I'm running PCL2012 / KDE4
Usually when I click on an MP4 file, VLC opens to run then closes again so I have to click on the file again to get VLC to open a second time to run and play the file.
Any clues as to why VLC doesn't run on the first attempt?
linuxsnow, firstly are you running the latest version of VLC ?
I checked through Tools - Preferences, to see if there's a list of Filetypes you can select for VLC to play by Default, thinking mp4 maybe unchecked, but no joy.
Right click on a mp4 file; in the context Menu go to open with, Other, Browse, select VLC, and tick the option; 'Remember application association for this type of file.'
Good Luck !