path: root/doc/protocol.xml

<?xml version='1.0' encoding="utf-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
               "docbook/dtd/xml/4.2/docbookx.dtd">
<book>
  <title>The Music Player Daemon protocol</title>

  <chapter>
    <title>General protocol syntax</title>

    <section>
      <title>Protocol overview</title>

      <para>
        The MPD command protocol exchanges line-based text records
        between client and server over TCP.  Once the client is
        connected to the server, they conduct a conversation until the
        client closes the connection. The conversation flow is always
        initiated by the client.
      </para>

      <para>
        The client transmits a command sequence, terminated by the
        newline character <constant>\n</constant>.  The server will
        respond with one or more lines, the last of which will be a
        completion code.
      </para>

      <para>
        When the client connects to the server, the server will answer
        with the following line:

        <synopsis>OK MPD version</synopsis>

        where <varname>version</varname> is a version identifier such as
        0.12.2.  This version identifier is the version of the protocol
        spoken, not the real version of the daemon.  (There is no way to
        retrieve this real version identifier from the connection.)
      </para>
    </section>

    <section>
      <title>Requests</title>

      <cmdsynopsis>
        <command>COMMAND</command>
        <arg rep="repeat"><replaceable>ARG</replaceable></arg>
      </cmdsynopsis>

      <para>
        If arguments contain spaces, they should be surrounded by double
        quotation marks.
      </para>

      <para>
        Argument strings are separated from the command and any other
        arguments by linear white-space (' ' or '\t').
      </para>

      <para>
        All data between the client and the server is encoded in
        UTF-8. (Note: In UTF-8 all standard ansi characters, 0-127 are
        the same as a standard ansi encoding.  Also, no ansi character
        appears in any multi-byte characters.  So, you can use
        standard C functions like <function>strlen</function>, and
        <function>strcpy</function> just fine with UTF-8 encoded
        strings. For example: <returnvalue>OK</returnvalue> encoded in
        UTF-8 is simply <returnvalue>OK</returnvalue>.  For more
        information on UTF=8:
        http://www.cl.cam.ac.uk/~mgk25/unicode.html#utf-8)
      </para>
    </section>

    <section>
      <title>Responses</title>

      <para>
        A command returns <returnvalue>OK</returnvalue> on completion or
        <returnvalue>ACK some error</returnvalue> on failure.  These
        denote the end of command execution.
      </para>

      <section>
        <title>Failure responses</title>

        <para>
          The nature of the error can be gleaned from the information
          that follows the <returnvalue>ACK</returnvalue>.
          <returnvalue>ACK</returnvalue> lines are of the form:

          <synopsis>ACK [error@command_listNum] {current_command} message_text\n</synopsis>

          These responses are generated by a call to
          <function>commandError</function>. They contain four separate
          terms. Let's look at each of them:

          <itemizedlist>
            <listitem>
              <para>
                <returnvalue>error</returnvalue>: numeric value of one
                of the <constant>ACK_ERROR</constant> constants defined
                in <filename>ack.h</filename>.
              </para>
            </listitem>
            <listitem>
              <para>
                <returnvalue>command_listNum</returnvalue>:
                offset of the command that caused the error in a <link
                  linkend="command_lists">Command List</link>.
                An error will always cause a command list to terminate
                at the command that causes the error.
              </para>
            </listitem>
            <listitem>
              <para>
                <returnvalue>current_command</returnvalue>:
                name of the command, in a <link
                  linkend="command_lists">Command List</link>,
                that was executing when the error occurred.
              </para>
            </listitem>
            <listitem>
              <para>
                <returnvalue>message_text</returnvalue>:
                some (hopefully) informative text that describes the
                nature of the error.
              </para>
            </listitem>
          </itemizedlist>
        </para>

        <example>
          <title>foo</title>
          <para>
            An example might help. Consider the following sequence
            sent from the client to the server.

            <synopsis>
              command_list_begin
              volume 86
              play 10240
              status
              command_list_end
            </synopsis>
          </para>

          <para>
            The server responds with:

            <returnvalue>
              ACK [50@1] {play} song doesn't exist: "10240"
            </returnvalue>
          </para>

          <para>
            This tells us that the play command, which was the
            second in the list (the first or only command is
            numbered 0), failed with error 50.  The number 50
            translates to <constant>ACK_ERROR_NO_EXIST</constant>--the
            song doesn't exist.  This is reiterated by the message text
            which also tells us which song doesn't exist.
          </para>

        </example>
      </section>
    </section>

    <section id="command_lists">
      <title>Command lists</title>

      <para>
        To facilitate faster adding of files etc. you can pass a list
        of commands all at once using a command list.  The command
        list begins with <command>command_list_begin</command> or
        <command>command_list_ok_begin</command> and ends with
        <command>command_list_end</command>.
      </para>

