Thumbnails for webm animated stickers

[tulir]

Currently the bridge sends the WebM file itself as the thumbnail for animated stickers, which means clients like Riot don't show anything before playing them. Either using the existing video thumbnailer or making an additional lottieconverter call to get a png thumbnail should work.

[androidacy-user]

It seems for animated stickers it just sends a link that leads to an invalid file atm

[tulir]

If you don't enable conversion, it sends a link to a perfectly valid gzipped JSON file.

[sot-tech]

Hello.

I think, that for webm there is no need to call lottieconverter twice: if I'm not mistaken, ffmpeg constructs webm from png series (pngs mode), which located in tmp dir, so before calling ffmpeg any of generated png could be used as thumb.