Merge mp4 files by converting to raw then using cat

./ffmpeg  -i gpsclip_seg1.mp4  -vn -f u16le -acodec pcm_s16le -ac 1 -ar 44100 - > temp1.a < /dev/null
./ffmpeg  -i gpsclip_seg2.mp4  -vn -f u16le -acodec pcm_s16le -ac 1 -ar 44100 - > temp2.a < /dev/null
./ffmpeg  -i gpsclip_seg3.mp4  -vn -f u16le -acodec pcm_s16le -ac 1 -ar 44100 - > temp3.a < /dev/null
cat temp1.a temp2.a temp3.a > all.a

./ffmpeg -i gpsclip_seg1.mp4 -an -f yuv4mpegpipe - > temp1.v < /dev/null &amp;
./ffmpeg -i gpsclip_seg2.mp4 -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v
./ffmpeg -i gpsclip_seg3.mp4 -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp3.v
cat temp1.v temp2.v temp3.v > all.v

./ffmpeg -f u16le -acodec pcm_s16le -ac 1 -ar 44100 -i all.a -f yuv4mpegpipe -i all.v -same_quant -y output.mp4

#rip each orig mp4 to separate raw tracks for audio / video
#once u have raw bits you can simply cat them in order to aggregate
#remux from raw to good codecs after the cat