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@@ -5,34 +5,11 @@
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.. module:: alsaaudio
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:platform: Linux
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.. % \declaremodule{builtin}{alsaaudio} % standard library, in C
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.. % not standard, in C
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.. moduleauthor:: Casper Wilstrup <cwi@aves.dk>
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.. moduleauthor:: Lars Immisch <lars@ibp.de>
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.. % Author of the module code;
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The :mod:`alsaaudio` module defines functions and classes for using ALSA.
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.. % ---- 3.1. ----
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.. % For each function, use a ``funcdesc'' block. This has exactly two
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.. % parameters (each parameters is contained in a set of curly braces):
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.. % the first parameter is the function name (this automatically
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.. % generates an index entry); the second parameter is the function's
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.. % argument list. If there are no arguments, use an empty pair of
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.. % curly braces. If there is more than one argument, separate the
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.. % arguments with backslash-comma. Optional parts of the parameter
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.. % list are contained in \optional{...} (this generates a set of square
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.. % brackets around its parameter). Arguments are automatically set in
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.. % italics in the parameter list. Each argument should be mentioned at
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.. % least once in the description; each usage (even inside \code{...})
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.. % should be enclosed in \var{...}.
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.. function:: pcms(pcmtype=PCM_PLAYBACK)
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List available PCM devices by name.
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@@ -63,6 +40,12 @@ The :mod:`alsaaudio` module defines functions and classes for using ALSA.
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useful. If you want to see a list of available PCM devices, use :func:`pcms`
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instead.
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..
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Omitted by intention due to being superseded by cards():
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.. function:: card_indexes()
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.. function:: card_name()
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.. function:: mixers(cardindex=-1, device='default')
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List the available mixers. The arguments are:
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@@ -72,6 +55,8 @@ The :mod:`alsaaudio` module defines functions and classes for using ALSA.
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the `device` keyword argument is ignored. ``0`` is the first hardware sound
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card.
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**Note:** This should not be used, as it bypasses most of ALSA's configuration.
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* *device* - the name of the device on which the mixer resides. The default
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is ``'default'``.
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@@ -101,6 +86,7 @@ The :mod:`alsaaudio` module defines functions and classes for using ALSA.
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Return a Python string containing the ALSA version found.
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.. _pcm-objects:
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PCM Objects
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@@ -110,7 +96,7 @@ PCM objects in :mod:`alsaaudio` can play or capture (record) PCM
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sound through speakers or a microphone. The PCM constructor takes the
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following arguments:
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.. class:: PCM(type=PCM_PLAYBACK, mode=PCM_NORMAL, rate=44100, channels=2, format=PCM_FORMAT_S16_LE, periodsize=32, device='default', cardindex=-1)
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.. 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)
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This class is used to represent a PCM device (either for playback and
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recording). The arguments are:
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@@ -128,7 +114,7 @@ following arguments:
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Format Description
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========================= ===============
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``PCM_FORMAT_S8`` Signed 8 bit samples for each channel
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``PCM_FORMAT_U8`` Signed 8 bit samples for each channel
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``PCM_FORMAT_U8`` Unsigned 8 bit samples for each channel
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``PCM_FORMAT_S16_LE`` Signed 16 bit samples for each channel Little Endian byte order)
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``PCM_FORMAT_S16_BE`` Signed 16 bit samples for each channel (Big Endian byte order)
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``PCM_FORMAT_U16_LE`` Unsigned 16 bit samples for each channel (Little Endian byte order)
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@@ -156,7 +142,11 @@ following arguments:
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``PCM_FORMAT_U24_3BE`` Unsigned 24 bit samples for each channel (Big Endian byte order in 3 bytes)
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========================= ===============
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* *periodsize* - the period size in frames. Each write should consist of *periodsize* frames. The default value is 32.
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* *periodsize* - the period size in frames.
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Make sure you understand :ref:`the meaning of periods <term-period>`.
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The default value is 32, which is below the actual minimum of most devices,
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and will therefore likely be larger in practice.
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* *periods* - the number of periods in the buffer. The default value is 4.
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* *device* - the name of the PCM device that should be used (for example
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a value from the output of :func:`pcms`). The default value is
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``'default'``.
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@@ -165,8 +155,14 @@ following arguments:
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the `device` keyword argument is ignored.
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``0`` is the first hardware sound card.
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**Note:** This should not be used, as it bypasses most of ALSA's configuration.
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This will construct a PCM object with the given settings.
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*Changed in 0.10:*
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- Added the optional named parameter `periods`.
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*Changed in 0.9:*
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- Added the optional named parameters `rate`, `channels`, `format` and `periodsize`.
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@@ -181,25 +177,96 @@ following arguments:
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The `card` keyword is deprecated because it guesses the real ALSA
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name of the card. This was always fragile and broke some legitimate usecases.
