How can I remove silence from an MP3 programmatically?

Question

I have MP3 files that sometimes have silence at the end. I would like to remove this silence automatically. From what I can tell, it is "perfect" silence (0 amplitude), not background noise. The length of the content and the silence varies.

I found some other questions about cropping to the first 30 seconds or cropping to X and X+N seconds using ffmpeg. I would think I could use a similar approach, as long as I have a way to find when the silence starts. How would I do that programatically?

For example, one possible solution would be to have a command that finds the beginning of the "silence". I'd expect a sequence like this

end=$(ffmpeg some-command-to-find-start-of-silence) ffmpeg -t "$end" -acodec copy -i inputfile.mp3 outputfile.mp3 

The solution does not have to use ffmpeg, but it does need to be available on Ubuntu.

Answer 1

sox inputfile.mp3 outputfile.mp3 silence 1 0.1 0.1% reverse silence 1 0.1 0.1% reverse 

This will trim any silence longer than 0.1 second from your file. If you're only concerned about trimming the end, this can be simplified to:

sox inputfile.mp3 outputfile.mp3 reverse silence 1 0.1 0.1% reverse 

A detailed look into how sox's silence works can be found here.