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PulseAudio is a networked sound server, similar in theory to the Enlightened Sound Daemon (EsounD). PulseAudio is however much more advanced and has numerous features.

A sound server can serve many functions:

  • Software mixing of multiple audio streams, bypassing any restrictions the hardware has.
  • Network transparency, allowing an application to play back or record audio on a different machine than the one it is running on.
  • Sound API abstraction, alleviating the need for multiple backends in applications to handle the wide diversity of sound systems out there.
  • Generic hardware abstraction, giving the possibility of doing things like individual volumes per application.

PulseAudio comes with many plugin modules. All audio from/to clients and audio interfaces goes through modules.

Manuel Amador created a diagram describing how the different parts of PulseAudio play together. (Not all modules are shown.) Another, simpler architecture diagram is attached to this page (scroll to the bottom).

PulseAudio clients can send audio to "sinks" and receive audio from "sources". A client can be GStreamer, xinelib, MPlayer or any other audio application. Only the device drivers/audio interfaces can be either sources or sinks (they are often hardware in- and out-puts).


OI-Hipster, PulseAudio-10.0 port:

→ /export/home/kmays$ uname -a

SunOS external 5.11 illumos-fd3bae1 i86pc i386 i86pc Solaris

→ /export/home/kmays$ /opt/pulseaudio-10.0/bin/pulseaudio --version

pulseaudio 10.0


→ /export/home/kmays$ /opt/pulseaudio-10.0/bin/pulseaudio --dump-modules
  • module-allow-passthrough                When a passthrough stream is requested, route all the other streams to a dummy device
  • module-always-sink                      Always keeps at least one sink loaded even if it's a null one
  • module-augment-properties               Augment the property sets of streams with additional static information
  • module-card-restore                     Automatically restore profile of cards
  • module-cli                              Command line interface
  • module-cli-protocol-tcp                 Command line interface protocol (TCP sockets)
  • module-cli-protocol-unix                Command line interface protocol (UNIX sockets)
  • module-combine                          Compatibility module (module-combine rename)
  • module-combine-sink                     Combine multiple sinks to one
  • module-console-kit                      Create a client for each ConsoleKit session of this user
  • module-dbus-protocol                    D-Bus interface
  • module-default-device-restore           Automatically restore the default sink and source
  • module-detect                           Detect available audio hardware and load matching drivers
  • module-device-manager                   Keep track of devices (and their descriptions) both past and present and prioritise by role
  • module-device-restore                   Automatically restore the volume/mute state of devices
  • module-echo-cancel                      Echo Cancellation
  • module-filter-apply                     Load filter sinks automatically when needed
  • module-filter-heuristics                Detect when various filters are desirable
  • module-http-protocol-tcp                HTTP (TCP sockets)
  • module-http-protocol-unix               HTTP (UNIX sockets)
  • module-intended-roles                   Automatically set device of streams based on intended roles of devices
  • module-ladspa-sink                      Virtual LADSPA sink
  • module-loopback                         Loopback from source to sink
  • module-match                            Playback stream expression matching module
  • module-native-protocol-fd               Native protocol autospawn helper
  • module-native-protocol-tcp              Native protocol (TCP sockets)
  • module-native-protocol-unix             Native protocol (UNIX sockets)
  • module-null-sink                        Clocked NULL sink
  • module-null-source                      Clocked NULL source
  • module-oss                              OSS Sink/Source
  • module-pipe-sink                        UNIX pipe sink
  • module-pipe-source                      UNIX pipe source
  • module-position-event-sounds            Position event sounds between L and R depending on the position on screen of the widget triggering them.
  • module-raop-discover                    mDNS/DNS-SD Service Discovery of RAOP devices
  • module-raop-sink                        RAOP Sink
  • module-remap-sink                       Virtual channel remapping sink
  • module-remap-source                     Virtual channel remapping source
  • module-rescue-streams                   When a sink/source is removed, try to move its streams to the default sink/source
  • module-role-cork                        Mute & cork streams with certain roles while others exist
  • module-role-ducking                     Apply a ducking effect based on streams roles
  • module-rtp-recv                         Receive data from a network via RTP/SAP/SDP
  • module-rtp-send                         Read data from source and send it to the network via RTP/SAP/SDP
  • module-rygel-media-server               UPnP MediaServer Plugin for Rygel
  • module-simple-protocol-tcp              Simple protocol (TCP sockets)
  • module-simple-protocol-unix             Simple protocol (UNIX sockets)
  • module-sine                             Sine wave generator
  • module-sine-source                      Sine wave generator source
  • module-solaris                          Solaris Sink/Source
  • module-stream-restore                   Automatically restore the volume/mute/device state of streams
  • module-suspend-on-idle                  When a sink/source is idle for too long, suspend it
  • module-switch-on-connect                When a sink/source is added, switch to it or conditionally switch to it
  • module-switch-on-port-available         n/a
  • module-tunnel-sink                      Tunnel module for sinks
  • module-tunnel-sink-new                  Create a network sink which connects via a stream to a remote PulseAudio server
  • module-tunnel-source                    Tunnel module for sources
  • module-tunnel-source-new                Create a network source which connects via a stream to a remote PulseAudio server
  • module-virtual-sink                     Virtual sink
  • module-virtual-source                   Virtual source
  • module-virtual-surround-sink            Virtual surround sink
  • module-volume-restore                   Compatibility module
  • module-x11-bell                         X11 bell interceptor
  • module-x11-cork-request                 Synthesize X11 media key events when cork/uncork is requested
  • module-x11-publish                      X11 credential publisher
  • module-x11-xsmp                         X11 session management
  • module-zeroconf-discover                mDNS/DNS-SD Service Discovery
  • module-zeroconf-publish                 mDNS/DNS-SD Service Publisher

