Join Songs and Loop a Video with FFmpeg

On my spare time I am learning how to produce electronic music with Logic Pro and recently I wanted to make one of those “infinity” like videos, such as those for Lo-Fi beats.

I had my tracks ready, and the video so I leveraged my developer skills to shine on the making of this video so I didn’t had to use any commercial software for this purpose thanks to FFmpeg.

Joinning the songs

The following command served me well for having a single MP3 file with the whole mix:

ffmpeg -i song1.mp3 -i song2.mp3 -i song3.mp3 -i song4.mp3 
    -filter_complex "[0:a][1:a][2:a][3:a]concat=n=4:v=0:a=1[a]" 
    -map "[a]" combined.mp3

Let’s destrcucture it:

• -i songN.mp3 declares every input file. FFmpeg numbers them from 0.
• [0:a][1:a][2:a][3:a] selects the audio stream of each input, in order.
• concat=n=4:v=0:a=1 joins 4 segments into one, with no video streams (v=0) and one audio stream (a=1). n must match the number of inputs.
• [a] names the resulting stream, and -map "[a]" writes it to combined.mp3.

The songs play back to back, in the order of the -i flags. If you add or remove a song, update both the list of [N:a] selectors and n.

Loop the video

To repeat the video until combined.mp3 ends I ran:

ffmpeg -stream_loop -1 -i video.mov -i combined.mp3 
    -map 0:v:0 -map 1:a:0 -c:v libx264 -c:a aac -shortest output.mp4

Let’s destrcucture it:

• -stream_loop -1 loops the next input (video.mov) forever. It must come before the -i it applies to.
• -map 0:v:0 -map 1:a:0 takes the video from the first input and the audio from the second, so the original audio of the clip, if any, is ignored.
• -c:v libx264 -c:a aac encodes to H.264 and AAC, which play nearly everywhere.
• -shortest stops encoding when the shortest input ends. Since the video loops forever, the audio is the shortest one, and the output is exactly as long as the combined songs.

Without -shortest FFmpeg would never stop, because the looped video has no end.

Result

The output.mp4 video lasts as long as the combined songs, the clip repeats in the background.