In order to fix a broken video where the camera stopped recording, I wanted to replace the part with a video with a sound wave overlay. There are many services for that, and it is also a feature of video editing software. But I am stingy and a geek, so I wanted to use FFMPEG on the command line instead. This also allows for batch processing.

Note: I didn't embed the videos in this post but GIFs instead. The real videos play the video and audio and the sound wave moves accordingly.

Let's say this is our original video:

This is what it looked like in the end:

Here's the command I used to create the above version:

ffmpeg -i Understandable.mp4 \
 -filter_complex "[0:a][email protected]\
 :scale=sqrt:mode=cline,format=yuva420p[v];\
 [v]scale=1280:400[bg];\
 [v][bg]overlay=(W-w)/2:H-h[outv]"\
  -map "[outv]" -map 0:a -c:v libx264 -c:a copy \
  waveform-sqrt-cline.mp4

OK, let's unwrap this:

• Understandable.mp4 is the input file
• [email protected] is the hexadecimal colour of the waves I want to create. The @0.3 is the opacity, 30%.
• The first scale is how the bars should be resized to stay in a certain range. I found squareroot to look the best. Other options are available in the documentation
• mode is what soundwave you want. This version, cline is a centered, filled line. Other options are point, line and p2p.
• scale is the size of the generated video of the wave, in this case 1280x400 pixels (as the video is 1280x1080)
• The overlay defines where on the background video the wave should appear. In this case centred in the horizontal direction and on the bottom of the video.
• waveform-sqrt-cline.mp4 is the name of the final video.

Change location of the sound wave

You can also center the sound wave in both directions using overlay=(W-w)/2:(H-h)/2:

ffmpeg -i Understandable.mp4 \
 -filter_complex "[0:a][email protected]\
 :scale=sqrt:mode=cline,format=yuva420p[v];\
 [v]scale=1280:400[bg];\
 [v][bg]overlay=(W-w)/2:(H-h)/2[outv]"\
  -map "[outv]" -map 0:a -c:v libx264 -c:a copy \
  waveform-sqrt-cline-centered.mp4

And the result looks like this:

Other sound wave styles

And you can change the output type to line and change the colour:

ffmpeg -i Understandable.mp4 \
 -filter_complex "[0:a][email protected]\
 :scale=sqrt:mode=line,format=yuva420p[v];\
 [v]scale=1280:400[bg];\
 [v][bg]overlay=(W-w)/2:H-h[outv]"\
  -map "[outv]" -map 0:a -c:v libx264 -c:a copy \
  waveform-sqrt-line.mp4

This is what the point to point mode looks like:

ffmpeg -i Understandable.mp4 \
 -filter_complex "[0:a]showwaves=colors=0xffffff\    
 :scale=sqrt:mode=p2p,format=yuva420p[v];\ 
 [v]scale=1280:400[bg];\
 [v][bg]overlay=(W-w)/2:H-h[outv]"\
  -map "[outv]" -map 0:a -c:v libx264 -c:a copy \
 waveform-sqrt-p2p.mp4 

Adding a sound wave to a static image

If you only want the audio from a video and use a background image instead, this is what to use. This creates a 400x400 pixel video with the image as the background and the sound wave on top:

ffmpeg -i Understandable.mp4  -i chris.jpg\
 -filter_complex "[0:a][email protected]\
 :scale=sqrt:mode=cline,format=yuva420p[v];\
 [1:v]scale=400:400[bg];\
 [bg][v]overlay=(W-w)/2:(H-h)/2[outv]"\
  -map "[outv]" -map 0:a -c:v libx264 -c:a copy \
  static-image.mp4

FFMPEG is amazing

Granted, the syntax of FFMPEG is pretty nuts, but it is also super powerful. Want to know for example how I created the GIFs of this post?

First, I resized all the MP4s in the folder to 1/3 of their size and saved them as small*:

for f in *.mp4 ; \
do ffmpeg -i "$f" -vf scale=w=iw/3:h=ih/3 "small-$f" ;\
done             

Then I took those and created gifs

for f in small-*.mp4 ; \
do ffmpeg -i "$f" -sws_dither ed -ss 5 -t 1 "e-$f.gif" ; \
done      

In English: Get all small-*.mp4s in the current folder, and create a GIF from second 5 of the video, one second long, using error diffusion.

Automate all the things!