Merge tag '0.10.0'

the tag was erroneously "orphaned".

fixes #140.

Conflicts:
	CHANGES.md

CHANGES.md

@@ -1,3 +1,16 @@
+# Version 0.10.1
+- restore previous xrun behaviour, #131
+- type hints
+
+# Version 0.10.0
+- assorted improvements (#123 from @ossilator)
+  - support for `periods` in the `PCM` constructor.
+  - new functions `PCM.state()`, `PCM.drop()` and `PCM.drain()`
+  - improved underrun/overrun handling
+  - documentation improvements/consolidation (docstrings were removed in favour of online documentation)
+  - more sampling rates
+  - bug fixes
+
 # Version 0.9.2
 - Fix alsamixer_getvolume (#112 from @stephensp)
 
@@ -15,15 +28,15 @@
     supported formats - e.g. `{"U8": 1, "S16_LE": 2}`,
   - `getchannels()` returns a list of the supported channel numbers, e.g. `[1, 2]`,
   - `getrates()` returns supported sample rates for the device, e.g. `[48000]`,
-  - `getratebounds()` returns the device's official minimum and maximum supported 
+  - `getratebounds()` returns the device's official minimum and maximum supported
     sample rates as a tuple, e.g. `(4000, 48000)`.
-  
+
   (#82 contributed by @jdstmporter)
 
 - Prevent hang on close after capturing audio (#80 contributed by @daym)
 
 # Version 0.8.5:
-- Return an empty string/bytestring when `read()` detects an 
+- Return an empty string/bytestring when `read()` detects an
   overrun. Previously the returned data was undefined (contributed by @jcea)
 
 - Unlimited setperiod buffer size when reading frames (contributed by @jcea)

doc/index.rst

@@ -1,8 +1,3 @@
-.. alsaaudio documentation documentation master file, created by
-   sphinx-quickstart on Thu Mar 30 23:52:21 2017.
-   You can adapt this file completely to your liking, but it should at least
-   contain the root `toctree` directive.
-
 alsaaudio documentation
 ===================================================
 
@@ -18,15 +13,13 @@ Download
 ========
 
 * `Download from pypi <https://pypi.python.org/pypi/pyalsaaudio>`_
-  
+
-      
 Github
 ======
 
 * `Repository <https://github.com/larsimmisch/pyalsaaudio/>`_
 * `Bug tracker <https://github.com/larsimmisch/pyalsaaudio/issues>`_
 
- 
 Indices and tables
 ==================
 
@@ -34,5 +27,3 @@ Indices and tables
 * :ref:`modindex`
 * :ref:`search`
 
-    
-  

doc/libalsaaudio.rst

@@ -5,38 +5,15 @@
 .. module:: alsaaudio
    :platform: Linux
 
-
-.. % \declaremodule{builtin}{alsaaudio}	% standard library, in C
-.. % not standard, in C
-
 .. moduleauthor:: Casper Wilstrup <cwi@aves.dk>
 .. moduleauthor:: Lars Immisch <lars@ibp.de>
-                  
-.. % Author of the module code;
-
-
 
 The :mod:`alsaaudio` module defines functions and classes for using ALSA.
 
-.. % ---- 3.1. ----
-.. % For each function, use a ``funcdesc'' block.  This has exactly two
-.. % parameters (each parameters is contained in a set of curly braces):
-.. % the first parameter is the function name (this automatically
-.. % generates an index entry); the second parameter is the function's
-.. % argument list.  If there are no arguments, use an empty pair of
-.. % curly braces.  If there is more than one argument, separate the
-.. % arguments with backslash-comma.  Optional parts of the parameter
-.. % list are contained in \optional{...} (this generates a set of square
-.. % brackets around its parameter).  Arguments are automatically set in
-.. % italics in the parameter list.  Each argument should be mentioned at
-.. % least once in the description; each usage (even inside \code{...})
-.. % should be enclosed in \var{...}.
-
-
 .. function:: pcms(pcmtype=PCM_PLAYBACK)
 
    List available PCM devices by name.
-   
+
    Arguments are:
 
    * *pcmtype* - can be either :const:`PCM_CAPTURE` or :const:`PCM_PLAYBACK`
@@ -62,7 +39,13 @@ The :mod:`alsaaudio` module defines functions and classes for using ALSA.
    List the available ALSA cards by name. This function is only moderately
    useful. If you want to see a list of available PCM devices, use :func:`pcms`
    instead.
-   
+
+..
+   Omitted by intention due to being superseded by cards():
+
+   .. function:: card_indexes()
+   .. function:: card_name()
+
 .. function:: mixers(cardindex=-1, device='default')
 
    List the available mixers. The arguments are:
@@ -72,12 +55,14 @@ The :mod:`alsaaudio` module defines functions and classes for using ALSA.
      the `device` keyword argument is ignored. ``0`` is the first hardware sound
      card.
 
+     **Note:** This should not be used, as it bypasses most of ALSA's configuration.
+
    * *device* - the name of the device on which the mixer resides. The default
      is ``'default'``.
 
    **Note:** For a list of available controls, you can also use ``amixer`` on
    the commandline::
-      
+
       $ amixer
 
    To elaborate the example, calling :func:`mixers` with the argument
@@ -91,7 +76,7 @@ The :mod:`alsaaudio` module defines functions and classes for using ALSA.
       $ amixer -D foo
 
    *Changed in 0.8*:
-   
+
    - The keyword argument `device` is new and can be used to
      select virtual devices. As a result, the default behaviour has subtly
      changed. Since 0.8, this functions returns the mixers for the default
@@ -101,6 +86,7 @@ The :mod:`alsaaudio` module defines functions and classes for using ALSA.
 
    Return a Python string containing the ALSA version found.
 
