Code change:
<ins> import ./make-test.nix ({ pkgs, ... }: let track = pkgs.fetchurl { # Sourced from http://freemusicarchive.org/music/Blue_Wave_Theory/Surf_Music_Month_Challenge/Skyhawk_Beach_fade_in # License: http://creativecommons.org/licenses/by-sa/4.0/ name = "Blue_Wave_Theory-Skyhawk_Beach.mp3"; url = https://freemusicarchive.org/file/music/ccCommunity/Blue_Wave_Theory/Surf_Music_Month_Challenge/Blue_Wave_Theory_-_04_-_Skyhawk_Beach.mp3; sha256 = "0xw417bxkx4gqqy139bb21yldi37xx8xjfxrwaqa0gyw19dl6mgp"; }; defaultCfg = rec { user = "mpd"; group = "mpd"; dataDir = "/var/lib/mpd"; musicDirectory = "${dataDir}/music"; }; defaultMpdCfg = with defaultCfg; { inherit dataDir musicDirectory user group; enable = true; }; musicService = { user, group, musicDirectory }: { description = "Sets up the music file(s) for MPD to use."; requires = [ "mpd.service" ]; after = [ "mpd.service" ]; wantedBy = [ "default.target" ]; script = '' mkdir -p ${musicDirectory} && chown -R ${user}:${group} ${musicDirectory} cp ${track} ${musicDirectory} chown ${user}:${group} ${musicDirectory}/$(basename ${track}) ''; }; mkServer = { mpd, musicService, }: { boot.kernelModules = [ "snd-dummy" ]; sound.enable = true; services.mpd = mpd; systemd.services.musicService = musicService; }; in { name = "mpd"; meta = with pkgs.stdenv.lib.maintainers; { maintainers = [ emmanuelrosa ]; }; nodes = { client = { config, pkgs, ... }: { }; serverALSA = { config, pkgs, ... }: (mkServer { mpd = defaultMpdCfg // { network.listenAddress = "any"; extraConfig = '' audio_output { type "alsa" name "ALSA" mixer_type "null" } ''; }; musicService = with defaultMpdCfg; musicService { inherit user group musicDirectory; }; }) // { networking.firewall.allowedTCPPorts = [ 6600 ]; }; serverPulseAudio = { config, pkgs, ... }: (mkServer { mpd = defaultMpdCfg // { extraConfig = '' audio_output { type "pulse" name "The Pulse" } ''; }; musicService = with defaultCfg; musicService { inherit user group musicDirectory; }; }) // { hardware.pulseaudio.enable = true; }; }; testScript = '' my $mpc = "${pkgs.mpc_cli}/bin/mpc --wait"; # Connects to the given server and attempts to play a tune. sub play_some_music { my $server = $_[0]; $server->waitForUnit("mpd.service"); $server->succeed("$mpc update"); my @tracks = $server->execute("$mpc ls"); for my $track (split(/n/, $tracks[1])) { $server->succeed("$mpc add $track"); }; my @added_tracks = $server->execute("$mpc listall"); (length $added_tracks[1]) > 0 or die "Failed to add audio tracks to the playlist."; $server->succeed("$mpc play"); my @status = $server->execute("$mpc status"); my @output = split(/n/, $status[1]); $output[1] =~ /.*playing.*/ or die "Audio track is not playing, as expected."; $server->succeed("$mpc stop"); }; play_some_music($serverALSA); play_some_music($serverPulseAudio); $client->succeed("$mpc -h serverALSA status"); # The PulseAudio-based server is configured not to accept external client connections # to perform the following test: $client->fail("$mpc -h serverPulseAudio status"); ''; }) </ins>

Related discussion:
text: As it stands, the NixOS MPD module runs MPD as a systemd system service. As such it expects that the MPD user account (mpd by default) has control over the audio device. This conflicts with PulseAudio when it's used as a systemd user service (the default configuration). The intent of this change is to extend the MPD module so that it can be configured to run as a systemd user service. The changes remain backwards-compatible so users can continue with a system-wide configuration or go with a per-user config. I have a proof-of-concept of the modified module which I'm currently experimenting with. It can be used in as follows: The result is MPD running within a user slice: [ ] Ability to use a different per user; Probably by providing a option which overrides the other options and simply points to a file in the users home directory (ex. ). [ ] See if it's possible to get realtime scheduling to work. [x] Add NixOS tests. Currently there aren't any. The different options make for numerous potential combinations; I'm to lazy to test all of them manually.
did you ever add support for running mpd as a user service? It looks like just tests in preparation for running it as a user service.
Wow, I forgot all about this. Perhaps because I soon after stopped using MDP. The implementation is still on Github:
An alternative could be to let it talk to pulseaudio over the network. In the past I have used a config in mpd like audio_output { type "pulse" name "pulseaudio" server "127.0.0.1" } and then some config in to allow this access.