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Status of SDP with more than 2 "m" lines

From: Iñaki Baz Castillo <ibc@aliax.net>
Date: Mon, 15 Sep 2014 12:22:29 +0200
Message-ID: <CALiegfnYw3xOErTQ3iaAT2WtD_x8cjACmQCfufdM48ev9Z1wZA@mail.gmail.com>
To: "public-webrtc@w3.org" <public-webrtc@w3.org>
Hi,

I'm afraid that, at least in my experiments, no browser supports a
remote SDP offer with more than 2 "m" lines, with or without Bundle,
with a single MediaStream or two.

In case of Chrome (Canary) the createAnswer() call fails. I've reported it:

https://code.google.com/p/chromium/issues/detail?can=2&start=0&num=100&q=&colspec=ID%20Pri%20M%20Iteration%20ReleaseBlock%20Cr%20Status%20Owner%20Summary%20OS%20Modified&groupby=&sort=&id=414202

In the case of Firefox (Nightly) I won't spend time reporting it given
that, after calling setRemoteDescription() with a 4 "m" lines SDP
offer, a call to createAnswer() produces a SDP answer with 2 "m"
lines, so I expect that nothing but a 2 "m" lines SDP is expected and
supported.


So, what is the *real* status of the (how to say...) multiple tracks
(I mean more than a single MediaStream with audio+video)?

Hangouts has a just-Chrome-WebRTC version which uses PlanA or PlanB,
this is, multiple a=ssrc per "m" line. Is it just that?


Note please that I'm not talking about Bundle or no Bundle. In my
experiments I provide Chrome and Chrome Canary with different remote
SDP offers:

a) Two MediaStream of audio and video in 4 "m" lines and no Bundle.
b) Same with Bundle.
c) A single MediaStream with 2 audio and 2 video tracks (just two of
them with "a=sendrecv").
d) etc etc


What I would like to know (and that is why I ask here) is: which is
supposed to be the level of multiple-tracks support expected for
WebRTC 1.0?


Thanks a lot.




-- 
Iñaki Baz Castillo
<ibc@aliax.net>
Received on Monday, 15 September 2014 10:23:16 UTC

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