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Re: Mangling a=extmap and a=mid before setLocalDescription

From: Iñaki Baz Castillo <ibc@aliax.net>
Date: Wed, 19 Jul 2017 14:12:44 +0200
Message-ID: <CALiegfmHMr-cDMckAELTkOvaMYY4X4_a0ZBsYoZ7VK3cMJTpgw@mail.gmail.com>
To: Adam Roach <adam@nostrum.com>
Cc: "public-webrtc@w3.org" <public-webrtc@w3.org>
2017-07-19 14:07 GMT+02:00 Adam Roach <adam@nostrum.com>:
> On 7/19/17 13:58, Iñaki Baz Castillo wrote:
>> I know that the idea is to not have to mangle the SDP to get some cool
>> things, but before that happens in the real world, is it allowed to
>> mangle the ID of a=extmap and the value of a=mid between createOffer()
>> and setLocalDescription()?
>> Are current browsers supposed to honor those new values given in
>> setLocalDescription() and use them within the RTP packets?
> JSEP makes this illegal; see
> https://tools.ietf.org/html/draft-ietf-rtcweb-jsep-21#section-5.4
> I'm sure Firefox won't honor such changes.

Nice to know that.

> I suspect Chrome doesn't; and, if it does, it shouldn't.

Yes, but currently a=ssrc, payload numbers (among others) can be
mangled and it works. Anyhow I agree that the app should not do this.

Once this is clear (thanks for the reference) I wonder why do we need
the "createOffer" + "setLocalDescription" ceremony at all? I mean, if
the SDP provided by createOffer() should not be changed in any way and
setLocalDescription() should be called with it, why does it even
exist? It provides nothing.

Iñaki Baz Castillo
Received on Wednesday, 19 July 2017 12:13:33 UTC

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