Support for OffscreenCanvas

[nahkd123]

It would be nice if webm writer support OffscreenCanvas, because I'm trying to do render stuffs inside web worker. As far I know, you can get the WebP blob by using OffscreenCanvas#convertToBlob({type: "image/webp"})

[guest271314]

You can pass the Blob from convertToBlob() to FileReader or FileReaderSync readAsDataURL(), then pass the data URL to addFrame()

(async _ => {
  const osc = new OffscreenCanvas(1,1);
  const osctx = osc.getContext('2d');
  const blob = await osc.convertToBlob({type:'image/webp'});
  const frs = new FileReaderSync();
  const canvas = frs.readAsDataURL(blob);
  videoWriter.addFrame(canvas);
})();

[dayaftereh]

I use the WebMWriter with an OffscreenCanvas inside a WebWorker and came across the exception:

Failed to find VP8 keyframe in WebP image, is this image mistakenly encoded in the Lossless WebP format?

To solve the issue I changed the quality of the conversion to

const blob = await osc.convertToBlob({type:'image/webp', quality: 0.9999});