I was looking for a straight-forward way to concatenate separate MP4 (MPEG 4) movies into a single movie. I am novice at all things video. I have at my disposal just some basic tools: iMovie, QuickTime Player, QuickTime Player 7 and MPEG Streamclip.
iMovie seemed like overkill. I couldn’t find any hint of a “concatenate” or “append” menu item in QuickTime Player or MPEG Streamclip.
Totally by accident, I found the trick in MPEG Streamclip. If you open multiple files at once, by command-clicking or shift-clicking them in the open dialog, MPEG Streamclip treats the group as one big video — instantly concatenating them together. It does not open multiple windows, but opens them all together in a single window as though they were a single continuous file.
Hopefully, you have named them in such a way that the sort order represents the order you want them to appear in the final video. Now, all you have to do is export that combined video into whatever format you want. It will take a while, but you didn’t have to fool around with trying to cut and paste video segments, which wasn’t working for me at all, anyway.