This Python package provides modules to read, write and calculate Replay Gain as well as 2 scripts that utilize these modules to do Replay Gain. Replay Gain [http://replaygain.org/] is a proposed standard (and has been for some time -- but it's widely accepted) that's designed to solve the problem of varying volumes between different audio files. I won't lay it all out for you here, go read it yourself.
- Python 2.5 (probably) [http://python.org/]
- Mutagen [http://code.google.com/p/mutagen/]
- GStreamer 0.10 [http://gstreamer.org/]
- pygst 0.10 [http://gstreamer.freedesktop.org/modules/gst-python.html]
Just install it like any other Python package: Unpack, then (as root/with sudo)
# python setup.py install
This is a program like, say, vorbisgain or mp3gain, the difference being that instead of supporting a mere one format, it supports several:
- Ogg Vorbis (or probably anything you can put into an Ogg container)
- MP3 (with 3 different formats)
- Basic usage is simple:
- $ replaygain AUDIOFILE1 AUDIOFILE2 ...
- There are some options; see 'em by running
- $ replaygain --help
This program is designed to apply Replay Gain to whole music collections, plus the ability to simply add new files, run collectiongain and have it replay-gain those files without asking twice. To use it, simply run
$ collectiongain PATH_TO_MUSIC
- and re-run it whenever you add new files. Run
- $ collectiongain --help
to see possible options. If, however, you want to find out how exactly collectiongain works, read on (but be warned: It's long, boring, technical, incomprehensible and awesome).
collectiongain runs in 2 phases: The file collecting phase and the actual run. Prior to analyzing any audio data, collectiongain gathers all audio files in the directory and determines a so-called album ID for each from the file's tags:
If the file contains a Musicbrainz album ID, that is used.
- Otherwise, if the file contains an 'album' tag, it is joined with either
- an 'albumartist' tag, if that exists,
- or the 'artist' tag
- or nothing if neither tag exists.
The resulting artist-album combination is the album ID for that file.
If the file doesn't contain a Musicbrainz album ID or an 'album' tag, it is presumed to be a single track without album; it will only get track gain, no album gain.
Since this step takes a relatively long time, the album IDs are cached between several runs of collectiongain. If a file was modified or a new file was added, the album ID will be (re-)calculated for that file only. The program will also cache an educated guess as to whether a file was already processed and had Replay Gain added -- if collectiongain thinks so, that file will totally ignored for the actual run. This flag is set whenever the file is processed in the actual run phase (save for dry runs, which you can enable with the '--dry-run' switch) and is cleared whenever a file was changed. You can disable these assumptions with the '--ignore-cache' switch; in that case, the program will actually physically check every file in your collection for Replay Gain data. For the actual run, collectiongain will simply look at all files that have survived the cleansing described above; for files that don't contain Replay Gain information, collectiongain will calculate it and write it to the files (use the '--force' flag to calculate gain even if the file already has gain data). Here comes the big moment of the album ID: files that have the same album ID are considered to be one album (duh) for the calculation of album gain. If only one file of an album is missing gain information, the whole album will be recalculated to make sure the data is up-to-date.
In contrast to modern audio file formats, there is no commonly accepted standard for Replay Gain information in MP3 files. There is the mp3gain program that directly changes the audio data, but this means you have to decide on one form of Replay Gain: Track gain or album gain. Plus, it's ugly. And it might kill your cat. Or make your plant eat your dog. Because there are several not-quite-standards to store Replay Gain data in MP3 files, both replaygain and collectiongain force you to make a choice (well, they don't force you technically, but don't let that fool you) through the '--mp3-format' option. They support 3 formats:
- 'ql' Replay Gain information is stored in ID3v2.4 RVA2 frames. Quod Libet uses this format, so choose this if you run QL. This is also the default setting.
- 'fb2k' Replay Gain information is stored in ID3v2 TXXX frames. Foobar2000 reads and writes this format; Quod Libet reads it, but converts it to 'ql' format without asking.
- 'mp3gain' Replay Gain information is stored in APE v2 tags. mp3gain writes these tags (this doesn't mean this format works like the mp3gain program; it doesn't, see above). Maybe there are programs that support this format. If you know, you could tell me.
I hope that's enough confusion for now.