How to normalize volume of FLAC files using MetaFLAC

The MetaFLAC tool can be used to normalize the volume of a set of FLAC files when they are played back. To achieve this, the audio data is left untouched, but a replay tag is added to the metadata.

MetaFLAC ships with the flac package, which can be installed easily:

$ sudo apt-get install flac

To add replay gain tag to FLAC files:

$ metaflac --add-replay-gain *.flac

Tried with: MetaFLAC 1.2.1 and Ubuntu 12.04