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

From: Roman Shpount <[email-masked]>
Date: Wed, 16 Jul 2014 14:45:27 -0400

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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From: "Timothy B. Terriberry" <[email-masked]>
Date: Wed, 16 Jul 2014 20:13:34 -0700

Roman Shpount wrote:
> 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.

That's what we agreed to on this list in June 2012 [1].

[1] http://www.ietf.org/mail-archive/web/rtcweb/current/msg04598.html

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From: Justin Uberti <[email-masked]>
Date: Wed, 16 Jul 2014 23:13:51 -0400

Yes, this is my understanding as well.

On Wed, Jul 16, 2014 at 2:45 PM, Roman Shpount <[email-masked]> wrote:

> _______________________________________________
> rtcweb mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/rtcweb
>
>

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From: Roman Shpount <[email-masked]>
Date: Wed, 16 Jul 2014 23:48:22 -0400

So, I guess the fact that neither Chrome no Firefox do this is an oversight
or an unimplemented feature.

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From: Justin Uberti <[email-masked]>
Date: Thu, 17 Jul 2014 11:02:24 -0400

For Chrome, we just haven't gotten to it yet. I think there is an open bug
on it.

On Wed, Jul 16, 2014 at 11:48 PM, Roman Shpount <[email-masked]> wrote:

> So, I guess the fact that neither Chrome no Firefox do this is an
> oversight or an unimplemented feature.
>>> 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?
>>>

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From: Adam Roach <[email-masked]>
Date: Thu, 17 Jul 2014 10:55:15 -0500

Same with Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=964282

> On Jul 17, 2014, at 10:02, Justin Uberti <[email-masked]> wrote:
> 
> For Chrome, we just haven't gotten to it yet. I think there is an open bug on it.
> 
> 
>> So, I guess the fact that neither Chrome no Firefox do this is an oversight or an unimplemented feature.
>> 
>>>> 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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From: Justin Uberti <[email-masked]>
Date: Thu, 17 Jul 2014 12:17:41 -0400

Chrome: https://code.google.com/p/webrtc/issues/detail?id=2795