"Autoplay GIFs and videos" option does not work when homeserver's media repo serves animated thumbnails

[anoadragon453]

Description

From what it looks like, if the option "Autoplay GIFs and videos" is off, Riot will serve the thumbnail of a gif instead of the gif itself:

https://github.com/matrix-org/matrix-react-sdk/blob/d4d51dc61f75bcaab50184e066da23fc5cabfbdc/src/components/views/messages/MImageBody.js#L469-L477

While this is successful if your homeserver has a media repo which does not animated thumbnails, if you do have one that does (such as @turt2live's popular matrix-media-repo) then you will be shown a thumbnail that's still animated.

Steps to reproduce

• Use a homeserver with animated media thumbnails
• Send a gif in the room
• Roll over the gif with your mouse and see that it animates no matter what

Logs being sent: no

Version information

• Platform: web
• Browser: Firefox v72.0a1
• OS: Debian
• URL: riot.im/develop

[turt2live]

Animated thumbnails are a non-standard feature. Proper spec is needed in this area.