Improve frame count for dom videos

[ivmartel]

The calculation of the number of frames for dom videos is based on a hard coded frame rate (see domReader.js#L133). This leads to the generation of images larger that necessary.

A first improvement would be to not store all frames but check the video.currentTime to see if it is close to the seeked one. Something like a if (Math.abs(nextTime - video.currentTime) < 1e-8).

Another one would be to use the `` (see video-rvfc draft and video-rvfc repo). For now it is only supported on chrome based browser: caniuse requestvideoframecallback). The code would look like:

video.addEventListener('ended', function () {
  onload({
    source: origin
  });
  onloadend({
    source: origin
  });
});

var frameCb = function (/*now, metadata*/) {
  // repeat
  video.requestVideoFrameCallback(frameCb);
  // store
  // warn: if placed before the frame request, will
  //   skip the second frame, I guess because of the call
  //   to context.draw...
  storeFrame();
};
video.requestVideoFrameCallback(frameCb);

video.loop = false;
video.autoplay = false;
video.muted = true;
video.currentTime = 0;

video.play();

Both solution need to rethink how the number of frames is passed to the app.

[ivmartel]

Some notes:

• video.getVideoPlaybackQuality(): no useful nfo...
• listen to timeupdate: ~1/2 frames... some posts say that firefox fires timeupdate at frame change, not in my case (firefox 85)... (https://stackoverflow.com/a/17048103)
• window.requestAnimationFrame: fired every 16ms... not meant for this (https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame)