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Found 'MUST not' in this paragraph: The offer, as described in An Offer/Answer Model Session Description Protocol [5], may contain a large number of delivery methods per single fmtp attribute, the answerer MUST remove every delivery-method and configuration-uri not supported. All the parameters MUST not be altered on answer otherwise. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (June 26, 2006) is 6508 days in the past. Is this intentional? 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'11') (Obsoleted by RFC 4648) ** Downref: Normative reference to an Informational RFC: RFC 1952 (ref. '12') -- Possible downref: Non-RFC (?) normative reference: ref. '13' -- Possible downref: Non-RFC (?) normative reference: ref. '14' Summary: 9 errors (**), 0 flaws (~~), 7 warnings (==), 10 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 AVT Working Group L. Barbato 3 Internet-Draft Xiph.Org 4 Expires: December 28, 2006 June 26, 2006 6 draft-barbato-avt-rtp-theora-01 7 RTP Payload Format for Theora Encoded Video 9 Status of this Memo 11 By submitting this Internet-Draft, each author represents that any 12 applicable patent or other IPR claims of which he or she is aware 13 have been or will be disclosed, and any of which he or she becomes 14 aware will be disclosed, in accordance with Section 6 of BCP 79. 16 Internet-Drafts are working documents of the Internet Engineering 17 Task Force (IETF), its areas, and its working groups. Note that 18 other groups may also distribute working documents as Internet- 19 Drafts. 21 Internet-Drafts are draft documents valid for a maximum of six months 22 and may be updated, replaced, or obsoleted by other documents at any 23 time. It is inappropriate to use Internet-Drafts as reference 24 material or to cite them other than as "work in progress." 26 The list of current Internet-Drafts can be accessed at 27 http://www.ietf.org/ietf/1id-abstracts.txt. 29 The list of Internet-Draft Shadow Directories can be accessed at 30 http://www.ietf.org/shadow.html. 32 This Internet-Draft will expire on December 28, 2006. 34 Copyright Notice 36 Copyright (C) The Internet Society (2006). 38 Abstract 40 This document describes a RTP payload format for transporting Theora 41 encoded video. It details the RTP encapsulation mechanism for raw 42 Theora data and configuration headers necessary to configure the 43 decoder. 45 Also included within the document are the necessary details for the 46 use of Theora with MIME and Session Description Protocol (SDP). 48 Editors Note 49 All references to RFC XXXX are to be replaced by references to the 50 RFC number of this memo, when published. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 56 2. Payload Format . . . . . . . . . . . . . . . . . . . . . . . . 4 57 2.1. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 4 58 2.2. Payload Header . . . . . . . . . . . . . . . . . . . . . . 5 59 2.3. Payload Data . . . . . . . . . . . . . . . . . . . . . . . 6 60 2.4. Example RTP Packet . . . . . . . . . . . . . . . . . . . . 7 61 3. Configuration Headers . . . . . . . . . . . . . . . . . . . . 8 62 3.1. In-band Header Transmission . . . . . . . . . . . . . . . 9 63 3.1.1. Packed Configuration . . . . . . . . . . . . . . . . . 9 64 3.2. Out of Band Transmission . . . . . . . . . . . . . . . . . 10 65 3.2.1. Packed Headers . . . . . . . . . . . . . . . . . . . . 11 66 3.3. Loss of Configuration Headers . . . . . . . . . . . . . . 13 67 4. Comment Headers . . . . . . . . . . . . . . . . . . . . . . . 13 68 5. Frame Packetizing . . . . . . . . . . . . . . . . . . . . . . 14 69 5.1. Example Fragmented Theora Packet . . . . . . . . . . . . . 15 70 5.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 17 71 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 72 6.1. Mapping MIME Parameters into SDP . . . . . . . . . . . . . 19 73 6.1.1. SDP Example . . . . . . . . . . . . . . . . . . . . . 20 74 6.2. Usage with the SDP Offer/Answer Model . . . . . . . . . . 20 75 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 76 7.1. Stream Video . . . . . . . . . . . . . . . . . . . . . . . 21 77 8. Security Considerations . . . . . . . . . . . . . . . . . . . 21 78 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22 79 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 80 10.1. Normative References . . . . . . . . . . . . . . . . . . . 22 81 10.2. Informative References . . . . . . . . . . . . . . . . . . 23 82 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 24 83 Intellectual Property and Copyright Statements . . . . . . . . . . 25 85 1. Introduction 87 Theora is a general purpose, lossy video codec. It is based on the 88 VP3 video codec produced by On2 Technologies and has been donated to 89 the Xiph.org Foundation. 