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+
+:mod:`ossaudiodev` --- Access to OSS-compatible audio devices
+=============================================================
+
+.. module:: ossaudiodev
+   :platform: Linux, FreeBSD
+   :synopsis: Access to OSS-compatible audio devices.
+
+
+.. versionadded:: 2.3
+
+This module allows you to access the OSS (Open Sound System) audio interface.
+OSS is available for a wide range of open-source and commercial Unices, and is
+the standard audio interface for Linux and recent versions of FreeBSD.
+
+.. % Things will get more complicated for future Linux versions, since
+.. % ALSA is in the standard kernel as of 2.5.x.  Presumably if you
+.. % use ALSA, you'll have to make sure its OSS compatibility layer
+.. % is active to use ossaudiodev, but you're gonna need it for the vast
+.. % majority of Linux audio apps anyways.
+.. % 
+.. % Sounds like things are also complicated for other BSDs.  In response
+.. % to my python-dev query, Thomas Wouters said:
+.. % 
+.. % > Likewise, googling shows OpenBSD also uses OSS/Free -- the commercial
+.. % > OSS installation manual tells you to remove references to OSS/Free from the
+.. % > kernel :)
+.. % 
+.. % but Aleksander Piotrowsk actually has an OpenBSD box, and he quotes
+.. % from its <soundcard.h>:
+.. % >  * WARNING!  WARNING!
+.. % >  * This is an OSS (Linux) audio emulator.
+.. % >  * Use the Native NetBSD API for developing new code, and this
+.. % >  * only for compiling Linux programs.
+.. % 
+.. % There's also an ossaudio manpage on OpenBSD that explains things
+.. % further.  Presumably NetBSD and OpenBSD have a different standard
+.. % audio interface.  That's the great thing about standards, there are so
+.. % many to choose from ... ;-)
+.. % 
+.. % This probably all warrants a footnote or two, but I don't understand
+.. % things well enough right now to write it!   --GPW
+
+
+.. seealso::
+
+   `Open Sound System Programmer's Guide <http://www.opensound.com/pguide/oss.pdf>`_
+      the official documentation for the OSS C API
+
+   The module defines a large number of constants supplied by the OSS device
+   driver; see ``<sys/soundcard.h>`` on either Linux or FreeBSD for a listing .
+
+:mod:`ossaudiodev` defines the following variables and functions:
+
+
+.. exception:: OSSAudioError
+
+   This exception is raised on certain errors.  The argument is a string describing
+   what went wrong.
+
+   (If :mod:`ossaudiodev` receives an error from a system call such as
+   :cfunc:`open`, :cfunc:`write`, or :cfunc:`ioctl`, it raises :exc:`IOError`.
+   Errors detected directly by :mod:`ossaudiodev` result in :exc:`OSSAudioError`.)
+
+   (For backwards compatibility, the exception class is also available as
+   ``ossaudiodev.error``.)
+
+
+.. function:: open([device, ]mode)
+
+   Open an audio device and return an OSS audio device object.  This object
+   supports many file-like methods, such as :meth:`read`, :meth:`write`, and
+   :meth:`fileno` (although there are subtle differences between conventional Unix
+   read/write semantics and those of OSS audio devices).  It also supports a number
+   of audio-specific methods; see below for the complete list of methods.
+
+   *device* is the audio device filename to use.  If it is not specified, this
+   module first looks in the environment variable :envvar:`AUDIODEV` for a device
+   to use.  If not found, it falls back to :file:`/dev/dsp`.
+
+   *mode* is one of ``'r'`` for read-only (record) access, ``'w'`` for
+   write-only (playback) access and ``'rw'`` for both. Since many sound cards
+   only allow one process to have the recorder or player open at a time, it is a
+   good idea to open the device only for the activity needed.  Further, some
+   sound cards are half-duplex: they can be opened for reading or writing, but
+   not both at once.
+
+   Note the unusual calling syntax: the *first* argument is optional, and the
+   second is required.  This is a historical artifact for compatibility with the
+   older :mod:`linuxaudiodev` module which :mod:`ossaudiodev` supersedes.
