E.g. if video is 1 minute, but audio is 1 hour. Make video loop throughout for 1 hour of the audio track.
I use this solution to loop image through the lenght of the audio
ffmpeg -y -loop 1 -r 6 -i image.jpg -i audio.mp3 -shortest -c:v libx264 -preset ultrafast -tune stillimage -pix_fmt yuv420p -c:a copy output.mp4
But it doesn't work for video, replacing image.jpg with video.mp4 will give error
no loop found.