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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET-DRAFT Katsushi Kobayashi 2 draft-ietf-avt-dv-video-01.txt Communication Research Laboratory 3 Akimichi Ogawa 4 Keio University 5 Stephen Casner 6 Cisco Systems 7 Carsten Bormann 8 Universitaet Bremen TZI 9 October 18, 1999 10 Expires March 2000 12 RTP Payload Format for DV Format Video 14 Status of this Memo 16 This document is an Internet-Draft and is in full conformance with all 17 provisions of Section 10 of RFC2026. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet- Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 1. Abstract 37 This document specifies the packetization scheme for encapsulating DV 38 compressed digital video data streams, commonly known as "DV", into a 39 payload format for the Real-Time Transport Protocol (RTP). There are 40 two kinds of DV format, one for consumer use and other for 41 professional. The original "DV" specification designed for consumer 42 use digital VCR is approved as IEC61834 standard sets. The 43 specifications for professional are also published as SMPTE 306M(D-7) 44 and 314M(D-9), the both are based on the consumer DV. The RTP 45 payload format specified in this document supports IEC61834 consumer 46 DV and professional SMPTE 306M and 314M(DV-Based) formats. 48 2. Introduction 49 DV compression video formats are designed for the recording format 50 of helical-scan magnetic tape media. The DV format only uses intra- 51 frame DCT compression technique, not using an interframe compression 52 different from MPEG. The DV standard for consumer market device 53 approved as IEC61834 series that comprises the whole specification of 54 consumer use digital video including mechanical specifications of a 55 cassette, helical magnetic recording format, error correction in the 56 magnetic tape, DCT video encoding format, and audio encoding 57 format[1]. And the digital interface specifications part splitted DV 58 standard are published as IEC61883 series that defines an interface 59 on IEEE1394 network[2,3]. The IEC specification set supports several 60 video formats: SD-VCR (including 525/60, 625/50), HD-VCR (1125/60, 61 1250/50), SDL-VCR (525/60, 625/50), PALPlus, DVB (Digital Video 62 Broadcast) and ATV (Advanced Television). 64 The other DV standard supposing professional use are published by 65 SMPTE as 306M and 314M. Both standards are based on the IEC61834 DV 66 standard and defines D-7 system (525/60, 625/50) and D-9 system 67 (525/60 25Mbps, 625/50 25Mbps, 525/60 50Mbps, 625/50 50Mbps)[4,5]. 69 This document basically specifies the RTP payload format for 70 encapsulating both consumer and professional use DV format data 71 streams into the Real-time Transport Protocol (RTP), version 2 [6]. 72 However, IEC61834 covers magnetic tape recording for digital TV 73 broadcasting system as DVB and ATV that are used in MPEG2 encoding. 74 The payload format for encapsulating MPEG2 into RTP has already been 75 defined in RFC 2250[7]. That RFC2250 payload format can provide more 76 optimized way for transmitting MPEG2 stream over the Internet than 77 would be encapsulation of MPEG2 first into the DVB or ATV and then 78 into RTP. Therefore, the packetization way of DV formats based on 79 MPEG2 is outside the scope of this document. 81 Consequently, the payload format specified in this document will 82 support the six video formats of the IEC standard: SD-VCR (525/60, 83 625/50), HD-VCR (1125/60, 1250/50) and SDL-VCR (525/60, 625/50), and 84 six SMPTE standard: D-7(525/60, 625/50), D-9 25Mbps(525/60, 625/50) 85 and D-9 50Mbps (525/60, 625/50). 87 Throughout this specification, we make extensive use of the 88 terminology of IEC and SMPTE standard. The reader should consult the 89 original references for definitions of these terms. 91 3. DV format encoding 93 The DV format is designed for magnetic tape applications and is 94 optimized in helical magnetic recording on tape media. All video 95 data including audio and other system data are managed within the 96 picture frame unit of video. 98 The DV encoding is composed of a three-level hierarchical structure. 99 A picture frame is divided into rectangle- or clipped-rectangle- 100 shaped DCT super blocks. DCT super blocks are divided into 27 101 rectangle- or square-shaped DCT macro blocks. Audio data part is 102 encoded with PCM format. Its frequency is 32 kHz, 44.1 kHz or 48 kHz, 103 the quantization is 16-bit linear, 12-bit non-linear or 20-bit 104 linear, and the number of channels may up to 8. Only certain 105 combinations of these parameters are allowed depending upon the video 106 format, the restrictions are specified in each document. A frame of 107 data in the DV format stream is divided into several "DIF sequence." 