+
+   .. % XXX it might also be motivated
+   .. % by my unfounded-but-still-possibly-true belief that the default
+   .. % audio device varies unpredictably across operating systems.  -GW
+
+
+.. function:: openmixer([device])
+
+   Open a mixer device and return an OSS mixer device object.   *device* is the
+   mixer device filename to use.  If it is not specified, this module first looks
+   in the environment variable :envvar:`MIXERDEV` for a device to use.  If not
+   found, it falls back to :file:`/dev/mixer`.
+
+
+.. _ossaudio-device-objects:
+
+Audio Device Objects
+--------------------
+
+Before you can write to or read from an audio device, you must call three
+methods in the correct order:
+
+#. :meth:`setfmt` to set the output format
+
+#. :meth:`channels` to set the number of channels
+
+#. :meth:`speed` to set the sample rate
+
+Alternately, you can use the :meth:`setparameters` method to set all three audio
+parameters at once.  This is more convenient, but may not be as flexible in all
+cases.
+
+The audio device objects returned by :func:`open` define the following methods
+and (read-only) attributes:
+
+
+.. method:: oss_audio_device.close()
+
+   Explicitly close the audio device.  When you are done writing to or reading from
+   an audio device, you should explicitly close it.  A closed device cannot be used
+   again.
+
+
+.. method:: oss_audio_device.fileno()
+
+   Return the file descriptor associated with the device.
+
+
+.. method:: oss_audio_device.read(size)
+
+   Read *size* bytes from the audio input and return them as a Python string.
+   Unlike most Unix device drivers, OSS audio devices in blocking mode (the
+   default) will block :func:`read` until the entire requested amount of data is
+   available.
+
+
+.. method:: oss_audio_device.write(data)
+
+   Write the Python string *data* to the audio device and return the number of
+   bytes written.  If the audio device is in blocking mode (the default), the
+   entire string is always written (again, this is different from usual Unix device
+   semantics).  If the device is in non-blocking mode, some data may not be written
+   ---see :meth:`writeall`.
+
+
+.. method:: oss_audio_device.writeall(data)
+
+   Write the entire Python string *data* to the audio device: waits until the audio
+   device is able to accept data, writes as much data as it will accept, and
+   repeats until *data* has been completely written. If the device is in blocking
+   mode (the default), this has the same effect as :meth:`write`; :meth:`writeall`
+   is only useful in non-blocking mode.  Has no return value, since the amount of
+   data written is always equal to the amount of data supplied.
+
+The following methods each map to exactly one :func:`ioctl` system call.  The
+correspondence is obvious: for example, :meth:`setfmt` corresponds to the
+``SNDCTL_DSP_SETFMT`` ioctl, and :meth:`sync` to ``SNDCTL_DSP_SYNC`` (this can
+be useful when consulting the OSS documentation).  If the underlying
+:func:`ioctl` fails, they all raise :exc:`IOError`.
+
+
+.. method:: oss_audio_device.nonblock()
+
+   Put the device into non-blocking mode.  Once in non-blocking mode, there is no
+   way to return it to blocking mode.
+
+
+.. method:: oss_audio_device.getfmts()
+
+   Return a bitmask of the audio output formats supported by the soundcard.  Some
+   of the formats supported by OSS are:
+
+   +-------------------------+---------------------------------------------+
+   | Format                  | Description                                 |
+   +=========================+=============================================+
+   | :const:`AFMT_MU_LAW`    | a logarithmic encoding (used by Sun ``.au`` |
+   |                         | files and :file:`/dev/audio`)               |
+   +-------------------------+---------------------------------------------+
+   | :const:`AFMT_A_LAW`     | a logarithmic encoding                      |
+   +-------------------------+---------------------------------------------+
+   | :const:`AFMT_IMA_ADPCM` | a 4:1 compressed format defined by the      |
+   |                         | Interactive Multimedia Association          |
+   +-------------------------+---------------------------------------------+
+   | :const:`AFMT_U8`        | Unsigned, 8-bit audio                       |
+   +-------------------------+---------------------------------------------+
+   | :const:`AFMT_S16_LE`    | Signed, 16-bit audio, little-endian byte    |
+   |                         | order (as used by Intel processors)         |
+   +-------------------------+---------------------------------------------+
+   | :const:`AFMT_S16_BE`    | Signed, 16-bit audio, big-endian byte order |
+   |                         | (as used by 68k, PowerPC, Sparc)            |
+   +-------------------------+---------------------------------------------+
+   | :const:`AFMT_S8`        | Signed, 8 bit audio                         |
+   +-------------------------+---------------------------------------------+
+   | :const:`AFMT_U16_LE`    | Unsigned, 16-bit little-endian audio        |
+   +-------------------------+---------------------------------------------+
+   | :const:`AFMT_U16_BE`    | Unsigned, 16-bit big-endian audio           |
+   +-------------------------+---------------------------------------------+
+
+   Consult the OSS documentation for a full list of audio formats, and note that
+   most devices support only a subset of these formats.  Some older devices only
+   support :const:`AFMT_U8`; the most common format used today is
+   :const:`AFMT_S16_LE`.
