[jjcm]

Nitpick - the question should have been:

> Why .avifs when we have .webps already?

Webp and avif are both image containers, both of which support animated images. The key difference here between avif|mp4 and webp|webm is the mime type and the associated UX with each of these. Image types are presented without controls, and are looping by default if they have multiple frames. Video types are presented with controls and with many other options.

It's a good question as to why avif though. Webp is entirely sufficient in most situations. Where AV1 as a codec shines is for more advanced compression, which may not be necessary for a simple looped gif-analog, but you'll still get some gains. The gains come at a processing speed tradeoff though, so they're good to use when you have advanced hardware on a low-bandwidth connection. I personally don't find the tradeoff worth it, so all of my media encoding pipelines opt for webp/webm by default.