Re: [rtcweb] Call for Consensus Regarding Selecting Recommended Audio Codecs

[Hadriel Kaplan <[e-mail]>]

On Jan 18, 2013, at 11:43 AM, Tim Panton <[e-mail]> wrote:
> 
> Just for clarity, lets make that 
> "If other suitable audio codecs are available to the browser to use it
> is beneficial that they are also included in the offer but at a lower priority than the MTI codecs
> in order to maximize the possibility to establish the session without the need for
> audio transcoding"

Umm... but then two endpoints both implementing a better non-MTI codec would pick the MTI one instead of the better one.

Generally you don't need to muck with the order to get transcoder-free operation - as long as both sides support at least one common one, they'll pick it if they follow the preference rules in RFC 3264.  That's because the gateway in the middle will usually add the additional codecs it can transcode for, later in the SDP m-line preference order (ie, make them lower preference in the offer).[1]

-hadriel
[1] I say "usually" because of course this is not always the case, because sometimes they change the pref order for other reasons; nor is it the case that gateways in the middle always add codecs for transcoding, but rather sometimes they let the INVITE fail first and then re-send it with additional codecs (though that's a far less common model).