108 A DIF sequence is composed of an integral number of 80 bytes length 109 DIF blocks. A DIF block is the primitive unit for all treatment of DV 110 stream. Each DIF block contains a 3-byte ID header that specifies the 111 type of the DIF block and its position in the DIF sequence. Five 112 types of DIF blocks are defined: DIF sequence header, Subcode, Video 113 Auxiliary information (VAUX), Audio and Video. Audio DIF block data 114 are also composed of 5 bytes Audio Auxiliary data (AAUX) and 72 bytes 115 audio data. 117 Each RTP packet starts with the RTP header as defined in RFC 1889 118 [6]. No additional payload-format-specific header is required for 119 this payload format. 121 4.1 RTP header usage 123 The meaning of RTP header fields that are specific to the DV format 124 is described in the following: 126 Payload type (PT): The payload type is dynamically assigned by means 127 outside the scope of this document. If multiple encoding formats are 128 to be used within one RTP session, then multiple dynamic payload 129 types MUST be assigned, one for each DV encoding format. The sender 130 MUST change to the corresponding payload type whenever the encoding 131 format is changed. Although VAUX data contains some encoding 132 attributes of the stream, the sender MUST NOT expect to notify the 133 receiver of an encoding format change with the information included 134 in VAUX. Because VAUX data only represents sub attribute information 135 which relies on the video encoding format. Even if VAUX data is 136 received, the receiver cannot obtain the attribute until the video 137 encoding format is determined. 139 Timestamp: 32-bit 90 kHz timestamp representing the time at which the 140 first data in the frame was sampled. All RTP packets within the same 141 video frame MUST have the same timestamp. The timestamp SHOULD 142 increment by a multiple of the nominal interval for one frame time, 143 as given in the following table: 145 Mode Frame rate (Hz) Increase of one frame 146 in 90kHz timestamp 148 525-60 29.97 3003 149 625-50 25 3600 150 1125-60 30 3000 151 1250-50 25 3600 153 When getting DV stream from IEEE1394 interface the progress of video 154 frame times MAY be monitored using the SYT timestamp carried in the 155 CIP header, as described in Appendix A. 157 Marker bit (M): The marker bit of the RTP fixed header is set to one 158 on the last packet of a video frame, and otherwise, must be zero. 159 The M bit allows the receiver to know that it has received the last 160 packet of a frame so it can display the image without waiting for the 161 first packet of the next frame to arrive to detect the frame change. 162 However, detection of a frame change MUST NOT rely on the marker bit 163 since the last packet of the frame might be lost. Detection of a 164 frame change MUST be done by differences in RTP timestamp. 166 4.2 DV data encapsulation into RTP payload 168 Integral DIF blocks are placed into the RTP payload beginning 169 immediately after the RTP header. Any number of DIF blocks may be 170 packed into one RTP packet, except that all DIF blocks in one RTP 171 packet must be from the same video frame. DIF blocks from the next 172 video frame MUST NOT be packed into the same RTP packet even if there 173 is more payload space remaining. This requirement stems from the 174 fact the transition from one video frame to the next is indicated by 175 a change in the RTP timestamp. It also reduces the processing 176 complexity on the receiver. Since the RTP payload contains an 177 integral number of DIF blocks, the length of the RTP payload will be 178 a multiple of 80 bytes. 180 Audio and video data may be transmitted as one bundled RTP stream or 181 in separate RTP streams(unbundled). The choice MUST be indicated as 182 part of the assignment of the dynamic payload type and MUST remain 183 unchanged for the duration of the RTP session to avoid complicated 184 procedures of sequence number synchronization. 