Python high-level interface and ctypes-based bindings for PulseAudio (libpulse)
Project description
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.
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.
Notes
Some less obvious things are described in this section.
Things not yet wrapped/exposed in python
There are plenty of information, methods and other things in libpulse not yet wrapped/exposed by this module, as they weren’t needed (yet) for author/devs use-case(s).
Making them accessible from python code can be as simple as adding an attribute name to the “c_struct_fields” value in PulseSomethingInfo objects.
See github #3 for a more concrete example of finding/adding such stuff.
For info and commands that are not available through libpulse introspection API, it is possible to use pulsectl.connect_to_cli() fallback function, which will open unix socket to server’s “module-cli” (signaling to load it, if necessary), which can be used in exactly same way as “pacmd” tool or pulseaudio startup files (e.g. “default.pa”).
Probably a bad idea to parse string output from commands there though, as these are not only subject to change, but can also vary depending on system locale.
Volume
All volume values in this module are float objects in 0-65536 range, with following meaning:
0.0 volume is “no sound” or PA_VOLUME_MUTED.
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 quality loss, e.g. by tweaking sink volume (which corresponds to ALSA/hardware volume), if that option is available.
Note that flat-volumes=yes option (“yes” by default on some distros, “no” in e.g. Arch Linux) in pulseaudio daemon.conf already scales device-volume with the volume of the “loudest” application, so already does what’s suggested above.
Fractional volume values used in the module get translated (in a linear fashion) to/from pa_volume_t integers for libpulse. See src/pulse/volume.h in pulseaudio sources for all the gory details on the latter (e.g. how it relates to sound level in dB).
String values
libpulse explicitly returns utf-8-encoded string values, which are always decoded to “abstract string” type in both python-2 (where it’s called “unicode”) and python-3 (“str”), for consistency.
It might be wise to avoid mixing these with encoded strings (“bytes”) in the code, especially in python-2, where “bytes” is often used as a default string type.
Event-handling code, 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:
Make a call to libpulse, specifying callback for when operation will be completed.
Run libpulse event loop until that callback gets called.
Return result passed to that callback call, if any (for various “get” methods).
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 blocking calls do same thing as event_listen() does (second step above), and can cause callable passed to event_callback_set() to be called (when loop is running).
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 multiple threads won’t do it at the same time.
For proper eventloop integration (think twisted or asyncio), _pulse_get_list / _pulse_method_call wrappers should be overidden to not run pulse loop, but rather return “future” object and register a set of fd’s (as passed to set_poll_func callback) with eventloop. Never needed that, so not implemented in the module, but should be rather easy to implement on top of it, as described.
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.
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