SHELL

ffmpeg combine audio and video

ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac output.mp4

ffmpeg merge all videos

ffmpeg -f concat -safe 0 -i <(for f in ./*.mp4; do echo "file '$PWD/$f'"; done) -c copy output.mp4

ffmpeg add two videos together

$ cat mylist.txt
file '/path/to/file1'
file '/path/to/file2'
file '/path/to/file3'
    
$ ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.mp4

ffmpeg concat videos

ffmpeg -i input1.mp3 -i input2.mp3 -i input3.mp3 -filter_complex "concat=n=3:v=0:a=1" -vn -y input.m4a

ffmpeg merge videos

ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.wav