The image is playing back correctly for me in Librewolf on Linux in the normal web UI for my instance (which is PyLova) and in the default Lemmy UI in some random Lemmy instance I tried.
On Android, it is also working fine in the default PyLova web UI in IronFox, as well as in Thunder, Blorp, and Voyager. It's just a static image in Jerboa, Summit, Raccoon, and Eternity.