Re: [rtcweb] codec and connection negotiation

[Harald Alvestrand <[e-mail]>]

Trying to doodle on the opinions (the alternative lists were quite 
useful to clear the mind - I liked them a lot, and will return to them!)

On 08/05/11 20:53, Matthew Kaufman wrote:
> Now, to follow up on my previous message with a bit of opinion...
>
> I think we should not use SDP as the API, and we should not have the 
> browser implementing SDP offer-answer.
>
> 1. If SDP offer-answer is all that is available to the Javascript 
> programmer (and server programmer), it becomes very difficult to know 
> what the full capability set is without complex probing. This 
> significantly complicates the building of future innovative 
> applications on top of the browser as platform. Many of the current 
> applications that show off browser capabilities do so by using 
> capabilities that were already present for other reasons, and we can 
> expect the same innovation to occur here, if we provide the tools.
This may be heretical ... but do we actually need to enumerate all 
capabilities?
It seems to me that we'll have exactly 2 groups of capabilities:
- Routine ones, which are generated automagically when saying "I want 
something working"
- Ones needed to "show off" specific new capabilities

The platforms, which are likely reusing code from outside WebRTC, may 
support many capabilities that are never required for any scenario 
(especially those that have been added over the years to support 
backwards compatibility in very baroque scenarios). Exposing those will 
just add clutter, not add quality.

The "show-offs" will be capable of probing.
>
> 2. Using SDP offer-answer has the advantage of reusing all the IETF 
> standards work that occurs to define SDP when a new codec comes along. 
> But it also has the *disadvantage* of having to wait for the IETF to 
> produce these standards, which may be incomplete, or unable to control 
> parameters which are necessary for web applications.
Hmmm.... since when have people *actually* waited for the IETF process 
to finish before starting to use newly defined capabilities?
This may argue for looking again at the IANA procedures for SDP, and 
institute something like the "provisional registries" that were 
introduced for email/web.
>
> 3. Anything that is missing in SDP (example: forcing the Opus codec to 
> "music" mode for encoding) will still need to be exposed as a 
> Javascript API on the encoder. Thus we end up with a mix of 
> possibly-conflicting settings that are adjusted via the explicit API 
> and the opaque SDP API.
Won't these be things people want in SDP too? See above.
>
> 4. Other work in browsers (like recording camera and microphone to 
> disk) will require the ability to directly control the encoders. If 
> these APIs exist then there will definitely be conflicting settings. 
> What happens if you feed in an SDP answer that requires VP8 encoding 
> and then set the encoder to H.264 mode via the Javascript?
Transcoding? :-)
The same problem exists today when trying to use cameras for multiple 
things concurrently.
>
>
> Matthew Kaufman
> _______________________________________________
> rtcweb mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/rtcweb
>