https://developers.google.com/youtube/v3/live/guides/ingesti...
YouTube serves vp9 but it always re-encodes my videos as AV1. Annoying.
(I would upload as AV1 but the encoder is slooooooooow.)
If you're using libaom, try switching to libsvtav1. It's still slow, but it's slooow instead of slooooooooow.