Concatenating Four MP4 Files

[pone44]

I have four MP4 files I wanted to concatenate and was hoping to just use VLC Convert/Save to do that. I load the four files in VLC Convert/Save, and I specify an alternate soundtrack. When I hit the Convert button, it does not let me name a single output file and seems to have hard coded a read-only message that there are multiple files selected. When I hit the final confirm, it creates four new output files, each larger than the next. But none of these has any concatenated video in them.

How do I force a merge?

Is there an easier way to do this using a free tool?

[sneaker]

ffmpeg
https://trac.ffmpeg.org/wiki/Concatenate

or MKVToolNix (to from mp4 to mkv)

[Selur]

iirc:

MP4Box -add 1.mp4 -cat 2.mp4 -cat 3.mp4 -cat 4.mp4 -cat 6.mp4 mergedOuput.mp4

should also work assuming it really just merge of mp4 files where the formats are compatible.