Network Working Group                                       K. Kobayashi
Request for Comments: 3189             Communication Research Laboratory
Category: Standards Track                                       A. Ogawa
                                                         Keio University
                                                               S. Casner
                                                           Packet Design
                                                              C. Bormann
                                                 Universitaet Bremen TZI
                                                            January 2002

              RTP Payload Format for DV (IEC 61834) Video

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.


   This document specifies the packetization scheme for encapsulating
   the compressed digital video data streams commonly known as "DV" into
   a payload format for the Real-Time Transport Protocol (RTP).

1. Introduction

   This document specifies payload formats for encapsulating both
   consumer- and professional-use DV format data streams into the Real-
   time Transport Protocol (RTP), version 2 [6].  DV compression audio
   and video formats were designed for helical-scan magnetic tape media.
   The DV standards for consumer-market devices, the IEC 61883 and 61834
   series, cover many aspects of consumer-use digital video, including
   mechanical specifications of a cassette, magnetic recording format,
   error correction on the magnetic tape, DCT video encoding format, and
   audio encoding format [1].  The digital interface part of IEC 61883
   defines an interface on an IEEE 1394 network [2,3].  This
   specification set supports several video formats: SD-VCR (Standard
   Definition), HD-VCR (High Definition), SDL-VCR (Standard Definition -
   Long), PALPlus, DVB (Digital Video Broadcast) and ATV (Advanced
   Television).  North American formats are indicated with a number of
   lines and "/60", while European formats use "/50".  DV standards

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RFC 3189      RTP Payload Format for DV (IEC 61834) Video   January 2002

   extended for professional use were published by SMPTE as 306M and
   314M, for different sampling systems, higher color resolution, and
   faster bit rates [4,5].

   There are two kinds of DV, one for consumer use and the other for
   professional.  The original "DV" specification designed for
   consumer-use digital VCRs is approved as the IEC 61834 standard set.
   The specifications for professional DV are published as SMPTE 306M
   and 314M.  Both encoding formats are based on consumer DV and used in
   SMPTE D-7 and D-9 video systems.  The RTP payload format specified in
   this document supports IEC 61834 consumer DV and professional SMPTE
   306M and 314M (DV-Based) formats.

   IEC 61834 also includes magnetic tape recording for digital TV
   broadcasting systems (such as DVB and ATV) that use MPEG2 encoding.
   The payload format for encapsulating MPEG2 into RTP has already been
   defined in RFC 2250 [7] and others.

   Consequently, the payload specified in this document will support six
   video formats of the IEC standard: SD-VCR (525/60, 625/50), HD-VCR
   (1125/60, 1250/50) and SDL-VCR (525/60, 625/50), and six of the SMPTE
   standards: 306M (525/60, 625/50), 314M 25Mbps (525/60, 625/50) and
   314M 50Mbps (525/60, 625/50).  In the future it can be extended into
   other high-definition formats.

   Throughout this specification, we make extensive use of the
   terminology of IEC and SMPTE standards.  The reader should consult
   the original references for definitions of these terms.

1.1 Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [8].

2. DV format encoding

   The DV format only uses the DCT compression technique within each
   frame, contrasted with the interframe compression of the MPEG video
   standards [9,10].  All video data, including audio and other system
   data, are managed within the picture frame unit of video.

   The DV video encoding is composed of a three-level hierarchical
   structure.  A picture frame is divided into rectangle- or clipped-
   rectangle-shaped DCT super blocks.  DCT super blocks are divided into
   27 rectangle- or square-shaped DCT macro blocks.

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RFC 3189      RTP Payload Format for DV (IEC 61834) Video   January 2002

   Audio data is encoded with PCM format.  The sampling frequency is 32
   kHz, 44.1 kHz or 48 kHz and the quantization is 12-bit non-linear,
   16-bit linear or 20-bit linear.  The number of channels may be up to
   8.  Only certain combinations of these parameters are allowed
   depending upon the video format; the restrictions are specified in
   each document.

   A frame of data in the DV format stream is divided into several "DIF
   sequences".  A DIF sequence is composed of an integral number of 80-
   byte DIF blocks.  A DIF block is the primitive unit for all treatment
   of DV streams.  Each DIF block contains a 3-byte ID header that
   specifies the type of the DIF block and its position in the DIF
   sequence.  Five types of DIF blocks are defined: DIF sequence header,
   Subcode, Video Auxiliary information (VAUX), Audio, and Video.  Audio
   DIF blocks are composed of 5 bytes of Audio Auxiliary data (AAUX) and
   72 bytes of audio data.

   Each RTP packet starts with the RTP header as defined in RFC 1889
   [6].  No additional payload-format-specific header is required for
   this payload format.

2.1 RTP header usage

   The RTP header fields that have a meaning specific to the DV format
   are described as follows:

   Payload type (PT): The payload type is dynamically assigned by means
   outside the scope of this document.  If multiple DV encoding formats
   are to be used within one RTP session, then multiple dynamic payload
   types MUST be assigned, one for each DV encoding format.  The sender
   MUST change to the corresponding payload type whenever the encoding
   format is changed.

