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Barbato 3 Internet-Draft Xiph 4 Expires: August 20, 2008 Feb 17, 2008 6 RTP Payload Format for Vorbis Encoded Audio 7 draft-ietf-avt-rtp-vorbis-09 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 August 20, 2008. 34 Copyright Notice 36 Copyright (C) The IETF Trust (2008). 38 Abstract 40 This document describes an RTP payload format for transporting Vorbis 41 encoded audio. It details the RTP encapsulation mechanism for raw 42 Vorbis data and details the delivery mechanisms for the decoder 43 probability model, referred to as a codebook and other setup 44 information. 46 Also included within this memo are media type registrations, and the 47 details necessary for the use of Vorbis with the Session Description 48 Protocol (SDP). 50 Editors Note 52 All references to RFC XXXX are to be replaced by references to the 53 RFC number of this memo, when published. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 1.1. Conformance and Document Conventions . . . . . . . . . . . 3 59 2. Payload Format . . . . . . . . . . . . . . . . . . . . . . . . 3 60 2.1. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 4 61 2.2. Payload Header . . . . . . . . . . . . . . . . . . . . . . 5 62 2.3. Payload Data . . . . . . . . . . . . . . . . . . . . . . . 6 63 2.4. Example RTP Packet . . . . . . . . . . . . . . . . . . . . 7 64 3. Configuration Headers . . . . . . . . . . . . . . . . . . . . 8 65 3.1. In-band Header Transmission . . . . . . . . . . . . . . . 9 66 3.1.1. Packed Configuration . . . . . . . . . . . . . . . . . 9 67 3.2. Out of Band Transmission . . . . . . . . . . . . . . . . . 11 68 3.2.1. Packed Headers . . . . . . . . . . . . . . . . . . . . 11 69 3.3. Loss of Configuration Headers . . . . . . . . . . . . . . 12 70 4. Comment Headers . . . . . . . . . . . . . . . . . . . . . . . 12 71 5. Frame Packetization . . . . . . . . . . . . . . . . . . . . . 13 72 5.1. Example Fragmented Vorbis Packet . . . . . . . . . . . . . 14 73 5.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 16 74 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 75 6.1. Packed Headers IANA Considerations . . . . . . . . . . . . 18 76 7. SDP related considerations . . . . . . . . . . . . . . . . . . 19 77 7.1. Mapping Media Type Parameters into SDP . . . . . . . . . . 20 78 7.1.1. SDP Example . . . . . . . . . . . . . . . . . . . . . 20 79 7.2. Usage with the SDP Offer/Answer Model . . . . . . . . . . 21 80 8. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 21 81 9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 82 9.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 21 83 10. Security Considerations . . . . . . . . . . . . . . . . . . . 22 84 11. Copying Conditions . . . . . . . . . . . . . . . . . . . . . . 22 85 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22 86 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23 87 13.1. Normative References . . . . . . . . . . . . . . . . . . . 23 88 13.2. Informative References . . . . . . . . . . . . . . . . . . 23 90 1. Introduction 92 Vorbis is a general purpose perceptual audio codec intended to allow 93 maximum encoder flexibility, thus allowing it to scale competitively 94 over an exceptionally wide range of bitrates. At the high quality/ 95 bitrate end of the scale (CD or DAT rate stereo, 16/24 bits), it is 96 in the same league as MPEG-4 AAC. Vorbis is also intended for lower 97 and higher sample rates (from 8kHz telephony to 192kHz digital 98 masters) and a range of channel representations (monaural, 99 polyphonic, stereo, quadraphonic, 5.1, ambisonic, or up to 255 100 discrete channels). 102 Vorbis encoded audio is generally encapsulated within an Ogg format 103 bitstream [11], which provides framing and synchronization. For the 104 purposes of RTP transport, this layer is unnecessary, and so raw 105 Vorbis packets are used in the payload. 107 1.1. Conformance and Document Conventions 109 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 110 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 111 document are to be interpreted as described in BCP 14, [1] and 112 indicate requirement levels for compliant implementations. 113 Requirements apply to all implementations unless otherwise stated. 115 An implementation is a software module that supports one of the media 116 types defined in this document. Software modules may support 117 multiple media types, but conformance is considered individually for 118 each type. 120 Implementations that fail to satisfy one or more "MUST" requirements 121 are considered non-compliant. Implementations that satisfy all 122 "MUST" requirements, but fail to satisfy one or more "SHOULD" 123 requirements, are said to be "conditionally compliant". All other 124 implementations are "unconditionally compliant". 126 2. Payload Format 128 For RTP based transport of Vorbis encoded audio the standard RTP 129 header is followed by a 4 octets payload header, then the payload 130 data. The payload headers are used to associate the Vorbis data with 131 its associated decoding codebooks as well as indicating if the 132 following packet contains fragmented Vorbis data and/or the number of 133 whole Vorbis data frames. The payload data contains the raw Vorbis 134 bitstream information. There are 3 types of Vorbis data, an RTP 135 payload MUST contain just one of them at a time. 137 2.1. RTP Header 139 The format of the RTP header is specified in [2] and shown in Figure 140 Figure 1. This payload format uses the fields of the header in a 141 manner consistent with that specification. 