MediaStreamTrack.getCapabilities() return a Map where some values are NativeJavaScriptObject

[wer-mathurin]

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• dart2js

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• Dart SDK Version (dart --version)
  Dart SDK version: 2.11.0-242.0.dev (dev) (Wed Oct 21 00:38:45 2020 -0700) on "windows_x64"

When calling

final mediaConstraints = <String, dynamic>{
    'audio': true,
    'video': {
      'mandatory': {
        'minWidth': '1280',
        'minHeight': '720',
        'minFrameRate': '30',
      },
    }
  };
var stream = await navigator.getUserMedia(mediaConstraints);
var _capabilities = stream.getVideoTracks()[0].getCapabilities();

If you inspect the map, you will have for example a NativeJavaScriptObject
_capabilities['aspectRatio']
_capabilities['width']
_capabilities['frameRate']
etc...

Seems to me a problem converting javascript type to dart equivalent.(double and int)

I just want to mention: @srujzs
Since the last commit was involving a similar problem, but in the opposite direction :-)

The method that is doing the conversion is:
convertNativeToDart_Dictionary

[srujzs]

Yup, it seems identical to #43802, with the problem being we don't handle nested dictionaries. The fix here will likely involve converting recursively for the same group of accepted types.

[wer-mathurin]

@srujzs: according to the specification:

aspectRatio is a double specifying the video aspect ratio or range of aspect ratios which are acceptable and/or required.

Not a tree of objects!

Same for other properties describe in the bug description.

[Hexer10]

Is there are update about solving this issue? I'm trying to port this code to Dart but I couldn't succeed:

(javascript)

const userMedia = await navigator.mediaDevices.getUserMedia({video: true, audio: true});

const videoTrack = userMedia.getVideoTracks()[0];
const capabilities = videoTrack.getCapabilities();
const aspectRatio = capabilities.aspectRatio;

console.log(aspectRatio.max);

(dart)

  final userMedia = await window.navigator.mediaDevices!
      .getUserMedia({'video': true, 'audio': false});
  
  final videoTrack = userMedia.getVideoTracks().first;
  final capabilities = videoTrack.getCapabilities();
  final aspectRatio = capabilities['aspectRatio'];
  
  print(aspectRatio['max']); // Here this is thrown:
  /*
  Uncaught (in promise) Error: NoSuchMethodError: '[]'
  Dynamic call of null.
  Receiver: Instance of 'NativeJavaScriptObject'
  */

Any suggested solutions/workarounds?

Check here for the full error stacktrace: https://stackoverflow.com/questions/67375720/call-to-videotrack-getcapabilities-returns-an-instance-of-nativejavascriptobje

[srujzs]

Hi,

Sorry for a lack of update on solving this issue. You can workaround this using js_util to work with the underlying JS object for now:

print(js_util.getProperty(aspectRatio, 'max'));

aspectRatio here is an object literal that hasn't been converted to a Dart type, which is why you're seeing the above.

[GabrielMCastro]

@srujzs would you recommend updating convertNativeToDart_Dictionary to handle nested values or adding separate method to handle it?

[srujzs]

I'd say update it. We had the same convo around convertDartToNative_Dictionary and I'm not sure what value there is in having separate methods. These conversions are for dart:html too, so I don't think the web APIs would benefit from both methods. Plus, if we do see that we want that option later, we can just add an optional arg to the method.

[srujzs]

One thing to maybe add a check for is recursive lists or maps. convertDartToNative_Dictionary is missing this check as well.