[adgjlsfhk1]

> Image encoding is a subset of video encoding

This isn't true. There are a number of things that make sense for images but not videos. 1. Progressive rendering. 2. Big images (up to 2^30 by 2^30) 3. More channels (up to 4099) (this can be useful for transparency, depth, or tracking random other things for scientific purposes) 5. High bit depth (up to 32 bit) (this is mostly useful for sciency stuff) 4. Lossless encoding. Basically no one wants lossless video (it's way too big), but lossless images often make sense.

[adgjlsfhk1]

Also images use a wider range of resolutions. AV1 has a minimum 4x4 block size (compared to 2x2 for jpeg-xl) which will hurt it for small images (e.g. icons). For example, The ycombinator icon is 18 by 18 pixels which would make AVIF store a 20x20 image which is 23% more pixels. (I can't find a source but I think I remember hearing that AV1 actually has a minimum size of 64x64 but I can't find a source for that)