Re: [rtcweb] JSEP-bis and WebRTC-Extensions Section 5.2

[Christer Holmberg <[e-mail]>]

Hi,

>> Are there actually some real implementation issues behind the proposed change, or is it only
>> about W3C and IETF using different terminology?
>
> It’s an API layer thing. At present there are no ways for a javascript application to manage which RTP
> header extensions are present in an offer*. So the current behaviour is to offer _everything_ the
> library/stack is capable of. The W3C is creating an API point that allows the javascript application to
> decide which extensions (of all the ones supported by the stack) are useful/relevant/safe for the application.
>
> If both side’s webRTC implementations support a lot of RTP header extensions, the current wording will have
> them _all_ offered and all accepted in an answer, even if none of them add any value to the application - bloating
> the packet size needlessly.  Specifically: ’supported’ is taken to mean supported by the user agent - rather than
> supported by the application as a whole.
>
> (This is my understanding of the issue at least)

Wouldn't it be better to have a generic statement, saying that for some features there are APIs that, for some features,
allow the JS application to control what options are offered. That would also be future proof, and we would not have
to update the JSEP spec every time there is a new API that allows the JS application to control what options are offered
for a certain feature.

Regards,

Christer



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________________________________
From: rtcweb <[e-mail]> on behalf of Tim Panton <[e-mail]>
Sent: Sunday, May 7, 2023 1:16:27 PM
To: Christer Holmberg <christer.holmberg=[e-mail]>
Cc: [e-mail] <[e-mail]>
Subject: Re: [rtcweb] JSEP-bis and WebRTC-Extensions Section 5.2

I was also thinking about this too - and I somewhat agree.

We could replace ‘supported' with 'supported by the current application’ since at a high level what this change does is to differentiate between extensions that the library (libwebrtc etc) can support vs extensions the current application wants to support.

It also makes it clearer that this is an editorial change.

T.

On 7 May 2023, at 11:10, Christer Holmberg <christer.holmberg=[e-mail]> wrote:

Hi,

I have issues with the proposed change.

First, AFAIK, "enabled" is not used in any other O/A specification.

Second, my reading of "supported" is that it is something that the endpoint is actually willing to/capable of using within the session.

Third, within the JSEP O/A procedures, "supported" is used for other features (e.g., FEC mechanisms). Using other terminology for one feature will only confuse the reader, in my opinion.

Fourth, if it is unclear what "supported" really means we should rather clarify that.

Regards,

Christer

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________________________________
From: rtcweb <[e-mail]> on behalf of Justin Uberti <[e-mail]>
Sent: Saturday, May 6, 2023 3:30:33 AM
To: [e-mail] <[e-mail]>; [e-mail] <[e-mail]>
Subject: [rtcweb] JSEP-bis and WebRTC-Extensions Section 5.2

The WebRTC W3C WG is working on an extension spec<https://w3c.github.io/webrtc-extensions/#rtp-header-extension-control-modifications> that suggests behavior for RTP header extension O/A that conflicts slightly with the current version of JSEP. Rather than have this sort of ad-hoc extensions extension to JSEP in the W3C spec, it was suggested that we could apply a tiny patch to JSEP before JSEP-bis is finalized (it's currently in the RFC Editor state). Murray was supportive of this but wanted to make sure the WG was fully behind this change first.

For context, Section 5.2 in the W3C extension spec basically says that WebRTC endpoints can control the extensions that are in use, and as a result O/A negotiation should a) use only the extensions that are enabled by the endpoint, and b) always reoffer all extensions, rather than the previously negotiated set.

I've made a PR that captures this request at https://github.com/rtcweb-wg/jsep/pull/1033/files<https://protect2.fireeye.com/v1/url?k=31323334-501d5122-313273af-454445555731-45f3175ddedc0fdc&q=1&e=d500064c-f63a-47ed-b1ec-2ff879fda6f4&u=https%3A%2F%2Fgithub.com%2Frtcweb-wg%2Fjsep%2Fpull%2F1033%2Ffiles>, and it basically makes two surgical changes:
1) replaces the use of "supported RTP header extensions" with "enabled RTP header extensions"
2) changes the text around "extensions... present in the most recent answer" to instead say "extensions... enabled on the associated transceiver" (similar to how codecs are handled in JSEP).

Please let me know if this sounds reasonable to you or you have concerns.

Thanks,
Justin

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