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Automated ALSA Configuration For BlueALSA PCMs

This project is a companion to, and requires installation of, BlueALSA - see https://github.com/Arkq/bluez-alsa

This is Alpha pre-release code. It requires capabilities of the BlueALSA bluealsa-cli utility that are available in the upstream bluez-alsa project sources, but not yet in a released version.

Applications can open PCM streams to bluetooth devices connected through BlueALSA without any need for specific ALSA configuration entries (see https://github.com/Arkq/bluez-alsa/blob/master/doc/bluealsa-plugins.7.rst). However, there is no equivalent way for an ALSA application to obtain a list of available bluetooth PCMs. For command-line users, the utility bluealsa-aplay will produce such a list, but for GUI applications we need a way have the connected bluetooth PCMs appear through the ALSA namehint API in the same way as sound card devices.

This project provides a bash script and associated system files to generate dynamic ALSA configuration changes as bluetooth audio devices connect or disconnect such that those devices appear as PCMs in the namehint API. The current version supports only a single running instance of the bluealsa service.

Optionally, the script can also load BlueALSA PCMs into PulseAudio as devices. This enables BlueALSA to be used in conjunction with PulseAudio. It is first necessary to disable PulseAudio's own bluetooth modules for this to work. See section Disabling PulseAudio bluetooth modules below for more information.

The script relies on the bluealsa-cli utility which is part of the above bluez-alsa project. bluez-alsa v3.1.0 or earlier did not have the needed capabilities in the bluealsa-cli utility required by this script, so you will need a more recent version. It is necessary to include the configure option --enable-cli when building BlueALSA to build this utility.

namehint configuration entries are created that cause ALSA client applications to include connected bluetooth PCMs in their listed PCM devices. For this to work correctly it requires the application to use the "official" namehint ALSA API for listing devices. There are some applications which ignore that API and attempt to parse the ALSA configuration using their own bespoke code; those applications generally will fail to list BlueALSA devices.

The script is designed to be run in a user session, in the background, and monitors D-Bus messages from BlueALSA. A temporary ALSA config file is created and managed by the script. The file is saved as $XDG_RUNTIME_DIR/bluealsa-montor/asoundrc, or if XDG_RUNTIME_DIR is not defined then as $HOME/.local/bluealsa-monitor/asoundrc. This path must be included in the user's ALSA_CONFIG_PATH environment variable. One way to ensure this environment variable is set for systemd base systems is to copy the file bluealsa-monitor-env.conf to the directory $HOME/.config/environment.d.

The namehint entries include a description string consisting of the device alias (i.e. its local name), profile, and codec. An example output of aplay -L

$ aplay -L
bluealsa:DEV=C4:67:B5:67:89:AB,PROFILE=sco
    Libratone Zipp Mini, HFP (CVSD)
bluealsa:DEV=C4:67:B5:67:89:AB,PROFILE=a2dp
    Libratone Zipp Mini, A2DP (aptX)

To send audio to that device, use the device id as given by aplay -L:

$ aplay -D bluealsa:DEV=01:23:45:67:89:AB,PROFILE=a2dp music.wav

to make it easier to type device ids on the command line with aplay and arecord, use a bash completion script, such as https://github.com/borine/alsa-utils-completions

Installation

A meson build specification file is included to simplify the installation. To use it, do:

meson setup builddir
sudo meson install -C builddir

The default install prefix is /usr/local. To install on a production system this should be overridden in the setup command:

meson setup --prefix=/usr builddir
sudo meson install -C builddir

To disable installation of the udev sudoers file, run setup as:

meson setup -D udev=disabled builddir
sudo meson install -C builddir

Usage

The script should be run as a user service, (not as root), and a systemd user service file is included for that purpose if desired (see below). There are some optional command line arguments:

-B, --dbus

Select the bluealsa d-bus suffix. Not normally required. See the bluez-alsa documentation for more information.

-d, --default

Make BlueALSA PCM the ALSA default (pcm.!default in the config file) when connected. The most recently connected device is used. Takes an optional value, a comma-separated list consisting of one or more of the tokens a2dp, sco, capture, playback to limit the device types that will be accepted as defaults. Only one of a2dp or sco may be specified. If this argument is used with no value given, the default is a2dp,capture,playback. For example:

bluealsa-monitor --default=a2dp,playback

This will set up the ALSA default playback PCM to be the most recently connected A2DP playback device. The default capture device will remain as the system default. If no A2DP playback device is connected, then the ALSA default playback PCM will revert to the system default.