+
 .. _pcm-objects:
 
 PCM Objects
@@ -110,7 +96,7 @@ PCM objects in :mod:`alsaaudio` can play or capture (record) PCM
 sound through speakers or a microphone. The PCM constructor takes the
 following arguments:
 
-.. class:: PCM(type=PCM_PLAYBACK, mode=PCM_NORMAL, rate=44100, channels=2, format=PCM_FORMAT_S16_LE, periodsize=32, device='default', cardindex=-1)
+.. class:: PCM(type=PCM_PLAYBACK, mode=PCM_NORMAL, rate=44100, channels=2, format=PCM_FORMAT_S16_LE, periodsize=32, periods=4, device='default', cardindex=-1)
 
    This class is used to represent a PCM device (either for playback and
    recording). The arguments are:
@@ -123,7 +109,7 @@ following arguments:
    * *channels* - the number of channels. The default value is 2 (stereo).
    * *format* - the data format. This controls how the PCM device interprets data for playback, and how data is encoded in captures. 
      The default value is :const:`PCM_FORMAT_S16_LE`.
-   
+
    =========================  ===============
         Format                Description
    =========================  ===============
@@ -156,7 +142,11 @@ following arguments:
    ``PCM_FORMAT_U24_3BE``     Unsigned 24 bit samples for each channel (Big Endian byte order in 3 bytes)
    =========================  ===============
 
-   * *periodsize* - the period size in frames. Each write should consist of *periodsize* frames. The default value is 32.
+   * *periodsize* - the period size in frames.
+     Make sure you understand :ref:`the meaning of periods <term-period>`.
+     The default value is 32, which is below the actual minimum of most devices,
+     and will therefore likely be larger in practice.
+   * *periods* - the number of periods in the buffer. The default value is 4.
    * *device* - the name of the PCM device that should be used (for example
      a value from the output of :func:`pcms`). The default value is
      ``'default'``.
@@ -165,14 +155,20 @@ following arguments:
      the `device` keyword argument is ignored.
      ``0`` is the first hardware sound card.
 
+     **Note:** This should not be used, as it bypasses most of ALSA's configuration.
+
    This will construct a PCM object with the given settings.
 
+   *Changed in 0.10:*
+
+   - Added the optional named parameter `periods`.
+
    *Changed in 0.9:*
 
    - Added the optional named parameters `rate`, `channels`, `format` and `periodsize`.
 
    *Changed in 0.8:*
-   
+
    - The `card` keyword argument is still supported,
      but deprecated. Please use `device` instead.
 
@@ -180,8 +176,7 @@ following arguments:
 
    The `card` keyword is deprecated because it guesses the real ALSA
    name of the card. This was always fragile and broke some legitimate usecases.
-   
+
-     
 PCM objects have the following methods:
 
 .. method:: PCM.info()
@@ -235,17 +230,43 @@ PCM objects have the following methods:
    Returns the type of PCM object. Either :const:`PCM_CAPTURE` or
    :const:`PCM_PLAYBACK`.
 
-
 .. method:: PCM.pcmmode()
 
    Return the mode of the PCM object. One of :const:`PCM_NONBLOCK`,
    :const:`PCM_ASYNC`, or :const:`PCM_NORMAL`
 
-
 .. method:: PCM.cardname()
 
    Return the name of the sound card used by this PCM object.
 
+..
+   Omitted by intention due to not really fitting the c'tor-based setup concept:
+
+   .. method:: PCM.getchannels()
+
+   Returns list of the device's supported channel counts.
+
+   .. method:: PCM.getratebounds()
+
+   Returns the card's minimum and maximum supported sample rates as
+   a tuple of integers.
+
+   .. method:: PCM.getrates()
+
+   Returns the sample rates supported by the device.
+   The returned value can be of one of the following, depending on
+   the card's properties:
+   * Card supports only a single rate: returns the rate
+   * Card supports a continuous range of rates: returns a tuple of
+     the range's lower and upper bounds (inclusive)
+   * Card supports a collection of well-known rates: returns a list of
+     the supported rates
+
+   .. method:: PCM.getformats()
+
+   Returns a dictionary of supported format codes (integers) keyed by
+   their standard ALSA names (strings).
+
 .. method:: PCM.setchannels(nchannels)
 
    .. deprecated:: 0.9 Use the `channels` named argument to :func:`PCM`.
@@ -255,13 +276,42 @@ PCM objects have the following methods:
    .. deprecated:: 0.9 Use the `rate` named argument to :func:`PCM`.
 
 .. method:: PCM.setformat(format)
-   
+
    .. deprecated:: 0.9 Use the `format` named argument to :func:`PCM`.
 
 .. method:: PCM.setperiodsize(period)
 
    .. deprecated:: 0.9 Use the `periodsize` named argument to :func:`PCM`.
 
+.. method:: PCM.info()
+
+   Returns a dictionary with the PCM object's configured parameters.
+
+   Values are retrieved from the ALSA library if they are available;
+   otherwise they represent those stored by pyalsaaudio, and their keys
+   are prefixed with ' (call value) '.
+
+   *New in 0.9.1*
+
+.. method:: PCM.dumpinfo()
+
+   Dumps the PCM object's configured parameters to stdout.
+
+.. method:: PCM.state()
+
+   Returs the current state of the stream, which can be one of
+   :const:`PCM_STATE_OPEN` (this should not actually happen),
+   :const:`PCM_STATE_SETUP` (after :func:`drop` or :func:`drain`),
+   :const:`PCM_STATE_PREPARED` (after construction),
+   :const:`PCM_STATE_RUNNING`,
+   :const:`PCM_STATE_XRUN`,
+   :const:`PCM_STATE_DRAINING`,
+   :const:`PCM_STATE_PAUSED`,
+   :const:`PCM_STATE_SUSPENDED`, and
+   :const:`PCM_STATE_DISCONNECTED`.
+
+   *New in 0.10*
+
 .. method:: PCM.read()
 
    In :const:`PCM_NORMAL` mode, this function blocks until a full period is
@@ -294,17 +344,42 @@ PCM objects have the following methods:
    return value of zero, if the buffer is full. In this case, the data
    should be written at a later time.
 
+   Note that this call completing means only that the samples were buffered
+   in the kernel, and playout will continue afterwards. Make sure that the
+   stream is drained before discarding the PCM handle.
 
 .. method:: PCM.pause([enable=True])
 
    If *enable* is :const:`True`, playback or capture is paused.
    Otherwise, playback/capture is resumed.
 
