Bluetooth headset autoconnects but is not recognised as sound card by PulseAudio Ubuntu on 20.04

Question

Problem: When my Bluetooth Headset (auvisio ZX-3182) autoconnects to my Ubuntu 20.04 the bluetooth daemon confirms a connection,

~$ hcitool con
Connections:
    > ACL 76:XX:XX:XX:XX:75 handle 256 state 1 lm MASTER

however PulseAudio (15.0) does not recognize the connected bluetooth device as a sound card automatically

~$ pactl list sinks short
0   alsa_output.pci-0000_00_1f.3.analog-stereo  module-alsa-card.c  s16le 2ch 48000Hz   RUNNING

~$ pacmd list-cards
1 card(s) available.
    index: 0
    name: <alsa_card.pci-0000_00_1f.3>
    driver: <module-alsa-card.c>

although the headset has the capabilities of being a sound card:

~$ hcitool info 76:XX:XX:XX:XX:75
Requesting information ...
    BD Address:  76:XX:XX:XX:XX:75
    Device Name: ZX-3182
    LMP Version: 5.1 (0xa) LMP Subversion: 0x22bb
    Manufacturer: not assigned (1494)
    Features page 0: 0xbf 0xfe 0x8d 0xfa 0xd8 0x3d 0x79 0x83
        <3-slot packets> <5-slot packets> <encryption> <slot offset> 
        <timing accuracy> <role switch> <sniff mode> <RSSI> 
        <channel quality> <SCO link> <HV2 packets> <HV3 packets> 
        <u-law log> <A-law log> <CVSD> <power control> 
        <transparent SCO> <broadcast encrypt> <EDR ACL 2 Mbps> 
        <enhanced iscan> <interlaced iscan> <interlaced pscan> 
        <inquiry with RSSI> <extended SCO> <AFH cap. slave> 
        <AFH class. slave> <LE support> <3-slot EDR ACL> 
        <5-slot EDR ACL> <pause encryption> <AFH cap. master> 
        <AFH class. master> <EDR eSCO 2 Mbps> <extended inquiry> 
        <simple pairing> <encapsulated PDU> <err. data report> 
        <non-flush flag> <LSTO> <inquiry TX power> <extended features> 
    Features page 1: 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00
    Features page 2: 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00

What works: When I connect to the bluetooth headset manually, the headset is recognised by PulseAudio correctly and I can use it as a A2DP headset as well as a HFS/HPS dual-mode headset+headphone. Only if the headset autoconnects, it is not recognised by PulseAudio.

What the logs say: Nothing, no error message. I looked into

• ~$ tail /var/log/syslog: No relevant output
• ~$ systemctl --user status pulseaudio: No relevant output
• ~$ dmesg | tail
[ 6751.711444] perf: interrupt took too long (3202 > 3167), lowering kernel.perf_event_max_sample_rate to 62250
[ 6853.470790] input: ZX-3182 (AVRCP) as /devices/virtual/input/inputXX

Questions:

• Does anybody know this behaviour, that autoconnected bluetooth devices are not recognized by PulseAudio?
• Does anybody have a tip where to find a log message to come closer to the actual error?
• Can I find out which processes are using the bluetooth connection? Maybe another process is "catching" the bluetooth connection before pulseaudio can get it?

What I already tried:

• Made sure that module-switch-on-connect, module-bluetooth-discover and module-bluetooth-policy are loaded by pulseaudio as suggested in Pulseaudio not detecting bluetooth headset automatically
• Tried adding Enable=Source,Sink,Media,Socket under [General] in /etc/bluetooth/main.conf as suggested in PulseAudio fails to set card profile to 'a2dp_sink'. How can I see the logs and figure out whats wrong?.
• Tried adding FastConnectable=true in /etc/bluetooth/main.conf as suggested in Why is my Bluetooth headset not working now?
• Tried removing pulseaudio from gdm as suggested in https://wiki.debian.org/BluetoothUser/a2dp
• Tried pipewire on top of pulseaudio

Any other ideas? Thanks for your help.

Answer 1

I had the same problem for a long time and was just able to (kind of) resolve the problem today for me:

Trusting the bluetooth headset in blueman (or however you manage your bluetooth devices) helped.

However, the volume is now super low when connecting automatically - although pulseaudio shows the same volume as when connecting manually.

Answer 2

Turns out that this behaviour changes from headphones to headphones. I tried several different headphones afterwards and some autoconnect successfully with sound and some don't. So it seems to be on a model-by-model basis, whether it is working or not.

A workaround that I used was to write a small script sudo nano /opt/bin/headset-reconnect.sh:

#!/bin/bash

bluetoothctl disconnect $1
bluetoothctl connect $1

Made it executable via sudo chmod +x /opt/bin/headset-reconnect.sh and finally added a custom keyboard shortcut under Settings -> Keyboard -> Keyboard-Shortcuts -> Custom Keyboard-Shortcuts that would call /usr/bin/headset-reconnect xx:xx:xx:xx:xx:xx with the bluetooth mac address of my headphones.

With this workaround I just had to press my defined keyboard shortcut to connect to my headphones after putting them in my ears.

Not perfect, but at least some kind of solution.