As I understand it, there used to be ways to do this, but I can't find a way to do it after the abdication of flash.
media4svg
\movie
multimedia
media4svg. Works well in all popular browsers across many platforms, F11 to put to fullscreen. – AlexG May 12 '22 at 14:15\moviecommand from themultimediapackage still works for me with regular mp4 videos. See the beamer user's guide, sec 14.1. – frabjous May 12 '22 at 14:20