Improving performance of rav1d video decoder

All being equal codecs ought to be in WUFFS† rather than Rust, but I can well imagine that it's a much bigger lift to take something as complicated as dav1d and write the analogous WUFFS than to clean up the c2rust translation, if you said a thousand times harder I'd have no trouble believing that. I just think it's worth it for us as a civilisation.

† Or an equivalent special purpose language, but WUFFS is right there

WUFFS would be great for parsing container files (Matroska, webm, mp4) but it does not seem at all suitable for a video decoder. Without dynamic memory allocation it would be challenging to deal with dynamic data. Video codecs are not simply parsing a file to get the data, they require quite a bit of very dynamic state to be managed.

Requiring dynamic state seems not obvious to me. At the end of the day you have a fixed number of pixels on the screen. If every single pixel changes from frame to frame that should constitute the most work your codec has to do, no? I'm not a codec writer but that's my intuition based on the assumption that codecs are basically designed to minimize the amount of 'work' being done from frame to frame.

> codecs are basically designed to minimize the amount of 'work' being done from frame to frame

But to do that they have to keep state and do computations on that state. If you've got frame 47 being a P frame, that means you need frame 46 to decode it correctly. Or frame 47 might be a B frame in which case you need frame 46 and possibly also frame 48 - which means you're having to unpack frames "ahead" of yourself and then keep them around for the next decode.

I think that all counts as "dynamic state"?

Memory usage can vary, but video codecs are designed to make it practical to derive bounds on those memory requirements because hardware implementations don't have the freedom to dynamically allocate more silicon.