ripped this from coub and made a proper vid of it, will post a nice compressed webm later

combine.bat

ffmpeg -i "video_output.mp4" -i "moonlight_audio.mp3" -map 0 -map 1 -c copy output_moonlight

video_concat.bat

ffmpeg -f concat -i mylist.txt -c copy video_output.mp4

mylist.txt

# this is a comment
file 'moonlight_video.mp4'
file 'moonlight_video.mp4'
file 'moonlight_video.mp4'
file 'moonlight_video.mp4'
file 'moonlight_video.mp4'
file 'moonlight_video.mp4'