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.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.

Acknowledgement

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

Perkins                     Standards Track                     [Page 4]