I recently ripped my DVD collection to play them on my media center PC, and several of them are two-disc movies (i.e. The Lord of the Rings). Since I ripped each DVD individually, that gives me two video files for some movies.

I am using Ubuntu Linux - how can I concatenate these two MP4/H.264 videos into a single MP4 video file? Preferably from the command line, and without re-encoding everything during the process (although I can try figuring out a video editor like Pitivi if that's the only solution.)