You are spectacularly incorrect about how Chrome and Chromium are built — the only difference between the two regarding <video> is which flags the bundled copy

You are spectacularly incorrect about how Chrome and Chromium are built — the only difference between the two regarding <video> is which flags the bundled copy of ffmpeg's libavcodec was built with. There is no secret source code. When you build Chromium, you can just swap in a symlink to your system's copy of libavcodec, and then it magically supports whatever codecs that one was built with.