If you have the file but it won't play, you may need a more versatile media player or a repair tool:

If the file is broken, tools like Fix.Video can sometimes recover the headers of MP4 files.

Right-click the file and select Properties (Windows) or Get Info (Mac) to see if there is a "Comment" or "Origin" tag.

The most reliable player for opening corrupted or unusual MP4 files. Download it at VideoLAN .

Do you have a or a description of what happens in the video so I can help identify it?