Inspired by stolen.shoes and FixTweet.
Put https://emb.arti.lol/
in front of the video URL, like so:
https://emb.arti.lol/https://download.blender.org/peach/bigbuckbunny_movies/BigBuckBunny_320x180.mp4
If the video URL has a query string, you'll need to url encode it.