XYplorer Beta Club

Until very recently, XYplorer always previewed mp4 files with no problem. All of a sudden it no longer displays them. It also does not say that it is not a previewed format. If I rename the mp4 file with an m4v extension, it knows that it is an mp4 file but it correctly displays it.
Not a big deal but still irritating.
Thornton.Stewart

Welcome to the forum.

Did you check what the standard applications for .mp4 and .mv4 are on your system and whether there is a difference between the two?
You could also check your settings in CFA/Open With within XY and see whether the settings there include one but not the other.

Is that audio or video?