We don't even need a new file type, we just need browsers to let us use video files like MP4 et al in IMG tags and give us gif-like behavior (muted, autostart, and loop).

I mean, I know everybody is really pumped about webGL and shadow DOMs and webcomponents and webASM, but I feel like the basic "html as document language" could use some loving to solve this.

This whole mess reminds me of SVG. I get that there are fantastic reasons why SVG has JavaScript and its own DOM and can pull in external resources, but sometimes we don't want a whole new framework for new forms of content, we just want an IMG.