Consider adding animated .webp support.

[hdk5]

The only thing that stops animated webp being allowed is that ffmpeg can't be used generate thumbnails for them. Would it be possible to use other tools to work around ffmpeg's restrictions?

[hdk5]

While animated webp patches for ffmpeg are being worked on (for over a year already!), at the moment it is possible to use vips to open multi-page (i.e. animated) files as a ~~"film reel"~~ "toilet roll"-like tall image, save it into a temporary file, and then turn it back into a video stream with ffmpeg's untile filter. The only dependencies change in that case would be ffmpeg compilation flags. See https://github.com/hdk5/danbooru/commit/4c482a388ad33051c7e4e4c1f9c43ac618a9ef27. Any major downsides to this approach?