Re: [rtcweb] Proposal for dealing with CNAMEs and MSIDs for synchronization

Stefan Hakansson LK <stefan.lk.hakansson@ericsson.com> Thu, 07 February 2013 19:27 UTC

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Date: Thu, 07 Feb 2013 20:27:52 +0100
From: Stefan Hakansson LK <stefan.lk.hakansson@ericsson.com>
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Subject: Re: [rtcweb] Proposal for dealing with CNAMEs and MSIDs for synchronization
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On 02/07/2013 08:22 PM, Eric Rescorla wrote:
> Here's what I was trying to say at the microphone.
>
> 1. When two MSTracks are in the same MediaStream on the sending side:
>   They must generate the same MSID in SDP and the same CNAME in RTP.
>
> 2. One the receiving side, any two tracks with the same MSID will appear in
> the same MediaStreamTrack.

Same _MediaStream_?

>
> 3. On the receiving side, any two RTP streams with the same CNAME will
> be synchronized.

Yes.

My question is basically: what if the sender creates two MediaStreams 
for which all tracks have local sources (cam's, mike's), sends them to a 
peer, will the RTP streams for both MediaStreams have the same or 
different CNAME?

I argued for that they should have the same.

>
> 4. There are two ways for MSID and CNAME to be inconsistent.
> - If MSID indicates synchronization but different CNAMEs are provided,
>    synchronization is not attempted.
> - If MSID indicates no synchronization but the same CNAME is used,
>    then the tracks shall be synchronized, even though they appear in
>    different MediaStreams.
>
> -Ekr
>
>
>
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