RE: [AVT] RE: [MMUSIC] questions about grouping media streams in RTP andSDP (RFC3388 etc), advice needed

["Thomas Schierl" <[e-mail]>]

Hi Dave, 

I think there is a strong relation of your problem and the
http://tools.ietf.org/wg/mmusic/draft-schierl-mmusic-layered-codec-03.txt .
In this draft, we described media dependency in general, not only for
scalable video. Currently, two types of dependencies are defined: layered
and mdc assuming the media is partially transported in different RTP
sessions. It would be easy to integrate your needs, if they should not be
already covered.


Thomas

> -----Original Message-----
> From: Dave Singer [mailto:[e-mail]]
> Sent: Tuesday, June 05, 2007 8:34 AM
> To: Even, Roni; mmusic; IETF AVT WG
> Cc: Clinton Priddle (KI/EAB)
> Subject: [AVT] RE: [MMUSIC] questions about grouping media streams in RTP
> andSDP (RFC3388 etc), advice needed
> 
> At 10:03  +0300 5/06/07, Even, Roni wrote:
> >Dave,
> >For layered encoding there is a proposal for a new grouping attribute in
> >http://tools.ietf.org/wg/mmusic/draft-schierl-mmusic-layered-codec-03.tx
> >t
> 
> I don't think this is a layered coding issue, either, alas.
> 
> >I looked at RFC3388 and I think that FID is not the answer to your
> >requirement as you mentioned
> >
> >To me it looks like what you are looking for is a way to specify
> >alternate offers.
> 
> No, these streams are not alternatives to each other in the regular
> sense.  Nor is this really used in offer/answer;  it's more an issue
> for multicast.  In multicast, you open the tune-in stream and the
> base stream, grab the first I-frame that arrives (in either) and then
> drop the tune-in stream.
> 
> Yes, we're aware that the recipient needs to be able to tell which is
> the base and which is the tune-in.
> 
> >If this is the case I have similar requirements and
> >would be happy to support such work.
> >
> >You also need a way to give semantics to the "repair" stream, this can
> >be done based on the content attribute from RFC 4796 or using a
> >dependency attribute see in Schierl's draft. The mid tag is not enough
> >for the receiver to know what you meant by this offer and which stream
> >is the repair.
> >
> >Here is an example for a solution using a new Alternatives grouping
> >attribute and giving semantics to the repair stream
> >
> >By using the grouping attribute in the offer you can know if the
> >answerer understood the grouping since if he does not than he will send
> >an answer with no a=group
> >
> >v=0
> >o=bob 280744730 28977631 IN IP4 host.example.com
> >s=
> >t=0 0
> >
> >a=group:ALTS 1 2
> >a=group:ALTS 1 3
> >
> >m=audio 6886 RTP/AVP 0
> >c=IN IP6 2001:0600::1
> >a=mid:1
> >
> >m=video 9000 RTP/AVP 100
> >c=IN IP4 192.0.2.2
> >a=rtpmap:100 H263-1998
> >a=mid:2
> >
> >m=video 9002 RTP/AVP 101
> >c=IN IP4 192.0.2.2
> >a=rtpmap:101 H263-1998
> >a=mid:3
> >a=content:repair=2 or a=depend:repair=2
> >
> >
> >Roni Even
> >
> >>  -----Original Message-----
> >>  From: Dave Singer [mailto:[e-mail]]
> >>  Sent: Monday, June 04, 2007 7:19 PM
> >>  To: mmusic; IETF AVT WG
> >>  Cc: Clinton Priddle (KI/EAB)
> >>  Subject: [MMUSIC] questions about grouping media streams in RTP and
> >SDP
> >>  (RFC3388 etc), advice needed
> >>
> >>  Hi
> >>
> >>  we have a need to group together two media streams, in the style of
> >RFC
> >>  3388 <http://www.ietf.org/rfc/rfc3388.txt> but we're unsure whether an
> >>  existing group type is suitable or not, and if it's not, we'd like to
> >>  agree on a new one, and document it (presumably in an RFC).
> >>
> >>  What we have is a normal media stream, and a separate 'repair' or
> >>  'entry' stream, that can be used when tuning in, or after loss, but is
> >>  otherwise un-needed.  An example might be a video stream with a low
> >>  I-frame interval (say every 15 seconds), with a repair stream which
> >has
> >>  only I-frames that are equivalent to the time-parallel non-I frame, at
> >a
> >>  frequency of say 1 per second.
> >>
> >>  It's not clear to us whether this is "one media flow" in the sense of
> >>  FID, or not.  The example offers AMR and GSM audio, which are
> >>  alternatives, and DTMF tones along with audio, which are supplementary
> >>  to each other.  Perhaps we fall afoul of this restriction:
> >>
> >>  "An application that encodes the same media using different codecs
> >>  simultaneously MUST NOT use FID to group those media lines."
> >>
> >>  or this one, for layered encoding:
> >>
> >>  "FID MUST NOT be used to group "m" lines that do not represent the
> >same
> >>  information."  (Though how DTMF tones and their associated audio pass
> >>  this test is not clear).
> >>
> >>  Nor is it clear that the FEC group of RFC 4756 is right, either.  For
> >a
> >>  start, we may wish to use this new ID in combination with FEC, and
> >>  secondly this tune-in stream has different characteristics.  For
> >>  example, one can typically ignore all FEC and (as long as there are no
> >>  errors) decode the stream correctly.  Ignoring the tune-in stream
> >  > entirely may mean that you will never find a tune-in point, making
> the
> >>  normal stream useless.
> >>
> >>  So, can we use FID for associating a repair stream with its base (we
> >tag
> >>  the streams so we know which is which, of course)?
> >>
> >>  p.s. RFC 4756 claims in the IANA section that the FEC group is
> >>  registered under SDP characteristics, but actually I can find no
> >>  registry anywhere in IANA of group types.
> >>
> >>
> >>  --
> >>  David Singer
> >>  Apple/QuickTime
> >>
> >>  _______________________________________________
> >>  mmusic mailing list
> >>  [e-mail]
> >>  https://www1.ietf.org/mailman/listinfo/mmusic
> 
> 
> --
> David Singer
> Apple/QuickTime
> 
> _______________________________________________
> Audio/Video Transport Working Group
> [e-mail]
> https://www1.ietf.org/mailman/listinfo/avt


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