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

[Christer Holmberg <[e-mail]>]

Hi,

>>> 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.

When I look at your two offer examples, I see the following differences:

1. The port numbers. That is obviously nothing you need to distinguish, as the same port will be used for everything when using m=anytype.

2. RTP sessions. Assuming that each m- line represents an RTP session, and you want to keep that within the m=anytype description, that is obviously something that needs to be defined. However, the basic assumption in BUNDLE is that all multiplexed media belongs to the same RTP sessions, and you'll need some other mechanism/extension (e.g. the SHIM mechanism) in order to use multiple RTP sessions.

Assuming you will use the SSRC attribute to indicate the number of streams, what else do you need to distinguish?

>> 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.

You are very welcome to present ideas on how to solve it :)

Regards,

Christer