Dear Sphinx developers,
I suppose the issue "Video support #7404" may be closed with a link to
https://docutils.sourceforge.io/HISTORY.html#release-0-17-2021-04-03
docutils/writers/html5_polyglot/__init__.py
[...]
Use <video> for images with video MIME types supported by HTML5.
(Unless Sphinx patches the image/figure directive handling in a way that
breaks Docutils support for moving images.)
Regards,
Günter