91 Theora I is a block-based lossy transform codec that utilizes an 8 x 92 8 Type-II Discrete Cosine Transform and block-based motion 93 compensation. This places it in the same class of codecs as MPEG-1, 94 MPEG-2, MPEG-4, and H.263. The details of how individual blocks are 95 organized and how DCT coefficients are stored in the bitstream differ 96 substantially from these codecs, however. Theora supports only intra 97 frames (I frames in MPEG) and inter frames (P frames in MPEG). 99 Theora provides none of its own framing, synchronization, or 100 protection against transmission errors. Instead, the codec expects 101 to receive a discrete sequence of data packets. Theora is a free- 102 form variable bit rate (VBR) codec, and these packets have no minimum 103 size, maximum size, or fixed/expected size. Theora packets are thus 104 intended to be used with a transport mechanism that provides free- 105 form framing, synchronization, positioning, and error correction in 106 accordance with these design assumptions, such as Ogg [1] or RTP/AVP 107 [3]. 109 Theora I currently supports progressive video data of arbitrary 110 dimensions at a constant frame rate in one of several Y'CbCr color 111 spaces. Three different chroma subsampling formats are supported: 112 4:2:0, 4:2:2, and 4:4:4. The Theora I format does not support 113 interlaced material, variable frame rates, bit-depths larger than 8 114 bits per component, nor alternate color spaces such as RGB or 115 arbitrary multi-channel spaces. Black and white content can be 116 efficiently encoded, however, because the uniform chroma planes 117 compress well. Arbitrary frame size will be encoded rounding to the 118 upper multiple of 16 both dimension for performance reason. The 119 original width and height will be encoded in the header and the 120 decoder will use this information to clip the decoded frame to the 121 right dimensions. 123 Theora is similar to the Vorbis audio [10] in that it the decoder 124 reads the probability model for the entropy coder and all 125 quantization parameters from special "header" packets at the start of 126 the compressed data. It is therefore impossible to decode any video 127 data without having previously fetched the codec info and codec setup 128 headers, although Theora can initiate decode at an arbitrary intra- 129 frame packet so long as the codec has been initialized with the 130 associated headers. 132 1.1. Terminology 134 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 135 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 136 document are to be interpreted as described in RFC 2119 [2]. 138 2. Payload Format 140 For RTP based transportation of Theora encoded video the standard RTP 141 header is followed by a 4 octets payload header, then the payload 142 data. The payload headers are used to associate the Theora data with 143 its associated decoding codebooks as well as indicating if the 144 following packet contains fragmented Theora data and/or the number of 145 whole Theora data frames. The payload data contains the raw Theora 146 bitstream information. 148 For RTP based transport of Theora encoded video the standard RTP 149 header is followed by a 4 octets payload header, then the payload 150 data. 152 2.1. RTP Header 154 The format of the RTP header is specified in [3] and shown in Figure 155 1. This payload format uses the fields of the header in a manner 156 consistent with that specification. 158 0 1 2 3 159 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 1 160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 161 |V=2|P|X| CC |M| PT | sequence number | 162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 163 | timestamp | 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 | synchronization source (SSRC) identifier | 166 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 167 | contributing source (CSRC) identifiers | 168 | ... | 169 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 171 Figure 1: RTP Header 173 The RTP header begins with an octet of fields (V, P, X, and CC) to 174 support specialized RTP uses (see [3] and [4] for details). For 175 Theora RTP, the following values are used. 177 Version (V): 2 bits 178 This field identifies the version of RTP. The version used by this 179 specification is two (2). 181 Padding (P): 1 bit 183 Padding MAY be used with this payload format according to section 5.1 184 of [3]. 186 Extension (X): 1 bit 188 The Extension bit is used in accordance with [3]. 190 CSRC count (CC): 4 bits 192 The CSRC count is used in accordance with [3]. 194 Marker (M): 1 bit 196 The Marker bit is used in accordance with [3]. 198 Payload Type (PT): 7 bits 200 An RTP profile for a class of applications is expected to assign a 201 payload type for this format, or a dynamically allocated payload type 202 SHOULD be chosen which designates the payload as Theora. 204 Sequence number: 16 bits 206 The sequence number increments by one for each RTP data packet sent, 207 and may be used by the receiver to detect packet loss and to restore 208 packet sequence. This field is detailed further in [3]. 