Package details
openSUSE:

AACGain is a modification to Glen Sawyer's excellent mp3gain program. It supports AAC (mp4/m4a/QuickTime) audio files in addtion to mp3 files. If you are not familiar with mp3gain, stop reading this, and go to http://mp3gain.sourceforge.net.
AACGain normalizes the volume of digital music files using the ReplayGain algorithm. It works by modifying the global_gain fields in the mp4 samples. Free-form metadata tags are added to the file to save undo information, making the normalization process reversable.
AACGain uses the same command-line user interface as mp3gain.
BACK UP YOUR MUSIC FILES BEFORE USING AACGAIN! THIS IS EXPERIMENTAL SOFTWARE.