Re: [rtcweb] Signalling, SDP, and the way we think about interconnecting RTCWEB applications

Wolfgang <> Sat, 15 October 2011 12:58 UTC

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Date: Sat, 15 Oct 2011 14:58:20 +0200
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From: Wolfgang <>
To: Neil Stratford <>
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Subject: Re: [rtcweb] Signalling, SDP, and the way we think about interconnecting RTCWEB applications
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On Sat, Oct 15, 2011 at 2:08 PM, Neil Stratford <> wrote:
> On Sat, Oct 15, 2011 at 12:29 PM, Harald Alvestrand <>
> wrote:

>> b) one of our aims for negotiation is that if application X is deployed in
>> browsers A and B, and both browser A and B support a "best codec" W that was
>> created *after* X was last updated, then the codec W should be used.
>> Given the last point - the app *cannot* "implicitly" what codec will be
>> used. And given that it doesn't know the codec, it can't know the parameters
>> either.
Is this goal worth all the complexity introduced with codec negotiation?

>> (that said... I'm all in favour of fewer parameters. The RTP format for
>> VP8 that we're in the process of finishing has zero parameters. I hope it
>> will remain that way.
That's nice if it really stays that way. MPEG2 had this, too. But then
people started using it in ways that haven't been anticipated and it
turned into a horrible mess.

>> We absolutely insist on interoperability between browser A and browser B, if both are runnning applications that want
>> to communicate.
No disagreement here.

>> Whether RTCWEB client A wants to communicate with RTCWEB client B should be entirely up to them. We're here >> to make it possible, not here to make it mandatory.
What does this requirement cost us in terms of complexity? If we have
to replicate SIP's and SDP's functionalities, it might be not worth

Neil Stratford wrote:
> Can we work around this issue by delegating parameter negotiation to the
> codec itself? Each codec in the codec capability list could present (at a
> minimum) it's name, priority and a codec specific parameter negotiation
> function. We can then delegate the complicated codec specific details (when
> necessary) without needing any advance knowledge in the javascript
> application. We would need to standardise the parameter lists such that
> different codec implementations can interop, but that is the same with SDP.
Do you mean moving codec parameter negotiation into the RTP stream? It
would require
transcoding if your media stream leaves RTCWEB. And you are just moving the
complexity to a different part of the system..