Re: [MMUSIC] "a=extmap" with BUNDLE

Taylor Brandstetter <deadbeef@google.com> Mon, 27 March 2017 22:24 UTC

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From: Taylor Brandstetter <deadbeef@google.com>
Date: Mon, 27 Mar 2017 15:24:22 -0700
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To: =?UTF-8?Q?I=C3=B1aki_Baz_Castillo?= <ibc@aliax.net>
Cc: Byron Campen <docfaraday@gmail.com>, mmusic WG <mmusic@ietf.org>
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Subject: Re: [MMUSIC] "a=extmap" with BUNDLE
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>
> Would it not be sufficient to specify that bundled m-sections not use the
> same identifier for _different_ extensions?


Yes, that's what I meant to describe.

It's just about getting the appropriate RtpReceiver
> associated to the current RTP packet (this can be done by MID, RID,
> SSRC or even PT, as the ORTC and JSEP "RTP Matching Rules" define).


Right. So, if you *can't* get the appropriate RtpReceiver with RID, SSRC or
PT, then you must do it with MID. And if the MID extension shares an ID
with another extension, it becomes impossible to know the MID. For example:

m=audio ...
a=extmap:1 urn:ietf:params:rtp-hdrext:sdes:mid
a=extmap:2 urn:foo
m=video ...
a=extmap:1 urn:bar
a=extmap:2 urn:ietf:params:rtp-hdrext:sdes:mid

I know it would be crazy to generate SDP like that, but there's nothing
I've found that disallows it.

On Mon, Mar 27, 2017 at 2:00 PM, Iñaki Baz Castillo <ibc@aliax.net> wrote:

> 2017-03-27 19:55 GMT+02:00 Byron Campen <docfaraday@gmail.com>om>:
> >   Would it not be sufficient to specify that bundled m-sections not use
> the
> > same identifier for _different_ extensions? There's no ambiguity if you
> use
> > '3' for mid on every m-section, which is the kind of thing
> implementations
> > do now anyway.
>
> Still one may use '3' for MID within a m=audio line and '4' for MID
> within a m=video line. And that's legal.
> Anyhow, current browsers use unique IDs across the whole SDP.
>
>
> --
> Iñaki Baz Castillo
> <ibc@aliax.net>
>