GIF to MP4 not working

[saladgoat]

It's a weird one but, when I try to convert an animated GIF to MP4, it does its thing and I end up with an MP4 file, but when I try to play it in Firefox, it shows an error message: Video can't be played because the file is corrupt. Opening in Windows 10's Film & TV app just shows a black screen.

But I can convert the same animated GIF to WEBM (which takes a very long time) and then convert the resulting WEBM file to MP4 and that MP4 will work just fine.

It is the same for every different GIF I have tried, and I have tried this on two different computers with the same result.

Everything else works great though, I love this program!