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

週末にはBoomerangエフェクトビデオエンコーダを使って遊んでいましたが、ほぼリアルタイムで動作させることができます(後で説明します)。私はそれをデスクトップ上のChromeで動作させましたが、AndroidのChromeでは正常に動作しません。 コードはここにあるを参照してください。

captureStream()を ` (私の場合は1280x720)、MediaRecorder APIはビデオをエンコードすることができず、エラーもなく、事前にビデオをエンコードできないことを検出できません。

(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: https://boomerang-video-chrome-on-android-bug.glitch.me/ Code: https://glitch.com/edit/#!/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 https://boomerang-video-chrome-on-android-bug.glitch.me 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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