Re: [MMUSIC] How does mmt grouping work with multiple streams of the same type?

["Stach, Thomas" <[e-mail]>]

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> -----Ursprüngliche Nachricht-----
> Von: Harald Alvestrand [mailto:[e-mail]] 
> Gesendet: Donnerstag, 11. Oktober 2012 16:45
> An: Stach, Thomas
> Cc: Christer Holmberg; Jonathan Lennox; mmusic WG
> Betreff: Re: AW: How does mmt grouping work with multiple 
> streams of the same type?
> 
> On 10/11/2012 04:13 PM, Stach, Thomas wrote:
> > Harald,
> >
> > thanks for the reply.
> > It helps for my second question, but not for my main question.
> > How can the answerer recognize (from the m=anymedia line 
> alone) that multiple video streams need to be set up in the 
> same RTP session?
> If each video stream is signalled by the presence of SSRC-associated 
> signalling for that video stream, you count the number of 
> video streams signalled.

Could that be done by e.g. enhancing the new a=mmtype with an ssrc element?
E.g.

       a=mmtype: 0 audio ssrc=1
       a=mmtype: 8 audio ssrc=1
       a=mmtype: 97 audio ssrc=2
       a=mmtype: 31 video ssrc=3
       a=mmtype: 32 video ssrc=4 

would mean 2 audio streams and 2 video streams, whereas 

       a=mmtype: 0 audio ssrc=1
       a=mmtype: 8 audio ssrc=1
       a=mmtype: 97 audio ssrc=1
       a=mmtype: 31 video ssrc=2
       a=mmtype: 32 video ssrc=2 

means 1 audio and 1 video stream based on the number of different SSRCs?

> 
> >
> > Regards
> > Thomas
> >
> >> -----Ursprüngliche Nachricht-----
> >> Von: Harald Alvestrand [mailto:[e-mail]]
> >> Gesendet: Donnerstag, 11. Oktober 2012 15:41
> >> An: Stach, Thomas
> >> Cc: Christer Holmberg; Jonathan Lennox; mmusic WG
> >> Betreff: Re: How does mmt grouping work with multiple streams
> >> of the same type?
> >>
> >> On 10/11/2012 03:12 PM, Stach, Thomas wrote:
> >>> Christer, Harald, Jonathan,
> >>>
> >>> I have the impression that the
> >> draft-holmberg-mmusic-sdp-mmt-negotiation is based on
> >> Jonathan's proposal
> >>> to have an explicit desrciption for the bundled streams as
> >> proposed in
> >>> http://www.ietf.org/mail-archive/web/mmusic/current/msg09454.html
> >>>
> >>> Among other points the following is stated:
> >>> * The m=bundle is a complete description of an entirely
> >> separate m-line; if it's used, the other m-lines in the group
> >> are rejected and the information they carry is ignored.
> >>> I think this a desirable property
> >>>
> >>> Now, consider a case were you have 4 streams, i.e. 4
> >> m-lines (e.g. 2 audio and 2 video).
> >>> How would that be mapped to the m=anymedia line?
> >>> How does mmt grouping work with multiple streams of the same type?
> >>>
> >>>   From the currently proposed syntax for the m=anymedia line
> >> I cannot deduce that multiple audio or video streams are offered.
> >>> I would have to look into the "legacy" m-lines to recognize this.
> >>> In case that e.g. the video stream use different codecs, I
> >> could also learn that only from the legacy m-lines.
> >>
> >> In the case where it's desirable to carry multiple video
> >> streams in one
> >> RTP session, and have different descriptions in SDP for 
> the different
> >> video streams, there has to be some signalling that tells the
> >> recipient
> >> which description applies to which video stream.
> >>
> >> The video streams will have different SSRCSs. Therefore, the only
> >> reasonable answer in the MMT grouping case seems to be
> >> SSRC-associated
> >> signalling.
> >>
> >> In the other variants, it's actually unclear to me how the
> >> video streams
> >> described by the different m= lines would be detected by the
> >> recipients;
> >> I'd been assuming SSRC-associated signalling for other
> >> reasons, so only
> >> when this discussion resurfaced, I started thinking about 
> this again,
> >> and discovered that I didn't have an answer.
> >>
> >> That is, in the description
> >>
> >> a=group:bundle foo bar baz
> >> m=video 4270
> >> a=mid:foo
> >> a=property-x:1
> >> m=video
> >> a=mid:bar
> >> a=property-x:2
> >> m=video
> >> a=mid:baz
> >> a=property-x:3
> >>
> >> one would expect a single RTP stream to be set up; when 
> the recipient
> >> gets 3 video streams with SSRCS 234, 235 and 236, how does he
> >> know which
> >> stream should have which value for "property-x"?
> >> One can solve it with SSRC-associated signalling in this case too:
> >>
> >> a=ssrc:234 property-x:1
> >>
> >> but then you're back to doing SSRC-associated signalling, and
> >> if you're
> >> already doing that, we're not very different from the MMT 
> description
> >> anyway.
> >>
> >> That's how I think of it at the moment, anyway - YMMV.
> >>
> >>
> >>
> 
>