Chrome Bug 897727 - MediaRecorder using Canvas.captureStream() fails for large canvas elements on Android

Le week-end, je jouais avec un encodeur vidéo à effet Boomerang, vous pouvez le faire fonctionner presque en temps réel (je l'expliquerai plus tard). Je l’ai obtenu sur Chrome sur le Bureau, mais cela ne fonctionnerait jamais correctement sur Chrome sur Android. Voir le code ici.

Cela ressemble à lorsque vous utilisez captureStream () sur un <canvas>Avec une résolution relativement importante (1280x720 dans mon cas), l’API MediaRecorder ne pourra pas encoder les vidéos, elle ne provoquera pas d’erreur et vous ne pourrez pas détecter qu’elle ne peut pas encoder la vidéo à l’avance.

(1) Capture a large res video (from getUM 1280x720) to a buffer for later processing. (2) Create a MediaRecorder with a stream from a canvas element (via captureStream) sized to 1280x720 (3) For each frame captured putImageData on the canvas (4) For each frame call canvasTrack.requestFrame() at 60fps

context.putImageData(frame, 0, 0); canvasStreamTrack.requestFrame();

Demo: Code:!/boomerang-video-chrome-on-android-bug?path=script.js:21:42

What is the expected result?

For the exact demo, I buffer the frames and then reverse them so you would see the video play forwards and backwards (it works on desktop). In generall I would expect all frames sent to the canvas to be processed by the MediaRecorder API - yet they are not.

What happens instead?

It only captures the stream from the canvas for a partial part of the video and then stops. It's not predicatable where it will stop.

I suspect there is a limit with the MediaRecorder API and what resolution it can encode depending on the device, and there is no way to know about these limits ahead of time.

As far as I can tell this has never worked on Android. If you use which has a 640x480 video frame it records just fine. The demo works at higher-resolution just fine on desktop.

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About Me: Paul Kinlan

I lead the Chrome Developer Relations team at Google.

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