+.. method:: PCM.drop()
+
+   Stop the stream and drop residual buffered frames.
+
+   *New in 0.9*
+
+.. method:: PCM.drain()
+
+   For :const:`PCM_PLAYBACK` PCM objects, play residual buffered frames
+   and then stop the stream. In :const:`PCM_NORMAL` mode,
+   this function blocks until all pending playback is drained.
+
+   For :const:`PCM_CAPTURE` PCM objects, this function is not very useful.
+
+   *New in 0.10*
+
+.. method:: PCM.close()
+
+   Closes the PCM device.
+
+   For :const:`PCM_PLAYBACK` PCM objects in :const:`PCM_NORMAL` mode,
+   this function blocks until all pending playback is drained.
 
 .. method:: PCM.polldescriptors()
 
-   Returns a tuple of *(file descriptor, eventmask)* that can be used to
+   Returns a list of tuples of *(file descriptor, eventmask)* that can be
-   wait for changes on the PCM with *select.poll*.
+   used to wait for changes on the PCM with *select.poll*.
 
    The *eventmask* value is compatible with `poll.register`__ in the Python 
    :const:`select` module.
@@ -347,7 +422,7 @@ PCM objects have the following methods:
    ``PCM_TSTAMP_TYPE_MONOTONIC_RAW``  Monotonic time from an unspecified starting
                                       time using only the system clock.
    =================================  ===========================================
-   
+
    The timestamp mode is controlled by the tstamp_mode, as described in the table below.
 
    =================================  ===========================================
@@ -358,9 +433,6 @@ PCM objects have the following methods:
                                       update.
    =================================  ===========================================
 
-
-__ poll_objects_
-
 **A few hints on using PCM devices for playback**
 
 The most common reason for problems with playback of PCM audio is that writes 
@@ -396,11 +468,10 @@ Mixer Objects
 
 Mixer objects provides access to the ALSA mixer API.
 
-
 .. class:: Mixer(control='Master', id=0, cardindex=-1, device='default')
 
    Arguments are:
-   
+
    * *control* - specifies which control to manipulate using this mixer
      object. The list of available controls can be found with the 
      :mod:`alsaaudio`.\ :func:`mixers` function.  The default value is
@@ -416,30 +487,27 @@ Mixer objects provides access to the ALSA mixer API.
 
    * *device* - the name of the device on which the mixer resides. The default
      value is ``'default'``.
-   
+
    *Changed in 0.8*:
-   
+
    - The keyword argument `device` is new and can be used to select virtual
      devices.
-  
+
 Mixer objects have the following methods:
 
 .. method:: Mixer.cardname()
 
    Return the name of the sound card used by this Mixer object
 
-
 .. method:: Mixer.mixer()
 
    Return the name of the specific mixer controlled by this object, For example
    ``'Master'`` or ``'PCM'``
 
-
 .. method:: Mixer.mixerid()
 
    Return the ID of the ALSA mixer controlled by this object.
 
-
 .. method:: Mixer.switchcap()
 
    Returns a list of the switches which are defined by this specific mixer.
@@ -460,7 +528,6 @@ Mixer objects have the following methods:
    To manipulate these switches use the :meth:`setrec` or
    :meth:`setmute` methods
 
-
 .. method:: Mixer.volumecap()
 
    Returns a list of the volume control capabilities of this
@@ -476,7 +543,7 @@ Mixer objects have the following methods:
    'Capture Volume'          Manipulate sound capture volume
    'Joined Capture Volume'   Manipulate sound capture volume for all channels at a time
    ========================  ================
-   
+
 .. method:: Mixer.getenum()
 
    For enumerated controls, return the currently selected item and  the list of
@@ -503,48 +570,43 @@ Mixer objects have the following methods:
    This method will return an empty tuple if the mixer is not an  enumerated
    control.
 
+.. method:: Mixer.setenum(index)
 
-.. method:: Mixer.getmute()
+   For enumerated controls, sets the currently selected item.
+   *index* is an index into the list of available enumerated items returned
+   by :func:`getenum`.
 
-   Return a list indicating the current mute setting for each
+.. method:: Mixer.getrange(pcmtype=PCM_PLAYBACK, units=VOLUME_UNITS_RAW)
-   channel. 0 means not muted, 1 means muted.
-
-   This method will fail if the mixer has no playback switch capabilities.
-
-
-.. method:: Mixer.getrange(pcmtype=PCM_PLAYBACK)
 
    Return the volume range of the ALSA mixer controlled by this object.
+   The value is a tuple of integers whose meaning is determined by the
+   *units* argument.
 
    The optional *pcmtype* argument can be either :const:`PCM_PLAYBACK` or
    :const:`PCM_CAPTURE`, which is relevant if the mixer can control both
    playback and capture volume.  The default value is :const:`PCM_PLAYBACK`
    if the mixer has playback channels, otherwise it is :const:`PCM_CAPTURE`.
 
+   The optional *units* argument can be one of :const:`VOLUME_UNITS_PERCENTAGE`,
+   :const:`VOLUME_UNITS_RAW`, or :const:`VOLUME_UNITS_DB`.
 
-.. method:: Mixer.getrec()
+.. method:: Mixer.getvolume(pcmtype=PCM_PLAYBACK, units=VOLUME_UNITS_PERCENTAGE)
-
-   Return a list indicating the current record mute setting for each channel. 0
-   means not recording, 1 means recording.
-
-   This method will fail if the mixer has no capture switch capabilities.
-
-
-.. method:: Mixer.getvolume(pcmtype=PCM_PLAYBACK)
 
    Returns a list with the current volume settings for each channel. The list
-   elements are integer percentages.
+   elements are integers whose meaning is determined by the *units* argument.
 
    The optional *pcmtype* argument can be either :const:`PCM_PLAYBACK` or
    :const:`PCM_CAPTURE`, which is relevant if the mixer can control both
    playback and capture volume. The default value is :const:`PCM_PLAYBACK`
    if the mixer has playback channels, otherwise it is :const:`PCM_CAPTURE`.
 