143 0 1 2 3 144 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 1 145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 146 |V=2|P|X| CC |M| PT | sequence number | 147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 148 | timestamp | 149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 150 | synchronization source (SSRC) identifier | 151 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 152 | contributing source (CSRC) identifiers | 153 | ... | 154 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 156 Figure 1: RTP Header 158 The RTP header begins with an octet of fields (V, P, X, and CC) to 159 support specialized RTP uses (see [2] and [3] for details). For 160 Vorbis RTP, the following values are used. 162 Version (V): 2 bits 164 This field identifies the version of RTP. The version used by this 165 specification is two (2). 167 Padding (P): 1 bit 169 Padding MAY be used with this payload format according to section 5.1 170 of [2]. 172 Extension (X): 1 bit 174 The Extension bit is used in accordance with [2]. 176 CSRC count (CC): 4 bits 178 The CSRC count is used in accordance with [2]. 180 Marker (M): 1 bit 182 Set to zero. Audio silence suppression not used. This conforms to 183 section 4.1 of [10]. 185 Payload Type (PT): 7 bits 187 An RTP profile for a class of applications is expected to assign a 188 payload type for this format, or a dynamically allocated payload type 189 SHOULD be chosen which designates the payload as Vorbis. 191 Sequence number: 16 bits 193 The sequence number increments by one for each RTP data packet sent, 194 and may be used by the receiver to detect packet loss and to restore 195 packet sequence. This field is detailed further in [2]. 197 Timestamp: 32 bits 199 A timestamp representing the sampling time of the first sample of the 200 first Vorbis packet in the RTP payload. The clock frequency MUST be 201 set to the sample rate of the encoded audio data and is conveyed out- 202 of-band (e.g. as an SDP parameter). 204 SSRC/CSRC identifiers: 206 These two fields, 32 bits each with one SSRC field and a maximum of 207 16 CSRC fields, are as defined in [2]. 209 2.2. Payload Header 211 The 4 octets following the RTP Header section are the Payload Header. 212 This header is split into a number of bitfields detailing the format 213 of the following payload data packets. 215 0 1 2 3 216 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 1 217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 218 | Ident | F |VDT|# pkts.| 219 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 221 Figure 2: Payload Header 223 Ident: 24 bits 225 This 24 bit field is used to associate the Vorbis data to a decoding 226 Configuration. It is stored as network byte order integer. 228 Fragment type (F): 2 bits 230 This field is set according to the following list 231 0 = Not Fragmented 232 1 = Start Fragment 233 2 = Continuation Fragment 234 3 = End Fragment 236 Vorbis Data Type (VDT): 2 bits 238 This field specifies the kind of Vorbis data stored in this RTP 239 packet. There are currently three different types of Vorbis 240 payloads. Each packet MUST contain only a single type of Vorbis 241 packet (e.g. you must not aggregate configuration and comment packets 242 in the same RTP payload) 244 0 = Raw Vorbis payload 245 1 = Vorbis Packed Configuration payload 246 2 = Legacy Vorbis Comment payload 247 3 = Reserved 249 The packets with a VDT of value 3 MUST be ignored 251 The last 4 bits represent the number of complete packets in this 252 payload. This provides for a maximum number of 15 Vorbis packets in 253 the payload. If the payload contains fragmented data the number of 254 packets MUST be set to 0. 256 2.3. Payload Data 258 Raw Vorbis packets are currently unbounded in length, application 259 profiles will likely define a practical limit. Typical Vorbis packet 260 sizes range from very small (2-3 bytes) to quite large (8-12 261 kilobytes). The reference implementation [12] typically produces 262 packets less than ~800 bytes, except for the setup header packets 263 which are ~4-12 kilobytes. Within an RTP context, to avoid 264 fragmentation, the Vorbis data packet size SHOULD be kept 265 sufficiently small so that after adding the RTP and payload headers, 266 the complete RTP packet is smaller than the path MTU. 268 0 1 2 3 269 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 1 270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 271 | length | vorbis packet data .. 272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 274 Figure 3: Payload Data Header 276 Each Vorbis payload packet starts with a two octet length header, 277 which is used to represent the size in bytes of the following data 278 payload, followed by the raw Vorbis data padded to the nearest byte 279 boundary, as explained by the vorbis specification [10]. The length 280 value is stored as network byte order integer. 