Not necessarily, as it's treated differently by the browser. Animated WebPs will autoplay without a `muted` or `autoplay` attribute. Under the hood they're no different than a webm video, with the exception of no support for audio tracks.
> Under the hood they're no different than a webm video
From a very high level point of view you are right. Yes, webm videos use vp8 and webp uses vp8 key frames, but there are still differences between animated webp and webm videos without sound.
A webm video is a video with a vp8/vp9 video stream contained inside an mkv container, while webp files, including the animated ones, are inside RIFF containers. Also, webp's animation mode does not have the full inter frame system that vp8 has. It does support carrying over of state from one frame to the next, but does this in the simplest way possible: just paint the next frame over the prior one, respecting the alphas. Most importantly, those frames are still encoded like vp8 Intraframes (keyframes), not like vp8 Interframes [1]. So you won't need a full vp8 decoder to write an animated webp decoder.