210 Timestamp: 32 bits 212 A timestamp representing the presentation time of the first sample of 213 the first Theora packet in the RTP packet. The clock frequency MUST 214 be set to 90kHz. 216 SSRC/CSRC identifiers: 218 These two fields, 32 bits each with one SSRC field and a maximum of 219 16 CSRC fields, are as defined in [3]. 221 2.2. Payload Header 223 The 4 octets following the RTP Header section are the Payload Header. 224 This header is split into a number of bitfields detailing the format 225 of the following Payload Data packets. 227 0 1 2 3 228 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 1 229 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 230 | Configuration Ident | F |TDT|# pkts.| 231 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 +-+-+-+-+-+-+-+-+ 235 Figure 2: Payload Header 237 Configuration Ident: 24 bits 239 This 24 bit field is used to associate the Theora data to a decoding 240 Packed Configuration. 242 Fragment type (F): 2 bit 244 This field is set according to the following list 246 0 = Not Fragmented 247 1 = Start Fragment 248 2 = Continuation Fragment 249 3 = End Fragment 251 This field must be zero if the number of packets field is non-zero. 253 Theora Data Type (TDT): 2 bits 255 This field sets the packet payload type for the Theora data. There 256 are currently three Theora payload types. 258 0 = Raw Theora payload 259 1 = Theora Packed Configuration payload 260 2 = Legacy Theora Comment payload 261 3 = Reserved 263 The packets with a TDT of value 3 MUST be ignored 265 The last 4 bits represent the number of complete packets in this 266 payload. This provides for a maximum number of 15 Theora packets in 267 the payload. If the packet contains fragmented data the number of 268 packets MUST be set to 0. 270 2.3. Payload Data 272 Each Theora payload section starts with a two octets length header 273 that is used to represent the size of the following data payload, 274 followed by the raw Theora packet data. 276 0 1 2 3 277 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 1 278 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 279 | Payload Length | Theora Data .. 280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 282 Figure 3: Payload Data 284 The Theora codec uses relatively unstructured raw packets containing 285 binary integer fields of arbitrary width that often do not fall on an 286 octet boundary. When a Theora encoder produces packets, unused space 287 in the last byte of a packet is always zeroed during the encoding 288 process. Thus, should this unused space be read, it will return 289 binary zeros. 291 For payloads which consist of multiple Theora packets the payload 292 data consists of the payload length field followed by the first 293 Theora packet's data, then the payload length followed by the second 294 Theora packet, and so on for each of the Theora packets in the 295 payload. 297 2.4. Example RTP Packet 299 Here is an example RTP packet containing two Theora packets. 301 RTP Packet Header: 303 0 1 2 3 304 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 1 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 | 2 |0|0| 0 |0| PT | sequence number | 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 | timestamp | 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 | synchronisation source (SSRC) identifier | 311 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 312 | contributing source (CSRC) identifiers | 313 | ... | 314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 316 Figure 4: Example RTP Packet 318 Payload Data: 320 0 1 2 3 321 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 1 322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 323 | Configuration Ident | 0 | 0 | 2 pks | 324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 325 | Payload Length | .. 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 .. Theora data .. 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 329 .. data | Payload Length | 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 .. Theora data | 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 334 Figure 5: Example Theora Payload Packet 336 The payload portion of the packet begins with the 24 bit 337 Configuration ident field followed by 8 bits describing the payload. 338 The Fragment type field is set to 0, indicating that this packet 339 contains whole Theora frame data. The Data type field is set to 0 340 since it is theora raw data. The number of whole Theora data packets 341 is set to 2. 343 Each of the payload blocks starts with the two octets length field 344 followed by the variable length Theora packet data. 346 3. Configuration Headers 348 To decode a Theora stream three configuration header packets are 349 needed. The first, called the Identification Header, indicates the 350 frame dimensions, quality, blocks used and the version of the Theora 351 encoder used. The second, called the Comment Header, contains stream 352 metadata and the third, called the Setup Header, contains details of 353 the dequantization and Huffman tables. 