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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-16) exists of draft-ietf-avtext-framemarking-01 ** Downref: Normative reference to an Experimental draft: draft-ietf-avtext-framemarking (ref. 'I-D.ietf-avtext-framemarking') == Outdated reference: A later version (-04) exists of draft-ietf-avtext-avpf-ccm-layered-01 == Outdated reference: A later version (-16) exists of draft-ietf-payload-vp9-02 Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Payload Working Group J. Lennox 3 Internet-Draft D. Hong 4 Intended status: Standards Track Vidyo 5 Expires: January 9, 2017 J. Uberti 6 S. Holmer 7 M. Flodman 8 Google 9 July 8, 2016 11 The Layer Refresh Request (LRR) RTCP Feedback Message 12 draft-ietf-avtext-lrr-03 14 Abstract 16 This memo describes the RTCP Payload-Specific Feedback Message "Layer 17 Refresh Request" (LRR), which can be used to request a state refresh 18 of one or more substreams of a layered media stream. It also defines 19 its use with several RTP payloads for scalable media formats. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on January 9, 2017. 38 Copyright Notice 40 Copyright (c) 2016 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Conventions, Definitions and Acronyms . . . . . . . . . . . . 2 57 2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. Layer Refresh Request . . . . . . . . . . . . . . . . . . . . 5 59 3.1. Message Format . . . . . . . . . . . . . . . . . . . . . 5 60 3.2. Semantics . . . . . . . . . . . . . . . . . . . . . . . . 7 61 4. Usage with specific codecs . . . . . . . . . . . . . . . . . 7 62 4.1. H264 SVC . . . . . . . . . . . . . . . . . . . . . . . . 7 63 4.2. VP8 . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 64 4.3. H265 . . . . . . . . . . . . . . . . . . . . . . . . . . 9 65 5. Usage with different scalability transmission mechanisms . . 10 66 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 67 7. SDP Definitions . . . . . . . . . . . . . . . . . . . . . . . 11 68 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 69 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 70 9.1. Normative References . . . . . . . . . . . . . . . . . . 12 71 9.2. Informative References . . . . . . . . . . . . . . . . . 13 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 74 1. Introduction 76 This memo describes an RTCP [RFC3550] Payload-Specific Feedback 77 Message [RFC4585] "Layer Refresh Request" (LRR). It is designed to 78 allow a receiver of a layered media stream to request that one or 79 more of its substreams be refreshed, such that it can then be decoded 80 by an endpoint which previously was not receiving those layers, 81 without requiring that the entire stream be refreshed (as it would be 82 if the receiver sent a Full Intra Request (FIR); [RFC5104] see also 83 [I-D.ietf-avtext-avpf-ccm-layered]). 85 The feedback message is applicable both to temporally and spatially 86 scaled streams, and to both single-stream and multi-stream 87 scalability modes. 89 2. Conventions, Definitions and Acronyms 91 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 92 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 93 document are to be interpreted as described in [RFC2119]. 95 2.1. Terminology 97 A "Layer Refresh Point" is a point in a scalable stream after which a 98 decoder, which previously had been able to decode only some (possibly 99 none) of the available layers of stream, is able to decode a greater 100 number of the layers. 102 For spatial (or quality) layers, layer refresh typically requires 103 that a spatial layer be encoded in a way that references only lower- 104 layer subpictures of the current picture, not any earlier pictures of 105 that spatial layer. Additionally, the encoder must promise that no 106 earlier pictures of that spatial layer will be used as reference in 107 the future. 