Can you really save much space by re-encoding an already encoded video in AV1? Wouldn’t the efficiency improvement be offset by the doubling up of compression artifacts?
The trick is if your encoder can adapt the quantizer based off a metric to compare the encode quality you can save a ton more space without visual degradation.
AV1 is ~30% more efficient than h.265. And h.265 is ~40% more efficient than h.264. The lower the resolution of the video, the less savings you will get.
I personally will wait until more devices support hardware AV1 decoding. I believe only Intel 12th gen, and Nvidia 3000 support AV1 currently. I don't plan on purchasing a new laptop or smartphone for 3-4 years, at that point I may start encoding in AV1.