Re: [MMUSIC] What is an m-line?
Paul Kyzivat <pkyzivat@alum.mit.edu> Mon, 13 May 2013 19:02 UTC
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Date: Mon, 13 May 2013 15:02:35 -0400
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: Re: [MMUSIC] What is an m-line?
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On 5/13/13 2:42 PM, Martin Thomson wrote: > We've had a great deal of discussion about plan A and B and the > various interactions of these proposals with bundling. But I still > don't get a good sense that there is a working consensus on what an > m-line actually represents. > > I think that we've each reached our own conclusions, but they > definitely are not consistent. We need a well-understood semantic for > m-lines if we have any chance of resolving these issues; Plan A/B > being only the first RTCWEB problem to address. > > RFC 4566 is helpfully devoid of detail, so we are free to come up with > any interpretation we choose. Here are the ones that I have seen: > > 1. an m-line represents a single RTP session > (or at least the part of the session that touches the client) > This appears to be consistent with the Plan B approach Well, it was my impression that Plan B still intends to allow bundling in order to combine audio and video into a single RTP session. So in that case neither of the m-lines represents a single RTP session in full. > 2. an m-line represents the set of RTP streams that decode into a > single rendering, including layers, simulcast and FEC Hmm. I was thinking *this* was what Cullen intended by Plan A. But now that you bring it up, I thing there is some existing SDP syntax for simulcast/FEC/FID that might only work with (3). (But I don't have the details of that stuff in my head.) > 3. an m-line represents a single RTP stream; multiple m-lines might > be required to obtain a single rendering if it uses layers, simulcast, > FEC or FID groupings > This appears to be consistent with the Plan A approach I offer another try: 4. an m-line represents one or more (zero or more?) sources/flows/tracks/captures (pick the name that suits you) that share a single RTP session and that all are consistent with the media description accompanying the m-line. IIUC this is what Plan B is trying to achieve. Thanks, Paul > In the first instance, an m-line can be multiple "things". In the > latter two cases, an m-line is consistently one "thing" (or part > thereof). > > The first interpretation has a natural advantage in terms of signaling > economy and natural bundling. The latter interpretations seem to have > advantages in dealing with call transfer and SSRC renumbering. > > So, which is correct? > _______________________________________________ > mmusic mailing list > mmusic@ietf.org > https://www.ietf.org/mailman/listinfo/mmusic >
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Colin Perkins
- Re: [MMUSIC] What is an m-line? Bernard Aboba
- [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Bernard Aboba
- Re: [MMUSIC] What is an m-line? Jonathan Lennox
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Cullen Jennings (fluffy)
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Colin Perkins
- Re: [MMUSIC] What is an m-line? Kevin Dempsey
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Colin Perkins
- Re: [MMUSIC] What is an m-line? Harald Alvestrand
- Re: [MMUSIC] What is an m-line? Bernard Aboba
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Emil Ivov
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Emil Ivov
- Re: [MMUSIC] What is an m-line? Martin Thomson
- Re: [MMUSIC] What is an m-line? Emil Ivov
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Harald Alvestrand
- Re: [MMUSIC] What is an m-line? Paul Kyzivat
- Re: [MMUSIC] What is an m-line? Suhas Nandakumar