[Freeswitch-users] OPUS Codec

Sat May 6 22:26:12 MSD 2017

FreeSWITCH can limit Opus to a configured sample rate but the OPUS
specification says that the SDP must always specify 48 kHz and 2
channels.

OPUS is a combination of SILK and CELT, with the original PLC+FEC
coming from SILK. There are effectively three modes in OPUS - SILK,
CELT, and hybrid. It's not clear to me how well PLC+FEC works in the
hybrid and CELT modes used at higher sample rates. I haven't looked at
it specifically (or tested it) but my suspicion is that PLC+FEC works
much better the closer you get to "pure" SILK mode, which is
essentially what limiting the sample rate to 8 kHz does.

On Sat, May 6, 2017 at 10:21 AM, Colin Morelli <colin.morelli at gmail.com> wrote:
> Transcoding != resampling. Often times you will have to do both to convert
> audio streams, where transcoding is the act of converting between the two
> audio codecs' data format, and resampling is changing the sampling rate of
> the audio (8khz in your case).  Opus is a completely different audio codec
> than G.711. Even if they're both at 8 khz, you'll have to transcode between
> the two, though you may be able to avoid the cost of resampling the audio to
> a different rate.
>
> Opus can handle sampling rates from 8khz-48khz. Sampling rates make a huge
> difference to audio quality (they'll effectively define the range of audio
> frequencies you can capture). If you're running opus at a constant 8khz, the
> reason G.722 sounds better is almost certainly because it's using a 16khz
> sampling rate. Most likely if you run opus at 16khz, it'll sound similar to
> G.722. If you have the capacity (and the devices support it), pushing opus
> to super-wideband or full band (24khz/48khz sampling rates, respectively)
> will yield much better audio quality.
>
> My guess (admittedly it's just an educated assumption), is that most WebRTC
> companies are using fullband opus in VBR mode simply because this is the
> default in WebRTC. Without mangling the SDP, this is what you're going to
> get.
>
> Best,
> Colin
>
> On Sat, May 6, 2017 at 10:41 AM, Colton Conor <colton.conor at gmail.com>
> wrote:
>>
>> So what does today support FEC/PLC today?
>>
>> We tested two Polycom VVX phones with the opus codec, and overall thought
>> that G.722 sounded much better than OPUS for some reason.
>>
>> So using Opus at 8 KHz, does that mean that there will be less or no
>> transcoding to G.711 since its also in 8 KHz?
>>
>> What are most of the web only WebRTC companies using as far as OPUS goes?
>> What bitrate and KHz?
>>
>> On Fri, May 5, 2017 at 8:33 AM, Brian West <brian at freeswitch.org> wrote:
>>>
>>> None of the hardware phones do FEC/PLC last I tested, Sonus has OPUS
>>> support, but again no FEC/PLC support.
>>>
>>> /b
>>>
>>>
>>> On Wed, May 3, 2017 at 2:16 AM, EL <fs.user at fordior.net> wrote:
>>>>
>>>>
>>>> Yealink is supporting OPUS on several other models since firmware
>>>> V81:
>>>>
>>>> Quote:
>>>> "We will support opus on the standard V81 of
>>>> SIP-T40P/T23P/T23G/T2 1(P) E2/T19(P) E2."
>>>>
>>>> Source:
>>>> http://forum.yealink.com/forum/showthread.php?tid=29650&pid=51262&mode=threaded
>>>>
>>>> I can confirm OPUS implementation on the 'T21P E2' model.
>>>>
>>>> --
>>>> EL
>>>>
>>>>
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>>>
>>>
>>>
>>> --
>>>
>>> Brian West
>>> brian at freeswitch.org
>>>
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>>
>>
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>
>
>
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-- 
Kristian Kielhofner