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Re: [mediacapture-main] what is the default channelCount (#775)

From: youennf via GitHub <sysbot+gh@w3.org>
Date: Tue, 02 Mar 2021 21:44:26 +0000
To: public-webrtc-logs@w3.org
Message-ID: <issue_comment.created-789241737-1614721465-sysbot+gh@w3.org>
> > Web Audio says the following: If contextOptions.sampleRate is specified, set the sampleRate of this AudioContext to this value. Otherwise, use the sample rate of the **_default output device_**.
> @youennf Exactly, and what singular testable value is that?

We can probably test it, by comparing WebAudio default sampleRate with getUserMedia default sample rate.
You first need to verify the input device has the same groupId as the output device. 

> The spec even mentions "[platform defaults](https://w3c.github.io/mediacapture-main/getusermedia.html#dom-constrainablepattern-getsettings)" as being useful (and preferable?) results, but shies away from mandating them.

The spec mentions platform defaults, but do not define them.
This is what we want to address here.

Also the spec mentions platform defaults but does not tell how or when they should apply.
This is again bad and I hope we can address it, though just defining defaults would be good.

> Part of the reason for that is that unlike output, there's no singular camera or microphone greater than another always.
We are talking constraints not devices here.
For some constraints, the OS provides default values and we should use them, like web audio is doing.
For other constraints, the OS does not provide default values, say echoCancellation.

AIUI, @bradisbell actually wants default values so that the browser processing is as thin as possible.
This means echoCancellation=false for instance. This does not mean 'no default'.

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