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PCM objects have the following methods:
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.. method:: PCM.info()
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The info function returns a dictionary containing the configuration of a PCM device. As ALSA takes into account limitations of the hardware and software devices the configuration achieved might not correspond to the values used during creation. There is therefore a need to check the realised configuration before processing the sound coming from the device or before sending sound to a device. A small subset of parameters can be set, but cannot be queried. These parameters are stored by alsaaudio and returned as they were given by the user, to distinguish them from parameters retrieved from ALSA these parameters have a name prefixed with **" (call value) "**. Yet another set of properties derives directly from the hardware and can be obtained through ALSA.
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=========================== ============================= ==================================================================
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Key Description (Reference) Type
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=========================== ============================= ==================================================================
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name PCM():device string
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card_no *index of card* integer (negative indicates device not associable with a card)
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device_no *index of PCM device* integer
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subdevice_no *index of PCM subdevice* integer
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state *name of PCM state* string
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access_type *name of PCM access type* string
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(call value) type PCM():type integer
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(call value) type_name PCM():type string
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(call value) mode PCM():mode integer
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(call value) mode_name PCM():mode string
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format PCM():format integer
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format_name PCM():format string
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format_description PCM():format string
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subformat_name *name of PCM subformat* string
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subformat_description *description of subformat* string
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channels PCM():channels integer
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rate PCM():rate integer (Hz)
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period_time *period duration* integer (:math:`\mu s`)
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period_size PCM():period_size integer (frames)
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buffer_time *buffer time* integer (:math:`\mu s`) (negative indicates error)
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buffer_size *buffer size* integer (frames) (negative indicates error)
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get_periods *approx. periods in buffer* integer (negative indicates error)
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rate_numden *numerator, denominator* tuple (integer (Hz), integer (Hz))
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significant_bits *significant bits in sample* integer (negative indicates error)
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is_batch *hw: double buffering* boolean (True: hardware supported)
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is_block_transfer *hw: block transfer* boolean (True: hardware supported)
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is_double *hw: double buffering* boolean (True: hardware supported)
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is_half_duplex *hw: half-duplex* boolean (True: hardware supported)
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is_joint_duplex *hw: joint-duplex* boolean (True: hardware supported)
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can_overrange *hw: overrange detection* boolean (True: hardware supported)
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can_mmap_sample_resolution *hw: sample-resol. mmap* boolean (True: hardware supported)
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can_pause *hw: pause* boolean (True: hardware supported)
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can_resume *hw: resume* boolean (True: hardware supported)
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can_sync_start *hw: synchronized start* boolean (True: hardware supported)
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=========================== ============================= ==================================================================
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The italicized descriptions give a summary of the "full" description as it can be found in the `ALSA documentation <https://www.alsa-project.org/alsa-doc>`_. "hw:": indicates that the property indicated relates to the hardware. Parameters passed to the PCM object during instantation are prefixed with "PCM():", they are described there for the keyword argument indicated after "PCM():".
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.. method:: PCM.pcmtype()
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Returns the type of PCM object. Either :const:`PCM_CAPTURE` or
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:const:`PCM_PLAYBACK`.
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.. method:: PCM.pcmmode()
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Return the mode of the PCM object. One of :const:`PCM_NONBLOCK`,
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:const:`PCM_ASYNC`, or :const:`PCM_NORMAL`
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.. method:: PCM.cardname()
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Return the name of the sound card used by this PCM object.
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..
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Omitted by intention due to not really fitting the c'tor-based setup concept:
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.. method:: PCM.getchannels()
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Returns list of the device's supported channel counts.
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.. method:: PCM.getratebounds()
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Returns the card's minimum and maximum supported sample rates as
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a tuple of integers.
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.. method:: PCM.getrates()
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Returns the sample rates supported by the device.
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The returned value can be of one of the following, depending on
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the card's properties:
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* Card supports only a single rate: returns the rate
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* Card supports a continuous range of rates: returns a tuple of
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the range's lower and upper bounds (inclusive)
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* Card supports a collection of well-known rates: returns a list of
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the supported rates
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.. method:: PCM.getformats()
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Returns a dictionary of supported format codes (integers) keyed by
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their standard ALSA names (strings).
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.. method:: PCM.setchannels(nchannels)
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.. deprecated:: 0.9 Use the `channels` named argument to :func:`PCM`.
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@@ -216,6 +283,35 @@ PCM objects have the following methods:
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.. deprecated:: 0.9 Use the `periodsize` named argument to :func:`PCM`.
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.. method:: PCM.info()
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Returns a dictionary with the PCM object's configured parameters.
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Values are retrieved from the ALSA library if they are available;
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otherwise they represent those stored by pyalsaaudio, and their keys
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are prefixed with ' (call value) '.
