[mindhunter]

While MP4s don't support transparency, both HEVC and VP9 do and their support is very good these days. I just recently used these formats to add a complex After Effects Animation to a website. It's a bit of extra work to encode two videos instead of just one but the result is great. I used this tutorial: https://rotato.app/blog/transparent-videos-for-the-web

[rfl890]

vp9 & av1 yes, hevc no. I personally own devices which don't support hevc because of licensing reasons.

[rchaud]

Remarkable that after 30 years, and all these changes, the GIF reigns supreme. Works on every browser, supports transparency out of the box.