[webkit-dev] Position on emerging standard: video.requestAnimationFrame()

Simon Fraser simon.fraser at apple.com
Wed Feb 5 17:09:11 PST 2020

> On Feb 5, 2020, at 4:52 PM, Thomas Guilbert <tguilbert at google.com> wrote:
> I am moving the execution of the video.rAF callbacks to be part of the rendering steps. This should guarantee that "changes made inside the callback appear at the same time as other changes in the same event loop cycle".
> I don't know if there is a place within the rendering steps where it makes most sense for them to run. I'm planning on having them run before the window.rAF callbacks, but I don't know after which of the other steps for now.
> That being said, if you paint a 24fps <video> into a <canvas> on every video.rAF call, the canvas might still be 1/60th of a second behind the video. This happens when we miss the rendering steps after jumping back on the main thread, and have to wait for the next rendering steps (waiting doesn't really change anything though, if the callbacks were fired earlier, their changes would still appear later).
> Simon, does having video.rAF callbacks run as part of the rendering steps address some of your concerns?

It does, although I still don't like the name.

The spec also needs somehow trigger the "update the rendering" steps if a new video frame is available and there is a pending video.rAF (video playback alone does not trigger the rendering steps, at least in WebKit, for performance reasons).


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