282 For payloads which consist of multiple Vorbis packets the payload 283 data consists of the packet length followed by the packet data for 284 each of the Vorbis packets in the payload. 286 The Vorbis packet length header is the length of the Vorbis data 287 block only and does not include the length field. 289 The payload packing of the Vorbis data packets MUST follow the 290 guidelines set-out in [3] where the oldest Vorbis packet occurs 291 immediately after the RTP packet header. Subsequent Vorbis packets, 292 if any, MUST follow in temporal order. 294 Channel mapping of the audio is in accordance with the Vorbis I 295 Specification [10]. 297 2.4. Example RTP Packet 299 Here is an example RTP payload containing two Vorbis packets. 301 0 1 2 3 302 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 1 303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 304 | 2 |0|0| 0 |0| PT | sequence number | 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 | timestamp (in sample rate units) | 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 | synchronisation source (SSRC) identifier | 309 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 310 | contributing source (CSRC) identifiers | 311 | ... | 312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 314 | Ident | 0 | 0 | 2 pks | 315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 316 | length | vorbis data .. 317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 318 .. vorbis data | 319 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 320 | length | next vorbis packet data .. 321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 322 .. vorbis data .. 323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 324 .. vorbis data | 325 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 326 Figure 4: Example Raw Vorbis Packet 328 The payload data section of the RTP packet begins with the 24 bit 329 Ident field followed by the one octet bitfield header, which has the 330 number of Vorbis frames set to 2. Each of the Vorbis data frames is 331 prefixed by the two octets length field. The Packet Type and 332 Fragment Type are set to 0. The Configuration that will be used to 333 decode the packets is the one indexed by the ident value. 335 3. Configuration Headers 337 Unlike other mainstream audio codecs Vorbis has no statically 338 configured probability model. Instead, it packs all entropy decoding 339 configuration, Vector Quantization and Huffman models into a data 340 block that must be transmitted to the decoder along with the 341 compressed data. A decoder also requires information detailing the 342 number of audio channels, bitrates and similar information to 343 configure itself for a particular compressed data stream. These two 344 blocks of information are often referred to collectively as the 345 "codebooks" for a Vorbis stream, and are nominally included as 346 special "header" packets at the start of the compressed data. In 347 addition, the Vorbis I specification [10] requires the presence of a 348 comment header packet which gives simple metadata about the stream, 349 but this information is not required for decoding the frame sequence. 351 Thus these two codebook header packets must be received by the 352 decoder before any audio data can be interpreted. These requirements 353 pose problems in RTP, which is often used over unreliable transports. 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 is detailed below. In order to 359 set up an initial state for the client application the configuration 360 MUST be conveyed via the signalling channel used to setup the 361 session. One example of such signalling is SDP [5] with the Offer/ 362 Answer Model [8]. Changes to the configuration MAY be communicated 363 via a re-invite, conveying new SDP, or sent in-band in the RTP 364 channel. Implementations MUST support in-band delivery of updated 365 codebooks, and SHOULD support out-of-band codebook update using a new 366 SDP file. The changes may be due to different codebooks as well as 367 different bitrates of the RTP stream. 369 For non chained streams, the recommended Configuration delivery 370 method is inline the Packed Configuration (Section 3.1.1) in the SDP 371 as explained in the IANA considerations (Section 7.1). 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 Vorbis data associated until 379 it 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 Vorbis Data Type. Clients MUST 385 be capable of dealing with fragmentation and periodic re-transmission 386 of [14] the configuration headers. The RTP timestamp value MUST 387 reflect the transmission time of the first data packet for which this 388 configuration applies. 390 3.1.1. Packed Configuration 392 A Vorbis Packed Configuration is indicated with the Vorbis Data Type 393 field set to 1. Of the three headers defined in the Vorbis I 394 specification [10], the Identification and the Setup MUST be packed 395 as they are, while the comment header MAY be replaced with a dummy 396 one. 398 The packed configuration follows a generic way to store Xiph codec 399 configurations: The first field stores the number of the following 400 packets minus one (count field), the next ones represent the size of 401 the headers (length fields), the headers immediately follow the list 402 of length fields. The size of the last header is implicit. 