      <para>
        It does not execute any commands until the list has ended.
        The return value is whatever the return for a list of commands
        is.  On success for all commands,
        <returnvalue>OK</returnvalue> is returned.  If a command
        fails, no more commands are executed and the appropriate
        <returnvalue>ACK</returnvalue> error is returned. If
        <command>command_list_ok_begin</command> is used,
        <returnvalue>list_OK</returnvalue> is returned for each
        successful command executed in the command list.
      </para>
    </section>

    <section>
      <title>Ranges</title>

      <para>
        Some commands (e.g. <link
        linkend="command_delete"><command>delete</command></link>)
        allow specifying a range in the form
        <parameter>START:END</parameter> (the <varname>END</varname>
        item is not included in the range, similar to ranges in the
        Python programming language).  If <varname>END</varname> is
        omitted, then the maximum possible value is assumed.
      </para>
    </section>
  </chapter>

  <chapter>
    <title>Recipes</title>

    <section>
      <title>Queuing</title>

      <para>
        Often, users run MPD with "<link
        linkend="command_random">random</link>" enabled, but want to
        be able to insert songs "before" the rest of the playlist.
        That is commonly called "queuing".
      </para>

      <para>
        MPD implements this by allowing the client to specify a
        "priority" for each song in the playlist (commands <link
        linkend="command_prio"><command>prio</command></link> and
        <link
        linkend="command_prioid"><command>prioid</command></link>).  A
        higher priority means that the song is going to be played
        before the other songs.
      </para>

      <para>
        In "random" mode, MPD maintains an internal randomized
        sequence of songs.  In this sequence, songs with a higher
        priority come first, and all songs with the same priority are
        shuffled (by default, all songs are shuffled, because all have
        the same priority "0").  When you increase the priority of a
        song, it is moved to the front of the sequence according to
        its new priority, but always after the current one.  A song
        that has been played already (it's "before" the current song
        in that sequence) will only be scheduled for repeated playback
        if its priority has become bigger than the priority of the
        current song.  Decreasing the priority of a song will moved it
        farther to the end of the sequence.  Changing the priority of
        the current song has no effect on the sequence.
      </para>
    </section>
  </chapter>

  <chapter>
    <title>Command reference</title>

    <note>
      <para>
        For manipulating playlists and playing, there are two sets of
        commands.  One set uses the song id of a song in the playlist,
        while another set uses the playlist position of the song. The
        commands using song ids should be used instead of the commands
        that manipulate and control playback based on playlist
        position. Using song ids is a safer method when multiple
        clients are interacting with MPD.
      </para>
    </note>

    <section>
      <title>Querying MPD's status</title>

      <variablelist>
        <varlistentry id="command_clearerror">
          <term>
            <cmdsynopsis>
              <command>clearerror</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Clears the current error message in status (this is also
              accomplished by any command that starts playback).
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_currentsong">
          <term>
            <cmdsynopsis>
              <command>currentsong</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Displays the song info of the current song (same song that
              is identified in status).
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_idle">
          <term>
            <cmdsynopsis>
              <command>idle</command>
              <arg choice="opt" rep="repeat"><replaceable>SUBSYSTEMS</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              <footnote id="since_0_14"><simpara>Introduced with MPD 0.14</simpara></footnote>
              Waits until there is a noteworthy change in one or more
              of MPD's subsystems.  As soon as there is one, it lists
              all changed systems in a line in the format
              <returnvalue>changed: SUBSYSTEM</returnvalue>, where
              SUBSYSTEM is one of the following:
            </para>
            <itemizedlist>
              <listitem>
                <para>
                  <returnvalue>database</returnvalue>: the song database
                  has been modified after <command>update</command>.
                </para>
              </listitem>
              <listitem>
                <para>
                  <returnvalue>update</returnvalue>: a database update
                  has started or finished.  If the database was
                  modified during the update, the
                  <returnvalue>database</returnvalue> event is also
                  emitted.
                </para>
              </listitem>
              <listitem>
                <para>
                  <returnvalue>stored_playlist</returnvalue>: a stored
                  playlist has been modified, renamed, created or
                  deleted
                </para>
              </listitem>
              <listitem>
                <para>
                  <returnvalue>playlist</returnvalue>: the current
                  playlist has been modified
                </para>
              </listitem>
              <listitem>
                <para>
                  <returnvalue>player</returnvalue>: the player has been
                  started, stopped or seeked
                </para>
              </listitem>
              <listitem>
                <para>
                  <returnvalue>mixer</returnvalue>: the volume has been
                  changed
                </para>
              </listitem>
              <listitem>
                <para>
                  <returnvalue>output</returnvalue>: an audio output has
                  been enabled or disabled
                </para>
              </listitem>
              <listitem>
                <para>
                  <returnvalue>options</returnvalue>: options like
                  <option>repeat</option>, <option>random</option>,
                  <option>crossfade</option>, replay gain
                </para>
              </listitem>
              <listitem>
                <para>
                    <returnvalue>sticker</returnvalue>: the sticker database
                    has been modified.
                </para>
              </listitem>
              <listitem>
                <para>
                  <returnvalue>subscription</returnvalue>: a client
                  has subscribed or unsubscribed to a channel
                </para>
              </listitem>
              <listitem>
                <para>
                  <returnvalue>message</returnvalue>: a message was
                  received on a channel this client is subscribed to;
                  this event is only emitted when the queue is empty
                </para>
              </listitem>
            </itemizedlist>
            <para>
              While a client is waiting for <command>idle</command>
              results, the server disables timeouts, allowing a client
              to wait for events as long as mpd runs.  The
              <command>idle</command> command can be canceled by
              sending the command <command>noidle</command> (no other
              commands are allowed). MPD will then leave
              <command>idle</command> mode and print results
              immediately; might be empty at this time.
            </para>
            <para>
              If the optional <varname>SUBSYSTEMS</varname> argument is used,
              MPD will only send notifications when something changed in
              one of the specified subsytems.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_status">
          <term>
            <cmdsynopsis>
              <command>status</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Reports the current status of the player and the volume
              level.
            </para>
            <itemizedlist>
              <listitem>
                <para>
                  <varname>volume</varname>:
                  <returnvalue>0-100</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>repeat</varname>:
                  <returnvalue>0 or 1</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>random</varname>:
                  <returnvalue>0 or 1</returnvalue>
                </para>
              </listitem>
              <listitem>
               <para>
                <varname>single</varname>:
                <footnote id="since_0_15"><simpara>Introduced with MPD 0.15</simpara></footnote>
                <returnvalue>0 or 1</returnvalue>
               </para>
              </listitem>
              <listitem>
               <para>
                <varname>consume</varname>:
                <footnoteref linkend="since_0_15"/>
                <returnvalue>0 or 1</returnvalue>
               </para>
              </listitem>
              <listitem>
                <para>
                  <varname>playlist</varname>:
                  <returnvalue>31-bit unsigned integer, the playlist
                  version number</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>playlistlength</varname>:
                  <returnvalue>integer, the length of the
                  playlist</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>state</varname>:
                  <returnvalue>play, stop, or pause</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>song</varname>:
                  <returnvalue> playlist song number of the current
                  song stopped on or playing
                  </returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>songid</varname>:
                  <returnvalue>playlist songid of the current song
                  stopped on or playing
                  </returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>nextsong</varname>:
                  <footnoteref linkend="since_0_15"/>
                  <returnvalue> playlist song number of the next
                  song to be played
                  </returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>nextsongid</varname>:
                  <footnoteref linkend="since_0_15"/>
                  <returnvalue>playlist songid of the next song
                  to be played
                  </returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>time</varname>:
                  <returnvalue>total time elapsed (of current
                  playing/paused song)</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>elapsed</varname>:
                  <footnote id="since_0_16"><simpara>Introduced with MPD 0.16</simpara></footnote>
                  <returnvalue>
                    Total time elapsed within the current song, but
                    with higher resolution.
                  </returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>bitrate</varname>:
                  <returnvalue>instantaneous bitrate in
                  kbps</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>xfade</varname>:
                  <returnvalue>crossfade in seconds</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>mixrampdb</varname>:
                  <returnvalue>mixramp threshold in dB</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>mixrampdelay</varname>:
                  <returnvalue>mixrampdelay in seconds</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>audio</varname>:
                  <returnvalue>sampleRate:bits:channels</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>updatings_db</varname>:
                  <returnvalue>job id</returnvalue>
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>error</varname>:
                  <returnvalue>if there is an error, returns message
                  here</returnvalue>
                </para>
                </listitem>
            </itemizedlist>
          </listitem>
        </varlistentry>
        <varlistentry id="command_stats">
          <term>
            <cmdsynopsis>
              <command>stats</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Displays statistics.
            </para>
            <itemizedlist>
              <listitem>
                <para>
                  <varname>artists</varname>: number of artists
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>songs</varname>: number of albums
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>uptime</varname>: daemon uptime in seconds
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>db_playtime</varname>: sum of all song
                  times in the db
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>db_update</varname>: last db update in UNIX
                  time
                </para>
              </listitem>
              <listitem>
                <para>
                  <varname>playtime</varname>: time length of music played
                </para>
              </listitem>
            </itemizedlist>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>

    <section>
      <title>Playback options</title>

      <variablelist>
        <varlistentry id="command_consume">
          <term>
            <cmdsynopsis>
              <command>consume</command>
              <arg choice="req"><replaceable>STATE</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              <footnoteref linkend="since_0_15"/>
              Sets consume state to <varname>STATE</varname>,
              <varname>STATE</varname> should be 0 or 1.
	      When consume is activated, each song played is removed from playlist.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_crossfade">
          <term>
            <cmdsynopsis>
              <command>crossfade</command>
              <arg choice="req"><replaceable>SECONDS</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Sets crossfading between songs.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_mixrampdb">
          <term>
            <cmdsynopsis>
              <command>mixrampdb</command>
              <arg choice="req"><replaceable>deciBels</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Sets the threshold at which songs will be overlapped. Like crossfading but doesn't fade the track volume, just overlaps. The songs need to have MixRamp tags added by an external tool. 0dB is the normalized maximum volume so use negative values, I prefer -17dB. In the absence of mixramp tags crossfading will be used. See http://sourceforge.net/projects/mixramp
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_mixrampdelay">
          <term>
            <cmdsynopsis>
              <command>mixrampdelay</command>
              <arg choice="req"><replaceable>SECONDS</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Additional time subtracted from the overlap calculated by mixrampdb. A value of "nan" disables MixRamp overlapping and falls back to crossfading.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_random">
          <term>
            <cmdsynopsis>
              <command>random</command>
              <arg choice="req"><replaceable>STATE</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Sets random state to <varname>STATE</varname>,
              <varname>STATE</varname> should be 0 or 1.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_repeat">
          <term>
            <cmdsynopsis>
              <command>repeat</command>
              <arg choice="req"><replaceable>STATE</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Sets repeat state to <varname>STATE</varname>,
              <varname>STATE</varname> should be 0 or 1.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_setvol">
          <term>
            <cmdsynopsis>
              <command>setvol</command>
              <arg choice="req"><replaceable>VOL</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Sets volume to <varname>VOL</varname>, the range of
              volume is 0-100.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_single">
          <term>
            <cmdsynopsis>
              <command>single</command>
              <arg choice="req"><replaceable>STATE</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              <footnoteref linkend="since_0_15"/>
              Sets single state to <varname>STATE</varname>,
              <varname>STATE</varname> should be 0 or 1.
	      When single is activated, playback is stopped after current song, or
	      song is repeated if the 'repeat' mode is enabled.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_replay_gain_mode">
          <term>
            <cmdsynopsis>
              <command>replay_gain_mode</command>
              <arg choice="req"><replaceable>MODE</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Sets the replay gain mode.  One of
              <parameter>off</parameter>,
              <parameter>track</parameter>,
              <parameter>album</parameter>,
              <parameter>auto</parameter><footnote
                        id="replay_gain_auto_since_0_16">
                <simpara>added in MPD 0.16</simpara>
              </footnote>.
            </para>
            <para>
              Changing the mode during playback may take several
              seconds, because the new settings does not affect the
              buffered data.
            </para>
            <para>
              This command triggers the
              <returnvalue>options</returnvalue> idle event.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_replay_gain_status">
          <term>
            <cmdsynopsis>
              <command>replay_gain_status</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Prints replay gain options.  Currently, only the
              variable <varname>replay_gain_mode</varname> is
              returned.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>

    <section>
      <title>Controlling playback</title>

      <variablelist>
        <varlistentry id="command_next">
          <term>
            <cmdsynopsis>
              <command>next</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Plays next song in the playlist.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_pause">
          <term>
            <cmdsynopsis>
              <command>pause</command>
              <arg choice="req"><replaceable>PAUSE</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Toggles pause/resumes playing, <varname>PAUSE</varname> is 0 or 1.
            </para>
            <note>
              <para>
                The use of pause command w/o the PAUSE argument is
                deprecated.
              </para>
            </note>
          </listitem>
        </varlistentry>
        <varlistentry id="command_play">
          <term>
            <cmdsynopsis>
              <command>play</command>
              <arg><replaceable>SONGPOS</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Begins playing the playlist at song number
              <varname>SONGPOS</varname>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_playid">
          <term>
            <cmdsynopsis>
              <command>playid</command>
              <arg><replaceable>SONGID</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Begins playing the playlist at song
              <varname>SONGID</varname>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_previous">
          <term>
            <cmdsynopsis>
              <command>previous</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Plays previous song in the playlist.
            </para>
          </listitem>
        </varlistentry>

        <varlistentry id="command_seek">
          <term>
            <cmdsynopsis>
              <command>seek</command>
              <arg choice="req"><replaceable>SONGPOS</replaceable></arg>
              <arg choice="req"><replaceable>TIME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Seeks to the position <varname>TIME</varname> (in
              seconds) of entry <varname>SONGPOS</varname> in the
              playlist.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_seekid">
          <term>
            <cmdsynopsis>
              <command>seekid</command>
              <arg choice="req"><replaceable>SONGID</replaceable></arg>
              <arg choice="req"><replaceable>TIME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Seeks to the position <varname>TIME</varname> (in
              seconds) of song <varname>SONGID</varname>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_stop">
          <term>
            <cmdsynopsis>
              <command>stop</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Stops playing.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>

    <section>
      <title>The current playlist</title>

      <variablelist>
        <varlistentry id="command_add">
          <term>
            <cmdsynopsis>
              <command>add</command>
              <arg choice="req"><replaceable>URI</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Adds the file <varname>URI</varname> to the playlist
              (directories add recursively). <varname>URI</varname>
              can also be a single file.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_addid">
          <term>
            <cmdsynopsis>
              <command>addid</command>
              <arg choice="req"><replaceable>URI</replaceable></arg>
              <arg><replaceable>POSITION</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Adds a song to the playlist (non-recursive) and returns the song id.
            </para>
            <para>
              <varname>URI</varname> is always a single file or
              URL.  For example:
            </para>
            <screen>
addid "foo.mp3"
Id: 999
OK
            </screen>
          </listitem>
        </varlistentry>
        <varlistentry id="command_clear">
          <term>
            <cmdsynopsis>
              <command>clear</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Clears the current playlist.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_delete">
          <term>
            <cmdsynopsis>
              <command>delete</command>
              <group>
                <arg choice="req"><replaceable>POS</replaceable></arg>
                <arg choice="req"><replaceable>START:END</replaceable></arg>
              </group>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Deletes a song from the playlist.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_deleteid">
          <term>
            <cmdsynopsis>
              <command>deleteid</command>
              <arg choice="req"><replaceable>SONGID</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Deletes the song <varname>SONGID</varname> from the
              playlist
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_move">
          <term>
            <cmdsynopsis>
              <command>move</command>
              <group>
                  <arg choice="req"><replaceable>FROM</replaceable></arg>
                  <arg choice="req"><replaceable>START:END</replaceable></arg>
              </group>
              <arg choice="req"><replaceable>TO</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Moves the song at <varname>FROM</varname> or range of songs
              at <varname>START:END</varname> to <varname>TO</varname>
              in the playlist.
              <footnote id="range_since_0_15">
                <simpara>Ranges are supported since MPD 0.15</simpara>
              </footnote>
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_moveid">
          <term>
            <cmdsynopsis>
              <command>moveid</command>
              <arg choice="req"><replaceable>FROM</replaceable></arg>
              <arg choice="req"><replaceable>TO</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Moves the song with <varname>FROM</varname> (songid) to
              <varname>TO</varname> (playlist index) in the
              playlist.  If <varname>TO</varname> is negative, it
              is relative to the current song in the playlist (if
              there is one).
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_playlist">
          <term>
            <cmdsynopsis>
              <command>playlist</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Displays the current playlist.
            </para>
            <note>
              <para>
                Do not use this, instead use <command>playlistinfo</command>.
              </para>
            </note>
          </listitem>
        </varlistentry>
        <varlistentry id="command_playlistfind">
          <term>
            <cmdsynopsis>
              <command>playlistfind</command>
              <arg choice="req"><replaceable>TAG</replaceable></arg>
              <arg choice="req"><replaceable>NEEDLE</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Finds songs in the current playlist with strict
              matching.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_playlistid">
          <term>
            <cmdsynopsis>
              <command>playlistid</command>
              <arg choice="req"><replaceable>SONGID</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Displays a list of songs in the playlist.
              <varname>SONGID</varname> is optional and specifies a
              single song to display info for.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_playlistinfo">
          <term>
            <cmdsynopsis>
              <command>playlistinfo</command>
              <group>
                  <arg><replaceable>SONGPOS</replaceable></arg>
                  <arg><replaceable>START:END</replaceable></arg>
              </group>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Displays a list of all songs in the playlist, or if the optional
              argument is given, displays information only for the song
              <varname>SONGPOS</varname> or the range of songs
              <varname>START:END</varname>
              <footnoteref linkend="range_since_0_15"/>
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_playlistsearch">
          <term>
            <cmdsynopsis>
              <command>playlistsearch</command>
              <arg choice="req"><replaceable>TAG</replaceable></arg>
              <arg choice="req"><replaceable>NEEDLE</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Searches case-sensitively for partial matches in the
              current playlist.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_plchanges">
          <term>
            <cmdsynopsis>
              <command>plchanges</command>
              <arg choice="req"><replaceable>VERSION</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Displays changed songs currently in the playlist since
              <varname>VERSION</varname>.
            </para>
            <para>
              To detect songs that were deleted at the end of the
              playlist, use playlistlength returned by status command.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_plchangesposid">
          <term>
            <cmdsynopsis>
              <command>plchangesposid</command>
              <arg choice="req"><replaceable>VERSION</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Displays changed songs currently in the playlist since
              <varname>VERSION</varname>.  This function only
              returns the position and the id of the changed song, not
              the complete metadata. This is more bandwidth efficient.
            </para>
            <para>
              To detect songs that were deleted at the end of the
              playlist, use playlistlength returned by status command.
            </para>
          </listitem>
        </varlistentry>

        <varlistentry id="command_prio">
          <term>
            <cmdsynopsis>
              <command>prio</command>
              <arg choice="req"><replaceable>PRIORITY</replaceable></arg>
              <arg choice="req" rep="repeat"><replaceable>START:END</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Set the priority of the specified songs.  A higher
              priority means that it will be played first when
              "random" mode is enabled.
            </para>

            <para>
              A priority is an integer between 0 and 255.  The default
              priority of new songs is 0.
            </para>
          </listitem>
        </varlistentry>

        <varlistentry id="command_prioid">
          <term>
            <cmdsynopsis>
              <command>prioid</command>
              <arg choice="req"><replaceable>PRIORITY</replaceable></arg>
              <arg choice="req" rep="repeat"><replaceable>ID</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Same as <link
              linkend="command_prio"><command>prio</command></link>,
              but address the songs with their id.
            </para>
          </listitem>
        </varlistentry>

        <varlistentry id="command_shuffle">
          <term>
            <cmdsynopsis>
              <command>shuffle</command>
              <arg><replaceable>START:END</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Shuffles the current playlist.
              <varname>START:END</varname> is optional and specifies
              a range of songs.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_swap">
          <term>
            <cmdsynopsis>
              <command>swap</command>
              <arg choice="req"><replaceable>SONG1</replaceable></arg>
              <arg choice="req"><replaceable>SONG2</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Swaps the positions of <varname>SONG1</varname> and
              <varname>SONG2</varname>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_swapid">
          <term>
            <cmdsynopsis>
              <command>swapid</command>
              <arg choice="req"><replaceable>SONG1</replaceable></arg>
              <arg choice="req"><replaceable>SONG2</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Swaps the positions of <varname>SONG1</varname> and
              <varname>SONG2</varname> (both song ids).
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>

    <section>
      <title>Stored playlists</title>

      <para>
        Playlists are stored inside the configured playlist directory.
        They are addressed with their file name (without the directory
        and without the <filename>.m3u</filename> suffix).
      </para>

      <para>
        Some of the commands described in this section can be used to
        run playlist plugins instead of the hard-coded simple
        <filename>m3u</filename> parser.  They can access playlists in
        the music directory (relative path including the suffix) or
        remote playlists (absolute URI with a supported scheme).
      </para>

      <variablelist>
        <varlistentry id="command_listplaylist">
          <term>
            <cmdsynopsis>
              <command>listplaylist</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Lists the songs in the playlist.  Playlist plugins are
              supported.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_listplaylistinfo">
          <term>
            <cmdsynopsis>
              <command>listplaylistinfo</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Lists the songs with metadata in the playlist.  Playlist
              plugins are supported.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_listplaylists">
          <term>
            <cmdsynopsis>
              <command>listplaylists</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Prints a list of the playlist directory.
            </para>
            <para>
              After each playlist name the server sends its last
              modification time as attribute "Last-Modified" in ISO
              8601 format.  To avoid problems due to clock differences
              between clients and the server, clients should not
              compare this value with their local clock.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_load">
          <term>
            <cmdsynopsis>
              <command>load</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Loads the playlist into the current queue.  Playlist
              plugins are supported.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_playlistadd">
          <term>
            <cmdsynopsis>
              <command>playlistadd</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
              <arg choice="req"><replaceable>URI</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Adds <varname>URI</varname> to the playlist
              <filename>NAME.m3u</filename>.
            </para>
            <para>
             <filename>NAME.m3u</filename> will be created if it does
             not exist.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_playlistclear">
          <term>
            <cmdsynopsis>
              <command>playlistclear</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Clears the playlist <filename>NAME.m3u</filename>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_playlistdelete">
          <term>
            <cmdsynopsis>
              <command>playlistdelete</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
              <arg choice="req"><replaceable>SONGPOS</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Deletes <varname>SONGPOS</varname> from the
              playlist <filename>NAME.m3u</filename>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_playlistmove">
          <term>
            <cmdsynopsis>
              <command>playlistmove</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
              <arg choice="req"><replaceable>SONGID</replaceable></arg>
              <arg choice="req"><replaceable>SONGPOS</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Moves <varname>SONGID</varname> in the playlist
              <filename>NAME.m3u</filename> to the position
              <varname>SONGPOS</varname>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_rename">
          <term>
            <cmdsynopsis>
              <command>rename</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
              <arg choice="req"><replaceable>NEW_NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Renames the playlist <filename>NAME.m3u</filename> to <filename>NEW_NAME.m3u</filename>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_rm">
          <term>
            <cmdsynopsis>
              <command>rm</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Removes the playlist <filename>NAME.m3u</filename> from
              the playlist directory.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_save">
          <term>
            <cmdsynopsis>
              <command>save</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Saves the current playlist to
              <filename>NAME.m3u</filename> in the playlist directory.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>

