Add `captureStream()` method

[piranna]

Add missing captureStream Canvas method. It returns a MediaStream object, where on each canvas change a new frame is being added with the actual canvas contest. This is similar to using node-webrtc RTCVideoSource class and calling to its onFrame() method, so probably some code could be reused between both projects. A polyfill can also be created to add that feature, but it would need first to have merged my changes to notify paint operations.

[BrandonQDixon]

I see this issue is 2 years old almost, but this repository is still being maintained. Would it be possible to get that previous PR merged as described in the issue so we can move forward on implementing the missing "captureStream" functionality? Alternatively, is there a different way we can get a MediaStream object (or otherwise something which we can use to serve a video stream via express js?)

[LeviPesin]

As a workaround the following can be used instead:

const i420Frame = {width, height, data: new Uint8ClampedArray(1.5 * width * height)};
const imagesSource = new WebRTC.nonstandard.RTCVideoSource();
const imagesTrack = imagesSource.createTrack();
const mediaStream = new WebRTC.MediaStream([imagesTrack]);

// on each frame
const frame = context.getImageData(0, 0, width, height);
WebRTC.nonstandard.rgbaToI420(frame, i420Frame);
imagesSource.onFrame(i420Frame);

[princefishthrower]

@LeviPesin - can you elaborate? That code snippet doesn't include the canvas object at all.

[LeviPesin]

frame is an image data that should be added to track, I've added a line getting it from the canvas.

[LIMPIX31]

I'm surprised we still don't have it

[tempranova]

Another vote to get this working!