Concatenate multiple MP4 files using MP4Box in Linux

To concatenate 2 or more .mp4 files in Linux use MP4Box. Open a terminal window and enter the command below:
$ MP4Box -add file1.mp4 -cat file2.mp4 output.mp4 <enter>

If you cannot find MP4Box on your computer, open a terminal window and install it with:
$ sudo apt-get install gpac <enter>