Re: [MMUSIC] BUNDLE TEXT: De-mux procedures (June 19th)

[Christer Holmberg <[e-mail]>]

Hi,

>>>> The question is whether we shall specify exactly how entities associate RTP packets with the correct m= lines, or whether we shall simply give some guidelines and hints.
>>>>
>>>> For example, a client can choose to use unique PT values per m- 
>>>> values, within a given BUNDLE group, and everything should work 
>>>> fine. And, if the endpoint runs out of PT values, the create a new 
>>>> BUNDLE group. Now, whether it's religiously correct, I don't know :)
>>>>
>>>> OR, if the endpoints are able to signal which SSRCs they are going to use, they can use that.
>>>>
>>>> OR, if the endpoints support some kind of RTP header extension for this purpose, they can use that.
>>>>
>>> OR, if they don't care which M-line the stream is associated with, the question may be moot.
>>
>> Correct.
>>
>>> In all cases, the payload type MUST clearly identify the codec configuration it's associated with.
>>
>> *IF* you have a way to find the right m= line, couldn't PT X have different codec configurations in different m= lines?
>
> Let's assume that it could ... but then how would you know that your peer also supports the same demuxing technique as yourself?

In the PT case, he doesn't have to, because he is going to tell you what PT values he wants you to send him.

> In SIP for example, when constructing a first offer, you may want to map both Opus and VP8 to 96, then add SSRCs for demuxing. This means that you expect your peer to support SSRC demuxing and you can't expect that unless we mandate it.
>
> Or am I missing something?

No. In case of support of extensions (e.g. the SDP ssrc attribute), you either have to perform some kind of capability exchange before you send the initial Offer. Or, you will figure out in the response to the initial Offer, and then you can "fix" it in a new Offer (as BUNDLE is currently specified, you will have to send a second Offer anyway).

But, again, what I want to discuss now is whether/what we are going to specify regarding the usage of multiple m= lines with the same transport protocol (RTP, or whatever other there could be).

Regards,

Christer