Introduction
------------
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.

Requirements
------------
 - Python 2.4 (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]

Installation
------------
Just install it like any other Python package: Unpack, then (as root/with
``sudo``)
 # python setup.py install

``replaygain``
--------------
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)
 - Flac
 - WavPack
 - MP3 (with 3 different formats)
Basic usage is simple:
 $ replaygain AUDIOFILE1 AUDIOFILE2 ...
There are some options; see 'em by running
 $ replaygain --help

``collectiongain``
------------------
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 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 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.

MP3 formats
-----------
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.