355 Since this information must be transmitted reliably, and as the RTP 356 stream may change certain configuration data mid-session, there are 357 different methods for delivering this configuration data to a client, 358 both in-band and out-of-band which are detailed below. SDP delivery 359 is used to set up an initial state for the client application. The 360 changes may be due to different dequantization and Huffman tables as 361 well as different bitrates of the stream. 363 The delivery vectors in use are specified by an SDP attribute to 364 indicate the method and the optional URI where the Theora Packed 365 Configuration (Section 3.1.1) Packets could be fetched. Different 366 delivery methods MAY be advertised for the same session. The in-band 367 codebook delivery SHOULD be considered as baseline, out-of-band 368 delivery methods that don't use RTP will not be described in this 369 document. For non chained streams, the Configuration delivery method 370 RECOMMENDED is inline the Packed Configuration (Section 3.1.1) in the 371 SDP as explained in the IANA considerations (Section 6.1) 373 The 24 bit Ident field is used to map which Configuration will be 374 used to decode a packet. When the Ident field changes, it indicates 375 that a change in the stream has taken place. The client application 376 MUST have in advance the correct configuration and if the client 377 detects a change in the Ident value and does not have this 378 information it MUST NOT decode the raw data associated until it 379 fetches the correct Configuration. 381 3.1. In-band Header Transmission 383 The Packed Configuration (Section 3.1.1) Payload is sent in-band with 384 the packet type bits set to match the payload type. Clients MUST be 385 capable of dealing with periodic re-transmission of the configuration 386 headers. 388 3.1.1. Packed Configuration 390 A Theora Packed Configuration is indicated with the payload type 391 field set to 1. Of the three headers, defined in the Theora I 392 specification [16], the identification and the setup will be packed 393 together, the comment header is completely suppressed. It is up to 394 the client to provide a minimal size comment header to the decoder if 395 required by the implementation. 397 0 1 2 3 398 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 1 399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 400 |V=2|P|X| CC |M| PT | xxxx | 401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 402 | xxxxx | 403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 404 | synchronization source (SSRC) identifier | 405 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 406 | contributing source (CSRC) identifiers | 407 | ... | 408 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 409 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 410 | Configuration Ident | 0 | 1 | 1| 411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 412 | length | Identification .. 413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 414 .. Identification .. 415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 416 .. Identification .. 417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 418 .. Identification | 419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 420 .. | Setup .. 421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 422 .. Setup .. 423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 424 .. Setup | 425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 427 Figure 6: Packed Configuration Figure 429 The Ident field is set with the value that will be used by the Raw 430 Payload Packets to address this Configuration. The Fragment type is 431 set to 0 since the packet bears the full Packed configuration, the 432 number of packet is set to 1. In practice, Packed Headers usually 433 need to be fragmented to fit the path MTU. 435 3.2. Out of Band Transmission 437 This section, as stated above, does not cover all the possible out- 438 of-band delivery methods since they rely on different protocols and 439 be linked to specific applications. The following packet definition 440 SHOULD be used in out-of-band delivery and MUST be used when 441 Configuration is inlined in the SDP. 443 3.2.1. Packed Headers 445 As mentioned above, the recommended delivery vector for Theora 446 configuration data is via a retrieval method that can be performed 447 using a reliable transport protocol. As the RTP headers are not 448 required for this method of delivery the structure of the 449 configuration data is slightly different. The packed header starts 450 with a 32 bit count field which details the number of packed headers 451 that are contained in the bundle. Next is the Packed header payload 452 for each setup id. 454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 455 | Number of packed headers | 456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 458 | Packed header | 459 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 461 | Packed header | 462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 464 Figure 7: Packed Headers Overview 466 Since the Configuration Ident and the Identification Header are fixed 467 length there is only a 16bit Length tag to define the length of the 468 packed headers. 