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Versions: 05 06 07 08 RFC 2029

Internet Engineering Task Force                 Michael F. Speer
Audio-Video Transport Working Group             Don Hoffman
draft-ietf-avt-cellb-08.txt                     Sun Microsystems, Inc.
                                                July 7th, 1996
                                                Expires: January 7th, 1997


            RTP Payload Format of Sun's CellB Video Encoding

                          Status of this Memo

This document is an Internet Draft.  Internet Drafts are working documents
of the Internet Engineering Task Force (IETF), its Areas, and its Working
Groups.   Note that other groups may also distribute working documents as
Internet Drafts.

Internet Drafts are draft documents valid for a maximum of six months.
Internet Drafts may be updated, replaced, or obsoleted by other documents
at any time.   It is not appropriate to use Internet Drafts as reference
material or to cite them other than as a ``working draft'' or ``work in
progress.''

Please check the I-D abstract listing contained in each Internet Draft
directory to learn the current status of this or any other Internet Draft.

Distribution of this document is unlimited.

                                Abstract

        This draft describes a packetization scheme for the CellB video
        encoding. The scheme proposed allows applications to transport
        CellB video flows over protocols used by RTP.  This document is
        meant for implementors of video applications that want to use RTP
        and CellB.

















draft-ietf-avt-cellb-08.txt                                     [Page 1]


INTERNET-DRAFT           CellB Payload Format                  July 1996


1 Introduction

The Cell image compression algorithm is a variable bit-rate video
coding scheme.  It provides "high" quality, low bit-rate image
compression at low computational cost.   The bytestream that is
produced by the Cell encoder consists of instructional codes and
information about the compressed image.

For futher information on Cell compression technology, refer to [1].
Currently, there are two versions of the Cell compression technology:
CellA and CellB.  CellA is primarily designed for the encoding of
stored video intended for local display, and will not be discussed in
this memo.

CellB, derived from CellA, has been optimized for network-based video
applications.  It is computationally symmetric in both encode and
decode.  CellB utilizes a fixed colormap and vector quantization
techniques in the YUV color space to achieve compression.

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                     |
|                             ....                              |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+




draft-ietf-avt-cellb-08.txt                                     [Page 2]


INTERNET-DRAFT           CellB Payload Format                  July 1996


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.





































draft-ietf-avt-cellb-08.txt                                     [Page 3]


INTERNET-DRAFT           CellB Payload Format                  July 1996


3 References

        1.      "Cell Image Compression Byte Stream Description,"
                ftp://playground.sun.com:/pub/multimedia/video/
                cellbytestream.ps.Z

        2.      Thierry Turletti, Christian Huitema INRIA, "RTP
                Packetization of H.261 Video Streams", Internet Draft,
                March 8th, 1995.

        3.      H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson,
                "RTP: A Transport Protocol for Real-Time Applications",
                Internet RFC 1889

        4.      H. Schulzrinne, "RTP Profile for Audio and Video Conferences
                with Minimal Control", Internet RFC 1890


4 Address of the Authors

        Michael F. Speer
        Sun Microsystems Computer Corporation
        2550 Garcia Ave MailStop UMPK14-305
        Mountain View, CA 94043

        Voice: +1 415 786 6368
        Fax: +1 415 786 6445
        E-mail: michael.speer@eng.sun.com

        Don Hoffman
        Sun Microsystems Computer Corporation
        2550 Garcia Ave MailStop UMPK14-305
        Mountain View, CA 94043

        Voice: +1 415 786 6370
        Fax: +1 415 786 6445
        E-mail: don.hoffman@eng.sun.com














draft-ietf-avt-cellb-08.txt                                     [Page 4]


INTERNET-DRAFT           CellB Payload Format                  July 1996


Appendix A - Structure of the CellB Video Stream

The CellB bytestream consists of cell codes, skip codes and
quantization-table specific codes.  These are now described.