+   The optional *units* argument can be one of :const:`VOLUME_UNITS_PERCENTAGE`,
+   :const:`VOLUME_UNITS_RAW`, or :const:`VOLUME_UNITS_DB`.
 
-.. method:: Mixer.setvolume(volume, channel=None, pcmtype=PCM_PLAYBACK)
+.. method:: Mixer.setvolume(volume, channel=None, pcmtype=PCM_PLAYBACK, units=VOLUME_UNITS_PERCENTAGE)
 
    Change the current volume settings for this mixer. The *volume* argument
-   controls the new volume setting as an integer percentage.
+   is an integer whose meaning is determined by the *units* argument.
 
    If the optional argument *channel* is present, the volume is set
    only for this channel. This assumes that the mixer can control the
@@ -555,6 +617,16 @@ Mixer objects have the following methods:
    playback and capture volume. The default value is :const:`PCM_PLAYBACK`
    if the mixer has playback channels, otherwise it is :const:`PCM_CAPTURE`.
 
+   The optional *units* argument can be one of :const:`VOLUME_UNITS_PERCENTAGE`,
+   :const:`VOLUME_UNITS_RAW`, or :const:`VOLUME_UNITS_DB`.
+
+.. method:: Mixer.getmute()
+
+   Return a list indicating the current mute setting for each channel.
+   0 means not muted, 1 means muted.
+
+   This method will fail if the mixer has no playback switch capabilities.
+
 .. method:: Mixer.setmute(mute, [channel])
 
    Sets the mute flag to a new value. The *mute* argument is either 0 for not
@@ -565,6 +637,12 @@ Mixer objects have the following methods:
 
    This method will fail if the mixer has no playback mute capabilities
 
+.. method:: Mixer.getrec()
+
+   Return a list indicating the current record mute setting for each channel.
+   0 means not recording, 1 means recording.
+
+   This method will fail if the mixer has no capture switch capabilities.
 
 .. method:: Mixer.setrec(capture, [channel])
 
@@ -578,20 +656,22 @@ Mixer objects have the following methods:
 
 .. method:: Mixer.polldescriptors()
 
-   Returns a tuple of *(file descriptor, eventmask)* that can be used to
+   Returns a list of tuples of *(file descriptor, eventmask)* that can be
-   wait for changes on the mixer with *select.poll*.
+   used to wait for changes on the mixer with *select.poll*.
 
    The *eventmask* value is compatible with `poll.register`__ in the Python 
    :const:`select` module.
 
-__ poll_objects_
-
 .. method:: Mixer.handleevents()
 
-   Acknowledge events on the *polldescriptors* file descriptors
+   Acknowledge events on the :func:`polldescriptors` file descriptors
    to prevent subsequent polls from returning the same events again.
    Returns the number of events that were acknowledged.
 
+.. method:: Mixer.close()
+
+   Closes the Mixer device.
+
 **A rant on the ALSA Mixer API**
 
 The ALSA mixer API is extremely complicated - and hardly documented at all.
@@ -614,8 +694,6 @@ Unfortunately, I'm not able to create such a HOWTO myself, since I only
 understand half of the API, and that which I do understand has come from a
 painful trial and error process.
 
-.. % ==== 4. ====
-
 
 .. _pcm-example:
 
@@ -657,6 +735,7 @@ To test PCM playback (on your default soundcard), run::
 
 recordtest.py and playbacktest.py
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
 **recordtest.py** and **playbacktest.py** will record and play a raw
 sound file in CD quality.
 
@@ -678,7 +757,7 @@ Without arguments, **mixertest.py** will list all available *controls* on the
 default soundcard.
 
 The output might look like this::
-   
+
   $ ./mixertest.py
   Available mixer controls:
      'Master'
@@ -726,9 +805,3 @@ argument::
   Capabilities: Playback Volume Playback Mute
   Channel 0 volume: 61%
   Channel 1 volume: 61%
-
-.. rubric:: Footnotes
-
-.. [#f1]   ALSA also allows ``PCM_ASYNC``, but this is not supported yet.
-
-.. _poll_objects: http://docs.python.org/library/select.html#poll-objects

doc/pyalsaaudio.rst

@@ -7,33 +7,19 @@ Introduction
 
 .. |release| replace:: version
 
-.. % At minimum, give your name and an email address.  You can include a
-.. % snail-mail address if you like.
-
-.. % This makes the Abstract go on a separate page in the HTML version;
-.. % if a copyright notice is used, it should go immediately after this.
-.. % 
-
-
 .. _front:
 
 This software is licensed under the PSF license - the same one used by the
 majority of the python distribution. Basically you can use it for anything you
 wish (even commercial purposes). There is no warranty whatsoever.
 
-.. % Copyright statement should go here, if needed.
-
-.. % The abstract should be a paragraph or two long, and describe the
-.. % scope of the document.
-
-
 .. topic:: Abstract
 
    This package contains wrappers for accessing the ALSA API from Python. It is
    currently fairly complete for PCM devices and Mixer access. MIDI sequencer
    support is low on our priority list, but volunteers are welcome.
 
-   If you find bugs in the wrappers please use thegithub issue tracker. 
+   If you find bugs in the wrappers please use the github issue tracker.
    Please don't send bug reports regarding ALSA specifically. There are several
    bugs in this API, and those should be reported to the ALSA team - not me.
 
@@ -64,8 +50,8 @@ More information about ALSA may be found on the project homepage
 ALSA and Python
 ===============
 
-The older Linux sound API (OSS) which is now deprecated is well supported from
+The older Linux sound API (OSS) -- which is now deprecated -- is well supported
-the standard Python library, through the ossaudiodev module. No native ALSA
+by the standard Python library, through the ossaudiodev module. No native ALSA
 support exists in the standard library.
 
 There are a few other "ALSA for Python" projects available, including at least
@@ -106,6 +92,7 @@ And then as root:  ---   ::
 
    # python setup.py install
 
+
 *******
 Testing
 *******
@@ -130,7 +117,7 @@ with ``Ctl-C``.
 
