>>105968982nta, but there are a couple of cases where av1 on jewtube actually looks better than vp9
case 1: livestreams, which have always looked like complete dogshit with h264/vp9, it seems the reason they recently introduced av1 for livestreams is to fix the quality a bit rather than to save bitrate, which was already quite low anyways.
case 2: videos with lots of motion which hit the bitrate limit with vp9, this happens especially frequently with 4k60, very often you'll see the 4k vp9 encode be about 25000 kbps (upper bitrate constraint that cannot be exceeded by the encoder), and the 4k av1 encode will also be about 25000 kbps or just slightly lower, in this case the av1 encode will be marginally better, since it requires less bitrate it's less likely for it to bump into the bitrate limit and if it does, it of course will still lead to better quality compared to same bitrate vp9.