Re: [rtcweb] inactive m-lines in draft-ietf-rtcweb-jsep-05

Martin Thomson <martin.thomson@gmail.com> Tue, 29 October 2013 19:07 UTC

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Date: Tue, 29 Oct 2013 12:07:42 -0700
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From: Martin Thomson <martin.thomson@gmail.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: Re: [rtcweb] inactive m-lines in draft-ietf-rtcweb-jsep-05
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On 29 October 2013 11:53, Paul Kyzivat <pkyzivat@alum.mit.edu> wrote:
> This maps each MediaStreamTracks of a given type to a different m-line. I
> *thought* the use of "specified type" above meant audio/video. Am I missing
> something?

Yes.  sort of, though I'd expand "type" to encompass the concept of
compatibility.  Obviously a source with an H.264 encoder can't be
bound to an m= section that only has VP8 negotiated.

1. RTCPeerConnection binds tracks to m= sections
2. For sending tracks, that binding is tentatively made when an offer
or answer is constructed
3. Sending tracks are bound when setLocalDescription is called
4. For receiving tracks, that binding is made when the track is made,
which is when setRemoteDescription is called

When generating offers or answers, the set of bindings (including
tentative ones) - plus the enabled state of the track - determines
what of the send/recv attributes is attached to that m= section.