A.1 CellB Cell Code

Cell codes are 4 bytes in length, and describe a 4x4 pixel cell.  There
are two possible luminance (Y) levels for each cell, but only one pair
of chrominance (UV) values.  The CellB cell code is shown below:


 0                   1                   2                   3
 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 M M M M M M M M M M M M M M M|U V U V U V U V|Y Y Y Y Y Y Y Y|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             4x4 Bitmask             U/V Code       Y/Y Code

The first two bytes of the cell code are a bitmask.  Each bit in the
mask represents a pixel in a 16-pixel cell.  Bit 0 represents the value
of the upper right-hand pixel of the cell, and subsequent bits represent
the pixels in row-major order.  If a pixel's bit is set in the 4x4
Bitmask, then the pixel will be rendered with the pixel value <Y(1), U,
V>.  If the pixel's bit is not set in the bitmask, then the pixel's
value will be rendered with the value <Y(0), U, V>.  The bitmask for
the cell is normalized so that the most significant bit is always 0 (i.e.,
corresponding to <Y(0), U, V>).

The U/V field of the cell code represents the chrominance component.  This
code is in index into a table of vectors that represents two independent
components of chrominance.

The Y/Y field of the cell code represents two luminance values (Y(0) and Y(1)).
This code is an index into a table of two-compoment luminance vectors.

The derivation of the U/V and Y/Y tables is outside the scope of this
memo. A complete discussion can be found in [1].


A.2 CellB Skip Code

The single byte CellB skip code tells the CellB decoder to skip the
next S+1 cells in the current video frame being decoded.  The maximum
number of cells that can be skipped is 32.  The format of the skip code
is shown below.

                         0 1 2 3 4 5 6 7



draft-ietf-avt-cellb-08.txt                                     [Page 5]


INTERNET-DRAFT           CellB Payload Format                  July 1996


                        +-+-+-+-+-+-+-+-+
                        |1 0 0 S S S S S|
                        +-+-+-+-+-+-+-+-+

A.3 CellB Y/Y Table Code

The single byte "new Y/Y table" code is used to tell the decoder that the
next 512 bytes are a new Y/Y quantization table.  The code and the
representation of the table are shown below.  The sample encoder/decoder pair
in this document do not implement this feature of the CellB compression.
However, future CellB codecs may implement this feature.

                         0 1 2 3 4 5 6 7
                        +-+-+-+-+-+-+-+-+
                        |1 1 1 1 1 1 1 0|
                        +-+-+-+-+-+-+-+-+

The format of the new Y/Y table is:

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Y1_000     |    Y2_000     |   Y1_001      |   Y2_001      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                .
                .
                .

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Y1_254     |    Y2_254     |   Y1_255      |   Y2_255      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A.4 CellB U/V Table Code

The single byte "new U/V table" code is used to tell the decoder that the
next 512 bytes represent a new U/V quantization table.  The code is shown
below.  The sample encoder/decoder pair provided in this document do not
implement this feature of the CellB compression. However, future CellB
codecs may implement this feature.

                         0 1 2 3 4 5 6 7
v                        +-+-+-+-+-+-+-+-+
                        |1 1 1 1 1 1 1 1|
                        +-+-+-+-+-+-+-+-+




draft-ietf-avt-cellb-08.txt                                     [Page 6]


INTERNET-DRAFT           CellB Payload Format                  July 1996


The bytes of the new U/V quantization table are arranged as:

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    U_000      |    V_000      |   U_001       |   V_001       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                .
                .
                .

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    U_254      |    V_254      |   U_255       |   V_255       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


































draft-ietf-avt-cellb-08.txt                                     [Page 7]


INTERNET-DRAFT           CellB Payload Format                  July 1996


Appendix B - Availability of CellB

It is the viewpoint of Sun Microsystems, Inc, that CellB is publically
available for use without any license.















































draft-ietf-avt-cellb-08.txt                                     [Page 8]


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