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Re: API changes to clarify ICE/SDP split, and align with MediaStream mapping

From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
Date: Fri, 23 Sep 2011 09:40:15 +0200
Message-ID: <4E7C37DF.4070008@ericsson.com>
To: public-webrtc@w3.org
On 2011-09-22 22:51, Timothy B. Terriberry wrote:
> Harald Alvestrand wrote:
>> I concluded from that discussion that we can say that all tracks in a
>> MediaStream share a CNAME, but we can't say that all tracks with the
>> same CNAME go to the same MediaStream.
>
> So what happens when a stream is added, with the same CNAME as a set of
> existing streams? The current API has callbacks for adding/removing
> MediaStreams, but not individual tracks within a MediaStream.
>
I think we need to separate things that is observable in the API and 
what happens at the SDP/RTP level.

IMO, each MediaStream should have an identifier so that it can be 
referenced when transmitted over a PeerConnection. The current API draft 
has the "label" attribute for this purpose. So the web app developer 
works with MediaStreams.

CNAME, SSRC, RTCP, ... is to me tools used in the transport over a 
PeerConnection to make sure that what should be in sync is in sync and 
so on - nothing the web developer should know or care about. In addition 
they will probably be used, perhaps in combination with something 
additional, to convey the label attribute of the MediaStream in some way.

There may be situations when one track is part of two or more 
MediaStreams that are sent over the same PeerConnection. A natural 
optimization would be that that track is on an RTP level actually only 
sent once (i.e. only one RTP stream), but this is not visible to the web 
app.

Stefan
Received on Friday, 23 September 2011 07:40:51 UTC

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