AVIF is a lifesaver for animation with separate transparency layers so the transparency can change position frame by frame. The only other alternative is WebM which has Safari limitations.

But the performance is so bad it isn't worth using. You're better off encoding a double height AV1 and mashing it together with WebGL https://jakearchibald.com/2024/video-with-transparency/. That's how bad the situation is.

Is there an advantage to this as a separate layer compared to just having an alpha channel baked into the image data itself? If not premultiplied then it would not affect the other channels either.