109 In a layer refresh, however, other layers than the ones requested for 110 refresh may still maintain dependency on earlier content of the 111 stream. This is the difference between a layer refresh and a Full 112 Intra Request [RFC5104]. This minimizes the coding overhead of 113 refresh to only those parts of the stream that actually need to be 114 refreshed at any given time. 116 An illustration of spatial layer refresh of an enhancement layer is 117 shown below. 119 ... <-- S1 <-- S1 S1 <-- S1 <-- ... 120 | | | | 121 \/ \/ \/ \/ 122 ... <-- S0 <-- S0 <-- S0 <-- S0 <-- ... 124 1 2 3 4 126 In this illustration, frame 3 is a layer refresh point for spatial 127 layer S1; a decoder which had previously only been decoding spatial 128 layer S0 would be able to decode layer S1 starting at frame 3. 130 Figure 1 132 An illustration of spatial layer refresh of a base layer is shown 133 below. 135 ... <-- S1 <-- S1 <-- S1 <-- S1 <-- ... 136 | | | | 137 \/ \/ \/ \/ 138 ... <-- S0 <-- S0 S0 <-- S0 <-- ... 140 1 2 3 4 142 In this illustration, frame 3 is a layer refresh point for spatial 143 layer S0; a decoder which had previously not been decoding the stream 144 at all could decode layer S0 starting at frame 3. 146 Figure 2 148 For temporal layers, layer refresh requires that the layer be 149 "temporally nested", i.e. use as reference only earlier frames of a 150 lower temporal layer, not any earlier frames of this temporal layer, 151 and also promise that no future frames of this temporal layer will 152 reference frames of this temporal layer before the refresh point. In 153 many cases, the temporal structure of the stream will mean that all 154 frames are temporally nested, in which case decoders will have no 155 need to send LRR messages for the stream. 157 An illustration of temporal layer refresh is shown below. 159 ... <----- T1 <------ T1 T1 <------ ... 160 / / / 161 |_ |_ |_ 162 ... <-- T0 <------ T0 <------ T0 <------ T0 <--- ... 164 1 2 3 4 5 6 7 166 In this illustration, frame 6 is a layer refresh point for temporal 167 layer T1; a decoder which had previously only been decoding temporal 168 layer T0 would be able to decode layer T1 starting at frame 6. 170 Figure 3 172 An illustration of an inherently temporally nested stream is shown 173 below. 175 T1 T1 T1 176 / / / 177 |_ |_ |_ 178 ... <-- T0 <------ T0 <------ T0 <------ T0 <--- ... 180 1 2 3 4 5 6 7 182 In this illustration, the stream is temporally nested in its ordinary 183 structure; a decoder receiving layer T0 can begin decoding layer T1 184 at any point. 186 Figure 4 188 3. Layer Refresh Request 190 A layer refresh frame can be requested by sending a Layer Refresh 191 Request (LRR), which is an RTCP payload-specific feedback message 192 [RFC4585] asking the encoder to encode a frame which makes it 193 possible to upgrade to a higher layer. The LRR contains one or two 194 tuples, indicating the layer the decoder wants to upgrade to, and 195 (optionally) the currently highest layer the decoder can decode. 197 The specific format of the tuples, and the mechanism by which a 198 receiver recognizes a refresh frame, is codec-dependent. Usage for 199 several codecs is discussed in Section 4. 201 LRR follows the model of the Full Intra Request (FIR) 202 [RFC5104](Section 3.5.1) for its retransmission, reliability, and use 203 in multipoint conferences. 205 The LRR message is identified by RTCP packet type value PT=PSFB and 206 FMT=TBD. The FCI field MUST contain one or more LRR entries. Each 207 entry applies to a different media sender, identified by its SSRC. 209 3.1. Message Format 211 The Feedback Control Information (FCI) for the Layer Refresh Request 212 consists of one or more FCI entries, the content of which is depicted 213 in Figure 5. The length of the LRR feedback message MUST be set to 214 2+3*N, where N is the number of FCI entries. 216 0 1 2 3 217 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 1 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 | SSRC | 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 221 | Seq nr. |C| Payload Type| Reserved | 222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 223 | RES | TTID| TLID | RES | CTID| CLID (opt) | 224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 226 Figure 5 228 SSRC (32 bits) The SSRC value of the media sender that is requested 229 to send a layer refresh point. 