+
+
+.. method:: oss_audio_device.setfmt(format)
+
+   Try to set the current audio format to *format*---see :meth:`getfmts` for a
+   list.  Returns the audio format that the device was set to, which may not be the
+   requested format.  May also be used to return the current audio format---do this
+   by passing an "audio format" of :const:`AFMT_QUERY`.
+
+
+.. method:: oss_audio_device.channels(nchannels)
+
+   Set the number of output channels to *nchannels*.  A value of 1 indicates
+   monophonic sound, 2 stereophonic.  Some devices may have more than 2 channels,
+   and some high-end devices may not support mono. Returns the number of channels
+   the device was set to.
+
+
+.. method:: oss_audio_device.speed(samplerate)
+
+   Try to set the audio sampling rate to *samplerate* samples per second.  Returns
+   the rate actually set.  Most sound devices don't support arbitrary sampling
+   rates.  Common rates are:
+
+   +-------+-------------------------------------------+
+   | Rate  | Description                               |
+   +=======+===========================================+
+   | 8000  | default rate for :file:`/dev/audio`       |
+   +-------+-------------------------------------------+
+   | 11025 | speech recording                          |
+   +-------+-------------------------------------------+
+   | 22050 |                                           |
+   +-------+-------------------------------------------+
+   | 44100 | CD quality audio (at 16 bits/sample and 2 |
+   |       | channels)                                 |
+   +-------+-------------------------------------------+
+   | 96000 | DVD quality audio (at 24 bits/sample)     |
+   +-------+-------------------------------------------+
+
+
+.. method:: oss_audio_device.sync()
+
+   Wait until the sound device has played every byte in its buffer.  (This happens
+   implicitly when the device is closed.)  The OSS documentation recommends closing
+   and re-opening the device rather than using :meth:`sync`.
+
+
+.. method:: oss_audio_device.reset()
+
+   Immediately stop playing or recording and return the device to a state where it
+   can accept commands.  The OSS documentation recommends closing and re-opening
+   the device after calling :meth:`reset`.
+
+
+.. method:: oss_audio_device.post()
+
+   Tell the driver that there is likely to be a pause in the output, making it
+   possible for the device to handle the pause more intelligently.  You might use
+   this after playing a spot sound effect, before waiting for user input, or before
+   doing disk I/O.
+
+The following convenience methods combine several ioctls, or one ioctl and some
+simple calculations.
+
+
+.. method:: oss_audio_device.setparameters(format, nchannels, samplerate [, strict=False])
+
+   Set the key audio sampling parameters---sample format, number of channels, and
+   sampling rate---in one method call.  *format*,  *nchannels*, and *samplerate*
+   should be as specified in the :meth:`setfmt`, :meth:`channels`, and
+   :meth:`speed`  methods.  If *strict* is true, :meth:`setparameters` checks to
+   see if each parameter was actually set to the requested value, and raises
+   :exc:`OSSAudioError` if not.  Returns a tuple (*format*, *nchannels*,
+   *samplerate*) indicating the parameter values that were actually set by the
+   device driver (i.e., the same as the return values of :meth:`setfmt`,
+   :meth:`channels`, and :meth:`speed`).
+
+   For example,  ::
+
+      (fmt, channels, rate) = dsp.setparameters(fmt, channels, rate)
+
+   is equivalent to  ::
+
+      fmt = dsp.setfmt(fmt)
+      channels = dsp.channels(channels)
+      rate = dsp.rate(channels)
+
+
+.. method:: oss_audio_device.bufsize()
+
+   Returns the size of the hardware buffer, in samples.
