You can try doing this with ffmpeg:
mkfifo temp0 temp1 ffmpeg -i input0.mp4 -c copy -bsf h264_mp4toannexb -f mpegts -y temp0 2> /dev/null & \ ffmpeg -i input1.mp4 -c copy -bsf h264_mp4toannexb -f mpegts -y temp1 2> /dev/null & \ ffmpeg -f mpegts -i "concat:temp0|temp1" -c copy -absf aac_adtstoasc output.mp4 This doesn't re-encode anything, it places them in a new transport stream container, which makes them more easy to concatenate, and then concatenates them back into an MP4. If output.mp4 already exists, the command will fail. The version above uses named pipes, it you're on a system that doesn't support those you'd have to use intermediate files:
ffmpeg -i input0.mp4 -c copy -bsf h264_mp4toannexb temp0.ts ffmpeg -i input1.mp4 -c copy -bsf h264_mp4toannexb temp1.ts ffmpeg -i "concat:temp0.ts|temp1.ts" -c copy -absf aac_adtstoasc output.mp4