→ /opt/pulseaudio-10.0/bin/pulseaudio --dump-resample-methods

  • trivial
  • speex-float-0
  • speex-float-1
  • speex-float-2
  • speex-float-3
  • speex-float-4
  • speex-float-5
  • speex-float-6
  • speex-float-7
  • speex-float-8
  • speex-float-9
  • speex-float-10
  • speex-fixed-0
  • speex-fixed-1
  • speex-fixed-2
  • speex-fixed-3
  • speex-fixed-4
  • speex-fixed-5
  • speex-fixed-6
  • speex-fixed-7
  • speex-fixed-8
  • speex-fixed-9
  • speex-fixed-10
  • ffmpeg
  • auto
  • copy
  • peaks



After an update, the PulseAudio daemon may fail to start, for example:

Code Block
$ uname -rosv
SunOS 5.11 illumos-63982b82e6 Solaris

$ pkg info pulseaudio
          Name: library/audio/pulseaudio
       Summary: Sample Rate Converter for audio
      Category: System/Multimedia Libraries
         State: Installed
       Version: 10.0
        Branch: 2017.0.0.0
Packaging Date: Sun Apr 23 08:35:43 2017
          Size: 12.60 MB
          FMRI: pkg://
   Project URL:
    Source URL:

From syslog:

Code Block
[2017-04-25 14:59:10] xxx pulseaudio[2731]: [ID 295310 user.error] [solaris] sink.c: Assertion '!pa_thread_mq_get()' failed at pulsecore/sink.c:2229, function pa_sink_set_mute(). Aborting.
[2017-04-25 14:59:10] xxx genunix: [ID 603404 kern.notice] NOTICE: core_log: pulseaudio[2731] core dumped: /export/tmp/cores/core.pulseaudio.2731

and you see no elements in mate-volume-control-applet preferences (see ticket:

This is usually due to regressions in PulseAudio for handling modules and configuration databases: the only known workaround is to make sure the configuration files match the default Hipster files and remove the configuration in the user's home directory. Similar issues have been reported in Linux distributions.