Yeah as a result of this post I decided to look into AV1 grain synthesis again. That's the only way I can see that AV1 can meaningfully "improve" over h265 right now for noisy content like movies, which is what enthusiasts care about.

Grain synthesis is where you analyze noise on the original file, denoise the video stream and reapply artificial noise of a similar style as the original at decode time.

It relies on a lot of assumptions:

• The denoise doesn't kill your quality
• The grain synthesis looks convincingly like real film grain.
• decoding devices will support rendering the grain

From a short experiment, I found that VLC was able to render the synthetic grain, but MPV(.net) did not out of the box. I had to play around with gpu rendering modes to get it to work.

As for transcoding, it's unclear what happens to the synthetic grain, whether it is burnt in or simply ignored. At least one or two people have reported it will just be ignored and you'll get a weirdly smooth movie.