Re: [mediacapture-image] Document OverConstrainedError for PTZ in explainer (#229)

What would be unpredictable would be web devs needing to refer to a list over which constraints can be set from `getUserMedia` or not. It also seems rather pointless since they can just call `applyConstraints` right after for the same effect.

> Things are a bit simpler with applyConstraints since it starts with a device initial state that is exposed to the web page.

Does it? Isn't that only if people make the effort to call `getSettings` explicitly and take those into account when specifying their constraints somehow? E.g.:
```js
await track.applyConstraints(buildMyConstraintsFromSettings(track.getSettings()));
```
I don't think that's been common, until this spec at least where you're kinda forced to do that initially since the units of `pan`, `tilt` and `zoom` are unknown. However that doesn't preclude restoring settings from last visit, which should be good for the same `deviceId` at least.

> step 6.6 is potentially calling the applyConstraints constraints twice for audio and video tracks, so "In a single operation" is not always guaranteed. ... [because] ... step 6.6 is also handling the case of an error.

It also says about these steps: _"For each media type kind ... run the following sub steps, **preferably at the same time**"_

So it seems possible to implement this where all constraints failures from step 6.6. are dealt with before `pan`, `tilt` and `zoom` move the camera, or by simply doing audio first.

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Received on Friday, 28 August 2020 12:07:40 UTC