404 The count and the length fields are encoded using the following 405 logic: the data is in network byte order, every byte has the most 406 significant bit used as flag and the following 7 used to store the 407 value. The first N bit are to be taken, where N is number of bits 408 needed to represent the value, taken modulo 7, and stored in the 409 first byte. If there are more bits, the flag bit is set to 1 and the 410 subsequent 7bit are stored in the following byte, if there are 411 remaining bits set the flag to 1 and the same procedure is repeated. 412 The ending byte has the flag bit set to 0. In order to decode it is 413 enough to iterate over the bytes until the flag bit set to 0, for 414 every byte the data is added to the accumulated value multiplied by 415 128. 417 The headers are packed in the same order they are present in ogg: 418 Identification, Comment, Setup. 420 The 2 byte length tag defines the length of the packed headers as the 421 sum of the Configuration, Comment and Setup lengths. 423 0 1 2 3 424 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 1 425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 426 |V=2|P|X| CC |M| PT | xxxx | 427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 428 | xxxxx | 429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 430 | synchronization source (SSRC) identifier | 431 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 432 | contributing source (CSRC) identifiers | 433 | ... | 434 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 436 | Ident | 1 | 0 | 0| 437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 438 | length | n. of headers | length1 | 439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 440 | length2 | Identification .. 441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 442 .. Identification .. 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 444 .. Identification .. 445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 446 .. Identification .. 447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 448 .. Identification | Comment .. 449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 450 .. Comment .. 451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 452 .. Comment .. 453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 454 .. Comment .. 455 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 456 .. Comment | Setup .. 457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 458 .. Setup .. 459 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 460 .. Setup .. 461 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 463 Figure 5: Packed Configuration Figure 465 The Ident field is set with the value that will be used by the Raw 466 Payload Packets to address this Configuration. The Fragment type is 467 set to 0 since the packet bears the full Packed configuration, the 468 number of packet is set to 1. 470 3.2. Out of Band Transmission 472 The following packet definition MUST be used when Configuration is 473 inlined in the SDP. 475 3.2.1. Packed Headers 477 As mentioned above the RECOMMENDED delivery vector for Vorbis 478 configuration data is via a retrieval method that can be performed 479 using a reliable transport protocol. As the RTP headers are not 480 required for this method of delivery the structure of the 481 configuration data is slightly different. The packed header starts 482 with a 32 bit (network byte ordered) count field which details the 483 number of packed headers that are contained in the bundle. Next is 484 the Packed header payload for each chained Vorbis stream. 486 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 487 | Number of packed headers | 488 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 489 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 490 | Packed header | 491 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 492 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 493 | Packed header | 494 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 496 Figure 6: Packed Headers Overview 498 0 1 2 3 499 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 1 500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 501 | Ident | length .. 502 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 503 .. | n. of headers | length1 | length2 .. 504 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 505 .. | Identification Header .. 506 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 507 ................................................................. 508 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 509 .. | Comment Header .. 510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 511 ................................................................. 512 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 513 .. Comment Header | 514 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 515 | Setup Header .. 516 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 517 ................................................................. 518 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 519 .. Setup Header | 520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 522 Figure 7: Packed Headers Detail 524 The key difference between the in-band format and this one, is that 525 there is no need for the payload header octet. In this figure the 526 comment has a size bigger than 127 bytes. 