One document matched: draft-perkins-avt-uncomp-video-ext-00.txt

Network Working Group                                         C. Perkins
Internet-Draft                                     University of Glasgow
Expires: January 11, 2006                                  July 10, 2005


 RTP Payload Format for Uncompressed Video: Additional Colour Sampling
                                 Modes
               draft-perkins-avt-uncomp-video-ext-00.txt

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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This memo extends the RTP Payload Format for Uncompressed Video to
   support additional RGB sampling modes.

1.  Introduction

   The RTP Payload Format for Uncompressed Video [1] defines a scheme to
   packetise uncompressed, studio-quality, video streams for transport
   using RTP [2].  A range of standard and high definition video formats



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   are supported, and parameters are defined so sender and receiver can
   signal the image size, colour space, pixel depth, etc.

   A limitation of the format is that the number of bits per sample is
   signalled as being the same for each colour component.  For example,
   it is not possible to signal transport of RGB format video using 5
   bits each for the Red and Blue components and 6 bits for the Green,
   packing one pixel into two octets.  Such video formats can easily be
   supported in the payload format, but cannot be signalled using the
   parameters defined.  This memo extends [1] with additional colour
   sampling modes, to signal such video formats.

2.  Conventions Used in this Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [3].

3.  Payload Format Parameters

   This memo defines six new colour sampling modes that MAY be signalled
   for use with [1].  The new modes are "RGB+", "RG+B", "R+GB", "BGR+",
   "BG+R" and "B+GR".  These sampling modes use the same packing order
   of samples as do the RGB and BGR colour sampling modes respectively,
   except that an additional bit of colour depth is available for the
   component marked by the + symbol (i.e. when "depth=N" is signalled, N
   bits are allocated to unmarked components, but N+1 bits MUST be
   allocated to the marked component).  All other features of the
   payload format remain as defined in [1].

   The primary use of these colour sampling modes is to enable efficient
   packing of data into small pixel groups ("pgroups").  The most common
   use case is expected to be video with five bits per sample, where the
   additional bit of colour depth enables a single pixel to fit into two
   octets without padding.  The new colour sampling modes MAY be used
   for other depths, however, should that prove useful.

4.  Example

   A common uncompressed video format is RGB with 5 bits for the Red and
   Blue components and six bits for the Green component, for a total of
   16 bits per pixel.  Using the sampling modes defined in this memo,
   this can be signalled in SDP according to the following example:








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       v=0
       o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5
       s=-
       c=IN IP4 10.47.16.6
       t=2873397496 2873404696
       a=recvonly
       m=video 51372 RTP/AVP 99
       a=rtpmap:99 raw/90000
       a=fmtp:99 sampling=RG+B; width=1024; height=768; depth=5;
         colorimetry=SMPTE240M

   (some of the lines in have been wrapped due to formatting constraints
   on this memo).

5.  Security Considerations

   The security considerations of [1] apply.  No additional security
   considerations are introduced by support for new colour sampling
   modes.

6.  IANA Considerations

   The video/raw media type is extended with six new values for the
   "sampling" parameter according to the rules defined in section 6.2 of
   [1].  The new values are "RGB+", "RG+B", "R+GB", "BGR+", "BG+R" and
   "B+GR" as described in this memo.

7.  Acknowledgements

   Thanks to Jeremy Searle and Andrew Lee.

8.  Normative References

   [1]  Gharai, L. and C. Perkins, "RTP Payload Format for Uncompressed
        Video", draft-ietf-avt-uncomp-video-06 (work in progress),
        February 2004.

   [2]  Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
        "RTP: A Transport Protocol for Real-Time Applications", STD 64,
        RFC 3550, July 2003.

   [3]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.








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Author's Address

   Colin Perkins
   University of Glasgow
   Department of Computing Science
   17 Lilybank Gardens
   Glasgow  G12 8QQ
   UK

   Email: csp@csperkins.org









































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