Netflix’s AV1 Journey: From Android to TVs and Beyond

I had forgotten about the film-grain extraction, which is a clever approach to a huge problem for compression.

But... did I miss it, or was there no mention of any tool to specify grain parameters up front? If you're shooting "clean" digital footage and you decide in post that you want to add grain, how do you convey the grain parameters to the encoder?

It would degrade your work and defeat some of the purpose of this clever scheme if you had to add fake grain to your original footage, feed the grainy footage to the encoder to have it analyzed for its characteristics and stripped out (inevitably degrading real image details at least a bit), and then have the grain re-added on delivery.

So you need a way to specify grain characteristics to the encoder directly, so clean footage can be delivered without degradation and grain applied to it upon rendering at the client.

You just add it to your original footage, and accept whatever quality degradation that grain inherently provides.

Any movie or TV show is ultimately going to be streamed in lots of different formats. And when grain is added, it's often on a per-shot basis, not uniformly. E.g. flashback scenes will have more grain. Or darker scenes will have more grain added to emulate film.

Trying to tie it to the particular codec would be a crazy headache. For a solo project it could be doable but I can't ever imagine a streamer building a source material pipeline that would handle that.

Mmmm, no, because if the delivery conduit uses AV1, you can optimize for it and realize better quality by avoiding the whole degrading round of grain analysis and stripping.

"I can't ever imagine a streamer building a source material pipeline that would handle that."

That's exactly what the article describes, though. It's already built, and Netflix is championing this delivery mechanism. Netflix is also famous for dictating technical requirements for source material. Why would they not want the director to be able to provide a delivery-ready master that skips the whole grain-analysis/grain-removal step and provides the best possible image quality?

Presumably the grain extraction/re-adding mechanism described here handles variable grain throughout the program. I don't know why you'd assume that it doesn't. If it didn't, you'd wind up with a single grain level for the entire movie; an entirely unacceptable result for the very reason you mention.

This scheme loses a major opportunity for new productions unless the director can provide a clean master and an accompanying "grain track." Call it a GDL: grain decision list.

This would also be future-proof; if a new codec is devised that also supports this grain layer, the parameters could be translated from the previous master into the new codec. I wish Netflix could go back and remove the hideous soft-focus filtration from The West Wing, but nope; that's baked into the footage forever.

I believe you are speculating on digital mastering and not codec conversion.

From the creator's PoV their intention and quality is defined in post-production and mastering, color grading and other stuff I am not expert on. But I know a bit more from music mastering and you might be thinking of a workflow similar to Apple, which allows creators to master for their codec with "Mastered for iTuenes" flow, where the creators opt-in to an extra step to increase quality of the encoding and can hear in their studio the final quality after Apple encodes and DRMs the content on their servers.

In video I would assume that is much more complicated, since there are many quality the video is encoded to allow for slower connections and buffering without interruptions. So I assume the best strategy is the one you mentioned yourself, where AV1 obviously detects on a per scene or keyframe interval the grain level/type/characteristics and encode as to be accurate to the source material at this scene.

In other words: The artist/director preference for grain is already per scene and expressed in the high bitrate/low-compression format they provide to Netflix and competitors. I find it unlikely that any encoder flags would specifically benefit the encoding workflow in the way you suggested it might.