QuickTime 7 had this great feature of merging two videos together just by dragging a video file from the Finder to another QuickTime video. Unfortunately this is not possible in QuickTime X. But I still wanted to do it without installing additional software and came up with a solution that includes a small hack.
Assume we have 2 video files named video1.dv and video2.dv in the ~/Movies folder that we want to merge.
Open the Terminal and navigate to Movies folder
$ cd Movies
Concatenate two files
$ cat video1.dv video2.dv > video3.dv
This step will take a while and the result is a strange (I don't really want to say corrupted as it is just split in two MPEG containers) file, which will still play in most video players (I tried VLC and QuickTime X).
Open the new file in QuickTime X and re-save it.
Mac OS X Hints