470 0 1 2 3 471 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 1 472 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 473 | Configuration Ident | .. 474 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 475 .. Length | Identification Header .. 476 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 477 .. Identification Header | 478 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 479 | Setup Header .. 480 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 481 .. Setup Header | 482 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 484 Figure 8: Packed Headers Detail 486 The key difference from the in-band format is that there is no need 487 for the payload header octet. 489 3.2.1.1. Packed Headers IANA Considerations 491 The following IANA considerations MUST only be applied to the packed 492 headers. 494 MIME media type name: audio 496 MIME subtype: theora-config 498 Required Parameters: 500 None 502 Optional Parameters: 504 None 506 Encoding considerations: 508 This media type contains binary data. 510 Security Considerations: 512 See Section 6 of RFC XXXX. 514 Interoperability considerations: 516 None 518 Published specification: 520 RFC XXXX [RFC Editor: please replace by the RFC number of this 521 memo, when published] 523 Applications which use this media type: 525 Theora encoded video, configuration data. 527 Additional information: 529 None 531 Person & email address to contact for further information: 533 Luca Barbato: 534 IETF Audio/Video Transport Working Group 536 Intended usage: COMMON 538 Restriction on usage: 540 This media type does not depend on the transport. 542 Author: 544 Luca Barbato 546 Change controller: 548 IETF AVT Working Group 550 3.3. Loss of Configuration Headers 552 Unlike the loss of raw Theora payload data, the loss of a 553 configuration header can lead to a situation where it will not be 554 possible to successfully decode the stream. 556 A loss of a Configuration Packet results in the halting of stream 557 decoding and SHOULD be reported to the client as well as a loss 558 report sent via RTCP. 560 4. Comment Headers 562 When the payload type is set to 2, the packet contains the comment 563 metadata, such as artist name, track title and so on. These metadata 564 messages are not intended to be fully descriptive but to offer basic 565 title information. Clients MAY ignore them completely. The details 566 on the format of the comments can be found in the Theora 567 documentation [16]. 569 0 1 2 3 570 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 1 571 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 572 |V=2|P|X| CC |M| PT | xxxx | 573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 574 | xxxxx | 575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 576 | synchronization source (SSRC) identifier | 577 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 578 | contributing source (CSRC) identifiers | 579 | ... | 580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 581 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 582 | Configuration Ident | 0 | 2 | 1| 583 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 584 | length | Comment .. 585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 586 .. Comment .. 587 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 588 .. Comment | 589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 591 Figure 9: Comment Packet 593 The 2 byte length field is necessary since this Theora packet could 594 be fragmented. 596 5. Frame Packetizing 598 Each RTP packet contains either one complete Theora packet, one 599 Theora packet fragment, or an integer number of complete Theora 600 packets (up to a maximum of 15 packets, since the number of packets 601 is defined by a 4 bit value). 603 Any Theora data packet that is less than path MTU SHOULD be bundled 604 in the RTP packet with as many Theora packets as will fit, up to a 605 maximum of 15. Path MTU is detailed in [7] and [8]. 607 A fragmented packet has a zero in the last four bits of the payload 608 header. The RTP packet containing the first fragment will set the 609 Fragment type to 1. Each RTP packet after the first will set the 610 Fragment type to 2 in the payload header. The RTP packet containing 611 the last fragment of the Theora packet will have the Fragment type 612 set to 3. If the fragmented Theora packet spans only two RTP 613 packets, the first will set the Fragment type field to 1 and the 614 second will set it to 2. To maintain the correct sequence for 615 fragmented packet reception the timestamp field of fragmented packets 616 MUST be the same as the first packet sent, with the sequence number 617 incremented as normal for the subsequent RTP packets. 