MediaStreamTrack.applyConstraints() should resolve the Promise with the applied constraints

[yellowdoge]

At https://w3c.github.io/mediacapture-main/#dom-constrainablepattern-applyconstraints(), instead of resolving with void, it'd be better to resolve with the applied constraints.

[yellowdoge]

+@beaufortfrancois and re. https://crbug.com/723251

[burnburn]

@jan-ivar can you think of any reason why we couldn't do this?

[jan-ivar]

@yellowdoge What's the utility? You already have them, and they're synchronously available:

await track.applyConstraints(constraints);
console.log(constraints == track.getConstraints()); // true

[yellowdoge]

@beaufortfrancois what was the rationale...?

[beaufortfrancois]

I'd like to know which constraints have been applied after each call as they might not be the ones currently set.

track.applyConstraints(someConstraints).then(appliedConstraints => {
  console.log(appliedConstraints + ' may be different from ' + track.getConstraints());
)};
track.applyConstraints(otherConstraints).then(appliedConstraints => {
  console.log(appliedConstraints + ' may be different from ' + track.getConstraints());
)};

[jan-ivar]

they might not be the ones currently set.

@beaufortfrancois That cannot happen.

[beaufortfrancois]

Chrome's implementation actually makes this happen. Go to https://beaufortfrancois.github.io/sandbox/image-capture/playground.html and execute JS code below in your console (webcam is expected):

imageCapture.track.applyConstraints({advanced: [{brightness: 100}]}).then(_ => {
  var appliedBrightness = imageCapture.track.getConstraints().advanced[0].brightness;
  console.assert(appliedBrightness == 100, 'applied brightness should be 100');
});
imageCapture.track.applyConstraints({advanced: [{brightness: 200}]}).then(_ => {
  var appliedBrightness = imageCapture.track.getConstraints().advanced[0].brightness;
  console.assert(appliedBrightness == 200, 'applied brightness should be 200');
});

>>> Assertion failed: applied brightness should be 100

[guidou]

@beaufortfrancois : Chrome's implementation is not spec compliant and only works in a limited way for image capture. If applyConstraints is successful, getConstraints() should be the same (or equivalent) to the constraints that were requested.

[jan-ivar]

Isn't it also behind a flag still?

[beaufortfrancois]

It is not behind a flag after Chrome 59.

[guidou]

We should close this.
I'm preparing a change in Chromium to make applyConstraints resolve promises with void for image capture, since the applied constraints and current settings can always be obtained using getConstraints() and getSettings(), respectively.

[alvestrand]

Closing. You can get the most recently applied constraints by getConstraints(), and the settings that resulted by getSettings() (and they don't mean the same thing).