Weekly reminder that FFmpeg powers all online video (twitter.com)

The tweet says yes.

As someone who once had access to internal fleetwide profiling information, yes.

There is older evidence based on quirks in encoding. https://multimedia.cx/eggs/googles-youtube-uses-ffmpeg/

Why would they use anything else? I don't think there's any other software close in terms of cost/features. (unless you count libAV, which is a fork of ffmpeg)

neither are maintained by a single random person in the middle of nowhere. more like thanklessly maintained by a group of enthusiasts.

but, more to your point (i assume), i suppose they could use more support, especially from large users like google.