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[rtcweb] Rate for telephone-events in combination with OPUS

Roman Shpount <roman@telurix.com> Wed, 16 July 2014 18:45 UTC

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Date: Wed, 16 Jul 2014 14:45:27 -0400
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From: Roman Shpount <roman@telurix.com>
To: "rtcweb@ietf.org" <rtcweb@ietf.org>
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Subject: [rtcweb] Rate for telephone-events in combination with OPUS
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Should we specify two telephone-events payloads, one with 8000 rate to be
used with PCMU/PCMA and another with 48000 rate to be used with OPUS?

>From what I can see, based on RFC 7160, if OPUS codec is used
telephone-events should either be transmitted with the rate 48Khz or use a
different SSRC. On the other hand if PCMU/PCMA is selected then DTMF should
be transmitted using 8000 clock or use a different SSRC. Using different
SSRC is problematic since it will create synchronization issues with audio
playback (things like record your name and press pound will stop working)
apart from other webrtc related issues. I think the only solution that
makes sense is to advertise two telephone-events payloads and use the
appropriate one based on the selected transmit codec, similar to CN.
_____________
Roman Shpount

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