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docs/plugins/mpdstats.py

@@ -11,6 +11,19 @@ habits from `MPD`_.  It collects the following information about tracks::
 
 .. _MPD: http://mpd.wikia.com/wiki/Music_Player_Daemon_Wiki
 
+Installing Dependencies
+-----------------------
+
+This plugin requires the python-mpd library in order to talk to the MPD
+server.
+
+Install the library from `pip`_, like so::
+
+    $ pip install python-mpd
+
+Configuring
+-----------
+
 To use it, enable it in your ``config.yaml`` by putting ``mpdstats`` on your
 ``plugins`` line. Then, you'll probably want to configure the specifics of
 your MPD server. You can do that using an ``mpd:`` section in your
@@ -28,10 +41,66 @@ the config like this::
     mpdstats:
         music_directory: /PATH/TO/YOUR/FILES
 
+If you don't want the plugin to automatically update the rating, you can
+disable it with::
+
+    mpdstats:
+        rating: False
+
+If you want to change the way the rating is calculated, you can set the
+```rating_mix``` option like this::
+
+    mpdstats:
+        rating_mix: 1.0
+
+For details, see below.
+
+
+Usage
+-----
+
 Now use the ``mpdstats`` command to fire it up::
 
     $ beet mpdstats
 
+A Word On Ratings
+-----------------
+
+Ratings are calculated based on the *play_count*, *skip_count* and the last
+*action* (play or skip).  It consists in one part of a *stable_rating* and in
+another part on a *rolling_rating*.  The *stable_rating* is calculated like
+this::
+
+    stable_rating = (play_count + 1.0) / (play_count + skip_count + 2.0)
+
+So if the *play_count* equals the *skip_count*, the *stable_rating* is always
+0.5.  More *play_counts* adjust the rating up to 1.0.  More *skip_counts*
+adjust it down to 0.0.  One of the disadvantages of this rating system, is
+that it doesn't really cover *recent developments*.  e.g. a song that you
+loved last year and played over 50 times will keep a high rating even if you
+skipped it the last 10 times.  That's were the *rolling_rating* comes in.
+
+If a song has been fully played, the *rolling_rating* is calculated like
+this::
+
+    rolling_rating = old_rating + (1.0 - old_rating) / 2.0
+
+If a song has been skipped, like this::
+
+    rolling_rating = old_rating - old_rating / 2.0
+
+So *rolling_rating* adapts pretty fast to *recent developments*.  But it's too
+fast.  Taking the example from above, your old favorite with 50 plays will get
+a negative rating (<0.5) the first time you skip it.  Also not good.
+
+To take the best of both worlds, we mix the ratings together with the
+```rating_mix``` factor.  A ```rating_mix``` of 0.0 means all
+*rolling* and 1.0 means all *stable*.  We found 0.75 to be a good compromise,
+but fell free to play with that.
+
+Warning
+-------
+
 This has only been tested with MPD versions >= 0.16.  It may have difficulties
 on older versions.  If that is the case, please report an `Issue`_.