And finally, after some more tests it turned out that some videos have almost 2x bigger .webm variants than .mp4 so I had to extend my yt-dlp config like so (only showing the prioritization options here, my previous full config is still there upthread):
...OK, you made me double-check. Used this instead:
--format 'vcodec=av01/bestvideo*+bestaudio/best'
And it started downloading `.webm` streams and not `.mp4` (only one video had an AV1 stream). Tested with several videos, quality is the same and some files are actually 40% smaller.
...Whoa. Thanks for making me double-check!
Somebody down-voted you, I seem to recall seeing earlier, sorry about that. Your comment was valuable, though I'd definitely use more productive tone next time.
I am half-aware of the licensing troubles of various video formats but I wish those companies luck going after each and every home video user. ¯\_(ツ)_/¯