186 In the case of one bundled stream, DIF blocks for both audio and 187 video are packed into RTP packets in the same order as they were 188 generated. When audio and video are sent with unbundled streams, or 189 when only one medium is sent, then only the DIF blocks corresponding 190 to the selected medium are included. If VAUX DIF blocks are 191 included, they MUST only be sent in the video stream. When using 192 unbundled mode, it is RECOMMENDED that the audio stream data be 193 extracted from the DIF blocks and repackaged into the corresponding 194 RTP payload format for the audio encoding (L16, NL12, L20) in order 195 to maximize interoperability with non-DV-capable receivers within the 196 original source quality [8,9]. 198 In the case of unbundled transmission, the same timestamp SHOULD be 199 used for both audio and video data within the same frame to simplify 200 the lip synchronization effort on the receiver. Lip synchronization 201 may also be achieved using reference timestamps passed in RTCP as 202 described in RFC1889[6]. 204 The sender MAY send null AAUX information and omit VAUX DIF blocks if 205 the VAUX/AAUX information remains constant during the session. 206 However, the VAUX/AAUX information in the DV stream includes source 207 encoding parameters, such as video display aspect ratio, audio 208 quantization and number of audio channels, which are required to 209 decode the stream. Therefore, if VAUX/AAUX information is not 210 transmitted in the stream, the equivalent parameters essential to 211 playout MUST be provided by some out of band means beyond the scope 212 of this document. The receiver MUST be able to process a data stream 213 with null AAUX information and null or omitted VAUX DIF blocks if the 214 equivalent parameters are provided out of band. Therefore, if the 215 RTP receiver is feeding the DV stream to a device that requires AAUX 216 information and VAUX DIF blocks, the receiver MUST be able to 217 generate AAUX within audio DIF blocks and VAUX DIF blocks for the 218 device using the parameters provided out of band. 220 The sender MAY reduce the video frame rate by discarding the video 221 data and VAUX DIF blocks for some of the video frames. The RTP 222 timestamp must still be incremented to account for the discarded 223 frames. The sender MAY alternatively reduce bandwidth by discarding 224 video data DIF blocks for portions of the image which are unchanged 225 from the previous image. To enable this bandwidth reduction, 226 receivers SHOULD implement an error concealment strategy to 227 accommodate lost or missing DIF blocks by repeating the corresponding 228 DIF block from the previous image. 230 5. SDP Signaling for RTP/DV 232 When using SDP(Session Description Protocol) for negotiation of the 233 RTP payload information, the format described in this document SHOULD 234 be used. SDP description will be slightly different for a bundled 235 stream and an unbundled stream. 237 5.1 SDP description for unbundled stream 239 When using an unbundled stream, an RTP stream for video and audio 240 will be sent separately to a different port or a different multicast 241 group. When this is done, SDP carries several m=?? lines which is for 242 media type of the stream (see RFC2327[10]). For example, when audio 243 is sent by port 31394 and RTP payload type identifier 111, the m=?? 244 line will be like; 246 m=video 31394 RTP/AVP 111 248 The a=rtpmap attribute will be like; 250 a=rtpmap:111 DV/90000 252 "DV" is the encoding name for the DV video payload format defined in 253 this document. 90000 shows the clock rate. The clock used for the 254 payload format defined in this document uses 90kHz clock. 256 In SDP, format specific parameters are defined as a=fmtp, as below. 258 a=fmtp: 260 In the DV video payload format, the a=fmtp line will be used to show 261 the encoding type within the DV video and will be used as below. 263 a=fmtp: v-encode: 265 The block with the parameters, is used to 266 describe which type of DV format is used. The parameters for will be one of the following; 269 o SD-VCR/525-60 270 o SD-VCR/625-50 271 o HD-VCR/1125-60 272 o HD-VCR/1250-50 273 o SDL-VCR/525-60 274 o SDL-VCR/625-50 275 o 306M/525-60 276 o 306M/625-50 277 o 314M-25/525-60 278 o 314M-25/625-50 279 o 314M-50/525-60 280 o 314M-50/625-50 282 An example of SDP description using these attributes is: 284 v=0 285 o=mhandley 2890844526 2890842807 IN IP4 126.16.64.4 286 s=SDP Seminar 287 i=A Seminar on the session description protocol 288 u=http://www.cs.ucl.ac.uk/staff/M.Handley/sdp.03.ps 289 e=mjh@isi.edu (Mark Handley) 290 c=IN IP4 224.2.17.12/127 291 t=2873397496 2873404696 292 m=audio 49170 RTP/AVP 112 293 a=rtpmap:112 L16/32000/2 294 m=video 50000 RTP/AVP 113 295 a=rtpmap:113 DV/90000 296 a=fmtp:113 encode:SD-VCR/525-60 298 This describes a session where audio and video streams are sent 299 separately. The session is sent