[AVT] Re: I-D ACTION:draft-lakaniemi-avt-rtp-evbr-00.txt

On 13 Nov 2007, at 19:15, Internet-Drafts@ietf.org wrote:
> A New Internet-Draft is available from the on-line Internet-Drafts
> directories.
>
>
> 	Title		: RTP payload format for the ITU-T Embedded Variable Bit- 
> Rate speech/audio codec
> 	Author(s)	: A. Lakaniemi
> 	Filename	: draft-lakaniemi-avt-rtp-evbr-00.txt
> 	Pages		: 28
> 	Date		: 2007-11-13
> 	
>    This document specifies the Real-Time Transport Protocol (RTP)
>    payload format for the Embedded Variable Bit-Rate (EV-VBR)
>    speech/audio codec. A media type registration for this RTP payload
>    format is also included.
>
>
> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-lakaniemi-avt-rtp- 
> evbr-00.txt

 From a quick initial read through, this seems generally very  
reasonable. Two areas seem problematic, however:

Section 3.5 discusses RTP header usage, stating "In case the EV-VBR  
session consists multiple RTP sessions, the RTP sessions are further  
separated by using different payload type (PT) values for each of the  
RTP streams" and "Each of the RTP sessions involved in the EV-VBR  
session SHALL use the same SSRC value". A better approach would be to  
allow the usual choice of SSRC, and use a common RTCP CNAME to  
associate the streams, reusing the mechanism needed for lip-sync  
between audio and video.

Section 4 defines a new RTCP APP packet. I generally find APP packets  
to be the wrong approach for anything other than application-specific  
information. Either define a new RTCP packet type (with its own RTCP  
PT value), or use an AVPF feedback packet type.

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

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