 Play back the recording with::
 
-   $ python playbacktest.py-d <device>  <filename>
+   $ python playbacktest.py -d <device> <filename>
 
 There is a minimal test suite in :code:`test.py`, but it is
 a bit dependent on the ALSA configuration and may fail without indicating

doc/terminology.rst

@@ -19,7 +19,7 @@ Sample
 
    Musically, the sample size determines the dynamic range. The
    dynamic range is the difference between the quietest and the
-   loudest signal that can be resproduced.
+   loudest signal that can be reproduced.
 
 Frame
    A frame consists of exactly one sample per channel. If there is only one 
@@ -28,9 +28,9 @@ Frame
 
 Frame size
    This is the size in bytes of each frame. This can vary a lot: if each sample
-    is 8 bits, and we're handling mono sound, the frame size is one byte. 
+   is 8 bits, and we're handling mono sound, the frame size is one byte.
-	Similarly in 6 channel audio with 64 bit floating point samples, the frame 
+   For six channel audio with 64 bit floating point samples, the frame size
-	size is 48 bytes
+   is 48 bytes.
 
 Rate
    PCM sound consists of a flow of sound frames. The sound rate controls how 
@@ -38,7 +38,7 @@ Rate
    means that a new frame is played or captured 8000 times per second.
 
 Data rate
-   This is the number of bytes, which must be recorded or provided per
+   This is the number of bytes which must be consumed or provided per
    second at a certain frame size and rate.
 
    8000 Hz mono sound with 8 bit (1 byte) samples has a data rate of
@@ -46,24 +46,40 @@ Data rate
 
    At the other end of the scale, 96000 Hz, 6 channel sound with 64
    bit (8 bytes) samples has a data rate of 96000 \* 6 \* 8 = 4608
-   kb/s (almost 5 MB sound data per second)
+   kb/s (almost 5 MB sound data per second).
+
+   If the data rate requirement is not met, an overrun (on capture) or
+   underrun (on playback) occurs; the term "xrun" is used to refer to
+   either event.
+
+.. _term-period:
 
 Period
-   When the hardware processes data this is done in chunks of frames. The time
+   The CPU processes sample data in chunks of frames, so-called periods
-   interval between each processing (A/D or D/A conversion) is known
+   (also called fragments by some systems). The operating system kernel's
-   as the period.
+   sample buffer must hold at least two periods (at any given time, one
-   The size of the period has direct implication on the latency of the
+   is processed by the sound hardware, and one by the CPU).
-   sound input or output. For low-latency the period size should be
+
-   very small, while low CPU resource usage would usually demand
+   The completion of a *period* triggers a CPU interrupt, which causes
-   larger period sizes. With ALSA, the CPU utilization is not impacted
+   processing and context switching overhead. Therefore, a smaller period
-   much by the period size, since the kernel layer buffers multiple
+   size causes higher CPU resource usage at a given data rate.
-   periods internally, so each period generates an interrupt and a
+
-   memory copy, but userspace can be slower and read or write multiple
+   A bigger size of the *buffer* improves the system's resilience to xruns.
-   periods at the same time.
+   The buffer being split into a bigger number of smaller periods also does
+   that, as it allows it to be drained / topped up sooner.
+
+   On the other hand, a bigger size of the *buffer* also increases the
+   playback latency, that is, the time it takes for a frame from being
+   sent out by the application to being actually audible.
+
+   Similarly, a bigger *period* size increases the capture latency.
+
+   The trade-off between latency, xrun resilience, and resource usage
+   must be made depending on the application.
 
 Period size
-   This is the size of each period in Hz. *Not bytes, but Hz!.* In 
+   This is the size of each period in frames. *Not bytes, but frames!*
-   :mod:`alsaaudio` the period size is set directly, and it is
+   In :mod:`alsaaudio` the period size is set directly, and it is
    therefore important to understand the significance of this
    number. If the period size is configured to for example 32,
    each write should contain exactly 32 frames of sound data, and each

