This normally works but if not use my mencoder solution if the output video does not play past the joined time.
the contents of list.txt need to look like this:
file somefile.mp4
file somefile2.mp4
then run ffmpeg
ffmpeg -f concat -i list.txt -c copy CME-2-router-dial-peer-final.mp4
The result is almost instant joining since there is no video processing since we are........