   Timestamp: 32-bit 90 kHz timestamp representing the time at which the
   first data in the frame was sampled.  All RTP packets within the same
   video frame MUST have the same timestamp.  The timestamp SHOULD
   increment by a multiple of the nominal interval for one frame time,
   as given in the following table:

       Mode        Frame rate (Hz)      Increase of one frame
                                        in 90kHz timestamp

      525-60         29.97                   3003
      625-50         25                      3600
      1125-60        30                      3000
      1250-50        25                      3600

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RFC 3189      RTP Payload Format for DV (IEC 61834) Video   January 2002

   When the DV stream is obtained from an IEEE 1394 interface, the
   progress of video frame times MAY be monitored using the SYT
   timestamp carried in the CIP header as specified in IEC 61883 [2].

   Marker bit (M): The marker bit of the RTP fixed header is set to one
   on the last packet of a video frame, and otherwise, must be zero.
   The M bit allows the receiver to know that it has received the last
   packet of a frame so it can display the image without waiting for the
   first packet of the next frame to arrive to detect the frame change.
   However, detection of a frame change MUST NOT rely on the marker bit
   since the last packet of the frame might be lost.  Detection of a
   frame change MUST be based on a difference in the RTP timestamp.

2.2 DV data encapsulation into RTP payload

   Integral DIF blocks are placed into the RTP payload beginning
   immediately after the RTP header.  Any number of DIF blocks may be
   packed into one RTP packet, except that all DIF blocks in one RTP
   packet must be from the same video frame.  DIF blocks from the next
   video frame MUST NOT be packed into the same RTP packet even if more
   payload space remains.  This requirement stems from the fact that the
   transition from one video frame to the next is indicated by a change
   in the RTP timestamp.  It also reduces the processing complexity on
   the receiver.  Since the RTP payload contains an integral number of
   DIF blocks, the length of the RTP payload will be a multiple of 80

   Audio and video data may be transmitted as one bundled RTP stream or
   in separate RTP streams (unbundled).  The choice MUST be indicated as
   part of the assignment of the dynamic payload type and MUST remain
   unchanged for the duration of the RTP session to avoid complicated
   procedures of sequence number synchronization.  The RTP sender MAY
   omit DIF-sequence header and subcode DIF blocks from a stream since
   the information is either known out-of-band or may not be required
   for RTP transport.  When sending DIF-sequence header and subcode DIF
   blocks, both types of blocks MUST be included in the video stream.

   DV streams include "source" and "source control" packs that carry
   information indispensable for proper decoding, such as aspect ratio,
   picture position, quantization of audio sampling, number of audio
   channels, audio channel assignment, and language of the audio.
   However, describing all of these attributes with a signaling protocol
   would require large descriptions to enumerate all the combinations.
   Therefore, no Session Description Protocol (SDP) [13] parameters for
   these attributes are defined in this document.  Instead, the RTP
   sender MUST transmit at least those VAUX DIF blocks and/or audio DIF
   blocks with AAUX information bytes that include "source" and "source
   control" packs containing the indispensable information for decoding.

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RFC 3189      RTP Payload Format for DV (IEC 61834) Video   January 2002

   In the case of one bundled stream, DIF blocks for both audio and
   video are packed into RTP packets in the same order as they were

   In the case of an unbundled stream, only the header, subcode, video
   and VAUX DIF blocks are sent within the video stream.  Audio is sent
   in a different stream if desired, using a different RTP payload type.
   It is also possible to send audio duplicated in a separate stream, in
   addition to bundling it in with the video stream.

   When using unbundled mode, it is RECOMMENDED that the audio stream
   data be extracted from the DIF blocks and repackaged into the
   corresponding RTP payload format for the audio encoding (DAT12, L16,
   L20) [11,12] in order to maximize interoperability with non-DV-
   capable receivers while maintaining the original source quality.

   In the case of unbundled transmission where both audio and video are
   sent in the DV format, the same timestamp SHOULD be used for both
   audio and video data within the same frame to simplify the lip
   synchronization effort on the receiver.  Lip synchronization may also
   be achieved using reference timestamps passed in RTCP as described in
   RFC 1889 [6].

   The sender MAY reduce the video frame rate by discarding the video
   data and VAUX DIF blocks for some of the video frames.  The RTP
   timestamp must still be incremented to account for the discarded
   frames.  The sender MAY alternatively reduce bandwidth by discarding
   video data DIF blocks for portions of the image which are unchanged
   from the previous image.  To enable this bandwidth reduction,
   receivers SHOULD implement an error concealment strategy to
   accommodate lost or missing DIF blocks, e.g., repeating the
   corresponding DIF block from the previous image.

3. SDP Signaling for RTP/DV

   When using SDP (Session Description Protocol) [13] for negotiation of
   the RTP payload information, the format described in this document
   SHOULD be used.  SDP descriptions will be slightly different for a
   bundled stream and an unbundled stream.

   When a DV stream is sent to port 31394 using RTP payload type
   identifier 111, the m=?? line will be like:

      m=video 31394 RTP/AVP 111

   The a=rtpmap attribute will be like:

      a=rtpmap:111 DV/90000

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RFC 3189      RTP Payload Format for DV (IEC 61834) Video   January 2002

   "DV" is the encoding name for the DV video payload format defined in
   this document.  The "90000" specifies the RTP timestamp clock rate,
   which for the payload format defined in this document is a 90kHz

   In SDP, format-specific parameters are defined as a=fmtp, as below:


   In the DV video payload format, the a=fmtp line will be used to show
   the encoding type within the DV video and will be used as below:

      a=fmtp: encode=

   The required parameter  specifies which type of DV
   format is used.  The DV format name will be one of the following:


   In order to show whether the audio data is bundled into the DV stream
   or not, a format specific parameter is defined as below:

      a=fmtp: audio=