loopback.py

@@ -0,0 +1,397 @@
+#!/usr/bin/env python3
+# -*- mode: python; indent-tabs-mode: t; c-basic-offset: 4; tab-width: 4 -*-
+
+import sys
+import select
+import logging
+import re
+import struct
+import subprocess
+from datetime import datetime, timedelta
+from alsaaudio import (PCM, pcms, PCM_PLAYBACK, PCM_CAPTURE, PCM_NONBLOCK, Mixer,
+	PCM_STATE_OPEN, PCM_STATE_SETUP, PCM_STATE_PREPARED, PCM_STATE_RUNNING, PCM_STATE_XRUN, PCM_STATE_DRAINING,
+	PCM_STATE_PAUSED, PCM_STATE_SUSPENDED, ALSAAudioError)
+from argparse import ArgumentParser
+
+poll_names = {
+	select.POLLIN: 'POLLIN',
+	select.POLLPRI: 'POLLPRI',
+	select.POLLOUT: 'POLLOUT',
+	select.POLLERR: 'POLLERR',
+	select.POLLHUP: 'POLLHUP',
+	select.POLLRDHUP: 'POLLRDHUP',
+	select.POLLNVAL: 'POLLNVAL'
+}
+
+state_names = {
+	PCM_STATE_OPEN: 'PCM_STATE_OPEN',
+	PCM_STATE_SETUP: 'PCM_STATE_SETUP',
+	PCM_STATE_PREPARED: 'PCM_STATE_PREPARED',
+	PCM_STATE_RUNNING: 'PCM_STATE_RUNNING',
+	PCM_STATE_XRUN: 'PCM_STATE_XRUN',
+	PCM_STATE_DRAINING: 'PCM_STATE_DRAINING',
+	PCM_STATE_PAUSED: 'PCM_STATE_PAUSED',
+	PCM_STATE_SUSPENDED: 'PCM_STATE_SUSPENDED'
+}
+
+def poll_desc(mask):
+	return '|'.join([poll_names[bit] for bit, name in poll_names.items() if mask & bit])
+
+class PollDescriptor(object):
+	'''File Descriptor, event mask and a name for logging'''
+	def __init__(self, name, fd, mask):
+		self.name = name
+		self.fd = fd
+		self.mask = mask
+
+	def as_tuple(self):
+		return (self.fd, self.mask)
+
+	@classmethod
+	def from_alsa_object(cls, name, alsaobject, mask=None):
+		# TODO maybe refactor: we ignore objects that have more then one polldescriptor
+		fd, alsamask = alsaobject.polldescriptors()[0]
+
+		if mask is None:
+			mask = alsamask
+
+		return cls(name, fd, mask)
+
+class Loopback(object):
+	'''Loopback state and event handling'''
+
+	def __init__(self, capture, playback_args, volume_handler, run_after_stop=None, run_before_start=None):
+		self.playback_args = playback_args
+		self.playback = None
+		self.volume_handler = volume_handler
+		self.capture_started = None
+		self.last_capture_event = None
+
+		self.capture = capture
+		self.capture_pd = PollDescriptor.from_alsa_object('capture', capture)
+
+		self.run_after_stop = run_after_stop.split(' ')
+		self.run_before_start = run_before_start.split(' ')
+		self.run_after_stop_did_run = False
+
+		self.waitBeforeOpen = False
+		self.queue = []
+
+		self.period_size = 0
+		self.silent_periods = 0
+
+	@staticmethod
+	def compute_energy(data):
+		values = struct.unpack(f'{len(data)//2}h', data)
+		e = 0
+		for v in values:
+			e = e + v * v
+
+		return e
+
+	@staticmethod
+	def run_command(cmd):
+		if cmd:
+			rc = subprocess.run(cmd)
+			if rc.returncode:
+				logging.warning(f'run {cmd}, return code {rc.returncode}')
+			else:
+				logging.info(f'run {cmd}, return code {rc.returncode}')
+
+	def register(self, reactor):
+		reactor.register_timeout_handler(self.timeout_handler)
+		reactor.register(self.capture_pd, self)
+
+	def start(self):
+		# start reading data
+		size, data = self.capture.read()
+		if size:
+			self.queue.append(data)
+
+	def timeout_handler(self):
+		if self.playback and self.capture_started:
+			if self.last_capture_event:
+				if datetime.now() - self.last_capture_event > timedelta(seconds=2):
+					logging.info('timeout - closing playback device')
+					self.playback.close()
+					self.playback = None
+					self.capture_started = None
+					if self.volume_handler:
+						self.volume_handler.stop()
+					self.run_command(self.run_after_stop)
+			return
+
+		self.waitBeforeOpen = False
+
+		if not self.run_after_stop_did_run and not self.playback:
+			if self.volume_handler:
+				self.volume_handler.stop()
+			self.run_command(self.run_after_stop)
+			self.run_after_stop_did_run = True
+
+	def pop(self):
+		if len(self.queue):
+			return self.queue.pop()
+		else:
+			return None
+
+	def handle_capture_event(self, eventmask, name):
+		'''called when data is available for reading'''
+		self.last_capture_event = datetime.now()
+		size, data = self.capture.read()
+		if not size:
+			logging.warning(f'capture event but no data')
+			return False
+
+		energy = self.compute_energy(data)
+		logging.debug(f'energy: {energy}')
+
+		# the usecase is a USB capture device where we get perfect silence when it's idle
+		if energy == 0:
+			self.silent_periods = self.silent_periods + 1
+
+			# turn off playback after two seconds of silence
+			# 2 channels * 2 seconds * 2 bytes per sample
+			fps = self.playback_args['rate']  * 8 // (self.playback_args['periodsize'] * self.playback_args['periods'])
+
+			logging.debug(f'{self.silent_periods} of {fps} silent periods: {self.playback}')
+
+			if self.silent_periods > fps and self.playback:
+				logging.info(f'closing playback due to silence')
+				self.playback.close()
+				self.playback = None
+				if self.volume_handler:
+					self.volume_handler.stop()
+				self.run_command(self.run_after_stop)
+				self.run_after_stop_did_run = True
+
+			if not self.playback:
+				return
+		else:
+			self.silent_periods = 0
+
+		if not self.playback:
+			if self.waitBeforeOpen:
+				return False
+			try:
+				if self.volume_handler:
+					self.volume_handler.start()
+				self.run_command(self.run_before_start)
+				self.playback = PCM(**self.playback_args)
+				self.period_size = self.playback.info()['period_size']
+				logging.info(f'opened playback device with period_size {self.period_size}')
+			except ALSAAudioError as e:
+				logging.info('opening PCM playback device failed: %s', e)
+				self.waitBeforeOpen = True
+				return False
+
+			self.capture_started = datetime.now()
+			logging.info(f'{self.playback} capture started: {self.capture_started}')
+
+		self.queue.append(data)
+
+		if len(self.queue) <= 2:
+			logging.info(f'buffering: {len(self.queue)}')
+			return False
+
+		try:
+			data = self.pop()
+			if data:
+				space = self.playback.avail()
+				written = self.playback.write(data)
+				logging.debug(f'wrote {written} bytes while space was {space}')
+		except ALSAAudioError:
+			logging.error('underrun', exc_info=1)
+
+		return True
+
+	def __call__(self, fd, eventmask, name):
+
+		if fd == self.capture_pd.fd:
+			real_mask = self.capture.polldescriptors_revents([self.capture_pd.as_tuple()])
+			if real_mask:
