There’s also the issue of non-browser support. I recently advocated for replacing some GIFs with WEBM because WEBM was faster to encode and took up 3% as much space. Technically it sounded great. Then we talked to users.

It turns out some users wanted to embed moving pictures in Word documents, which you can only do with a GIF because it’s an image format that happens to move, so Word treats it as an image (by rendering it to the page). If it’s a video format, Word treats it as an attachment that you have to click on so it’ll open Media Player and show you.