NAME

bt_pa_auto_switcher.pl - Switch Bluetooth headset between A2DP and HSP automatically with Pulseaudio

DESCRIPTION

Bluetooth headsets generally support two profiles: High Fidelity Playback, a.k.a., A2DP, and Telephony Duplex, a.k.a., HSP/HFP or just HSP. A2DP is for stereo audio output with the microphone disabled; HSP is for mono output and mono microphone input.

Cell phones seem to be smart enough to know how to do the right thing automatically, switching back and forth between the A2DP and HSP profile automatically depending on whether the Microphone is in use, but Pulseaudio and Bluez, the most common audio and Bluetooth frameworks for Linux, don't know how to do this.

This script "eavesdrops" on Pulseaudio events and automatically switches from A2DP to HSP if an application tries to use both output and input at the same time, then it switches back when everyone is finished using the microphone.

Furthermore, the script automatically mutes other sound sources while the microphone is in use and unmutes them afterward.

Finally, it also tries to remember the volume that was set on the headset for A2DP and HSP/HFP, and restore it when switching between them, because Pulseaudio doesn't seem to do this automatically and it's really annoying when it switches to full volume HSP/HFP and your ears get blasted.

CONFIGURATION

You need the "Expect" perl module installed for this script to work.

Set $mute_corked to 0 below if you don't want other applications muted while you're using the microphone. However, see the caveat below.

Edit the $valid_clients variable below to match the names of clients for which you want the profile switching to be done. This is necessary because there are all kinds of "fake" connection events, e.g., from the sound settings applet. You can find out the correct client name to use by running pacmd list-sink-inputs while the client is using the microphone and locating its "application.name" property. Feel free to email me additions to the list of clients; I've initially populated it with the apps that I use frequently.

Once the script is configured properly, either start it up manually or configure something to run it automatically when you log in, e.g., by adding it as a startup program in gnome-session-properties. When the script starts up it will wait for up to 30 seconds for Pulseaudio to start, in case it gets started on login before Pulseaudio is started.

CAVEATS / TODO

The script in its current form works only with Pulseaudio and Bluez. It could probably be made more generalized, and I'd happy take patches to do that.

I'd happily take a patch to replace the usage of the non-standard Expect module with code that uses only standard Perl modules.

The "module-role-cork" plugin does not seem to play nicely with this script, so if you want to use this script, you need to disable that plugin, e.g., by commenting it out in /etc/pulse/default.pa and restarting pulseaudio, even if you set $mute_corked to 0. I'd gladly accept patches to make the script work better with the plugin.

I probably should have written this as a Pulseaudio plugin. However, I wanted to solve the problem fast, and for me, personally, a Perl script was the fastest solution.

THEORY OF OPERATION

The script uses "pactl subscribe" to subscribe to Pulseaudio events and watch for the birth and death of "sink-input" and "source-output" connections to Pulseaudio. It filters these events using $valid_clients to only pay attention to clients that are known to actually use the microphone.

When the script notices that there is at least one active sink-input and source-output that made it through the filter, it finds the active Bluetooth audio device and switches it to the HSP profile. Before doing the switch, it saves the current audio volume and then mutes other clients generating output, unless $mute_corked is set to 0.

After doing the switch, it checks to see if it has a saved volume level from the last time the HSP profile was used, and if so, restores the volume setting to that level.

When all of the 2-way audio clients have stopped using audio, the script works in reverse to switch back to A2DP: it saves the volume for next time, switches back to the A2DP profile, restores the previous A2DP volume, and unmutes the muted audio output clients.

SEE ALSO

You may also find useful my script to switch to a Bluetooth or USB headset automatically when it's plugged in or paired.

PEEVES

Like many other things in Pulseaudio, the "division of labor" between pactl and pacmd is entirely incomprehensible and seemingly unnecessary. It's impossible to understand why there isn't one tool that does everything both of these existing tools do, rather than functionality being split seemingly arbitrarily between the two tools.

REPOSITORY

http://github.com/jikamens/bt_pa_auto_switcher

AUTHOR

Jonathan Kamens <[email protected]>

COPYRIGHT

Copyright (c) 2013,2017,2020 Jonathan Kamens.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.