+				return self.handle_capture_event(real_mask, name)
+			else:
+				logging.debug('null capture event')
+				return False
+		else:
+			real_mask = self.playback.polldescriptors_revents([self.playback_pd.as_tuple()])
+			if real_mask:
+				return self.handle_playback_event(real_mask, name)
+			else:
+				logging.debug('null playback event')
+				return False
+
+class VolumeForwarder(object):
+	'''Volume control event handling'''
+
+	def __init__(self, capture_control, playback_control):
+		self.playback_control = playback_control
+		self.capture_control = capture_control
+		self.active = True
+
+	def start(self):
+		self.active = True
+		if self.volume:
+			self.volume = playback_control.setvolume(self.volume)
+
+	def stop(self):
+		self.active = False
+		self.volume = self.playback_control.getvolume(pcmtype=PCM_CAPTURE)[0]
+
+	def __call__(self, fd, eventmask, name):
+		if not self.active:
+			return
+
+		volume = self.capture_control.getvolume(pcmtype=PCM_CAPTURE)
+		# indicate that we've handled the event
+		self.capture_control.handleevents()
+		logging.info(f'{name} adjusting volume to {volume}')
+		if volume:
+			self.playback_control.setvolume(volume[0])
+
+
+class Reactor(object):
+	'''A wrapper around select.poll'''
+
+	def __init__(self):
+		self.poll = select.poll()
+		self.descriptors = {}
+		self.timeout_handlers = set()
+
+	def register(self, polldescriptor, callable):
+		logging.debug(f'registered {polldescriptor.name}: {poll_desc(polldescriptor.mask)}')
+		self.descriptors[polldescriptor.fd] = (polldescriptor, callable)
+		self.poll.register(polldescriptor.fd, polldescriptor.mask)
+
+	def unregister(self, polldescriptor):
+		self.poll.unregister(polldescriptor.fd)
+		del self.descriptors[polldescriptor.fd]
+
+	def register_timeout_handler(self, callable):
+		self.timeout_handlers.add(callable)
+
+	def unregister_timeout_handler(self, callable):
+		self.timeout_handlers.remove(callable)
+
+	def run(self):
+		last_timeout_ev = datetime.now()
+		while True:
+			# poll for a bit, then send a timeout to registered handlers
+			events = self.poll.poll(0.25)
+			for fd, ev in events:
+				polldescriptor, handler = self.descriptors[fd]
+
+				# very chatty - log all events
+				# logging.debug(f'{polldescriptor.name}: {poll_desc(ev)} ({ev})')
+
+				handler(fd, ev, polldescriptor.name)
+
+			if datetime.now() - last_timeout_ev > timedelta(seconds=0.25):
+				for t in self.timeout_handlers:
+					t()
+				last_timeout_ev = datetime.now()
+
+
+if __name__ == '__main__':
+
+	logging.basicConfig(format='%(asctime)s %(levelname)s %(message)s', level=logging.INFO)
+
+	parser = ArgumentParser(description='ALSA loopback (with volume forwarding)')
+
+	playback_pcms = pcms(pcmtype=PCM_PLAYBACK)
+	capture_pcms = pcms(pcmtype=PCM_CAPTURE)
+
+	if not playback_pcms:
+		logging.error('no playback PCM found')
+		sys.exit(2)
+
+	if not capture_pcms:
+		logging.error('no capture PCM found')
+		sys.exit(2)
+
+	parser.add_argument('-d', '--debug', action='store_true')
+	parser.add_argument('-i', '--input', default=capture_pcms[0])
+	parser.add_argument('-o', '--output', default=playback_pcms[0])
+	parser.add_argument('-r', '--rate', type=int, default=44100)
+	parser.add_argument('-c', '--channels', type=int, default=2)
+	parser.add_argument('-p', '--periodsize', type=int, default=444) # must be divisible by 6 for 44k1
+	parser.add_argument('-P', '--periods', type=int, default=2)
+	parser.add_argument('-I', '--input-mixer', help='Control of the input mixer, can contain the card index, e.g. Digital:2')
+	parser.add_argument('-O', '--output-mixer', help='Control of the output mixer, can contain the card index, e.g. PCM:1')
+	parser.add_argument('-A', '--run-after-stop', help='command to run when the capture device is idle/silent')
+	parser.add_argument('-B', '--run-before-start', help='command to run when the capture device becomes active')
+	parser.add_argument('-V', '--volume', help='Initial volume (default is leave unchanged)')
+
+	args = parser.parse_args()
+
+	if args.debug:
+		logging.getLogger().setLevel(logging.DEBUG)
+
+	playback_args = {
+		'type': PCM_PLAYBACK,
+		'mode': PCM_NONBLOCK,
+		'device': args.output,
+		'rate': args.rate,
+		'channels': args.channels,
+		'periodsize': args.periodsize,
+		'periods': args.periods
+	}
+
+	reactor = Reactor()
+
+	# If args.input_mixer and args.output_mixer are set, forward the capture volume to the playback volume.
+	# The usecase is a capture device that is implemented using g_audio, i.e. the Linux USB gadget driver.
+	# When a USB device (eg. an iPad) is connected to this machine, its volume events will go to the volume control
+	# of the output device
+
+	capture = None
+	playback = None
+	volume_handler = None
+	if args.input_mixer and args.output_mixer:
+		re_mixer = re.compile(r'([a-zA-Z0-9]+):?([0-9+])?')
+
+		input_mixer_card = None
+		m = re_mixer.match(args.input_mixer)
+		if m:
+			input_mixer = m.group(1)
+			if m.group(2):
+				input_mixer_card = int(m.group(2))
+		else:
+			parser.print_usage()
+			sys.exit(1)
+
+		output_mixer_card = None
+		m = re_mixer.match(args.output_mixer)
+		if m:
+			output_mixer = m.group(1)
+			if m.group(2):
+				output_mixer_card = int(m.group(2))
+		else:
+			parser.print_usage()
+			sys.exit(1)
+
+		if input_mixer_card is None:
+			capture = PCM(type=PCM_CAPTURE, mode=PCM_NONBLOCK, device=args.input, rate=args.rate,
+				channels=args.channels, periodsize=args.periodsize, periods=args.periods)
+			input_mixer_card = capture.info()['card_no']
+
+		if output_mixer_card is None:
+			playback = PCM(**playback_args)
+			output_mixer_card = playback.info()['card_no']
+			playback.close()
+
+		playback_control = Mixer(control=output_mixer, cardindex=int(output_mixer_card))
+		capture_control = Mixer(control=input_mixer, cardindex=int(input_mixer_card))
+
+		volume_handler = VolumeForwarder(capture_control, playback_control)
+		reactor.register(PollDescriptor.from_alsa_object('capture_control', capture_control, select.POLLIN), volume_handler)
+
+	if args.volume and playback_control:
+		playback_control.setvolume(int(args.volume))
+
+	loopback = Loopback(capture, playback_args, volume_handler, args.run_after_stop, args.run_before_start)
+	loopback.register(reactor)
+	loopback.start()
+
+	reactor.run()

