AudioController enabled multiple audio applications to coexist on the same server and provides a central control to all of them.

When having multiple audio sources like Airplay, Bluetooth and Spotify, they all run in independently. If you're playing a song from your iPhone via Airplay and you start Spotify, the Airplay playback will still be active. Listening to two different audio sources usually isn't what you want to to. That's where AudioController helps you. It can detect the playback status of different sources and stop playback of active sources if a new source becomes active. This means it will automatically stop Airplay when you start Spotify playback.

AudioController needs to understand the specifics of an audio source. To support different sources, AudioController uses so-called "backends" that represent a specific music service running on the system. The simplest backend does only provide a service to stop playback for this audio source.

Airplay is usually implemented using shairport-sync. This backend allows to control shairport-sync. However, as there is functionality to stop playback of an audio source, we use a quite aggressive way to stop playback - by killing the shairport-sync process. This means you have to configure systemd to automatically restart shairport-sync once it has been killed.

A configuration could look like this:

[Unit]
Description=Shairport Sync - AirPlay Audio Receiver
After=sound.target
Requires=avahi-daemon.service
After=avahi-daemon.service
Wants=network-online.target
After=network.target network-online.target

[Service]
ExecStart=/usr/local/bin/shairport-sync -c /etc/shairport-sync.conf
User=shairport-sync
Group=shairport-sync
Restart=always
RestartSec=3

[Install]
WantedBy=multi-user.target

To control Spotify, the spotify backend needs to be connected to the backend servcie first. To do this, go to [http://spotify-registration.local:14281/]

When the application has been connected it receives a Spotify authorisation code that is used to control Spotify playback. This is only stored locally. No Spotify data are send somewhere else.

MPD - the music player daemon is very popular for users with a collection of music files stored locally. mpd comes with the control tool mpc that will be used by audiocontrol.

AudioController creates a named pipe /tmp/audiostatus. Services can report their playback status into this pipe

Right now only "START" and "STOP" messages are implemented

As the communication is handled via fifos, writes can block if the AudioController isn't running. Therefore it is recommended to set a timeout and abort the write if it isn't finished after the timeout. This can be done simply in a shell script:

#!/bin/bash
/bin/echo $*  > /tmp/audiostatus &
sleep 2
kill $!

Shairport can call an external script when playback starts on stops. This can be used to post the START/STOP messages to the named pipe. You need to add this to the sessioncontrol section of your shairport-sync.conf file:

sessioncontrol =
{
  run_this_before_play_begins = "/opt/hifiberry/bin/write-status START AIRPLAY";
  run_this_after_play_ends = "/opt/hifiberry/bin/write-status STOP AIRLAY"; 
  wait_for_completion = "no";
  allow_session_interruption = "yes";
  session_timeout = 20;
};

Similar to shairport, spotifyd can also call external programs on play/pause. Put the following lines in the "[global] section of the Spotify configuration file

[global]
onstart = /opt/hifiberry/bin/write-status START SPOTIFY
onstop = /opt/hifiberry/bin/write-status STOP SPOTIFY

While the main functionality of a backend is the playback of music, a controller is used to send and recieve control messages. A controller can actively send command (e.g. based on a keypress, rotary controller, infrared remote or many more). A controller can also just listen to events (e.g. meta data of the song currently playing or the volume level). If can also combine both

The Senic Nuimo is a rotary controller with additional touch functionality that can send command via Bluetooth LE. The Nuimo module allows to use the rotary control for volume control and the touch panel to seek forward and backward

The Keyboard can map key pressed to control actions. Ideally you will use multimedia keys or function keys for this. Many RF remote controls that use an USB dongle also act as a keyboard and can be integrated using this controller

ALSAVolume provides a bi-directional control to an ALSA mixer device. It can directly control the volume, but also report changes that were made by other programs.

As AudioControl has to control different processed that might run under their own user id, the easiest way is to run it as root.