231 Seq nr. (8 bits) Command sequence number. The sequence number space 232 is unique for each pairing of the SSRC of command source and the 233 SSRC of the command target. The sequence number SHALL be 234 increased by 1 modulo 256 for each new command. A repetition 235 SHALL NOT increase the sequence number. The initial value is 236 arbitrary. 238 C (1 bit) A flag bit indicating whether the "Current Layer Index" 239 field is present in the FCI. If this bit is false, the sender of 240 the LRR message is requesting refresh of all layers up to and 241 including the target layer. 243 Payload Type (7 bits) The RTP payload type for which the LRR is 244 being requested. This gives the context in which the target layer 245 index is to be interpreted. 247 Reserved (RES) (16 bits / 5 bits / 5 bits) All bits SHALL be set to 248 0 by the sender and SHALL be ignored on reception. 250 Target Temporal Layer ID (TTID) (3 bits) The temporal ID of the 251 target layer for which the receiver wishes a refresh point. 253 Target Layer ID (TLID) (8 bits) The layer ID of the target layer for 254 which the receiver wishes a refresh point. Its format is 255 dependent on the payload type field. 257 Current Temporal Layer ID (CTID) (3 bits) If C is 1, the ID of the 258 current temporal layer being decoded by the receiver. This 259 message is not requesting refresh of layers at or below this 260 layer. If C is 0, this field SHALL be set to 0 by the sender and 261 SHALL be ignored on reception. 263 Current Layer ID (CLID) (8 bits) If C is 1, the layer ID of the 264 current layer being decoded by the receiver. This message is not 265 requesting refresh of layers at or below this layer. If C is 0, 266 this field SHALL be set to 0 by the sender and SHALL be ignored on 267 reception. 269 Note: the syntax of the TTID, TLID, CTID, and TLID fields are 270 designed to match the TID and LID fields in 271 [I-D.ietf-avtext-framemarking]. 273 3.2. Semantics 275 Within the common packet header for feedback messages (as defined in 276 section 6.1 of [RFC4585]), the "SSRC of packet sender" field 277 indicates the source of the request, and the "SSRC of media source" 278 is not used and SHALL be set to 0. The SSRCs of the media senders to 279 which the LRR command applies are in the corresponding FCI entries. 280 A LRR message MAY contain requests to multiple media senders, using 281 one FCI entry per target media sender. 283 Upon reception of LRR, the encoder MUST send a decoder refresh point 284 (see section Section 2.1) as soon as possible. 286 The sender MUST consider congestion control as outlined in section 5 287 of [RFC5104], which MAY restrict its ability to send a layer refresh 288 point quickly. 290 4. Usage with specific codecs 292 In order for LRR to be used with a scalable codec, the format of the 293 target layer and current target layer fields needs to be specified 294 for that codec's RTP packetization. New RTP packetization 295 specifications for scalable codecs SHOULD define how this is done. 296 (The VP9 payload [I-D.ietf-payload-vp9], for instance, has done so.) 297 If the payload also specifies how it is used with the Frame Marking 298 RTP Header Extension [I-D.ietf-avtext-framemarking], the syntax MUST 299 be defined in the same manner as the TID and LID fields in that 300 header. 302 4.1. H264 SVC 304 H.264 SVC [RFC6190] defines temporal, dependency (spatial), and 305 quality scalability modes. 307 +---------------+---------------+ 308 |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7| 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 | RES | TID |R| DID | QID | 311 +---------------+---------------+ 313 Figure 6 315 Figure 6 shows the format of the layer index field for H.264 SVC 316 streams. The "R" and "RES" fields MUST be set to 0 on transmission 317 and ignored on reception. See [RFC6190] Section 1.1.3 for details on 318 the DID, QID, and TID fields. 