Re: [rtcweb] inactive m-lines in draft-ietf-rtcweb-jsep-05
Paul Kyzivat <pkyzivat@alum.mit.edu> Tue, 29 October 2013 18:53 UTC
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Date: Tue, 29 Oct 2013 14:53:22 -0400
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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To: Martin Thomson <martin.thomson@gmail.com>
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Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] inactive m-lines in draft-ietf-rtcweb-jsep-05
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On 10/29/13 2:27 PM, Martin Thomson wrote: > On 29 October 2013 08:05, Paul Kyzivat <pkyzivat@alum.mit.edu> wrote: >> How is this expected to work? Is the browser supposed to do this in the >> absence of a MediaStreamTrack? > > As I understand it, and my understanding is probably imperfect [22], > the idea is that at all points where an offer or answer is > constructed, the using application has access to MediaStreamTrack > objects that relate to the various m-lines. Mostly. My question only pertains to those cases where it doesn't. > That is, prior to creating an offer, you have the MediaStreamTrack > instances that relate to what you are sending. And Prior to creating > an answer, you have both the tracks you want to send and the ones that > you want to receive. Adam has proposed [2] that enabling or disabling > these tracks causes the appropriate a=sendonly/etc. attribute to be > set. This confuses me a little, probably because I am not well informed about JSEP. The above implies that for a sendrecv m-line there will be two MediaStreamTracks, one for sending and one for receiving. But section 5.3.1 of JSEP seems inconsistent with that: For each non-rejected m= section of a given media type, if there is a local MediaStreamTrack of the specified type which has been added to the PeerConnection via addStream and not yet associated with a m= section, the MediaStreamTrack is associated with the m= section at this time. If there are more m= sections of a certain type than MediaStreamTracks, some m= sections will not have an associated MediaStreamTrack. If there are more MediaStreamTracks of a certain type than m= sections, only the first N MediaStreamTracks will be able to be associated in the constructed answer. The remainder will need to be associated in a subsequent offer. 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? > The only case that is a little strange is the one relating to the > received streams when creating an initial offer, where you use the > OfferToReceiveAudio or OfferToReceiveVideo constraint in order to > indirectly control the send/recv attributes. I know that is one way of creating the situation I was wondering about. It isn't clear to me if that is the only way. Thanks, Paul
- Re: [rtcweb] inactive m-lines in draft-ietf-rtcwe… Paul Kyzivat
- [rtcweb] inactive m-lines in draft-ietf-rtcweb-js… Paul Kyzivat
- Re: [rtcweb] inactive m-lines in draft-ietf-rtcwe… Martin Thomson
- Re: [rtcweb] inactive m-lines in draft-ietf-rtcwe… Martin Thomson
- Re: [rtcweb] inactive m-lines in draft-ietf-rtcwe… Paul Kyzivat
- Re: [rtcweb] inactive m-lines in draft-ietf-rtcwe… Martin Thomson
- Re: [rtcweb] inactive m-lines in draft-ietf-rtcwe… Paul Kyzivat
- Re: [rtcweb] inactive m-lines in draft-ietf-rtcwe… Harald Alvestrand
- Re: [rtcweb] inactive m-lines in draft-ietf-rtcwe… Justin Uberti