[SIP Beyond VoIP] Opus at lower sample rate
Juha Heinanen
jh at tutpro.com
Wed Aug 27 16:34:42 CEST 2014
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.
-- Juha
More information about the SIPBeyondVoIP
mailing list