pulsectl 16.4.5

Python high-level interface and ctypes-based bindings for PulseAudio (libpulse)

Python (3.x and 2.x) high-level interface and ctypes-based bindings for PulseAudio (libpulse), mostly focused on mixer-like controls and introspection-related operations (as opposed to e.g. submitting sound samples to play, player-like client).

Originally forked from pulsemixer project, which had this code bundled.

Contents

• Usage

• Concepts

  • Volume

  • Event-handling code and threads

• Installation

• Links

Usage

Simple example:

from pulsectl import Pulse

with Pulse('volume-increaser') as pulse:
  for sink in pulse.sink_list():
    # Volume is usually in 0-1.0 range, with >1.0 being soft-boosted
    pulse.volume_change_all_chans(sink, 0.1)

Listening for server state change events:

from pulsectl import Pulse, PulseLoopStop

with Pulse('event-printer') as pulse:
  # print('Event types:', ', '.join(pulse.event_types))
  # print('Event facilities:', ', '.join(pulse.event_facilities))
  # print('Event masks:', ', '.join(pulse.event_masks))

  def print_events(ev):
    print('Pulse event:', ev)
    ### Raise PulseLoopStop for event_listen() to return before timeout (if any)
    # raise PulseLoopStop

  pulse.event_mask_set('all')
  pulse.event_callback_set(print_events)
  pulse.event_listen(timeout=10)

Misc other tinkering:

>>> from pulsectl import Pulse
>>> pulse = Pulse('my-client-name')

>>> pulse.sink_list()
[<PulseSinkInfo at 7f85cfd053d0 - desc='Built-in Audio', index=0L, mute=0, name='alsa-speakers', channels=2, volumes='44.0%, 44.0%'>]

>>> pulse.sink_input_list()
[<PulseSinkInputInfo at 7fa06562d3d0 - index=181L, mute=0, name='mpv Media Player', channels=2, volumes='25.0%, 25.0%'>]

>>> pulse.sink_input_list()[0].proplist
{'application.icon_name': 'mpv',
 'application.language': 'C',
 'application.name': 'mpv Media Player',
 ...
 'native-protocol.version': '30',
 'window.x11.display': ':1.0'}

>>> pulse.source_list()
[<PulseSourceInfo at 7fcb0615d8d0 - desc='Monitor of Built-in Audio', index=0L, mute=0, name='alsa-speakers.monitor', channels=2, volumes='100.0%, 100.0%'>,
 <PulseSourceInfo at 7fcb0615da10 - desc='Built-in Audio', index=1L, mute=0, name='alsa-mic', channels=2, volumes='100.0%, 100.0%'>]

>>> sink = pulse.sink_list()[0]
>>> pulse.volume_change_all_chans(sink, -0.1)
>>> pulse.volume_set_all_chans(sink, 0.5)

>>> help(pulse)
...

Current code logic is that all methods are invoked through the Pulse instance, and everything returned from these are “Pulse-Something-Info” objects - thin wrappers around C structs that describe the thing, without any methods attached.

Pulse client can be integrated into existing eventloop (e.g. asyncio, twisted, etc) using Pulse.set_poll_func() or Pulse.event_listen() in a separate thread.

Somewhat extended usage example can be found in pulseaudio-mixer-cli project code.

Concepts

Some less obvious things are described in this section.

Volume

All volume values in this module are float objects in 0-65536.0 range, with following meaning:

• 0.0 volume there is “no sound”.

• 1.0 value is “current sink volume level”, 100% or PA_VOLUME_NORM.

• >1.0 and up to 65536.0 (PA_VOLUME_MAX / PA_VOLUME_NORM) - software-boosted sound volume (higher values will negatively affect sound quality).

Probably a good idea to set volume only in 0-1.0 range and boost volume in hardware without any quality loss, e.g. by tweaking sink volume, which corresponds to ALSA/hardware volume, if that option is available.

See src/pulse/volume.h in pulseaudio sources for all the gory details.

Event-handling code and threads

libpulse clients always work as an event loop, though this module kinda hides it, presenting a more conventional blocking interface.

So what happens on any call (e.g. pulse.mute(...)) is:

• Send command to libpulse, specifying callback for when its done.

• Run libpulse event loop until that callback gets called.

• Return result of that callback.

event_callback_set() and event_listen() calls essentally do raw first and second step here.

Which means that any pulse calls from callback function can’t be used when event_listen() (or any other pulse call through this module, for that matter) waits for return value and runs libpulse loop already.

One can raise PulseLoopStop exception there to make event_listen() return, run whatever pulse calls after that, then re-start the event_listen() thing.

This will not miss any events, as all calls do same thing as event_listen() does (second step above), and can cause callable passed to event_callback_set() to fire.

Also, same instance of libpulse eventloop can’t be run from different threads, naturally, so if threads are used, client can be initialized with threading_lock=True option (can also accept lock instance instead of True) to create a mutex around step-2 (run event loop) from the list above, so two threads won’t try to do it at the same time.

Installation

It’s a regular package for Python (3.x or 2.x).

Be sure to use python3/python2, pip3/pip2, easy_install-… binaries below, based on which python version you want to install the module for, if you have several on the system (as is norm these days for py2-py3 transition).

Using pip is the best way:

% pip install pulsectl

If you don’t have pip:

% easy_install pip
% pip install pulsectl

Alternatively (see also pip2014.com and pip install guide):

% curl https://raw.github.com/pypa/pip/master/contrib/get-pip.py | python
% pip install pulsectl

Or, if you absolutely must:

% easy_install pulsectl

But, you really shouldn’t do that.

Current-git version can be installed like this:

% pip install 'git+https://github.com/mk-fg/python-pulse-control.git#egg=pulsectl'

Note that to install stuff in system-wide PATH and site-packages, elevated privileges are often required. Use “…install –user”, ~/.pydistutils.cfg or virtualenv to do unprivileged installs into custom paths.

Links

• pulsemixer - initial source for this project (embedded in the tool).

• libpulseaudio - different libpulse bindings module, more low-level, auto-generated from pulseaudio header files.

  Branches there have bindings for different (newer) pulseaudio versions.

• pulseaudio-mixer-cli - alsamixer-like script built on top of this module.