528 3.3. Loss of Configuration Headers 530 Unlike the loss of raw Vorbis payload data, loss of a configuration 531 header lead to a situation where it will not be possible to 532 successfully decode the stream. Implementations MAY try to recover 533 from error by requesting again the missing Configuration or, if the 534 delivery method is in-band, by buffering the payloads waiting for the 535 Configuration needed to decode them. The baseline reaction SHOULD be 536 either reset or end the RTP session. 538 4. Comment Headers 540 With the Vorbis Data Type flag set to 2, this indicates that the 541 packet contain the comment metadata, such as artist name, track title 542 and so on. These metadata messages are not intended to be fully 543 descriptive but to offer basic track/song information. Clients MAY 544 ignore it completely. The details on the format of the comments can 545 be found in the Vorbis documentation [10]. 547 0 1 2 3 548 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 1 549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 550 |V=2|P|X| CC |M| PT | xxxx | 551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 552 | xxxxx | 553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 554 | synchronization source (SSRC) identifier | 555 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 556 | contributing source (CSRC) identifiers | 557 | ... | 558 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 559 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 560 | Ident | 0 | 2 | 1| 561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 562 | length | Comment .. 563 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 564 .. Comment .. 565 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 566 .. Comment | 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 569 Figure 8: Comment Packet 571 The 2 bytes length field is necessary since this packet could be 572 fragmented. 574 5. Frame Packetization 576 Each RTP payload contains either one Vorbis packet fragment, or an 577 integer number of complete Vorbis packets (up to a maximum of 15 578 packets, since the number of packets is defined by a 4 bit value). 580 Any Vorbis data packet that is less than path MTU SHOULD be bundled 581 in the RTP payload with as many Vorbis packets as will fit, up to a 582 maximum of 15, except when such bundling would exceed an 583 application's desired transmission latency. Path MTU is detailed in 584 [6] and [7]. 586 A fragmented packet has a zero in the last four bits of the payload 587 header. The first fragment will set the Fragment type to 1. Each 588 fragment after the first will set the Fragment type to 2 in the 589 payload header. The consecutive fragments MUST be sent without any 590 other payloads being sent between the first and the last fragment. 591 The RTP payload containing the last fragment of the Vorbis packet 592 will have the Fragment type set to 3. To maintain the correct 593 sequence for fragmented packet reception the timestamp field of 594 fragmented packets MUST be the same as the first packet sent, with 595 the sequence number incremented as normal for the subsequent RTP 596 payloads, this will affect the RTCP jitter measurement. The length 597 field shows the fragment length. 599 5.1. Example Fragmented Vorbis Packet 601 Here is an example fragmented Vorbis packet split over three RTP 602 payloads. Each of them contains the standard RTP headers as well as 603 the 4 octets Vorbis headers. 605 Packet 1: 607 0 1 2 3 608 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 1 609 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 610 |V=2|P|X| CC |M| PT | 1000 | 611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 612 | 12345 | 613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 614 | synchronization source (SSRC) identifier | 615 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 616 | contributing source (CSRC) identifiers | 617 | ... | 618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 619 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 620 | Ident | 1 | 0 | 0| 621 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 622 | length | vorbis data .. 623 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 624 .. vorbis data | 625 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 627 Figure 9: Example Fragmented Packet (Packet 1) 629 In this payload the initial sequence number is 1000 and the timestamp 630 is 12345. The Fragment type is set to 1, the number of packets field 631 is set to 0, and as the payload is raw Vorbis data the VDT field is 632 set to 0. 634 Packet 2: 636 0 1 2 3 637 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 1 638 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 639 |V=2|P|X| CC |M| PT | 1001 | 640 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 641 | 12345 | 642 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 643 | synchronization source (SSRC) identifier | 644 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 645 | contributing source (CSRC) identifiers | 646 | ... | 647 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 648 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 649 | Ident | 2 | 0 | 0| 650 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 651 | length | vorbis data .. 