MP4Box -cat 1.mp4 -cat 2.mp4 finalbox.mp4
Appending file 1.mp4
No suitable destination track found - creating new one (type vide)
No suitable destination track found - creating new one (type soun)
Appending file 2.mp4     
No suitable destination track found - creating new one (type vide)
Saving to finalbox.mp4: 0.500 secs Interleaving