If you do not wish the system default PCM to be used as fallback, you can choose a different PCM by defining the config keys bluealsa.default.capture.fallback and/or bluealsa.default.playback.fallback in your ~/.asoundrc file. For example:

bluealsa.default.playback.fallback "plughw:1,0"

-u, --udev

Emit a synthesized udev event on BlueALSA device connect and disconnect. This option may be useful for some applications that do not refresh their audio device list unless a soundcard change is signalled via udev (e.g. kodi). The script will invoke sudo with no password to raise necessary privileges when needed, so it is important that the user has permission to do this. This project includes a sudoers config file that grants required permission to all members of the audio group. The permission is specifically limited to raising a udev change event on the default sound card; no other permission is granted. On systems that do not support sudo, alternative means to manage privileges will be required.

Takes an optional value, a comma-separated list consisting of one or more of the tokens a2dp, sco, capture, playback to limit the device types that will generate events to a particular profile (either a2dp or sco) and/or a specific direction (playback or capture). If no argument is given, this option generates udev events for all devices.

-p, --pulse

Add connected devices to PulseAudio. Takes an optional value, a comma-separated list consisting of one or more of the tokens a2dp, sco, capture, playback to limit the device types that will be used to a particular profile (either a2dp or sco) and/or a specific direction (playback or capture). If no argument is given, this option adds all connected devices to PulseAudio.

-i, --icon

Select a particular icon to be used by PulseAudio for the BlueALSA devices. Defaults to bluetooth. The available icons will depend on your distribution.

systemd

The script can be started and stopped manually using:

systemctl --user start bluealsa-monitor
systemctl --user stop bluealsa-monitor

To enable the script to start automatically on user login, the user should enter the command:

systemctl --user enable bluealsa-monitor

The included systemd service file starts the script with no command-line options. The recommended way to add options is to use systemctl. A quirk of systemd is that the existing service command line has to be cancelled in order to insert a new one.

Suppose we want to enable the udev trigger and restrict the default to A2DP playback only - so we do the following;

  • start the systemctl editor:
systemctl --user edit bluealsa-monitor.service
  • then insert the following lines:
[Service]
ExecStart=
ExecStart=/usr/local/bin/bluealsa-monitor --udev --default=a2dp,playback
  • save and exit from the editor, then restart the service:
systemctl --user restart bluealsa-monitor

To prevent the script from starting at login, the user should enter the command:

systemctl --user disable bluealsa-monitor

Disabling PulseAudio bluetooth modules

Bluez allows only one service to register as provider of a bluetooth profile, so it is necessary to disable the PulseAudio bluetooth modules in order to use Pulseaudio in combination with BlueALSA.

There are three ways to disable the PulseAudio bluetooth modules.

  1. Uninstall the module packages

    Many distributions deliver the PulseAudio bluetooth modules as separate packages, and so for these the simplest solution is to uninstall those packages. For example, on Ubuntu

    sudo apt purge pulseaudio-module-bluetooth

  2. Remove the modules from the PulseAudio configuration

    If the modules cannot be uninstalled, then they can still be disabled in the PulseAudio configuration. This is achieved by editing the file /etc/pulse/default.pa to comment out the bluetooth module entries as shown here:

    ### Automatically load driver modules for Bluetooth hardware
#.ifexists module-bluetooth-policy.so
#load-module module-bluetooth-policy
#.endif

#.ifexists module-bluetooth-discover.so
#load-module module-bluetooth-discover
#.endif

    Restart the PulseAudio service to read the new configuration. On most desktop systems this service is configured to automatically restart, so it is sufficient to type:

    pulseaudio --kill

  3. Unload the PulseAudio bluetooth modules at runtime

    It is possible to temporarily remove the modules at runtime with the commands:

    pactl unload-module module-bluetooth-policy
pactl unload-module module-bluetooth-discover

    Note that these commands will have to be re-run each time PulseAudio is restarted.