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rfc:rfc4421

Network Working Group C. Perkins Request for Comments: 4421 University of Glasgow Updates: 4175 February 2006 Category: Standards Track

             RTP Payload Format for Uncompressed Video:
                  Additional Colour Sampling Modes

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 (2006).

Abstract

 The RFC Payload Format for Uncompressed Video, RFC 4175, defines a
 scheme to packetise uncompressed, studio-quality, video streams for
 transport using RTP.  This memo extends the format to support
 additional colour 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
 is supported, and parameters are defined so sender and receiver can
 negotiate the image size, colour space, pixel depth, and colour
 sampling mode.
 A limitation of the signalling is that the number of bits per sample
 is assumed to be the same for each colour component.  For example, it
 is possible to signal video using RGB colour sampling with 8 bits for
 each of the Red, Green, and Blue components (24 bits per pixel), but
 not video using RGB colour sampling with 5 bits each for the Red and
 Blue components, but 6 bits for the Green component (16 bits per
 pixel).  Such video formats can easily be transported by 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.

Perkins Standards Track [Page 1] RFC 4421 RTP Payload for Uncompressed Video February 2006

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
 (Section 4.3 of [1]), except that an additional bit per sample of
 colour depth MUST be used for the component marked by the + symbol.
 The mandatory parameter "depth=N" indicates that N bits per sample
 are used by the unmarked components, but N+1 bits are used by the
 marked component.  All other features of the payload format are 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 "depth=5", where the additional
 bit of colour depth for the marked component 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 6 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 Session Description Protocol (SDP) according to
 the following example:
     v=0
     o=jdoe 2890844526 2890842807 IN IP4 192.0.2.5
     s=-
     c=IN IP4 192.0.2.6
     t=2873397496 2873404696
     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
 The last line has been wrapped due to formatting constraints of this
 memo, and forms one complete line in the SDP file.

Perkins Standards Track [Page 2] RFC 4421 RTP Payload for Uncompressed Video February 2006

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 at Westland Helicopters.

8. Normative References

 [1]  Gharai, L. and C. Perkins, "RTP Payload Format for Uncompressed
      Video", RFC 4175, September 2005.
 [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.

Author's Address

 Colin Perkins
 University of Glasgow
 Department of Computing Science
 17 Lilybank Gardens
 Glasgow  G12 8QQ
 UK
 EMail: csp@csperkins.org

Perkins Standards Track [Page 3] RFC 4421 RTP Payload for Uncompressed Video February 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Perkins Standards Track [Page 4]

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