Re: [AVT] I-D Action:draft-ietf-avt-rtp-svc-07.txt

[Colin Perkins <csp at csperkins.org>]

On 1 Feb 2008, at 23:15, Internet-Drafts at ietf.org wrote:
> A New Internet-Draft is available from the on-line Internet-Drafts  
> directories.
> This draft is a work item of the Audio/Video Transport Working  
> Group of the IETF.
>
>
> 	Title           : RTP Payload Format for SVC Video
> 	Author(s)       : S. Wenger, et al.
> 	Filename        : draft-ietf-avt-rtp-svc-07.txt
> 	Pages           : 73
> 	Date            : 2008-02-01
>
> This memo describes an RTP payload format for scalable video coding
> (SVC) defined in_Annex G of the ITU-T Recommendation H.264 video
> codec which is technically identical to Amendment 3 of ISO/IEC
> International Standard 14496-10.  The RTP payload format allows for
> packetization of one or more Network Abstraction Layer (NAL) units,
> produced by the video encoder, in each RTP packet payload.  The
> payload format has wide applicability, such as low bit-rate
> conversational, Internet video streaming, or high bit-rate
> entertainment quality video.
>
> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-svc-07.txt

I had a couple of comments on section 8.1.1.  This section is much  
improved from the previous version, but is still unclear on what  
timestamp should be used for various stages of the process.  In  
particular, the bullets in part two need clarification:

      o NAL units with the same timestamp are grouped in decoding order
      to Operation Point representations in each RTP stream.

Since this refers to order within an RTP stream, I assume the RTP  
timestamp of the NAL units is used?

      o Operation Point representations with the same timestamp SHALL be
      grouped to access units in order of the RTP session dependency
      from lowest to highest Enhancement RTP session, where the highest
      Enhancement RTP session is the one which no other RTP session
      depends on and the lowest Enhancement RTP session may be the Base
      RTP session.

Since this is ordering data across RTP sessions, it presumably maps  
the RTP timestamp to an NTP format wall-clock value using the  
information contained in RTCP SR packets, and then uses those NTP  
format timestamps for ordering?

-- 
Colin Perkins
http://csperkins.org/


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