    <section>
      <title>The music database</title>

      <variablelist>
        <varlistentry id="command_count">
          <term>
            <cmdsynopsis>
              <command>count</command>
              <arg choice="req"><replaceable>TAG</replaceable></arg>
              <arg choice="req"><replaceable>NEEDLE</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Counts the number of songs and their total playtime in
              the db matching <varname>TAG</varname> exactly.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_find">
          <term>
            <cmdsynopsis>
              <command>find</command>
              <arg choice="req"><replaceable>TYPE</replaceable></arg>
              <arg choice="req"><replaceable>WHAT</replaceable></arg>
              <arg choice="opt"><replaceable>...</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Finds songs in the db that are exactly
              <varname>WHAT</varname>.  <varname>TYPE</varname> can
              be any tag supported by MPD, or one of the two special
              parameters — <parameter>file</parameter> to search by
              full path (relative to database root), and
              <parameter>any</parameter> to match against all
              available tags.  <varname>WHAT</varname> is what to find.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_findadd">
          <term>
            <cmdsynopsis>
              <command>findadd</command>
              <arg choice="req"><replaceable>TYPE</replaceable></arg>
              <arg choice="req"><replaceable>WHAT</replaceable></arg>
              <arg choice="opt"><replaceable>...</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Finds songs in the db that are exactly
              <varname>WHAT</varname> and adds them to current playlist.
              Parameters have the same meaning as for <command>find</command>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_list">
          <term>
            <cmdsynopsis>
              <command>list</command>
              <arg choice="req"><replaceable>TYPE</replaceable></arg>
              <arg><replaceable>ARTIST</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Lists all tags of the specified type.
              <varname>TYPE</varname> can be any tag supported by MPD or
              <parameter>file</parameter>.
            </para>
            <para>
              <varname>ARTIST</varname> is an optional parameter when
              type is album, this specifies to list albums by an
              artist.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_listall">
          <term>
            <cmdsynopsis>
              <command>listall</command>
              <arg><replaceable>URI</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Lists all songs and directories in
              <varname>URI</varname>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_listallinfo">
          <term>
            <cmdsynopsis>
              <command>listallinfo</command>
              <arg><replaceable>URI</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Same as <command>listall</command>, except it also
              returns metadata info in the same format as
              <command>lsinfo</command>.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_lsinfo">
          <term>
            <cmdsynopsis>
              <command>lsinfo</command>
              <arg><replaceable>URI</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Lists the contents of the directory
              <varname>URI</varname>.
            </para>
            <para>
              When listing the root directory, this currently returns
              the list of stored playlists.  This behavior is
              deprecated; use "listplaylists" instead.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_search">
          <term>
            <cmdsynopsis>
              <command>search</command>
              <arg choice="req"><replaceable>TYPE</replaceable></arg>
              <arg choice="req"><replaceable>WHAT</replaceable></arg>
              <arg choice="opt"><replaceable>...</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Searches for any song that contains
              <varname>WHAT</varname>. Parameters have the same meaning
              as for <command>find</command>, except that search is not
              case sensitive.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_update">
          <term>
            <cmdsynopsis>
              <command>update</command>
              <arg choice="opt"><replaceable>URI</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Updates the music database: find new files, remove
              deleted files, update modified files.
            </para>
            <para>
              <varname>URI</varname> is a particular directory or
              song/file to update.  If you do not specify it,
              everything is updated.
            </para>
            <para>
              Prints "updating_db: JOBID" where
              <varname>JOBID</varname> is a positive number
              identifying the update job.  You can read the current
              job id in the <command>status</command> response.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_rescan">
          <term>
            <cmdsynopsis>
              <command>rescan</command>
              <arg choice="opt"><replaceable>URI</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Same as <command>update</command>, but also rescans
              unmodified files.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>

    <section>
      <title>Stickers</title>

      <para>
        "Stickers"<footnoteref linkend="since_0_15"/> are pieces of
        information attached to existing MPD objects (e.g. song files,
        directories, albums).  Clients can create arbitrary name/value
        pairs.  MPD itself does not assume any special meaning in
        them.
      </para>

      <para>
        The goal is to allow clients to share additional (possibly
        dynamic) information about songs, which is neither stored on
        the client (not available to other clients), nor stored in the
        song files (MPD has no write access).
      </para>

      <para>
        Client developers should create a standard for common sticker
        names, to ensure interoperability.
      </para>

      <para>
        Objects which may have stickers are addressed by their object
        type ("song" for song objects) and their URI (the path within
        the database for songs).
      </para>

      <variablelist>
        <varlistentry id="command_sticker_get">
          <term>
            <cmdsynopsis>
              <command>sticker</command>
              <arg choice="plain">get</arg>
              <arg choice="req"><replaceable>TYPE</replaceable></arg>
              <arg choice="req"><replaceable>URI</replaceable></arg>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Reads a sticker value for the specified object.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_sticker_set">
          <term>
            <cmdsynopsis>
              <command>sticker</command>
              <arg choice="plain">set</arg>
              <arg choice="req"><replaceable>TYPE</replaceable></arg>
              <arg choice="req"><replaceable>URI</replaceable></arg>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
              <arg choice="req"><replaceable>VALUE</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Adds a sticker value to the specified object.  If a
              sticker item with that name already exists, it is
              replaced.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_sticker_delete">
          <term>
            <cmdsynopsis>
              <command>sticker</command>
              <arg choice="plain">delete</arg>
              <arg choice="req"><replaceable>TYPE</replaceable></arg>
              <arg choice="req"><replaceable>URI</replaceable></arg>
              <arg choice="opt"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Deletes a sticker value from the specified object.  If
              you do not specify a sticker name, all sticker values
              are deleted.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_sticker_list">
          <term>
            <cmdsynopsis>
              <command>sticker</command>
              <arg choice="plain">list</arg>
              <arg choice="req"><replaceable>TYPE</replaceable></arg>
              <arg choice="req"><replaceable>URI</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Lists the stickers for the specified object.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_sticker_find">
          <term>
            <cmdsynopsis>
              <command>sticker</command>
              <arg choice="plain">find</arg>
              <arg choice="req"><replaceable>TYPE</replaceable></arg>
              <arg choice="req"><replaceable>URI</replaceable></arg>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Searches the sticker database for stickers with the
              specified name, below the specified directory (URI).
              For each matching song, it prints the URI and that one
              sticker's value.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>

