[Freeswitch-users] OPUS Codec

[Michael Jerris]

> On May 10, 2017, at 12:40 PM, Kristian Kielhofner <kris at kriskinc.com> wrote:
> 
> Just because "according to Kristian Kielhofner" sounds strange to me;
> how about according to RFC 7587 :)?
> 
> https://tools.ietf.org/html/rfc7587#section-7
> 
> "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.”

- According to Kristian Kielhofner and RFC 7587….


> 
> On Wed, May 10, 2017 at 8:38 AM, Colton Conor <colton.conor at gmail.com> wrote:
>> Anyone know on Polycom VVX's using OPUS, what is the sample rate? 8Khz or
>> 48Khz or somewhere inbetween?
>> 
>> I looked a at call through VoIP Monitor, and it said OPUS48 as the codec.
>> Buy since "the OPUS
>> specification says that the SDP must always specify 48 kHz and 2 channels"
>> according to Kristian Kielhofner", I assume it just sadys OPUS 48 because of
>> this.
>> 
>> Like I mentioned, I though that G.722 between two Polycom's sounded better
>> than OPUS to my suprise. I assume this is because G.722 is at 16 kHZ, and
>> Polycom's opus is potentially at 8kHZ.
>> The softswitch we are using (Netsapiens) does not do any trasconding to my
>> knowledge, so the payload has to be whatever Polycom encodes/decodes at.
>> 
>> Is there a way to tell what kHz the Opus codec is running at on a Polcom
>> VVX, or by looked at a packet capture?
>> 
>> 
>> On Sat, May 6, 2017 at 1:26 PM, Kristian Kielhofner <kris at kriskinc.com>
>> wrote:
>>> 
>>> 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.