Subject: Re: [AVTCORE] comment on draft-westerlund-avtext-rtcp-sdes-srcname

From: Magnus Westerlund <[email-masked]>
Date: Fri, 6 Jul 2012 16:05:34 +0200

On 2012-06-29 09:43, Pascal Buhler (pabuhler) wrote:
> 
> One of the problems mentioned in the draft, that is the case when
> receiving the RTP streams before the SEDS has arrived is something
> that needs to be addressed. The option of including the mapping in
> the SDP is not always appropriate due to devices like an RTP
> Translator in the middle. Therefore I was wondering if you have
> considered including a definition of a RTP header extension
> (http://tools.ietf.org/html/rfc5285) to include the SRCNAME in the
> RTP stream. Yes it is potentially a lot of bits wasted but it is up
> to the sender to decide the size of the SRCNAME so that can mitigate
> it somewhat. Also it may not be required in every packet just packets
> that make sense for example only in the beginning of a stream, at key
> points in the stream or else periodically. When using the SRCNAME to
> correlate two or more separate encodings of the same source it is
> important as a receiver that when first receiving one encoding and
> then switching to receive a second encoding to make this correlation
> as soon as possible.
> 

Thanks for the support for the general use case.

Yes, using a header extension to provide the information is a potential
extension for certain use cases that clearly can be an extension on the
basis of our proposed solution. Yes, clearly you should have the
flexibility to include such information as often or seldom as makes
sense in your application.

> 
> There is also mention of using this as a way correlating FEC with
> media. How would this work in the simulcast case where there are
> multiple encodings of the same source. How to use only SRCNAME to map
> the FEC stream to the individual media streams when all media streams
> have the same SRCNAME.

Yes, this has been raised previously and I agree we need to support it.
We think we have an idea how to improve SRCNAME to work also in those
cases. Now it is only of matter of manage to write it up before the
draft deadline.

Cheers

Magnus Westerlund

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