320 A dependency or quality layer refresh of a given layer in H.264 SVC 321 can be identified by the "I" bit (idr_flag) in the extended NAL unit 322 header, present in NAL unit types 14 (prefix NAL unit) and 20 (coded 323 scalable slice). Layer refresh of the base layer can also be 324 identified by its NAL unit type of its coded slices, which is "5" 325 rather than "1". A dependency or quality layer refresh is complete 326 once this bit has been seen on all the appropriate layers (in 327 decoding order) above the current layer index (if any, or beginning 328 from the base layer if not) through the target layer index. 330 Note that as the "I" bit in a PACSI header is set if the 331 corresponding bit is set in any of the aggregated NAL units it 332 describes; thus, it is not sufficient to identify layer refresh when 333 NAL units of multiple dependency or quality layers are aggregated. 335 In H.264 SVC, temporal layer refresh information can be determined 336 from various Supplemental Encoding Information (SEI) messages in the 337 bitstream. 339 Whether an H.264 SVC stream is scalably nested can be determined from 340 the Scalability Information SEI message's temporal_id_nesting flag. 341 If this flag is set in a stream's currently applicable Scalability 342 Information SEI, receivers SHOULD NOT send temporal LRR messages for 343 that stream, as every frame is implicitly a temporal layer refresh 344 point. (The Scalability Information SEI message may also be 345 available in the signaling negotiation of H.264 SVC, as the sprop- 346 scalability-info parameter.) 348 If a stream's temporal_id_nesting flag is not set, the Temporal Level 349 Switching Point SEI message identifies temporal layer switching 350 points. A temporal layer refresh is satisfied when this SEI message 351 is present in a frame with the target layer index, if the message's 352 delta_frame_num refers to a frame with the requested current layer 353 index. (Alternately, temporal layer refresh can also be satisfied by 354 a complete state refresh, such as an IDR.) Senders which support 355 receiving LRR for non-temporally-nested streams MUST insert Temporal 356 Level Switching Point SEI messages as appropriate. 358 4.2. VP8 360 The VP8 RTP payload format [RFC7741] defines temporal scalability 361 modes. It does not support spatial scalability. 363 +---------------+---------------+ 364 |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7| 365 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 366 | RES | TID | RES | 367 +---------------+---------------+ 369 Figure 7 371 Figure 7 shows the format of the layer index field for VP8 streams. 372 The "RES" fields MUST be set to 0 on transmission and be ignored on 373 reception. See [RFC7741] Section 4.2 for details on the TID field. 375 A VP8 layer refresh point can be identified by the presence of the 376 "Y" bit in the VP8 payload header. When this bit is set, this and 377 all subsequent frames depend only on the current base temporal layer. 378 On receipt of an LRR for a VP8 stream, A sender which supports LRR 379 MUST encode the stream so it can set the Y bit in a packet whose 380 temporal layer is at or below the target layer index. 382 Note that in VP8, not every layer switch point can be identified by 383 the Y bit, since the Y bit implies layer switch of all layers, not 384 just the layer in which it is sent. Thus the use of LRR with VP8 can 385 result in some inefficiency in transmision. However, this is not 386 expected to be a major issue for temporal structures in normal use. 388 4.3. H265 390 The initial version of the H.265 payload format [RFC7798] defines 391 temporal scalability, with protocol elements reserved for spatial or 392 other scalability modes (which are expected to be defined in a future 393 version of the specification). 