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Re: [media-and-entertainment] Frame accurate seeking of HTML5 MediaElement

From: Google <sysbot+gh@w3.org>
Date: Fri, 29 Jun 2018 23:58:41 +0000
To: public-web-and-tv@w3.org
Message-ID: <issue_comment.created-401501174-1530316720-sysbot+gh@w3.org>
@Diaz I spoke with the TL of Chrome's video stack and they gave me a pointer to an implementation that you can play around with now.

First, behind --enable-experimental-canvas-feature, are some additional attributes on HTMLVideoElement that contain metadata about frames uploaded as WebGL textures, including timestamp. [1]

The longer term plan is a WebGL extension to expose this data [2], and implementation has begun [3] but I am not sure of its status.

I agree there are use cases outside of WebGL upload for accurate frame timing data, and it should be possible to provide it on HTMLVideoElement's that are not uploaded as textures.  However, if the canvas/WebGL solution works for you, then that makes a stronger case to expose it elsewhere.

Note that any solution may be racy with vsync depending on the implementation and it may be off by 16ms depending on where vsync happens in relation to the video frame rendering and the execution of rAF.

That's really all the help I can provide at this time.  There are many other use cases and scenarios discussed here that I don't have time to address or investigate them right now.

Thanks.

[1] https://bugs.chromium.org/p/chromium/issues/detail?id=639174
[2] https://www.khronos.org/registry/webgl/extensions/proposals/WEBGL_video_texture/
[3] https://bugs.chromium.org/p/chromium/issues/detail?id=776222




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