619 5.1. Example Fragmented Theora Packet 621 Here is an example fragmented Theora packet split over three RTP 622 packets. Each packet contains the standard RTP headers as well as 623 the 4 octets Theora headers. 625 Packet 1: 627 0 1 2 3 628 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 1 629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 630 |V=2|P|X| CC |M| PT | 1000 | 631 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 632 | xxxxx | 633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 634 | synchronization source (SSRC) identifier | 635 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 636 | contributing source (CSRC) identifiers | 637 | ... | 638 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 639 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 640 | Configuration Ident | 1 | 0 | 0| 641 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 642 | Payload Length | Theora data .. 643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 644 .. Theora data .. 645 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 647 Figure 10: Example Fragmented Packet (Packet 1) 649 In this packet the initial sequence number is 1000 and the timestamp 650 is xxxxx. The Fragment type field is set to one, indicating it is 651 the start packet of a serie of fragments. The number of packets 652 field is set to 0, and as the payload is raw Theora data the Theora 653 payload type field is set to 0. 655 Packet 2: 657 0 1 2 3 658 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 1 659 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 660 |V=2|P|X| CC |M| PT | 1001 | 661 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 662 | xxxxx | 663 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 664 | synchronization source (SSRC) identifier | 665 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 666 | contributing source (CSRC) identifiers | 667 | ... | 668 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 670 | Configuration Ident | 2 | 0 | 0| 671 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 672 | Payload Length | .. 673 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 674 .. Theora data .. 675 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 677 Figure 11: Example Fragmented Packet (Packet 2) 679 The Fragment type field is set to 2 and the number of packets field 680 is set to 0. For large Theora fragments there can be several of 681 these type of payload packets. The maximum RTP packet size SHOULD be 682 no greater than the path MTU, including all RTP and payload headers. 683 The sequence number has been incremented by one but the timestamp 684 field remains the same as the initial packet. 686 Packet 3: 688 0 1 2 3 689 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 1 690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 691 |V=2|P|X| CC |M| PT | 1002 | 692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 | xxxxx | 694 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 695 | synchronization source (SSRC) identifier | 696 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 697 | contributing source (CSRC) identifiers | 698 | ... | 699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 | Configuration Ident | 3 | 0 | 0| 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 | Payload Length | .. 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 705 .. Theora data .. 706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 708 Figure 12: Example Fragmented Packet (Packet 3) 710 This is the last Theora fragment packet. The Fragment type filed is 711 set to 3 and the packet count remains set to 0. As in the previous 712 packets the timestamp remains set to the first packet in the sequence 713 and the sequence number has been incremented. 715 5.2. Packet Loss 717 As there is no error correction within the Theora stream, packet loss 718 will result in a loss of signal. Packet loss is more of an issue for 719 fragmented Theora packets as the client will have to cope with the 720 handling of the Fragment type field. If we use the fragmented Theora 721 packet example above and the first packet is lost the client MUST 722 detect that the next packet has the packet count field set to 0 and 723 the Fragment type is set to 2 and MUST drop it. The next packet, 724 which is the final fragmented packet, MUST be dropped in the same 725 manner. Feedback reports on lost and dropped packets MUST be sent 726 back via RTCP.[note: reordering] 728 If a particular multicast session has a large number of participants 729 care must be taken to prevent an RTCP feedback implosion, [9], in the 730 event of packet loss from a large number of participants. 732 Loss of any of the Configuration fragment will result in the loss of 733 the full Configuration packet as detailed in the Loss of 734 Configuration Headers (Section 3.3) section. 736 6. IANA Considerations 738 MIME media type name: video 740 MIME subtype: theora 742 Required Parameters: 744 sampling: Determines the chroma subsampling format. 