652 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 653 .. vorbis data | 654 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 656 Figure 10: Example Fragmented Packet (Packet 2) 658 The Fragment type field is set to 2 and the number of packets field 659 is set to 0. For large Vorbis fragments there can be several of this 660 type of payloads. The maximum packet size SHOULD be no greater than 661 the path MTU, including all RTP and payload headers. The sequence 662 number has been incremented by one but the timestamp field remains 663 the same as the initial payload. 665 Packet 3: 667 0 1 2 3 668 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 1 669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 670 |V=2|P|X| CC |M| PT | 1002 | 671 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 672 | 12345 | 673 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 674 | synchronization source (SSRC) identifier | 675 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 676 | contributing source (CSRC) identifiers | 677 | ... | 678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 680 | Ident | 3 | 0 | 0| 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 682 | length | vorbis data .. 683 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 684 .. vorbis data | 685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 687 Figure 11: Example Fragmented Packet (Packet 3) 689 This is the last Vorbis fragment payload. The Fragment type is set 690 to 3 and the packet count remains set to 0. As in the previous 691 payloads the timestamp remains set to the first payload timestamp in 692 the sequence and the sequence number has been incremented. 694 5.2. Packet Loss 696 As there is no error correction within the Vorbis stream, packet loss 697 will result in a loss of signal. Packet loss is more of an issue for 698 fragmented Vorbis packets as the client will have to cope with the 699 handling of the Fragment Type. In case of loss of fragments the 700 client MUST discard all the remaining Vorbis fragments and decode the 701 incomplete packet. If we use the fragmented Vorbis packet example 702 above and the first RTP payload is lost the client MUST detect that 703 the next RTP payload has the packet count field set to 0 and the 704 Fragment type 2 and MUST drop it. The next RTP payload, which is the 705 final fragmented packet, MUST be dropped in the same manner. If the 706 missing RTP payload is the last, the received two fragments will be 707 kept and the incomplete Vorbis packet decoded. 709 Loss of any of the Configuration fragment will result in the loss of 710 the full Configuration packet with the result detailed in the Loss of 711 Configuration Headers (Section 3.3) section. 713 6. IANA Considerations 715 Type name: audio 717 Subtype name: vorbis 719 Required parameters: 721 rate: indicates the RTP timestamp clock rate as described in RTP 722 Profile for Audio and Video Conferences with Minimal Control. 723 [3] 725 channels: indicates the number of audio channels as described in 726 RTP Profile for Audio and Video Conferences with Minimal 727 Control. [3] 729 configuration: the base64 [9] representation of the Packed 730 Headers (Section 3.2.1). 732 Encoding considerations: 734 This media type is framed and contains binary data. 736 Security considerations: 738 See Section 10 of RFC XXXX. 740 Interoperability considerations: 742 None 744 Published specification: 746 RFC XXXX [RFC Editor: please replace by the RFC number of this 747 memo, when published] 749 Ogg Vorbis I specification: Codec setup and packet decode. 750 Available from the Xiph website, http://xiph.org 752 Applications which use this media type: 754 Audio streaming and conferencing tools 756 Additional information: 758 None 760 Person & email address to contact for further information: 762 Luca Barbato: IETF Audio/Video Transport 763 Working Group 765 Intended usage: 767 COMMON 769 Restriction on usage: 771 This media type depends on RTP framing, and hence is only defined 772 for transfer via RTP [2] 774 Author: 776 Luca Barbato 778 Change controller: 780 IETF AVT Working Group delegated from the IESG 782 6.1. Packed Headers IANA Considerations 784 The following IANA considerations refers to the split configuration 785 Packed Headers (Section 3.2.1) used within RFC XXXX. 787 Type name: audio 789 Subtype name: vorbis-config 791 Required parameters: 793 None 795 Optional parameters: 797 None 799 Encoding considerations: 801 This media type contains binary data. 803 Security considerations: 805 See Section 10 of RFC XXXX. 807 Interoperability considerations: 809 None 811 Published specification: 813 RFC XXXX [RFC Editor: please replace by the RFC number of this 814 memo, when published] 816 Applications which use this media type: 818 Vorbis encoded audio, configuration data. 820 Additional information: 822 None 824 Person & email address to contact for further information: 826 Luca Barbato: 827 IETF Audio/Video Transport Working Group 829 Intended usage: COMMON 831 Restriction on usage: 833 This media type doesn't depend on the transport. 