Feature request: auto-play externally linked gifs and gif-like videos (through hostname whitelist for gif-like video sharing platforms) in chat thumbnail

[ell1e]

Is your suggestion related to a problem? Please describe.
The easiest way to link GIFs without bothering to configure anything is to just paste a GIF url, which usually links either to a .gif directly or to an .mp4 directly from a major gif sharing site like giphy or imgur. I use this in all other messengers where it works fine, but in riot/element/matrix it results in a static preview and people need to click it for auto-play which is super clumsy. As pointed out in #2433 linking gifs is a pretty common alternative so it'd be cool if that also work

Describe the solution you'd like
Auto-play any linked gifs in the thumbnail preview, and auto-play (without sound!) any directly linked video if it comes from a user-configurable host whitelist (should be in local user settings) that should default to major gif sharing platforms.

Describe alternatives you've considered
There do appear to be more direct gif integrations already. But they need to be manually activated first, and also if I copy a giphy link from elsewhere (like some Telegram friend) into matrix that won't work then, right?

Additional context

[t3chguy]

Duplicate of #7473

[ell1e]

@t3chguy wait, but doesn't ask #7434 to stop autoplay of certain things? but linking mp4s just never seems to autoplay, so kind of the opposite problem (I want them to autoplay when coming from major gif platforms, to use them as gifs)

[t3chguy]

Its up to the server whether you get sent a still image of a GIF URL Preview or the GIF, I'd suggest a Synapse bug