To join two or more mp4 video files you can use
ffmpeg utility, just follow this simple steps:
- convert mp4 to ts (transport stream) format
ffmpeg -i file.mp4 -c copy -bsf:v h264_mp4toannexb -f mpegts file1.ts
- join several ts files into one mp4
ffmpeg -i "concat:file1.ts|file2.ts" -c copy -bsf:a aac_adtstoasc file12.mp4
- conversion from other formats to mp4
ffmpeg -i fileOLD.webm -strict -2 fileNEW.mp4