835 Author: 837 Luca Barbato 839 Change controller: 841 IETF AVT Working Group delegated from the IESG 843 7. SDP related considerations 845 The following paragraphs define the mapping of the parameters 846 described in the IANA considerations section and their usage in the 847 Offer/Answer Model [8]. In order to be forward compatible the 848 implementation MUST ignore unknown parameters. 850 7.1. Mapping Media Type Parameters into SDP 852 The information carried in the Media Type specification has a 853 specific mapping to fields in the Session Description Protocol (SDP) 854 [5], which is commonly used to describe RTP sessions. When SDP is 855 used to specify sessions the mapping are as follows: 857 o The type name ("audio") goes in SDP "m=" as the media name. 859 o The subtype name ("vorbis") goes in SDP "a=rtpmap" as the encoding 860 name. 862 o The parameter "rate" also goes in "a=rtpmap" as clock rate. 864 o The parameter "channels" also goes in "a=rtpmap" as channel count. 866 o The mandated parameters "configuration" MUST be included in the 867 SDP "a=fmtp" attribute. 869 If the stream comprises chained Vorbis files and all of them are 870 known in advance, the Configuration Packet for each file SHOULD be 871 passed to the client using the configuration attribute. 873 The port value is specified by the server application bound to the 874 address specified in the c= line. The channel count value specified 875 in the rtpmap attribute SHOULD match the current Vorbis stream or 876 considered the maximum number of channels to be expected. The 877 timestamp clock rate MUST be a multiple of the sample rate, different 878 payload number MUST be used if the clock rate changes. The 879 Configuration payload delivers the exact information, thus the SDP 880 information SHOULD be considered as a hint. An example is found 881 below. 883 7.1.1. SDP Example 885 The following example shows a basic SDP single stream. The first 886 configuration packet is inlined in the SDP, other configurations 887 could be fetched at any time from the URIs provided. The inline 888 base64 [9] configuration string is folded in this example due to RFC 889 line length limitations. 890 c=IN IP4 192.0.2.1 891 m=audio RTP/AVP 98 892 a=rtpmap:98 vorbis/44100/2 893 a=fmtp:98 configuration=AAAAAZ2f4g9NAh4aAXZvcmJpcwA...; 895 Note that the payload format (encoding) names are commonly shown in 896 upper case. Media Type subtypes are commonly shown in lower case. 898 These names are case-insensitive in both places. Similarly, 899 parameter names are case-insensitive both in Media Type types and in 900 the default mapping to the SDP a=fmtp attribute. The a=fmtp line is 901 a single line even if it is shown as multiple lines in this document 902 for clarity. 904 7.2. Usage with the SDP Offer/Answer Model 906 The are no negotiable parameters. All the of them are declarative. 908 8. Congestion Control 910 The general congestion control considerations for transporting RTP 911 data apply to vorbis audio over RTP as well. See the RTP 912 specification [2] and any applicable RTP profile (e.g., [3]). Audio 913 data can be encoded using a range of different bit rates, so it is 914 possible to adapt network bandwidth by adjusting the encoder bit rate 915 in real time or by having multiple copies of content encoded at 916 different bit rates. 918 9. Example 920 The following example shows a common usage pattern that MAY be 921 applied in such situation, the main scope of this section is to 922 explain better usage of the transmission vectors. 924 9.1. Stream Radio 926 This is one of the most common situation: one single server streaming 927 content in multicast, the clients may start a session at random time. 928 The content itself could be a mix of live stream, as the webjockey's 929 voice, and stored streams as the music she plays. 931 In this situation we don't know in advance how many codebooks we will 932 use. The clients can join anytime and users expect to start 933 listening to the content in a short time. 935 On join the client will receive the current Configuration necessary 936 to decode the current stream inlined in the SDP so that the decoding 937 will start immediately after. 939 When the streamed content changes the new Configuration is sent in- 940 band before the actual stream and the Configuration that has to be 941 sent inline in the SDP updated. Since the in-band method is 942 unreliable, an out of band fallback is provided. 944 The client may choose to fetch the Configuration from the alternate 945 source as soon as it discovers a Configuration packet got lost in- 946 band or use selective retransmission [13], if the server supports the 947 feature. 949 A serverside optimization would be to keep an hash list of the 950 Configurations per session to avoid packing all of them and send the 951 same Configuration with different Ident tags 953 A clientside optimization would be to keep a tag list of the 954 Configurations per session and don't process configuration packets 955 already known. 957 10. Security Considerations 959 RTP packets using this payload format are subject to the security 960 considerations discussed in the RTP specification [2], the base64 961 specification [9] and the URI Generic syntax specification [4]. 