On May 10, 2017, at 12:40 PM, Kristian Kielhofner <kris@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@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@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@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@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@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@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=threa... > > I can confirm OPUS implementation on the 'T21P E2' model.