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

Eric Rescorla <ekr@rtfm.com> Thu, 07 February 2013 19:23 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Thu, 07 Feb 2013 11:22:18 -0800
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Subject: [rtcweb] Proposal for dealing with CNAMEs and MSIDs for synchronization
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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.

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

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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