draft-ietf-avt-uncomp-video-ext-00.txt   draft-ietf-avt-uncomp-video-ext-01.txt 
Network Working Group C. Perkins Network Working Group C. Perkins
Internet-Draft University of Glasgow Internet-Draft University of Glasgow
Expires: March 6, 2006 September 2, 2005 Updates: 4175 (if approved) September 25, 2005
Expires: March 29, 2006
RTP Payload Format for Uncompressed Video: Additional Colour Sampling RTP Payload Format for Uncompressed Video: Additional Colour Sampling
Modes Modes
draft-ietf-avt-uncomp-video-ext-00.txt draft-ietf-avt-uncomp-video-ext-01.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
This memo extends the RTP Payload Format for Uncompressed Video to This memo extends the RTP Payload Format for Uncompressed Video to
support additional RGB sampling modes. support additional colour sampling modes.
1. Introduction 1. Introduction
The RTP Payload Format for Uncompressed Video [1] defines a scheme to The RTP Payload Format for Uncompressed Video [1] defines a scheme to
packetise uncompressed, studio-quality, video streams for transport packetise uncompressed, studio-quality, video streams for transport
using RTP [2]. A range of standard and high definition video formats using RTP [2]. A range of standard and high definition video formats
are supported, and parameters are defined so sender and receiver can are supported, and parameters are defined so sender and receiver can
signal the image size, colour space, pixel depth, etc. negotiate the image size, colour space, pixel depth, and colour
sampling mode.
A limitation of the format is that the number of bits per sample is A limitation of the signalling is that the number of bits per sample
signalled as being the same for each colour component. For example, is assumed to be the same for each colour component. For example, it
it is not possible to signal transport of RGB format video using 5 is possible to signal video using RGB colour sampling with 8-bits for
bits each for the Red and Blue components and 6 bits for the Green, each of the Red, Green and Blue components (24 bits per pixel), but
packing one pixel into two octets. Such video formats can easily be not video using RGB colour sampling with 5-bits each for the Red and
supported in the payload format, but cannot be signalled using the Blue components, but 6-bits for the Green component (16 bits per
parameters defined. This memo extends [1] with additional colour pixel). Such video formats can easily be transported by the payload
sampling modes, to signal such video formats. 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 2. Conventions Used in this Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [3]. document are to be interpreted as described in RFC 2119 [3].
3. Payload Format Parameters 3. Payload Format Parameters
This memo defines six new colour sampling modes that MAY be signalled 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+", 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 "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, of samples as do the RGB and BGR colour sampling modes respectively
except that an additional bit of colour depth is available for the ([1] Section 4.3), except that an additional bit per sample of colour
component marked by the + symbol (i.e. when "depth=N" is signalled, N depth MUST be used for the component marked by the + symbol. The
bits are allocated to unmarked components, but N+1 bits MUST be mandatory parameter "depth=N" indicates that N bits per sample are
allocated to the marked component). All other features of the used by the unmarked components, but N+1 bits are used by the marked
payload format remain as defined in [1]. 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 The primary use of these colour sampling modes is to enable efficient
packing of data into small pixel groups ("pgroups"). The most common 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 use case is expected to be video with "depth=5", where the additional
additional bit of colour depth enables a single pixel to fit into two bit of colour depth for the marked component enables a single pixel
octets without padding. The new colour sampling modes MAY be used to fit into two octets without padding. The new colour sampling
for other depths, however, should that prove useful. modes MAY be used for other depths, however, should that prove
useful.
4. Example 4. Example
A common uncompressed video format is RGB with 5 bits for the Red and 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 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, 16 bits per pixel. Using the sampling modes defined in this memo,
this can be signalled in SDP according to the following example: this can be signalled in SDP according to the following example:
v=0 v=0
o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5 o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5
s=- s=-
c=IN IP4 10.47.16.6 c=IN IP4 10.47.16.6
t=2873397496 2873404696 t=2873397496 2873404696
a=recvonly
m=video 51372 RTP/AVP 99 m=video 51372 RTP/AVP 99
a=rtpmap:99 raw/90000 a=rtpmap:99 raw/90000
a=fmtp:99 sampling=RG+B; width=1024; height=768; depth=5; a=fmtp:99 sampling=RG+B; width=1024; height=768; depth=5;
colorimetry=SMPTE240M colorimetry=SMPTE240M
(some of the lines in have been wrapped due to formatting constraints The last line has been wrapped due to formatting constraints of this
on this memo). memo, and forms one complete line in the SDP file.
5. Security Considerations 5. Security Considerations
The security considerations of [1] apply. No additional security The security considerations of [1] apply. No additional security
considerations are introduced by support for new colour sampling considerations are introduced by support for new colour sampling
modes. modes.
6. IANA Considerations 6. IANA Considerations
The video/raw media type is extended with six new values for the 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 "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 [1]. The new values are "RGB+", "RG+B", "R+GB", "BGR+", "BG+R" and
"B+GR" as described in this memo. "B+GR" as described in this memo.
7. Acknowledgements 7. Acknowledgements
Thanks to Jeremy Searle and Andrew Lee. Thanks to Jeremy Searle and Andrew Lee at Westland Helicopters.
8. Normative References 8. Normative References
[1] Gharai, L. and C. Perkins, "RTP Payload Format for Uncompressed [1] Perkins, C. and L. Gharai, "RTP Payload Format for Uncompressed
Video", draft-ietf-avt-uncomp-video-06 (work in progress), Video", RFC 4175, September 2005.
February 2004.
[2] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, [2] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", STD 64, "RTP: A Transport Protocol for Real-Time Applications", STD 64,
RFC 3550, July 2003. RFC 3550, July 2003.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
Author's Address Author's Address
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