When I edit an already encoded video like a .mp4 file with QuickTime Pro and try to save it, it saves as a QuickTime .mov file by default. So here's a few questions about doing that. 1. It seems to still be a .mp4 file but, with the extension .mov now. Does this change the file at all? When I change the extension back to .mp4, it no longer will open and play in QuickTime. 2. How come I can't re-save it as a .mp4 file without re-encoding it (such as when I cut out extra unwanted bits. 3. For some reason I like my files to stay in the original format that they were encoded in. How do I modify a .mp4 file without having to save it as a .mov file? I've always been kinda confused about how QuickTime re-saves a file as a .mov file. What format is this really? If the file was unaltered (still has the same encoding information and everything) then why can it have the .mov extension. I don't get it. Does anyone else do this? Or should I stay away from re-saving in QuickTime.