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

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

Christer Holmberg wrote:
> Hi,
> 
> Jumping in late - trying to catch up :)
> 
>>>>>> I think we should continue to use RFC 5576 for this purpose:
>>>>>> 
>>>>>> a=ssrc:1 <something follows>
>>>> I haven't thought about that, but yes it would work for as well.
>>>> For two audio streams (audio1 w/ PCMU or PCMA, audio2 w/ iLBC) it
>>>> would look like this? 
>>>> 
>>>>     a=rtpmap:0 PCMU/8000
>>>>     a=rtpmap:8 PCMA/8000
>>>>     a=rtpmap:97 iLBC/8000
>>>>     a=mmtype: 0 audio
>>>>     a=mmtype: 8 audio
>>>>     a=mmtype: 97 audio
>>>>     a=ssrc:12345 fmtp:0
>>>>     a=ssrc:12345 fmtp:8
>>>>     a=ssrc:67890 fmtp:97
>>> Yes, except that as far as I can tell from RFC 5576, you can't use
>>> fmtp: without an actual parameter value: "This parameter MUST only
>>> be used for media types for which source-level format parameters
>>> have explicitly been specified". (section 6.3).
>>> 
>>> If you need to use a field that's always present, use CNAME.
>>> 
>>> Note(1): If you only use one payload type for all your audio, you
>>> have no need to signal which format they're using.
>>> 
>>> Note(2): In the above, you have ssrc 12345 using both PCMU/8000 and
>>> PCMA/8000. I don't know if it's intentional or not.
>>> 
>> Yes, this was intentional,
>> I used two different ssrc (12345, 67890) in order to
> indicate that I want to establish two audio streams.
>> 
>> I used ssrc=12345 twice in order to give a hint that the
> first audio stream should either use PCMU or PCMA (and ssrc=12345).
>> The second audio stream would use ssrc=67890 and iLBC.
> 
> Even without BUNDLE, this is how you would do it if you offer
> multiple streams within a single m- line.
> 
>> However from your responses I'm not sure if we are on the
> same page with respect to what I want to achieve.
>> Let me tray to clarify.
>> 
>> My understanding is that
>> - the m=anymedia gives a complete description of what is offered,
>> - if the answerer understands m=anymedia, it accepts the
> m=anymedia line and rejects all other m-lines
> 
> Correct.
> 
> (All other m- lines associated with the MMT group, that is)

Of course

> 
>> - if the answerer understands m=anymedia, it can ignore all
> other m-lines in the SDP, it doesn't even have to look at
> them in order to build its answer.
> 
> Correct.
> 
> (All other m- lines associated with the MMT group, that is)
Yes, this is more precise again

> 
>> If this is correct, consider an SDP offer with e.g. 4 m-lines (2
>> audio+2 video) 
>> 
>>       v=0
>>       o=alice 2890844526 2890844526 IN IP4 host.atlanta.com       s=
>>       c=IN IP4 host.atlanta.com
>>       t=0 0
>>       m=audio 10000 RTP/AVP 0 8
>>       a=rtpmap:0 PCMU/8000
>>       a=rtpmap:8 PCMA/8000
>>       m=audio 10002 RTP/AVP 97
>>       a=rtpmap:97 iLBC/8000
>>       m=video 20000 RTP/AVP 31
>>       a=rtpmap:31 H261/90000
>>       m=video 20002 RTP/AVP 32
>>       a=rtpmap:32 MPV/90000
>> 
>> How would the associated m=anymedia line look like in this
> case, such that the answerer can see that 2 audio and 2 video
> streams are offered without having to look into the other m-lines?
> 
> Note that there are still some details (e.g. whether
> "RTP/AVP" is going to be used) that have to be sorted out,
> but something like this:
> 
> m=anytype 10000 RTP/AVP 0 8 97 31 32
> a=mmtype: 0 audio
> a=mmtype: 8 audio
> a=mmtype: 97 audio
> a=mmtype: 31 video
> a=mmtype: 32 video
> a=rtpmap:0 PCMU/8000
> a=rtpmap:8 PCMA/8000
> a=rtpmap:97 iLBC/8000
> a=rtpmap:31 H261/90000
> a=rtpmap:32 MPV/90000
> 
Yes, something like this. But this m=anymedia line could also be based on:

SDP Offer (1 audio + 1 video)
       v=0
       o=alice 2890844526 2890844526 IN IP4 host.atlanta.com
       s=
       c=IN IP4 host.atlanta.com
       t=0 0
       m=audio 10000 RTP/AVP 0 8 97
       a=rtpmap:0 PCMU/8000
       a=rtpmap:8 PCMA/8000
       a=rtpmap:97 iLBC/8000
       m=video 20000 RTP/AVP 31 32
       a=rtpmap:31 H261/90000
       a=rtpmap:32 MPV/90000

I think the a=anymedia line in the offer needs provide a means to dinstinguish this from the case above.


> Then, you will use the SSRC attribute to identify the
> streams. But, we do need to define how to associate SSRCs
> with media types and/or payload types.
> 

Thanks, 

once available I'll look into the updated draft on how you intend to solve that.

Regards
Thomas

> In one of your e-mails, you suggested to extend the mmtype
> attribute. That's for sure one possibility.
> 
> Regards,
> 
> Christer