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11.9.29 Audio Services

The (gnu services audio) module provides a service to start MPD (the Music Player Daemon).

Music Player Daemon

The Music Player Daemon (MPD) is a service that can play music while being controlled from the local machine or over the network by a variety of clients.

The following example shows the simplest configuration to locally expose, via PulseAudio, a music collection kept at /srv/music, with mpd running as the default ‘mpd’ user. This user will spawn its own PulseAudio daemon, which may compete for the sound card access with that of your own user. In this configuration, you may have to stop the playback of your user audio applications to hear MPD’s output and vice-versa.

(service mpd-service-type
         (mpd-configuration
          (music-directory "/srv/music")))

Important: The music directory must be readable to the MPD user, by default, ‘mpd’. Permission problems will be reported via ‘Permission denied’ errors in the MPD logs, which appear in /var/log/messages by default.

Most MPD clients will trigger a database update upon connecting, but you can also use the update action do to so:

herd update mpd

All the MPD configuration fields are documented below, and a more complex example follows.

Variable: mpd-service-type

The service type for mpd

Data Type: mpd-configuration

Available mpd-configuration fields are:

package (default: mpd) (type: file-like)

The MPD package.

user (type: user-account)

The user to run mpd as.

group (type: user-group)

The group to run mpd as.

The default %mpd-group is a system group with name “mpd”.

shepherd-requirement (default: '()) (type: list-of-symbols)

A list of symbols naming Shepherd services that this service will depend on.

environment-variables (default: '("PULSE_CLIENTCONFIG=/etc/pulse/client.conf" "PULSE_CONFIG=/etc/pulse/daemon.conf")) (type: list-of-strings)

A list of strings specifying environment variables.

log-file (type: maybe-string)

The location of the log file. Unless specified, logs are sent to the local syslog daemon. Alternatively, a log file name can be specified, for example /var/log/mpd.log.

log-level (type: maybe-string)

Supress any messages below this threshold. The available values, in decreasing order of verbosity, are: verbose, info, notice, warning and error.

music-directory (type: maybe-string)

The directory to scan for music files.

music-dir (type: maybe-string)

The directory to scan for music files.

playlist-directory (type: maybe-string)

The directory to store playlists.

playlist-dir (type: maybe-string)

The directory to store playlists.

db-file (type: maybe-string)

The location of the music database. When left unspecified, ~/.cache/db is used.

state-file (type: maybe-string)

The location of the file that stores current MPD’s state.

sticker-file (type: maybe-string)

The location of the sticker database.

default-port (default: 6600) (type: maybe-port)

The default port to run mpd on.

endpoints (type: maybe-list-of-strings)

The addresses that mpd will bind to. A port different from default-port may be specified, e.g. localhost:6602 and IPv6 addresses must be enclosed in square brackets when a different port is used. To use a Unix domain socket, an absolute path or a path starting with ~ can be specified here.

address (type: maybe-string)

The address that mpd will bind to. To use a Unix domain socket, an absolute path can be specified here.

database (type: maybe-mpd-plugin)

MPD database plugin configuration.

partitions (default: '()) (type: list-of-mpd-partition)

List of MPD "partitions".

neighbors (default: '()) (type: list-of-mpd-plugin)

List of MPD neighbor plugin configurations.

inputs (default: '()) (type: list-of-mpd-plugin)

List of MPD input plugin configurations.

archive-plugins (default: '()) (type: list-of-mpd-plugin)

List of MPD archive plugin configurations.

auto-update? (type: maybe-boolean)

Whether to automatically update the music database when files are changed in the music-directory.

input-cache-size (type: maybe-string)

MPD input cache size.

decoders (default: '()) (type: list-of-mpd-plugin)

List of MPD decoder plugin configurations.

resampler (type: maybe-mpd-plugin)

MPD resampler plugin configuration.

filters (default: '()) (type: list-of-mpd-plugin)

List of MPD filter plugin configurations.

outputs (type: list-of-mpd-plugin-or-output)

The audio outputs that MPD can use. By default this is a single output using pulseaudio.

playlist-plugins (default: '()) (type: list-of-mpd-plugin)

List of MPD playlist plugin configurations.

extra-options (default: '()) (type: alist)

An association list of option symbols/strings to string values to be appended to the configuration.

Data Type: mpd-plugin

Data type representing a mpd plugin.

plugin (type: maybe-string)

Plugin name.

name (type: maybe-string)

Name.

enabled? (type: maybe-boolean)

Whether the plugin is enabled/disabled.

extra-options (default: '()) (type: alist)

An association list of option symbols/strings to string values to be appended to the plugin configuration. See MPD plugin reference for available options.

Data Type: mpd-partition

Data type representing a mpd partition.

name (type: string)

Partition name.

extra-options (default: '()) (type: alist)

An association list of option symbols/strings to string values to be appended to the partition configuration. See Configuring Partitions for available options.