746 width: Determines the number of pixels per line. This is an 747 integer between 1 and 1048561 and MUST be in multiples of 16. 749 height: Determines the number of lines per frame encoded. This is 750 an integer between 1 and 1048561 and MUST be in multiples of 751 16. 753 delivery-method: indicates the delivery methods in use, the 754 possible values are: inline, in_band, out_band/specific_name 755 Where "specific_name" is the name of the out of band delivery 756 method. 758 configuration: the base16 [11] (hexadecimal) representation of the 759 Packed Headers (Section 3.2.1). 761 Optional Parameters: 763 configuration-uri: the URI of the configuration headers in case of 764 out of band transmission. In the form of 765 "protocol://path/to/resource/". Depending on the specific 766 method the single ident packets could be retrived by their 767 number or aggregated in a single stream, aggregates MAY be 768 compressed using gzip [12] or bzip2 [14] and an sha1 [13] 769 checksum MAY be provided in the form of 770 "protocol://path/to/resource/aggregated.bz2!sha1hash" 772 Encoding considerations: 774 This media type is framed and contains binary data. 776 Security Considerations: 778 See Section 6 of RFC XXXX. 780 Interoperability considerations: 782 None 784 Published specification: 786 RFC XXXX [RFC Editor: please replace by the RFC number of this 787 memo, when published] 789 Ogg Theora I specification: Codec setup and packet decode. 790 Available from the Xiph website, http://www.xiph.org 792 Applications which use this media type: 794 Audio streaming and conferencing tools 796 Additional information: 798 None 800 Person & email address to contact for further information: 802 Luca Barbato: 803 IETF Audio/Video Transport Working Group 805 Intended usage: 807 COMMON 809 Restriction on usage: 811 This media type depends on RTP framing, and hence is only defined 812 for transfer via RTP [3] 814 Author: 816 Luca Barbato 818 Change controller: 820 IETF AVT Working Group 822 6.1. Mapping MIME Parameters into SDP 824 The information carried in the MIME media type specification has a 825 specific mapping to fields in the Session Description Protocol (SDP) 826 [6], which is commonly used to describe RTP sessions. When SDP is 827 used to specify sessions the mapping are as follows: 829 o The MIME type ("video") goes in SDP "m=" as the media name. 831 o The MIME subtype ("theora") goes in SDP "a=rtpmap" as the encoding 832 name. 834 o The clock rate in the "a=rtpmap" line MUST be 90000 836 o The mandated parameters "delivery-method" and "configuration" MUST 837 be included in the SDP "a=fmpt" attribute. 839 o The optional parameter "configuration-uri", when present, MUST be 840 included in the SDP "a=fmpt" attribute and MUST follow the 841 delivery-method that applies. 843 If the stream uses multiple decoder setup configurations and all of 844 them are known in advance, the Configuration Packet for each file 845 SHOULD be packaged together and passed to the client using the 846 configuration attribute. 848 The URI specified in the configuration-uri attribute MUST point to a 849 location where all of the Configuration Packets needed for the life 850 of the session reside. 852 6.1.1. SDP Example 854 The following example shows a basic SDP for a single stream. The 855 first configuration packet is inlined in the sdp, other 856 configurations could be fetched at any time from the first provided 857 uri using or all the known configuration could be downloaded using 858 the second uri. The inline base16 [11] configuration string is 859 omitted because of the lenght. 860 c=IN IP4 192.0.0.1 861 m=video RTP/AVP 98 862 a=rtpmap:98 theora/90000 863 a=fmtp:98 sampling=YCbCr-4:2:2; width=1280; height=720; delivery- 864 method=inline; configuration=base16string1; delivery- 865 method=out_band/rtsp; delivery-method=out_band/rtsp; 866 configuration-uri=rtsp://path/to/resource/; delivery- 867 method=out_band/http; configuration-uri=http://another/path/to/ 868 resource/aggregate.bz2!sha1hash; 870 6.2. Usage with the SDP Offer/Answer Model 872 The offer, as described in An Offer/Answer Model Session Description 873 Protocol [5], may contain a large number of delivery methods per 874 single fmtp attribute, the answerer MUST remove every delivery-method 875 and configuration-uri not supported. All the parameters MUST not be 876 altered on answer otherwise. 878 7. Examples 880 The following examples are common usage patterns that MAY be applied 881 in such situations, the main scope of this section is to explain 882 better usage of the transmission vectors. 884 7.1. Stream Video 886 This is one of the most common situation: one single server streaming 887 content in multicast, the clients may start a session at random time. 888 The content itself could be a mix of live stream, as the wj's voice 889 or studio scenes, and stored streams, as the music she plays. 