Problem viewing embedded videos on Windows

Hi,

I'm trying to figure out how to view embedded mp4 videos in a pptx
presentation on Windows.

This works fine with LO 5.1.2 on Debian, but the same version on
Windows only gives me a big black question mark where the video should
be. (Same behaviour with older LO releases).

Converting the file to odp makes no difference, I also tried
extracting the videos, and they play fine in Windows Media Player, so
codecs doesn't seem to be an issue.

The videos are H264 with no sound track.

Any help appreciated!