If there is no helpful information in the terminal and you can’t fix it yourself, then the next step is to get help.
We are not VLC experts here so if it’s not a Whonix-specific issue, it would more useful for you to post in a VLC support forum.
To figure out if it’s a Whonix-specific issue (and if you trust the media file), try to play it on a non-Whonix VM, such as plain Debian.
Unless you post more specific information, it’s hard to give you any more specific advice. (You can get more information by typing vlc --verbose=2 yourfile.mp4)
I don’t understand this statement. Can you try saying it differently?