I was wondering how this can be done, I’ve seen it on other Discourse communities, was wondering how I can also do this on my local Discourse instance. I basically want it so the GIF will automatically play.
AI-generated summary
N3DSDude wants to know how to make a GIF play as a post/topic thumbnail on his local Discourse instance. merefield suggests that the Discourse Gifs Theme Component is required, but N3DSDude already has it installed and is looking for a way to display the GIF as a playable thumbnail next to the topic. merefield explains that this would require another Theme Component to expose the Topic’s image URL and notes that it might slow down the loading of the Topic List. merefield advises against recommending a specific component due to scalability issues and suggests that N3DSDude build a custom solution, offering a Beginner’s Guide to Developing Discourse Themes as a resource to get started.
You want this Theme Component:
Yeah I have that installed, my problem is I want the GIF to play as a post/topic thumbnail, was wondering if that’s possible?
This is how it works out of the box: it’s animated.
What’s the issue?
so what was missing in your description of the problem was “Topic List”. 
this might be possible but you’d need to use a Theme Component to expose the Topic’s image url.
And I believe it would only pick it up if it was in the OP.
This would really slow down the loading of Topic List.
Ahh, what theme component do you recommend?
I wouldn’t recommend doing this, because it is not scalable.
You would have to build this yourself. It’s not that hard, good learning exercise.
Would it be hard to build?
There would be a learning curve to begin with but this project would be a good first project.
Read more here: Developing Discourse Themes & Theme Components
Go for it then share your solution with the community!