Music Player Daemon (MPD) is a free and open sourcemusic player server. It plays audio files, organizes playlists and maintains a music database. In order to interact with it, a separate client is needed.
MPD simply runs in the background playing music from its playlist. Client programs communicate with MPD to manipulate playback, the playlist, and the database. It is not a full-featured music player program such as Amarok, but its clients can serve such role.
MPD uses a flat file database to maintain the basic music file information when it is not running. Once the daemon is started, the database is kept completely in-memory and no hard disk access is necessary to look up or search for local audio files. Usually, music files must be below the music root directory and are only added to the database when the update command is sent to the server. Playback of arbitrary files is only allowed for local clients which are connected to the server via Unix Domain Sockets. MPD does not provide a built-in tag editor; this functionality is handled by clients or external programs, though 3rd party patches do exist to add this functionality to the server.
The client–server model provides several advantages over all-inclusive music players. Clients may communicate with the server remotely over an intranet or over the Internet. The server can be a headless computer located anywhere on the network. Music playback can continue seamlessly when not using X or restarting X. Different clients can be used for different purposes – a lightweight client left open all the time for controlling playback with a more fully featured client used for intensive database searches. Several clients can use the same database, even running simultaneously – side-by-side, remotely or under different user accounts.
gmpc is the oldest maintained gtk+-2 (gtk+-3 development version) client, it provides many different ways of exploring the music collection and rich metadata like lyrics, covers, artist/album information, artist/album/backdrop images, similar artists and more. The client aims to be rich in features, but still lightweight enough to have constantly running on low end hardware.
Sonata uses GTK+ to provide a GUI for playing files and managing playlists.
Intelligent Music Player Client (IMPC) uses GTK+ 3.0 and supports loading related information (articles, covers, images) with actually playing song and it learns to classify related content.
Cantata uses Qt 4/5 to manage the library or playlists, with extras like tags editor, lyrics and cover fetching from Internet and support for mass storage devices.
Qmobilempd provides a Qt4 client especially for mobile devices like Symbian.
Qmpdplasmoid provides a client directly embedded into the KDE desktop.
Gimmix provides a simple interface with a very small memory footprint.
For a more complete list, see the Clients MPD Wiki.
Simple clients can script the mpc program to issue commands to the server. Some clients run within a web browser and can be located on the same computer as the server, requiring only a browser be installed on the client machine. There is a client implemented as a Firefox add-on, one as a Xfce panel plugin, and one as a Wii application, and one as a Windows Store application for Windows 8/Windows RT.