MPG is one of several file extensions for MPEG-1 computer files. QuickTime supports the playback of MPG files. However, if you want to import MPG files into iMovie for editing, you may find that the MPG files are grayed out! Or, some Mac users have discovered that when playing certain MPG videos in QuickTime (QT), there’s only audio, or even worse, QT crashes! In situations like these, you can convert your MPG videos to QuickTime MOV format on a Mac.