I found a video on one of the example sites and opened it on mobile, iOS and the Google Search app. The video didn't play. That is why Youtube is so dominant. 12 years later and nobody else has figured out how to make videos that actually play.
I figured it out. You need to store several encodings of the same file. One in webm for most cases, and one in mp4 for all other cases. If a platform doesn't support webm or Mp4, it probably couldn't play the video anyway.
