Bug#1117203: pulseaudio-module-bluetooth: Bluetooth audio stuttering after upgrading from Bookworm to Trixie

[Jan Stolarek]

Package: pulseaudio-module-bluetooth
Version: 17.0+dfsg1-2+b1
Severity: important
X-Debbugs-Cc: jan.stolarek at mailbox.org

Dear Maintainer,

I recently upgraded my Debian from Bookworm to Trixie.  After the upgrade, I am
frequently experiencing audio glitches and stuttering when using bluetooth
headphones, when previously there were none.  By frequently I mean at least once
every 2-3 minutes, usually more often.  The system is not under any heavy load
that would justify such stutters.

Here is what I tested in attempts to debug the problem:

  1. I tried using different headphones: Aurvana Ace 2 and Beats Fit Pro.  Both
     exhibit the problem.  With Bookworm, both worked without issues.

  2. I tested different codecs: aptX and SBC (both lower and higher bitrates).
     Changing the codec does not seem to have any effect.

  3. I verified that there are no problems with wired headphones (audio jack on
     the front panel) and with HDMI output.

  4. I tried to adjust default-fragments and default-fragment-size-msec, but
     with no positive result.  Defaults seem to work the best.  Note: I found
     info online that in order for these settings to take effect one must
     disable timer-based scheduling by specifying `load-module
     module-udev-detect tsched=0` in the configuration.  On my machine,
     default-fragment and default-fragment-size-msec seem to take effect both
     with `tsched=0` and `tsched=1`.

Lastly, I launched pulseaudio with debugging output enabled, like so:

 pulseaudio -vv --log-time 2> ~/pulse.log

Whenever a stutter happens, it appears in the logs.  Here is an excerpt from the
logs:

  ( 115.245|  87.131) D: [bluetooth] module-bluez5-device.c: Skipping 37301 us (= 6580 bytes) in audio stream
  ( 115.245|   0.000) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 38
  ( 115.245|   0.000) I: [bluetooth] module-bluez5-device.c: Changing bluetooth buffer size: Changed from 4096 to 5120
  ( 115.756|   0.510) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 39
  ( 116.267|   0.510) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 40
  ( 116.775|   0.507) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 41
  ( 117.282|   0.507) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 42
  ( 117.282|   0.000) I: [bluetooth] module-bluez5-device.c: Changing bluetooth buffer size: Changed from 5120 to 4096
  ( 117.785|   0.502) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 43
  ( 153.613|  35.828) D: [bluetooth] protocol-native.c: Implicit underrun of 'Audio Stream'
  ( 153.838|   0.224) D: [bluetooth] protocol-native.c: Requesting rewind due to end of underrun.
  ( 176.669|  22.831) D: [bluetooth] module-bluez5-device.c: Skipping 10068 us (= 1776 bytes) in audio stream
  ( 176.669|   0.000) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 38
  ( 176.669|   0.000) I: [bluetooth] module-bluez5-device.c: Changing bluetooth buffer size: Changed from 4096 to 5120
  ( 177.180|   0.510) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 39
  ( 177.688|   0.507) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 40
  ( 178.198|   0.510) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 41
  ( 178.706|   0.507) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 42
  ( 178.706|   0.000) I: [bluetooth] module-bluez5-device.c: Changing bluetooth buffer size: Changed from 5120 to 4096
  ( 179.209|   0.502) D: [bluetooth] a2dp-codec-sbc.c: Bitpool has changed to 43

I am happy to provide further information, if needed. At the moment bluetooth
headphones are essentially unusable for me, because the stuttering is so
annoying.

-- System Information:
Debian Release: 13.1
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 6.12.48+deb13-amd64 (SMP w/32 CPU threads; PREEMPT)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages pulseaudio-module-bluetooth depends on:
ii  bluez                           5.82-1.1
ii  libbluetooth3                   5.82-1.1
ii  libc6                           2.41-12
ii  libdbus-1-3                     1.16.2-2
ii  libglib2.0-0t64                 2.84.4-3~deb13u1
ii  libgstreamer-plugins-base1.0-0  1.26.2-1
ii  libgstreamer1.0-0               1.26.2-2
ii  libpulse0                       17.0+dfsg1-2+b1
ii  libsbc1                         2.1-1
ii  pulseaudio                      17.0+dfsg1-2+b1

Versions of packages pulseaudio-module-bluetooth recommends:
ii  gstreamer1.0-plugins-bad  1.26.2-3

pulseaudio-module-bluetooth suggests no packages.

-- no debconf information