Gitlab and GitHub both let you upload videos (and probably more). I still use ffmpeg to convert .mov to .mp4 to get a better file size. But either run circles around the quality and size of .gif

do they show them inline and play automatically?

the thing I love about gifs is that they play automatically so as soon as you open the issue you are seeing the animation of what the problem is.

They are shown inline but they don't play automatically. But they do let the reviewer pause and rewind to see something they've missed, rather than sit there and wait to hopefully catch what they missed.

I'm usually committing visual changes for reviewers without easy access to the environment, so I mark up the screenshots in my PRs. It's great