JPEG XL is mainly based on unique image-specific research, but you're right to say a lot of the techniques are compatible with videos in theory (the XYB color space comes to mind). AVIF is an AV1 OBU in an image-specific container, and required a lot of image-specific engineering to make AV1's tools useful for images; see libaom's tune "iq", and the same in SVT-AV1. The compression gains translated when engineering effort went into creating bespoke implementations, and the same may happen for LLMs if I had to guess.
replyThe XYB color space detail is really interesting — I wasn't aware of how much image-specific engineering went into making AV1 tools work for stills. The libaom 'iq' tuning makes sense in retrospect. So the compression gains in AVIF weren't just inherited from AV1 video work but required significant additional optimization. That makes the JXL comparison more nuanced too — JXL was designed image-first from the start, which might explain why it encodes faster despite similar or better compression ratios.
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