Jerky Video on Fedora/GNOME

[diet]

Using appimages 6.3.0 and 6.4.0 on Fedora 31 / GNOME, video playback is extremely jerky with files of type MPEG4 at 24 fps. The same files play well using the default video player. (The problem does not exist with H.264 at 23.98 or 50 fps.)