= Audio Volume Manipulation =

== Changing volume ==

To change the audio volume, you may use FFmpeg's [http://ffmpeg.org/ffmpeg-filters.html#volume volume] audio filter.

If we want our volume to be half of the input volume:
{{{
ffmpeg -i input.wav -filter:a "volume=0.5" output.wav
}}}

150% of current volume:
{{{
ffmpeg -i input.wav -filter:a "volume=1.5" output.wav
}}}

You can also use decibel measures. To increase the volume by 10dB:
{{{
ffmpeg -i input.wav -filter:a "volume=10dB" output.wav
}}}

To reduce the volume, use a negative value:
{{{
ffmpeg -i input.wav -filter:a "volume=-5dB" output.wav
}}}

Note that the `volume` filter only '''adjusts''' the volume. It does not '''set''' the volume. To set or otherwise normalize the volume of a stream, see the sections below.

== Peak and RMS Normalization ==

To normalize the volume to a given peak or RMS level, the file first has to be analyzed using the `volumedetect` filter:

{{{
ffmpeg -i input.wav -filter:a volumedetect -f null /dev/null
}}}

Read the output values from the command line log:

{{{
[Parsed_volumedetect_0 @ 0x7f8ba1c121a0] mean_volume: -16.0 dB
[Parsed_volumedetect_0 @ 0x7f8ba1c121a0] max_volume: -5.0 dB
...
}}}

... then calculate the required offset, and use the `volume` filter as shown above.

== Loudness Normalization ==

If you want to normalize the (perceived) loudness of the file, use the [http://ffmpeg.org/ffmpeg-filters.html#loudnorm loudnorm] filter, which implements the EBU R128 algorithm:

{{{
ffmpeg -i input.wav -filter:a loudnorm output.wav
}}}

This is recommended for most applications, as it will lead to a more uniform loudness level compared to simple peak-based normalization. However, it is recommended to run the normalization with two passes, extracting the measured values from the first run, then using the values in a second run with linear normalization enabled. See the loudnorm filter documentation for more.

== Automatization with `ffmpeg-normalize` ==

To automate the normalization processes with ffmpeg without having to manually perform two passes, and run normalization on multiple files (including video), you can also use the [https://github.com/slhck/ffmpeg-normalize ffmpeg-normalize Python program] via `pip install ffmpeg-normalize`.

The script defaults to EBU R128 normalization with two passes, but peak and RMS normalization are also supported.

For details, run `ffmpeg-normalize -h` or see the README file.