Who cares?
File size and quality. I'm seeing the same quality along with major size reductions. Just a few examples:
Current PNG image - 25k (see entry)
AVIF conversion - 15k - reduced by 40%
Current Pixia JPEG image - 222k (see entry)
AVIF conversion 79k - Reduced by 65%
AVIF conversion - 15k - reduced by 40%
Current Pixia JPEG image - 222k (see entry)
AVIF conversion 79k - Reduced by 65%
Needless to say, that's a lot of bandwidth saved over time.
Why not some other format like WEBP or HEIC?
HEIC has mixed support and has patent issues, likely not seeing support from Firefox or Chrome. WebP is certainly an improvement over JPEG, but AVIF appears to have higher quality and lower file size.
What about animation?
We have a lot of animated GIF and PNG (slideshow style) files here on the site. AVIF supposedly supports animation, but I haven't found any available tools that support that animation yet. Or at least Firefox isn't yet playing animated AVIF files, I'm not sure.
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It's also possible to add fail-over so that AVIF files are available but drop in favor of JPEG or PNG if there's no browser support.