volume

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doc

https://ffmpeg.org/ffmpeg-filters.html#volume

see also

(ffmpeg-utils)3. Expression Evaluation, acontrast

Halve the input audio volume:

[me@host: ~]$ ffplay snd.wav -af "volume=0.5"
[me@host: ~]$ ffplay snd.wav -af "volume=1/2"
[me@host: ~]$ ffplay snd.wav -af "volume=-6.0206dB"

You can use enable:

[me@host: ~]$ ffplay snd.wav -af "volume=0.5:enable='gt(t, 2)'"

And you can use expressions as volume value:

[me@host: ~]$ ffplay snd.wav -af "volume='max(0, 1 - (t - 2) / 5.0)':eval=frame:enable='gt(t, 2)'"

[me@host: ~]$ ffplay snd.wav -af "volume='abs(1 - mod(t, 2))':eval=frame"

Applying volume filter to each channel separately:

[me@host: ~]$ ffplay snd.wav -af "
> channelsplit[Lo][Ro];
> [Lo]volume='abs(1 - mod(t, 2))':eval=frame[L];
> [Ro]volume='abs(1 - mod(t + 1, 2))':eval=frame[R];
> [L][R]join"

see also

aeval