Data Type: mpd-output

Available mpd-output fields are:

name (default: "MPD") (type: string)

The name of the audio output.

type (default: "pulse") (type: string)

The type of audio output.

enabled? (default: #t) (type: boolean)

Specifies whether this audio output is enabled when MPD is started. By default, all audio outputs are enabled. This is just the default setting when there is no state file; with a state file, the previous state is restored.

format (type: maybe-string)

Force a specific audio format on output. See Global Audio Format for a more detailed description.

tags? (default: #t) (type: boolean)

If set to #f, then MPD will not send tags to this output. This is only useful for output plugins that can receive tags, for example the httpd output plugin.

always-on? (default: #f) (type: boolean)

If set to #t, then MPD attempts to keep this audio output always open. This may be useful for streaming servers, when you don’t want to disconnect all listeners even when playback is accidentally stopped.

mixer-type (type: maybe-string)

This field accepts a string that specifies which mixer should be used for this audio output: the hardware mixer, the software mixer, the null mixer (allows setting the volume, but with no effect; this can be used as a trick to implement an external mixer External Mixer) or no mixer (none). When left unspecified, a hardware mixer is used for devices that support it.

replay-gain-handler (type: maybe-string)

This field accepts a string that specifies how Replay Gain is to be applied. software uses an internal software volume control, mixer uses the configured (hardware) mixer control and none disables replay gain on this audio output.

extra-options (default: '()) (type: alist)

An association list of option symbols/strings to string values to be appended to the audio output configuration.

The following example shows a configuration of mpd that configures some of its plugins and provides a HTTP audio streaming output.

(service mpd-service-type
         (mpd-configuration
           (outputs
             (list (mpd-output
                     (name "streaming")
                     (type "httpd")
                     (mixer-type 'null)
                     (extra-options
                      `((encoder . "vorbis")
                        (port    . "8080"))))))
           (decoders
             (list (mpd-plugin
                     (plugin "mikmod")
                     (enabled? #f))
                   (mpd-plugin
                     (plugin "openmpt")
                     (enabled? #t)
                     (extra-options `((repeat-count . -1)
                                      (interpolation-filter . 1))))))
           (resampler (mpd-plugin
                        (plugin "libsamplerate")
                        (extra-options `((type . 0)))))))

myMPD

myMPD is a web server frontend for MPD that provides a mobile friendly web client for MPD.

The following example shows a myMPD instance listening on port 80, with album cover caching disabled.

(service mympd-service-type
         (mympd-configuration
          (port 80)
          (covercache-ttl 0)))
Variable: mympd-service-type

The service type for mympd.

Data Type: mympd-configuration

Available mympd-configuration fields are:

package (default: mympd) (type: file-like)

The package object of the myMPD server.

shepherd-requirement (default: '()) (type: list-of-symbols)

This is a list of symbols naming Shepherd services that this service will depend on.

user (default: %mympd-user) (type: user-account)

Owner of the mympd process.

The default %mympd-user is a system user with the name “mympd”, who is a part of the group group (see below).

group (default: %mympd-group) (type: user-group)

Owner group of the mympd process.

The default %mympd-group is a system group with name “mympd”.

work-directory (default: "/var/lib/mympd") (type: string)

Where myMPD will store its data.

cache-directory (default: "/var/cache/mympd") (type: string)

Where myMPD will store its cache.

acl (type: maybe-mympd-ip-acl)

ACL to access the myMPD webserver.

covercache-ttl (default: 31) (type: maybe-integer)

How long to keep cached covers, 0 disables cover caching.

http? (default: #t) (type: boolean)

HTTP support.

host (default: "[::]") (type: string)

Host name to listen on.

port (default: 80) (type: maybe-port)

HTTP port to listen on.

log-level (default: 5) (type: integer)

How much detail to include in logs, possible values: 0 to 7.

log-to (type: maybe-string)

Where to send logs. Unless specified, the service logs to the local syslog service under the ‘daemon’ facility. Alternatively, a log file name can be specified, for example /var/log/mympd.log.

lualibs (default: "all") (type: maybe-string)

See https://jcorporation.github.io/myMPD/scripting/#lua-standard-libraries.

uri (type: maybe-string)

Override URI to myMPD. See https://github.com/jcorporation/myMPD/issues/950.

script-acl (default: (mympd-ip-acl (allow '("127.0.0.1")))) (type: maybe-mympd-ip-acl)

ACL to access the myMPD script backend.

ssl? (default: #f) (type: boolean)

SSL/TLS support.

ssl-port (default: 443) (type: maybe-port)

Port to listen for HTTPS.

ssl-cert (type: maybe-string)

Path to PEM encoded X.509 SSL/TLS certificate (public key).

ssl-key (type: maybe-string)

Path to PEM encoded SSL/TLS private key.

pin-hash (type: maybe-string)

SHA-256 hashed pin used by myMPD to control settings access by prompting a pin from the user.

save-caches? (type: maybe-boolean)

Whether to preserve caches between service restarts.

Data Type: mympd-ip-acl

Available mympd-ip-acl fields are:

allow (default: '()) (type: list-of-strings)

Allowed IP addresses.

deny (default: '()) (type: list-of-strings)

Disallowed IP addresses.


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