to a multicast group 224.2.17.12. The 300 audio is sent using L16 format, and the video is sent using SD-VCR 301 525/60 format which corresponds to NTSC format in consumer DV. 303 5.2 SDP description for bundled stream 305 When sending a bundled stream, all of DIF blocks including system 306 data will be sent through a single RTP stream. Too many audio format 307 attributes are defined in DV, such as sampling,quantization, number 308 of audio channel, channel assignment, language, emphasis and the 309 picture flame locking. These attribute information are carried as 310 AAUX data within audio DIF blocks. Describing all these attributes 311 with SDP requires large number of entry definition corresponding each 312 attribute, and also requires larger size of SDP record to enumerate 313 the combination of attribute. Therefore, the entry to describe audio 314 format attribute does not define in DV over RTP. The attribute 315 information for audio and video format is taken from AAUX data 316 carried within audio data and VAUX DIF blocks, respectively. The 317 AAUX and VAUX data associated with the encoding attribute are 318 multiply contained within one picture frame. Even if the AAUX and 319 VAUX data are lost, the receiver can recover the lost part with other 320 data in the same video frame. In order for the receiver to know 321 audio format information, the RTP sender MUST transmit AAUX data into 322 the audio stream at least AAUX source and AAUX source control pack 323 when using this mode. The encoding name for bundled DV streams is 324 defined as "BDV" in this document. The a=rtpmap attribute in the 325 session information will be like as: 327 a=rtpmap:111 BDV/90000 329 The parameters to represent the DV video encoding format will use 330 "fmtp" attribute and the same format will be used described in 5.1. 332 An example of SDP description for bundled DV stream is : 334 v=0 335 o=mhandley 2890844526 2890842807 IN IP4 126.16.64.4 336 s=SDP Seminar 337 i=A Seminar on the session description protocol 338 u=http://www.cs.ucl.ac.uk/staff/M.Handley/sdp.03.ps 339 e=mjh@isi.edu (Mark Handley) 340 c=IN IP4 224.2.17.12/127 341 t=2873397496 2873404696 342 m=video 49170 RTP/AVP 112 113 343 a=rtpmap:112 BDV/90000 344 a=fmtp: 112 encode:SD-VCR/525-60 345 a=fmtp: 113 encode:306M/525-60 347 Above SDP record describes a session where audio and video streams 348 are sent bundled. The session is sent to a multicast group 349 224.2.17.12. The video is sent using 525/60 consumer DV and 350 SMPTE306M format, when the payload type is 112 and 113, respectively. 352 6. Security Considerations 354 RTP packets using the payload format defined in this specification 355 are subject to the security considerations discussed in the RTP 356 specification [6], and any appropriate RTP profile. This implies 357 that confidentiality of the media streams is achieved by encryption. 358 Because the data compression used with this payload format is applied 359 to end-to-end, encryption may be performed after compression so there 360 is no conflict between the two operations. 362 A potential denial-of-service threat exists for data encodings using 363 compression techniques that have non-uniform receiver-end 364 computational load. The attacker can inject pathological datagrams 365 into the stream which are complex to decode and cause the receiver to 366 be overloaded. However, this encoding does not exhibit any 367 significant non-uniformity. 369 As with any IP-based protocol, in some circumstances a receiver may 370 be overloaded simply by the receipt of too many packets, either 371 desired or undesired. Network-layer authentication may be used to 372 discard packets from undesired sources, but the processing cost of 373 the authentication itself may be too high. In a multicast 374 environment, pruning of specific sources may be implemented in future 375 versions of IGMP [11] and in multicast routing protocols to allow a 376 receiver to select which sources are allowed to reach it. 378 7. Full Copyright Statement 380 Copyright (C) The Internet Society (1999). All Rights Reserved. 382 This document and translations of it may be copied and furnished to 383 others, and derivative works that comment on or otherwise explain it 384 or assist in its implementation may be prepared, copied, published 385 and distributed, in whole or in part, without restriction of any 386 kind, provided that the above copyright notice and this paragraph are 387 included on all such copies and derivative works. 