[SIP Beyond VoIP] Opus at lower sample rate

[Saúl Ibarra Corretgé]

On 27 Aug 2014, at 16:34, Juha Heinanen <jh at tutpro.com> wrote:

> Saúl Ibarra Corretgé writes:
> 
>> Opus is always advertised at 48KHz but it self adjusts. IIRC you
>> always need to specify it at 48KHz.
> 
> That is correct, but the problem is that number of channels=2 is
> missing.  According to
> 
> http://tools.ietf.org/html/draft-ietf-payload-rtp-opus-03#section-3
> 
>      The media subtype ("opus") goes in SDP "a=rtpmap" as the encoding
>      name.  The RTP clock rate in "a=rtpmap" MUST be 48000 and the
>      number of channels MUST be 2.
> 
> Blink generates
> 
> a=rtpmap:113 opus/48000
> 
> when it should generate
> 
> a=rtpmap:113 opus/48000/2
> 
> Now when /2 is missing, blink is not able to negotiate opus with webrtc
> clients such as google chrome browser.
> 

Yeah, I’m aware of this :-/ Hopefully I can fix that for the next release. I recall I had some interoperability issues because we used to do it like that in the beginning, but I’d assume this is no longer a problem.

--
Saúl Ibarra Corretgé
AG Projects



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