The HTMLVideoElement.requestVideoFrameCallback specification is available here: https://wicg.github.io/video-rvfc
GitHub repository: https://github.com/WICG/video-rvfc
File an issue: https://github.com/wicg/video-rvfc/issues/new
Theses tests are still basic. The specification is still WIP, and rendering tests will be added to ensure consistenty of behavior/timing relative to other AnimationFrameProviders (e.g. window.rAF).