What are the downsides ( if any ) of using OPUS ?

[Kushtrim Pacaj]

I saw that in the AppRTC android sample by google OPUS is used as audio codec, though I've seen countless samples online that change the SDP to prefer ISAC instead of OPUS?

I'm developing an app that uses WebRTC, and thought of using OPUS since it's both the default one in AppRTC, and also based on what I've read is superior to many other codecs in bad network conditions.

So, is there a downside to using OPUS in comparison to ISAC ? 

[Alexandre GOUAILLARD]

bandwidth usage. OPUS is a 2-channels (stereo) codec. In webrtc, if I remember correctly, it is using 48khz sampling (as one can see in the Offer/Answer SDPs). Isac is one channel at 16khz (in webrtc). All other things being equals, opus is then using 6 times more bandwidth.

early on, CPU consumption was also much higher than iSAC, but new version of opus is better in that regard, so I don't know if it's still bottleneck.

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[Silvia Pfeiffer]

On Sun, Oct 23, 2016 at 3:05 PM, Alexandre GOUAILLARD
<agoua...@gmail.com> wrote:
> bandwidth usage. OPUS is a 2-channels (stereo) codec. In webrtc, if I
> remember correctly, it is using 48khz sampling (as one can see in the
> Offer/Answer SDPs). Isac is one channel at 16khz (in webrtc). All other
> things being equals, opus is then using 6 times more bandwidth.

That doesn't necessarily follow, because Opus compresses differently to iSAC.

However, it seems that others have found that iSAC works better in
poor quality networks:
https://groups.google.com/forum/#!topic/discuss-webrtc/gyisRe6PZGw .

Kushtrim, you might want to read http://opus-codec.org/comparison/ and
then do your own experiments. :-)

Cheers,
Silvia.

[Philipp Hancke]

2016-10-23 9:22 GMT+02:00 Silvia Pfeiffer <silviap...@gmail.com>:

On Sun, Oct 23, 2016 at 3:05 PM, Alexandre GOUAILLARD
<agoua...@gmail.com> wrote:
> bandwidth usage. OPUS is a 2-channels (stereo) codec. In webrtc, if I
> remember correctly, it is using 48khz sampling (as one can see in the
> Offer/Answer SDPs). Isac is one channel at 16khz (in webrtc). All other
> things being equals, opus is then using 6 times more bandwidth.


That doesn't necessarily follow, because Opus compresses differently to iSAC.

As can be observed on https://webrtc.github.io/samples/src/content/peerconnection/audio/

Opus uses ~40kbps in Chrome (50kbps in Firefox), ISAC slightly above 30kbps.

[Silvia Pfeiffer]

Good data.

Is that with default settings, so Opus providing 48kHz audio and iSAC
16kHz? That would imply a huge difference in audio quality with
minimally more bandwidth use...

You should be able to change the used bandwidth by setting the
bandwidth limit in SDP, right? Then you should be able to get Opus at
the same bandwidth as iSAC?

[Alexandre GOUAILLARD]

hence the "all other things being equals".

I did not want to go into compression, quantization, ......

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[Alexandre GOUAILLARD]

nice data, thanks.

What about the CPU consumption? I remember the difference to be drastic especially on mobile. Opus would actually saturate the CPU on an iPhone 4 and almost on an iPhone 5 before google upgraded to v1.1. I have not made new benchmark since.

Alex.

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