mixertest.py

@@ -72,8 +72,13 @@ def show_mixer(name, kwargs):
     volumes = mixer.getvolume()
     volumes_dB = mixer.getvolume(units=alsaaudio.VOLUME_UNITS_DB)
     for i in range(len(volumes)):
-        print("Channel %i volume: %i%% (%.1f dB)" % (i, volumes[i], volumes_dB[i] / 100.0))
+        print("Channel %i playback volume: %i%% (%.1f dB)" % (i, volumes[i], volumes_dB[i] / 100.0))
-        
+
+    volumes = mixer.getvolume(pcmtype=alsaaudio.PCM_CAPTURE)
+    volumes_dB = mixer.getvolume(pcmtype=alsaaudio.PCM_CAPTURE, units=alsaaudio.VOLUME_UNITS_DB)
+    for i in range(len(volumes)):
+        print("Channel %i capture volume: %i%% (%.1f dB)" % (i, volumes[i], volumes_dB[i] / 100.0))
+
     try:
         mutes = mixer.getmute()
         for i in range(len(mutes)):
@@ -113,7 +118,7 @@ def set_mixer(name, args, kwargs):
             mixer.setmute(1, channel)
         else:
             mixer.setmute(0, channel)
-        
+
     elif args in ['rec','unrec']:
         # Enable/disable recording
         if args == 'rec':

playbacktest.py

@@ -49,5 +49,5 @@ if __name__ == '__main__':
     while data:
         out.write(data)
         data = f.read(320)
-            
+    out.close()
         

setup.py

@@ -8,7 +8,7 @@ from setuptools import setup
 from setuptools.extension import Extension
 from sys import version
 
-pyalsa_version = '0.9.2'
+pyalsa_version = '0.10.1'
 
 if __name__ == '__main__':
     setup(
@@ -29,12 +29,12 @@ if __name__ == '__main__':
             'License :: OSI Approved :: Python Software Foundation License',
             'Operating System :: POSIX :: Linux',
             'Programming Language :: Python :: 2',
-            'Programming Language :: Python :: 3',    
+            'Programming Language :: Python :: 3',
             'Topic :: Multimedia :: Sound/Audio',
             'Topic :: Multimedia :: Sound/Audio :: Mixers',
             'Topic :: Multimedia :: Sound/Audio :: Players',
             'Topic :: Multimedia :: Sound/Audio :: Capture/Recording',
             ],
-        ext_modules=[Extension('alsaaudio',['alsaaudio.c'], 
+        ext_modules=[Extension('alsaaudio',['alsaaudio.c'],
                                libraries=['asound'])]
     )

test.py

@@ -11,6 +11,7 @@
 import unittest
 import alsaaudio
 import warnings
+from contextlib import closing
 
 # we can't test read and write well - these are tested otherwise
 PCMMethods = [
@@ -20,7 +21,7 @@ PCMMethods = [
 ]
 
 PCMDeprecatedMethods = [
-	('setchannels', (2,)), 
+	('setchannels', (2,)),
 	('setrate', (44100,)),
 	('setformat', (alsaaudio.PCM_FORMAT_S8,)),
 	('setperiodsize', (320,))
@@ -49,10 +50,10 @@ class MixerTest(unittest.TestCase):
 
 	def testMixer(self):
 		"""Open the default Mixers and the Mixers on every card"""
-		
+
 		for c in alsaaudio.card_indexes():
 			mixers = alsaaudio.mixers(cardindex=c)
-			
+
 			for m in mixers:
 				mixer = alsaaudio.Mixer(m, cardindex=c)
 				mixer.close()
@@ -73,7 +74,7 @@ class MixerTest(unittest.TestCase):
 		mixer.close()
 
 	def testMixerClose(self):
-		"""Run common Mixer methods on a closed object and verify it raises an 
+		"""Run common Mixer methods on a closed object and verify it raises an
 		error"""
 
 		mixers = alsaaudio.mixers()
@@ -133,7 +134,7 @@ class PCMTest(unittest.TestCase):
 				pcm = alsaaudio.PCM(card='default')
 			except alsaaudio.ALSAAudioError:
 				pass
-				
+
 			# Verify we got a DepreciationWarning
 			self.assertEqual(len(w), 1, "PCM(card='default') expected a warning" )
 			self.assertTrue(issubclass(w[-1].category, DeprecationWarning), "PCM(card='default') expected a DeprecationWarning")
@@ -156,5 +157,31 @@ class PCMTest(unittest.TestCase):
 				self.assertEqual(len(w), 1, method + " expected a warning")
 				self.assertTrue(issubclass(w[-1].category, DeprecationWarning), method + " expected a DeprecationWarning")
 
+class PollDescriptorArgsTest(unittest.TestCase):
+	'''Test invalid args for polldescriptors_revents (takes a list of tuples of 2 integers)'''
+	def testArgsNoList(self):
+		with closing(alsaaudio.PCM()) as pcm:
+			with self.assertRaises(TypeError):
+				pcm.polldescriptors_revents('foo')
+
+	def testArgsListButNoTuples(self):
+		with closing(alsaaudio.PCM()) as pcm:
+			with self.assertRaises(TypeError):
+				pcm.polldescriptors_revents(['foo', 1])
+
+	def testArgsListButInvalidTuples(self):
+		with closing(alsaaudio.PCM()) as pcm:
+			with self.assertRaises(TypeError):
+				pcm.polldescriptors_revents([('foo', 'bar')])
+
+	def testArgsListTupleWrongLength(self):
+		with closing(alsaaudio.PCM()) as pcm:
+			with self.assertRaises(TypeError):
+				pcm.polldescriptors_revents([(1, )])
+
+			with self.assertRaises(TypeError):
+				pcm.polldescriptors_revents([(1, 2, 3)])
+
+
 if __name__ == '__main__':
 	unittest.main()