891 In this situation we don't know in advance how many codebooks we will 892 use. The clients can join anytime and users expect to start the 893 fruition of the content in a short time. 895 On join the client will receive the current Configuration necessary 896 to decode the current streams inlined in the SDP so that the decoding 897 will start immediately after. 899 When the streamed content changes the new Configuration is sent in- 900 band before the actual stream, and the Configuration that has to be 901 sent inline in the SDP updated. Since the inline method is 902 unreliable, an out of band fallback is provided. 904 The client could choose to fetch the Configuration from the alternate 905 source as soon it discovers a Configuration packet got lost inline or 906 use selective retransmission [17], if the server supports the 907 feature. 909 A serverside optimization would be to keep an hash list of the 910 Configurations per session to avoid packing all of them and send the 911 same Configuration with different Ident tags 913 A clientside optimization would be to keep a tag list of the 914 Configurations per session and don't process configuration packets 915 already known. 917 8. Security Considerations 919 RTP packets using this payload format are subject to the security 920 considerations discussed in the RTP specification [3]. This implies 921 that the confidentiality of the media stream is achieved by using 922 encryption. Because the data compression used with this payload 923 format is applied end-to-end, encryption may be performed on the 924 compressed data. Where the size of a data block is set care MUST be 925 taken to prevent buffer overflows in the client applications. 927 9. Acknowledgments 929 This document is a continuation of draft-kerr-avt-theora-rtp-00.txt 931 Thanks to the AVT, Ogg Theora Communities / Xiph.org, Fluendo, Ralph 932 Giles, Mike Smith, Phil Kerr, Timothy Terriberry, Stefan Ehmann, 933 Alessandro Salvatori, Politecnico di Torino (LS)^3/IMG Group in 934 particular Federico Ridolfo, Francesco Varano, Giampaolo Mancini, 935 Juan Carlos De Martin. 937 10. References 939 10.1. Normative References 941 [1] Pfeiffer, S., "The Ogg Encapsulation Format Version 0", 942 RFC 3533. 944 [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement 945 Levels", RFC 2119. 947 [3] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, 948 "RTP: A Transport Protocol for real-time applications", 949 RFC 3550. 951 [4] Schulzrinne, H. and S. Casner, "RTP Profile for video and Video 952 Conferences with Minimal Control.", RFC 3551. 954 [5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with 955 Session Description Protocol (SDP)", RFC 3264. 957 [6] Handley, M. and V. Jacobson, "SDP: Session Description 958 Protocol", RFC 2327. 960 [7] Mogul et al., J., "Path MTU Discovery", RFC 1063. 962 [8] McCann et al., J., "Path MTU Discovery for IP version 6", 963 RFC 1981. 965 [9] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 966 "Extended RTP Profile for RTCP-based Feedback (RTP/AVPF)", 967 Internet Draft (draft-ietf-avt-rtcp-feedback-11: Work in 968 progress). 970 [10] Barbato, L., "RTP Payload Format for Vorbis Encoded Audio - 971 draft-ietf-avt-vorbis-rtp-00", Internet Draft (Work in 972 progress). 974 [11] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", 975 RFC 3548. 977 [12] Deutsch, P., "GZIP file format specification version 4.3", 978 RFC 1952. 980 [13] National Institute of Standards and Technology, "Secure Hash 981 Standard", May 1993. 983 [14] Seward, J., "libbz2 and bzip2". 985 10.2. Informative References 987 [15] "libTheora: Available from the Xiph website, 988 http://www.xiph.org". 990 [16] "Theora I specification: Codec setup and packet decode. 991 http://www.xiph.org/theora/doc/Theora_I_spec.pdf". 993 [17] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol 994 Extended Reports (RTCP XR)", RFC 3611, November 2003. 996 [18] "ITU-T Recommendation V.42, 1994, Rev. 1. Error-correcting 997 Procedures for DCEs Using Asynchronous-to-Synchronous 998 Conversion. International Telecommunications Union. Available 999 from the ITU website, http://www.itu.int". 1001 [19] "ISO 3309, October 1984, 3rd Edition. Information Processing 1002 Systems--Data Communication High-Level Data Link Control 1003 Procedure--Frame Structure. International Organization for 1004 Standardization.". 1006 Author's Address 1008 Luca Barbato 1009 Xiph.Org 1011 Email: lu_zero@gentoo.org 1012 URI: http://www.xiph.org/ 1014 Intellectual Property Statement 1016 The IETF takes no position regarding the validity or scope of any 1017 Intellectual Property Rights or other rights that might be claimed to 1018 pertain to the implementation or use of the technology described in 1019 this document or the extent to which any license under such rights 1020 might or might not be available; nor does it represent that it has 1021 made any independent effort to identify any such rights. 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