RFC 2029 (rfc2029) - Page 2 of 6


RTP Payload Format of Sun's CellB Video Encoding



Alternative Format: Original Text Document



RFC 2029                   RTP Payload Format               October 1996


2. Network Packetization and Encapsulation

2.1 RTP Usage

   The RTP timestamp is in units of 90KHz. The same timestamp value is
   used for all packet payloads of a frame.  The RTP maker bit denotes
   the end of a frame.

2.2 CellB Header

   The packetization of the CellB bytestream is designed to make the
   resulting packet stream robust to packet loss.  To achieve this goal,
   an additional header is added to each RTP packet to uniquely identify
   the location of the first cell of the packet within the current
   frame.  In addition, the width and height of the frame in pixels is
   carried in each CellB packet header.  Although the size can only
   change between frames, it is carried in every packet to simplify the
   packet encoding.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Cell X Location         |      Cell Y Location          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Width of Image          |      Height of Image          |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |                     Compressed CellB Data                     |
   |                             ....                              |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+

   All fields are 16-bit unsigned integers in network byte order, and
   are placed at the beginning of the payload for each RTP packet.  The
   Cell X and the Cell Y Location coordinates are expressed as cell
   coordinates, not pixel coordinates. Since cells represent 4x4 blocks
   of pixels, the X or Y dimension of the cell coordinates range in
   value from 0 through 1/4 of the of the same dimension in pixel
   coordinates.

2.3 Packetization Rules

   A packet can be of any size chosen by the implementor, up to a full
   frame.  All multi-byte codes must be completely contained within a
   packet.  In general, the implementor should avoid packet sizes that
   result in fragmentation by the network.







Speer & Hoffman             Standards Track