962 Among other considerations, this implies that the confidentiality of 963 the media stream is archieved by using encryption. Because the data 964 compression used with this payload format is applied end-to-end, 965 encryption may be performed on the compressed data. 967 11. Copying Conditions 969 The authors agree to grant third parties the irrevocable right to 970 copy, use and distribute the work, with or without modification, in 971 any medium, without royalty, provided that, unless separate 972 permission is granted, redistributed modified works do not contain 973 misleading author, version, name of work, or endorsement information. 975 12. Acknowledgments 977 This document is a continuation of draft-moffitt-vorbis-rtp-00.txt 978 and draft-kerr-avt-vorbis-rtp-04.txt. The Media Type declaration is 979 a continuation of draft-short-avt-rtp-vorbis-mime-00.txt. 981 Thanks to the AVT, Vorbis Communities / Xiph.Org Foundation including 982 Steve Casner, Aaron Colwell, Ross Finlayson, Fluendo, Ramon Garcia, 983 Pascal Hennequin, Ralph Giles, Tor-Einar Jarnbjo, Colin Law, John 984 Lazzaro, Jack Moffitt, Christopher Montgomery, Colin Perkins, Barry 985 Short, Mike Smith, Phil Kerr, Michael Sparks, Magnus Westerlund, 986 David Barrett, Silvia Pfeiffer, Stefan Ehmann, Alessandro Salvatori. 987 Politecnico di Torino (LS)^3/IMG Group in particular Federico 988 Ridolfo, Francesco Varano, Giampaolo Mancini, Dario Gallucci, Juan 989 Carlos De Martin. 991 13. References 992 13.1. Normative References 994 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 995 Levels", RFC 2119. 997 [2] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, 998 "RTP: A Transport Protocol for real-time applications", STD 64, 999 RFC 3550. 1001 [3] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video 1002 Conferences with Minimal Control.", STD 65, RFC 3551. 1004 [4] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 1005 Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986. 1007 [5] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1008 Description Protocol", RFC 4566, July 2006. 1010 [6] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 1011 November 1990. 1013 [7] McCann et al., J., "Path MTU Discovery for IP version 6", 1014 RFC 1981. 1016 [8] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with 1017 Session Description Protocol (SDP)", RFC 3264. 1019 [9] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", 1020 RFC 3548. 1022 [10] "Ogg Vorbis I specification: Codec setup and packet decode. 1023 Available from the Xiph website, 1024 http://xiph.org/vorbis/doc/Vorbis_I_spec.html". 1026 13.2. Informative References 1028 [11] Pfeiffer, S., "The Ogg Encapsulation Format Version 0", 1029 RFC 3533. 1031 [12] "libvorbis: Available from the dedicated website, 1032 http://vorbis.com". 1034 [13] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol 1035 Extended Reports (RTCP XR)", RFC 3611, November 2003. 1037 [14] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg, 1038 "RTP Retransmission Payload Format", RFC 4588, July 2006. 1040 Author's Address 1042 Luca Barbato 1043 Xiph.Org Foundation 1045 EMail: lu_zero@gentoo.org 1046 URI: http://xiph.org/ 1048 Full Copyright Statement 1050 Copyright (C) The IETF Trust (2008). 1052 This document is subject to the rights, licenses and restrictions 1053 contained in BCP 78, and except as set forth therein, the authors 1054 retain all their rights. 1056 This document and the information contained herein are provided on an 1057 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 1058 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 1059 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 1060 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1061 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1062 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1064 Intellectual Property 1066 The IETF takes no position regarding the validity or scope of any 1067 Intellectual Property Rights or other rights that might be claimed to 1068 pertain to the implementation or use of the technology described in 1069 this document or the extent to which any license under such rights 1070 might or might not be available; nor does it represent that it has 1071 made any independent effort to identify any such rights. Information 1072 on the procedures with respect to rights in RFC documents can be 1073 found in BCP 78 and BCP 79. 1075 Copies of IPR disclosures made to the IETF Secretariat and any 1076 assurances of licenses to be made available, or the result of an 1077 attempt made to obtain a general license or permission for the use of 1078 such proprietary rights by implementers or users of this 1079 specification can be obtained from the IETF on-line IPR repository at 1080 http://www.ietf.org/ipr. 1082 The IETF invites any interested party to bring to its attention any 1083 copyrights, patents or patent applications, or other proprietary 1084 rights that may cover technology that may be required to implement 1085 this standard. Please address the information to the IETF at 1086 ietf-ipr@ietf.org. 1088 Acknowledgement 1090 Funding for the RFC Editor function is provided by the IETF 1091 Administrative Support Activity (IASA).