    <section>
      <title>Connection settings</title>

      <variablelist>
        <varlistentry id="command_close">
          <term>
            <cmdsynopsis>
              <command>close</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Closes the connection to MPD.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_kill">
          <term>
            <cmdsynopsis>
              <command>kill</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Kills MPD.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_password">
          <term>
            <cmdsynopsis>
              <command>password</command>
              <arg choice="req"><replaceable>PASSWORD</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              This is used for authentication with the server.
              <varname>PASSWORD</varname> is simply the plaintext
              password.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_ping">
          <term>
            <cmdsynopsis>
              <command>ping</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Does nothing but return "OK".
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>

    <section>
      <title>Audio output devices</title>

      <variablelist>
        <varlistentry id="command_disableoutput">
          <term>
            <cmdsynopsis>
              <command>disableoutput</command>
              <arg choice="req"><replaceable>ID</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Turns an output off.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_enableoutput">
          <term>
            <cmdsynopsis>
              <command>enableoutput</command>
              <arg choice="req"><replaceable>ID</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Turns an output on.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_outputs">
          <term>
            <cmdsynopsis>
              <command>outputs</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Shows information about all outputs.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>

    <section>
      <title>Reflection</title>

      <variablelist>
        <varlistentry id="command_commands">
          <term>
            <cmdsynopsis>
              <command>commands</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Shows which commands the current user has access to.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_notcommands">
          <term>
            <cmdsynopsis>
              <command>notcommands</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Shows which commands the current user does not have
              access to.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_tagtypes">
          <term>
            <cmdsynopsis>
              <command>tagtypes</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Shows a list of available song metadata.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_urlhandlers">
          <term>
            <cmdsynopsis>
              <command>urlhandlers</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Gets a list of available URL handlers.
            </para>
          </listitem>
        </varlistentry>
        <varlistentry id="command_decoders">
          <term>
            <cmdsynopsis>
              <command>decoders</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Print a list of decoder plugins, followed by their
              supported suffixes and MIME types.  Example response:
            </para>
            <programlisting>plugin: mad
suffix: mp3
suffix: mp2
mime_type: audio/mpeg
plugin: mpcdec
suffix: mpc</programlisting>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>

    <section>
      <title>Client to client</title>

      <para>
        Clients can communicate with each others over "channels".  A
        channel is created by a client subscribing to it.  More than
        one client can be subscribed to a channel at a time; all of
        them will receive the messages which get sent to it.
      </para>

      <para>
        Each time a client subscribes or unsubscribes, the global idle
        event <varname>subscription</varname> is generated.  In
        conjunction with the <command>channels</command> command, this
        may be used to auto-detect clients providing additional
        services.
      </para>

      <para>
        A new messages is indicated by the <varname>message</varname>
        idle event.
      </para>

      <variablelist>
        <varlistentry id="command_subscribe">
          <term>
            <cmdsynopsis>
              <command>subscribe</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Subscribe to a channel.  The channel is created if it
              does not exist already.  The name may consist of
              alphanumeric ASCII characters plus underscore, dash, dot
              and colon.
            </para>
          </listitem>
        </varlistentry>

        <varlistentry id="command_unsubscribe">
          <term>
            <cmdsynopsis>
              <command>unsubscribe</command>
              <arg choice="req"><replaceable>NAME</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Unsubscribe from a channel.
            </para>
          </listitem>
        </varlistentry>

        <varlistentry id="command_channels">
          <term>
            <cmdsynopsis>
              <command>channels</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Obtain a list of all channels.  The response is a list
              of "channel:" lines.
            </para>
          </listitem>
        </varlistentry>

        <varlistentry id="command_readmessages">
          <term>
            <cmdsynopsis>
              <command>readmessages</command>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Reads messages for this client.  The response is a list
              of "channel:" and "message:" lines.
            </para>
          </listitem>
        </varlistentry>

        <varlistentry id="command_sendmessage">
          <term>
            <cmdsynopsis>
              <command>sendmessage</command>
              <arg choice="req"><replaceable>CHANNEL</replaceable></arg>
              <arg choice="req"><replaceable>TEXT</replaceable></arg>
            </cmdsynopsis>
          </term>
          <listitem>
            <para>
              Send a message to the specified channel.
            </para>
          </listitem>
        </varlistentry>
      </variablelist>
    </section>
  </chapter>
</book>