additional information: N/A 785 Person & email address to contact for further information: 787 james.barrett@bbc.co.uk 789 Intended usage: 791 COMMON 793 Restrictions on usage: 795 This media type depends on RTP framing, and hence is only defined 796 for transfer via RTP [RFC3550]. Transport within other framing 797 protocols is not defined at this time. 799 Author: 801 Change controller: 803 IETF Payload working group delegated from the IESG. 805 Provisional registration? (standards tree only): 807 No 809 6.2. Mapping to SDP 811 The mapping of the above defined payload format media type and its 812 parameters SHALL be done according to Section 3 of RFC 4855 813 [RFC4855]. 815 o The type name ("video") goes in SDP "m=" as the media name. 817 o The subtype name ("vc2") goes in SDP "a=rtpmap" as the encoding 818 name, followed by a slash ("/") and the rate parameter. 820 o The required parameter profile and the optional parameters version 821 and level, when present, are included in the "a=fmtp" attribute 822 line of SDP as a semicolon-separated list of parameter=value 823 pairs. 825 Version and level SHALL be specified in decimal when present. 827 For example, a sample SDP mapping for VC-2 could be as follows: 829 m=video 30000 RTP/AVP 112 830 a=rtpmap:112 vc2/90000 831 a=fmtp:112 profile=HQ;version=3;level=0 833 In this example, a dynamic payload type 112 is used for vc-2 data. 834 The 90 kHz RTP timestamp rate is specified in the "a=rtpmap" line 835 after the subtype. In the "a=fmtp:" line, profile HQ, version 3, and 836 level 0 (unknown or non-standard level) are specified. 838 6.3. Offer/Answer Considerations 840 All parameters are declarative. 842 7. IANA Considerations 844 This memo requests that IANA registers video/vc2 as specified in 845 Section 6.1. The media type is also requested to be added to the 846 IANA registry for "RTP Payload Format MIME types" 847 (http://www.iana.org/assignments/rtp-parameters). 849 8. Security Considerations 851 RTP packets using the payload format defined in this specification 852 are subject to the security considerations discussed in the RTP 853 specification [RFC3550] , and in any applicable RTP profile such as 854 RTP/AVP [RFC3551], RTP/AVPF [RFC4585], RTP/SAVP [RFC3711] or RTP/ 855 SAVPF [RFC5124]. However, as "Securing the RTP Protocol Framework: 856 Why RTP Does Not Mandate a Single Media Security Solution" [RFC7202] 857 discusses, it is not an RTP payload format's responsibility to 858 discuss or mandate what solutions are used to meet the basic security 859 goals like confidentiality, integrity and source authenticity for RTP 860 in general. This responsibility lies with anyone using RTP in an 861 application. They can find guidance on available security mechanisms 862 and important considerations in Options for Securing RTP Sessions 863 [RFC7201]. Applications SHOULD use one or more appropriate strong 864 security mechanisms. The rest of this security consideration section 865 discusses the security impacting properties of the payload format 866 itself. 868 This RTP payload format and its media decoder do not exhibit any 869 significant non-uniformity in the receiver-side computational 870 complexity for packet processing, and thus are unlikely to pose a 871 denial-of-service threat due to the receipt of pathological data. 872 Nor does the RTP payload format contain any active content. 874 To avoid buffer overruns when processing these packets the receiver 875 MUST consider both the reported fragment length and the actual 876 received size of a packet containing slice data. 878 In some cases the transmitter may need to decode variable length 879 coded headers in order to extract some data from the VC-2 bitstream 880 before assembling packets. This process is potentially subject to 881 buffer overruns if not implemented carefully. 883 9. RFC Editor Considerations 885 Note to RFC Editor: This section may be removed after carrying out 886 all the instructions of this section. 888 RFCXXXX is to be replaced by the RFC number this specification 889 receives when published. 891 10. References 893 10.1. Normative References 895 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 896 Requirement Levels", BCP 14, RFC 2119, 897 DOI 10.17487/RFC2119, March 1997, 898 . 900 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 901 Jacobson, "RTP: A Transport Protocol for Real-Time 902 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 903 July 2003, . 905 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 906 Video Conferences with Minimal Control", STD 65, RFC 3551, 907 DOI 10.17487/RFC3551, July 2003, 908 . 910 [RFC4855] Casner, S., "Media Type Registration of RTP Payload 911 Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007, 912 . 914 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 915 Specifications and Registration Procedures", BCP 13, 916 RFC 6838, DOI 10.17487/RFC6838, January 2013, 917 . 919 [RFC8083] Perkins, C. and V. Singh, "Multimedia Congestion Control: 920 Circuit Breakers for Unicast RTP Sessions", RFC 8083, 921 DOI 10.17487/RFC8083, March 2017, 922 . 924 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 925 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 926 March 2017, . 928 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 929 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 930 May 2017, . 932 [VC2] Society of Motion Picture and Television Engineers, "VC-2 933 Video Compression", Society of Motion Picture and 934 Television Engineers Standard ST 2042-1, 2017, 935 . 937 10.2. Informative References 939 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 940 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 941 RFC 3711, DOI 10.17487/RFC3711, March 2004, 942 . 944 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 945 "Extended RTP Profile for Real-time Transport Control 946 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 947 DOI 10.17487/RFC4585, July 2006, 948 . 950 [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for 951 Real-time Transport Control Protocol (RTCP)-Based Feedback 952 (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February 953 2008, . 955 [RFC7201] Westerlund, M. and C. Perkins, "Options for Securing RTP 956 Sessions", RFC 7201, DOI 10.17487/RFC7201, April 2014, 957 . 959 [RFC7202] Perkins, C. and M. Westerlund, "Securing the RTP 960 Framework: Why RTP Does Not Mandate a Single Media 961 Security Solution", RFC 7202, DOI 10.17487/RFC7202, April 962 2014, . 964 Author's Address 966 James P. Weaver 967 BBC 969 Email: james.barrett@bbc.co.uk