389 However, this document itself may not be modified in any way, such as 390 by removing the copyright notice or references to the Internet Soci- 391 ety or other Internet organizations, except as needed for the purpose 392 of developing Internet standards in which case the procedures for 393 copyrights defined in the Internet Standards process must be fol- 394 lowed, or as required to translate it into languages other than 395 English. 397 The limited permissions granted above are perpetual and will not be 398 revoked by the Internet Society or its successors or assigns. 400 This document and the information contained herein is provided on an 401 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 402 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 403 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 404 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MER- 405 CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." 407 8. Authors' Addresses 409 Katsushi Kobayashi Communication Research Laboratory 4-2-1 Nukii-kita 410 machi, Koganei Tokyo 184-8795 JAPAN EMail: ikob@koganei.wide.ad.jp 412 Akimichi Ogawa Keio University 5322 Endo, Fujisawa Kanagawa 252 JAPAN 413 EMail: akimichi@sfc.wide.ad.jp 415 Stephen L. Casner Cisco Systems, Inc. 170 West Tasman Drive San 416 Jose, CA 95134-1706 United States EMail: casner@cisco.com 418 Carsten Bormann Universitaet Bremen FB3 TZI Postfach 330440 D-28334 419 Bremen, GERMANY Phone: +49.421.218-7024 Fax: +49.421.218-7000 EMail: 420 cabo@tzi.org 422 9. Bibliography 424 [1] IEC 61834, Helical-scan digital video cassette recording system 425 using 6,35 mm magnetic tape for consumer use (525-60, 625-50, 426 1125-60 and 1250-50 systems) 428 [2] IEC 61883, Consumer audio/video equipment - Digital interface 430 [3] IEEE Std 1394-1995, Standard for a High Performance Serial Bus 432 [4] SMPTE 306M, 6.35-mm type D-7 component format - video 433 compression at 25Mb/s -525/60 and 625/50 435 [5] SMPTE 314M, Data structure for DV-based audio and compressed 436 video 25 and 50Mb/s 438 [6] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson.,"RTP: A 439 transport protocol for real-time applications", January 1996. 440 RFC1889. 442 [7] D. Hoffman, G. Fernando, V. Goyal and M. Civanlar, "RTP Payload 443 Format for MPEG1/MPEG2 Video", RFC 2250, January 1998 445 [8] Schulzrinne, H., "RTP Profile for Audio and Video Conferences 446 with Minimal Control", RFC 1890, January 1996. 448 [9] K. Kobayashi, A. Ogawa, S. Casner and C. Bormann, "RTP Payload 449 Format for nonlinear 12 bits and 20 bits Audio", internet-draft, 450 work in progress. 452 [10] M.Handley, V.Jacobson, "SDP: Session Description Protocol", 453 RFC 2327, April 1998 455 [11] Deering, S., "Host Extensions for IP Multicasting", STD 5, 456 RFC 1112, August 1989. 458 Appendix A. Sequence number difference in DV over IEEE 1394 460 The specification of the Digital Interface defines a transport 461 protocol for transmission of video stream data in the isochronous 462 stream mode of IEEE 1394 called "real time data transmission 463 protocol". The protocol defines the general Common Isochronous 464 Packet (CIP) header that does not depend on the encoding format of 465 the payload. Several real time transmission encodings have been 466 defined on CIP, including MPEG2 and MIDI in addition to DV format 467 [1,2]. All of the information in the CIP header is either implicit in 468 the RTP payload format or supplanted by information in the RTP 469 header, so the CIP header is not required. For this payload format, 470 the CIP header MUST be removed from IEEE 1394 packet, leaving just a 471 sequence of DIF blocks. 473 The CIP header for DV video includes SYT field. The SYT is a 16-bit 474 timestamp copied from lower 16 bits of CYCLE_TIME register defined in 475 IEEE 1394. The CYCLE_TIME register is incremented by a 24.576 MHz 476 clock, but the lower 12 bits count to a maximum of 3071 before 477 wrapping around to zero and adding a carry to the high 4 bits. 478 Therefore, the SYT timestamp is not increment in linear. The RTP 479 timestamp could be derived from the SYT in the CIP header, but 480 implementer must care the non-linear behavior of SYT field. 482 If the encoding format requires synchronization between devices 483 connected within same IEEE 1394 network, it should adopt the CIP 484 header with SYT. The CIP header of DV is reserved SYT field, but the 485 valid SYT timestamp value is required only once in each video frames. 486 In the remaining CIP headers, the SYT field may fill with the "no 487 information" value (all ones).