395 +---------------+---------------+ 396 |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7| 397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 398 | RES | TID |RES| LayerId | 399 +---------------+---------------+ 401 Figure 8 403 Figure 8 shows the format of the layer index field for H.265 streams. 404 The "RES" fields MUST be set to 0 on transmission and ignored on 405 reception. See [RFC7798] Section 1.1.4 for details on the LayerId 406 and TID fields. 408 H.265 streams signal whether they are temporally nested, using the 409 vps_temporal_id_nesting_flag in the Video Parameter Set (VPS), and 410 the sps_temporal_id_nesting_flag in the Sequence Parameter Set (SPS). 411 If this flag is set in a stream's currently applicable VPS or SPS, 412 receivers SHOULD NOT send temporal LRR messages for that stream, as 413 every frame is implicitly a temporal layer refresh point. 415 If a stream's sps_temporal_id_nesting_flag is not set, the NAL unit 416 types 2 to 5 inclusively identify temporal layer switching points. A 417 layer refresh to any higher target temporal layer is satisfied when a 418 NAL unit type of 4 or 5 with TID equal to 1 more than current TID is 419 seen. Alternatively, layer refresh to a target temporal layer can be 420 incrementally satisfied with NAL unit type of 2 or 3. In this case, 421 given current TID = TO and target TID = TN, layer refresh to TN is 422 satisfied when NAL unit type of 2 or 3 is seen for TID = T1, then TID 423 = T2, all the way up to TID = TN. During this incremental process, 424 layer refresh to TN can be completely satisfied as soon as a NAL unit 425 type of 2 or 3 is seen. 427 Of course, temporal layer refresh can also be satisfied whenever any 428 Intra Random Access Point (IRAP) NAL unit type (with values 16-23, 429 inclusively) is seen. An IRAP picture is similar to an IDR picture 430 in H.264 (NAL unit type of 5 in H.264) where decoding of the picture 431 can start without any older pictures. 433 In the (future) H.265 payloads that support spatial scalability, a 434 spatial layer refresh of a specific layer can be identified by NAL 435 units with the requested layer ID and NAL unit types between 16 and 436 21 inclusive. A dependency or quality layer refresh is complete once 437 NAL units of this type have been seen on all the appropriate layers 438 (in decoding order) above the current layer index (if any, or 439 beginning from the base layer if not) through the target layer index. 441 5. Usage with different scalability transmission mechanisms 443 Several different mechanisms are defined for how scalable streams can 444 be transmitted in RTP. The RTP Taxonomy [RFC7656] Section 3.7 445 defines three mechanisms: Single RTP Stream on a Single Media 446 Transport (SRST), Multiple RTP Streams on a Single Media Transport 447 (MRST), and Multiple RTP Streams on Multiple Media Transports (MRMT). 449 The LRR message is applicable to all these mechanisms. For MRST and 450 MRMT mechanisms, the "media source" field of the LRR FCI is set to 451 the SSRC of the RTP stream containing the layer indicated by the 452 Current Layer Index (if "C" is 1), or the stream containing the base 453 encoded stream (if "C" is 0). For MRMT, it is sent on the RTP 454 session on which this stream is sent. On receipt, the sender MUST 455 refresh all the layers requested in the stream, simultaneously in 456 decode order. 458 6. Security Considerations 460 All the security considerations of FIR feedback packets [RFC5104] 461 apply to LRR feedback packets as well. Additionally, media senders 462 receiving LRR feedback packets MUST validate that the payload types 463 and layer indices they are receiving are valid for the stream they 464 are currently sending, and discard the requests if not. 466 7. SDP Definitions 468 Section 7 of [RFC5104] defines SDP procedures for indicating and 469 negotiating support for codec control messages (CCM) in SDP. This 470 document extends this with a new codec control command, "lrr", which 471 indicates support of the Layer Refresh Request (LRR). 