wiki:

How to change audio volume up-down with FFmpeg


Version 2 (modified by degenerate, 4 years ago) (diff)

the 'single quote' syntax on this page doesn't work with windows ffmpeg so I am changing it to double quote and adding some more examples too

To turn the audio volume up or down, you may use FFmpeg's Audio Filter named volume, like in the following example. If we want our volume to be half of the input volume:

ffmpeg -i input.wav -af "volume=0.5" output.wav

150% of current volume:

ffmpeg -i input.wav -af "volume=1.5" output.wav

If you are familiar with decibels you can also use dB:

ffmpeg -i input.wav -af "volume=10dB" output.wav

In older versions of FFmpeg, the option "-af" wasn't implemented, so we had to use this:

ffmpeg -f lavfi -i "amovie=input.wav,volume=0.5" output.wav

More info here: http://ffmpeg.org/trac/ffmpeg/ticket/720