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*New in 0.9.1*
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.. method:: PCM.dumpinfo()
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Dumps the PCM object's configured parameters to stdout.
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.. method:: PCM.state()
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Returs the current state of the stream, which can be one of
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:const:`PCM_STATE_OPEN` (this should not actually happen),
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:const:`PCM_STATE_SETUP` (after :func:`drop` or :func:`drain`),
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:const:`PCM_STATE_PREPARED` (after construction),
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:const:`PCM_STATE_RUNNING`,
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:const:`PCM_STATE_XRUN`,
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:const:`PCM_STATE_DRAINING`,
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:const:`PCM_STATE_PAUSED`,
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:const:`PCM_STATE_SUSPENDED`, and
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:const:`PCM_STATE_DISCONNECTED`.
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*New in 0.10*
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.. method:: PCM.read()
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In :const:`PCM_NORMAL` mode, this function blocks until a full period is
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@@ -248,17 +344,42 @@ PCM objects have the following methods:
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return value of zero, if the buffer is full. In this case, the data
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should be written at a later time.
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Note that this call completing means only that the samples were buffered
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in the kernel, and playout will continue afterwards. Make sure that the
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stream is drained before discarding the PCM handle.
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.. method:: PCM.pause([enable=True])
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If *enable* is :const:`True`, playback or capture is paused.
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Otherwise, playback/capture is resumed.
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.. method:: PCM.drop()
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Stop the stream and drop residual buffered frames.
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*New in 0.9*
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.. method:: PCM.drain()
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For :const:`PCM_PLAYBACK` PCM objects, play residual buffered frames
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and then stop the stream. In :const:`PCM_NORMAL` mode,
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this function blocks until all pending playback is drained.
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For :const:`PCM_CAPTURE` PCM objects, this function is not very useful.
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*New in 0.10*
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.. method:: PCM.close()
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Closes the PCM device.
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For :const:`PCM_PLAYBACK` PCM objects in :const:`PCM_NORMAL` mode,
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this function blocks until all pending playback is drained.
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.. method:: PCM.polldescriptors()
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Returns a tuple of *(file descriptor, eventmask)* that can be used to
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wait for changes on the PCM with *select.poll*.
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Returns a list of tuples of *(file descriptor, eventmask)* that can be
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used to wait for changes on the PCM with *select.poll*.
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The *eventmask* value is compatible with `poll.register`__ in the Python
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:const:`select` module.
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@@ -312,9 +433,6 @@ PCM objects have the following methods:
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update.
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================================= ===========================================
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__ poll_objects_
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**A few hints on using PCM devices for playback**
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The most common reason for problems with playback of PCM audio is that writes
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@@ -350,7 +468,6 @@ Mixer Objects
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Mixer objects provides access to the ALSA mixer API.
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.. class:: Mixer(control='Master', id=0, cardindex=-1, device='default')
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Arguments are:
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@@ -382,18 +499,15 @@ Mixer objects have the following methods:
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Return the name of the sound card used by this Mixer object
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.. method:: Mixer.mixer()
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Return the name of the specific mixer controlled by this object, For example
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``'Master'`` or ``'PCM'``
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.. method:: Mixer.mixerid()
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Return the ID of the ALSA mixer controlled by this object.
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.. method:: Mixer.switchcap()
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Returns a list of the switches which are defined by this specific mixer.
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@@ -414,7 +528,6 @@ Mixer objects have the following methods:
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To manipulate these switches use the :meth:`setrec` or
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:meth:`setmute` methods
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.. method:: Mixer.volumecap()
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Returns a list of the volume control capabilities of this
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@@ -457,48 +570,43 @@ Mixer objects have the following methods:
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This method will return an empty tuple if the mixer is not an enumerated
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control.
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.. method:: Mixer.setenum(index)
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.. method:: Mixer.getmute()
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For enumerated controls, sets the currently selected item.
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*index* is an index into the list of available enumerated items returned
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by :func:`getenum`.
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Return a list indicating the current mute setting for each
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channel. 0 means not muted, 1 means muted.
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This method will fail if the mixer has no playback switch capabilities.
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.. method:: Mixer.getrange(pcmtype=PCM_PLAYBACK)
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.. method:: Mixer.getrange(pcmtype=PCM_PLAYBACK, units=VOLUME_UNITS_RAW)
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Return the volume range of the ALSA mixer controlled by this object.
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The value is a tuple of integers whose meaning is determined by the
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*units* argument.
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The optional *pcmtype* argument can be either :const:`PCM_PLAYBACK` or
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:const:`PCM_CAPTURE`, which is relevant if the mixer can control both
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playback and capture volume. The default value is :const:`PCM_PLAYBACK`
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if the mixer has playback channels, otherwise it is :const:`PCM_CAPTURE`.
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The optional *units* argument can be one of :const:`VOLUME_UNITS_PERCENTAGE`,
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:const:`VOLUME_UNITS_RAW`, or :const:`VOLUME_UNITS_DB`.
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.. method:: Mixer.getrec()
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Return a list indicating the current record mute setting for each channel. 0
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means not recording, 1 means recording.
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This method will fail if the mixer has no capture switch capabilities.
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.. method:: Mixer.getvolume(pcmtype=PCM_PLAYBACK)
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.. method:: Mixer.getvolume(pcmtype=PCM_PLAYBACK, units=VOLUME_UNITS_PERCENTAGE)
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Returns a list with the current volume settings for each channel. The list
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elements are integer percentages.
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elements are integers whose meaning is determined by the *units* argument.
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The optional *pcmtype* argument can be either :const:`PCM_PLAYBACK` or
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:const:`PCM_CAPTURE`, which is relevant if the mixer can control both
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playback and capture volume. The default value is :const:`PCM_PLAYBACK`
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if the mixer has playback channels, otherwise it is :const:`PCM_CAPTURE`.
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The optional *units* argument can be one of :const:`VOLUME_UNITS_PERCENTAGE`,
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:const:`VOLUME_UNITS_RAW`, or :const:`VOLUME_UNITS_DB`.
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.. method:: Mixer.setvolume(volume, channel=None, pcmtype=PCM_PLAYBACK)
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.. method:: Mixer.setvolume(volume, channel=None, pcmtype=PCM_PLAYBACK, units=VOLUME_UNITS_PERCENTAGE)
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Change the current volume settings for this mixer. The *volume* argument
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controls the new volume setting as an integer percentage.
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is an integer whose meaning is determined by the *units* argument.
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If the optional argument *channel* is present, the volume is set
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only for this channel. This assumes that the mixer can control the
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@@ -509,6 +617,16 @@ Mixer objects have the following methods:
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playback and capture volume. The default value is :const:`PCM_PLAYBACK`
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if the mixer has playback channels, otherwise it is :const:`PCM_CAPTURE`.
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The optional *units* argument can be one of :const:`VOLUME_UNITS_PERCENTAGE`,
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:const:`VOLUME_UNITS_RAW`, or :const:`VOLUME_UNITS_DB`.
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.. method:: Mixer.getmute()
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Return a list indicating the current mute setting for each channel.
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0 means not muted, 1 means muted.
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This method will fail if the mixer has no playback switch capabilities.
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.. method:: Mixer.setmute(mute, [channel])
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Sets the mute flag to a new value. The *mute* argument is either 0 for not
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@@ -519,6 +637,12 @@ Mixer objects have the following methods:
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This method will fail if the mixer has no playback mute capabilities
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.. method:: Mixer.getrec()
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Return a list indicating the current record mute setting for each channel.
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0 means not recording, 1 means recording.
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This method will fail if the mixer has no capture switch capabilities.
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.. method:: Mixer.setrec(capture, [channel])
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@@ -532,20 +656,22 @@ Mixer objects have the following methods:
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.. method:: Mixer.polldescriptors()
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Returns a tuple of *(file descriptor, eventmask)* that can be used to
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wait for changes on the mixer with *select.poll*.
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Returns a list of tuples of *(file descriptor, eventmask)* that can be
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used to wait for changes on the mixer with *select.poll*.
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The *eventmask* value is compatible with `poll.register`__ in the Python
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:const:`select` module.
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__ poll_objects_
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.. method:: Mixer.handleevents()
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Acknowledge events on the *polldescriptors* file descriptors
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Acknowledge events on the :func:`polldescriptors` file descriptors
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to prevent subsequent polls from returning the same events again.
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Returns the number of events that were acknowledged.
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.. method:: Mixer.close()
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Closes the Mixer device.
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**A rant on the ALSA Mixer API**
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The ALSA mixer API is extremely complicated - and hardly documented at all.
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@@ -568,8 +694,6 @@ Unfortunately, I'm not able to create such a HOWTO myself, since I only
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understand half of the API, and that which I do understand has come from a
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painful trial and error process.
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.. % ==== 4. ====
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.. _pcm-example:
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@@ -611,6 +735,7 @@ To test PCM playback (on your default soundcard), run::
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recordtest.py and playbacktest.py
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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**recordtest.py** and **playbacktest.py** will record and play a raw
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sound file in CD quality.
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@@ -680,9 +805,3 @@ argument::
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Capabilities: Playback Volume Playback Mute
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Channel 0 volume: 61%
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Channel 1 volume: 61%
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.. rubric:: Footnotes
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.. [#f1] ALSA also allows ``PCM_ASYNC``, but this is not supported yet.
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.. _poll_objects: http://docs.python.org/library/select.html#poll-objects
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