473 Figure 9 gives a formal Augmented Backus-Naur Form (ABNF) [RFC5234] 474 showing this grammar extension, extending the grammar defined in 475 [RFC5104]. 477 rtcp-fb-ccm-param =/ SP "lrr" ; Layer Refresh Request 479 Figure 9: Syntax of the "lrr" ccm 481 The Offer-Answer considerations defined in [RFC5104] Section 7.2 482 apply. 484 8. IANA Considerations 486 This document defines a new entry to the "Codec Control Messages" 487 subregistry of the "Session Description Protocol (SDP) Parameters" 488 registry, according to the following data: 490 Value name: lrr 492 Long name: Layer Refresh Request Command 494 Usable with: ccm 496 Reference: RFC XXXX 497 This document also defines a new entry to the "FMT Values for PSFB 498 Payload Types" subregistry of the "Real-Time Transport Protocol (RTP) 499 Parameters" registry, according to the following data: 501 Name: LRR 503 Long Name: Layer Refresh Request Command 505 Value: TBD 507 Reference: RFC XXXX 509 9. References 511 9.1. Normative References 513 [I-D.ietf-avtext-framemarking] 514 Berger, E., Nandakumar, S., and M. Zanaty, "Frame Marking 515 RTP Header Extension", draft-ietf-avtext-framemarking-01 516 (work in progress), March 2016. 518 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 519 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 520 RFC2119, March 1997, 521 . 523 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 524 Jacobson, "RTP: A Transport Protocol for Real-Time 525 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 526 July 2003, . 528 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 529 "Extended RTP Profile for Real-time Transport Control 530 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, DOI 531 10.17487/RFC4585, July 2006, 532 . 534 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 535 "Codec Control Messages in the RTP Audio-Visual Profile 536 with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, 537 February 2008, . 539 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 540 Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/ 541 RFC5234, January 2008, 542 . 544 [RFC6190] Wenger, S., Wang, Y., Schierl, T., and A. Eleftheriadis, 545 "RTP Payload Format for Scalable Video Coding", RFC 6190, 546 DOI 10.17487/RFC6190, May 2011, 547 . 549 [RFC7741] Westin, P., Lundin, H., Glover, M., Uberti, J., and F. 550 Galligan, "RTP Payload Format for VP8 Video", RFC 7741, 551 DOI 10.17487/RFC7741, March 2016, 552 . 554 [RFC7798] Wang, Y., Sanchez, Y., Schierl, T., Wenger, S., and M. 555 Hannuksela, "RTP Payload Format for High Efficiency Video 556 Coding (HEVC)", RFC 7798, DOI 10.17487/RFC7798, March 557 2016, . 559 9.2. Informative References 561 [I-D.ietf-avtext-avpf-ccm-layered] 562 Wenger, S., Lennox, J., Burman, B., and M. Westerlund, 563 "Using Codec Control Messages in the RTP Audio-Visual 564 Profile with Feedback with Layered Codecs", draft-ietf- 565 avtext-avpf-ccm-layered-01 (work in progress), May 2016. 567 [I-D.ietf-payload-vp9] 568 Uberti, J., Holmer, S., Flodman, M., Lennox, J., and D. 569 Hong, "RTP Payload Format for VP9 Video", draft-ietf- 570 payload-vp9-02 (work in progress), March 2016. 572 [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and 573 B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms 574 for Real-Time Transport Protocol (RTP) Sources", RFC 7656, 575 DOI 10.17487/RFC7656, November 2015, 576 . 578 Authors' Addresses 580 Jonathan Lennox 581 Vidyo, Inc. 582 433 Hackensack Avenue 583 Seventh Floor 584 Hackensack, NJ 07601 585 US 587 Email: jonathan@vidyo.com 588 Danny Hong 589 Vidyo, Inc. 590 433 Hackensack Avenue 591 Seventh Floor 592 Hackensack, NJ 07601 593 US 595 Email: danny@vidyo.com 597 Justin Uberti 598 Google, Inc. 599 747 6th Street South 600 Kirkland, WA 98033 601 USA 603 Email: justin@uberti.name 605 Stefan Holmer 606 Google, Inc. 607 Kungsbron 2 608 Stockholm 111 22 609 Sweden 611 Email: holmer@google.com 613 Magnus Flodman 614 Google, Inc. 615 Kungsbron 2 616 Stockholm 111 22 617 Sweden 619 Email: mflodman@google.com