+
+
+.. method:: oss_audio_device.obufcount()
+
+   Returns the number of samples that are in the hardware buffer yet to be played.
+
+
+.. method:: oss_audio_device.obuffree()
+
+   Returns the number of samples that could be queued into the hardware buffer to
+   be played without blocking.
+
+Audio device objects also support several read-only attributes:
+
+
+.. attribute:: oss_audio_device.closed
+
+   Boolean indicating whether the device has been closed.
+
+
+.. attribute:: oss_audio_device.name
+
+   String containing the name of the device file.
+
+
+.. attribute:: oss_audio_device.mode
+
+   The I/O mode for the file, either ``"r"``, ``"rw"``, or ``"w"``.
+
+
+.. _mixer-device-objects:
+
+Mixer Device Objects
+--------------------
+
+The mixer object provides two file-like methods:
+
+
+.. method:: oss_mixer_device.close()
+
+   This method closes the open mixer device file.  Any further attempts to use the
+   mixer after this file is closed will raise an :exc:`IOError`.
+
+
+.. method:: oss_mixer_device.fileno()
+
+   Returns the file handle number of the open mixer device file.
+
+The remaining methods are specific to audio mixing:
+
+
+.. method:: oss_mixer_device.controls()
+
+   This method returns a bitmask specifying the available mixer controls ("Control"
+   being a specific mixable "channel", such as :const:`SOUND_MIXER_PCM` or
+   :const:`SOUND_MIXER_SYNTH`).  This bitmask indicates a subset of all available
+   mixer controls---the :const:`SOUND_MIXER_\*` constants defined at module level.
+   To determine if, for example, the current mixer object supports a PCM mixer, use
+   the following Python code::
+
+      mixer=ossaudiodev.openmixer()
+      if mixer.controls() & (1 << ossaudiodev.SOUND_MIXER_PCM):
+          # PCM is supported
+          ... code ...
+
+   For most purposes, the :const:`SOUND_MIXER_VOLUME` (master volume) and
+   :const:`SOUND_MIXER_PCM` controls should suffice---but code that uses the mixer
+   should be flexible when it comes to choosing mixer controls.  On the Gravis
+   Ultrasound, for example, :const:`SOUND_MIXER_VOLUME` does not exist.
+
+
+.. method:: oss_mixer_device.stereocontrols()
+
+   Returns a bitmask indicating stereo mixer controls.  If a bit is set, the
+   corresponding control is stereo; if it is unset, the control is either
+   monophonic or not supported by the mixer (use in combination with
+   :meth:`controls` to determine which).
+
+   See the code example for the :meth:`controls` function for an example of getting
+   data from a bitmask.
+
+
+.. method:: oss_mixer_device.reccontrols()
+
+   Returns a bitmask specifying the mixer controls that may be used to record.  See
+   the code example for :meth:`controls` for an example of reading from a bitmask.
+
+
+.. method:: oss_mixer_device.get(control)
+
+   Returns the volume of a given mixer control.  The returned volume is a 2-tuple
+   ``(left_volume,right_volume)``.  Volumes are specified as numbers from 0
+   (silent) to 100 (full volume).  If the control is monophonic, a 2-tuple is still
+   returned, but both volumes are the same.
+
+   Raises :exc:`OSSAudioError` if an invalid control was is specified, or
+   :exc:`IOError` if an unsupported control is specified.
+
+
+.. method:: oss_mixer_device.set(control, (left, right))
+
+   Sets the volume for a given mixer control to ``(left,right)``. ``left`` and
+   ``right`` must be ints and between 0 (silent) and 100 (full volume).  On
+   success, the new volume is returned as a 2-tuple. Note that this may not be
+   exactly the same as the volume specified, because of the limited resolution of
+   some soundcard's mixers.
+
+   Raises :exc:`OSSAudioError` if an invalid mixer control was specified, or if the
+   specified volumes were out-of-range.
+
+
+.. method:: oss_mixer_device.get_recsrc()
+
+   This method returns a bitmask indicating which control(s) are currently being
+   used as a recording source.
+
+
+.. method:: oss_mixer_device.set_recsrc(bitmask)
+
+   Call this function to specify a recording source.  Returns a bitmask indicating
+   the new recording source (or sources) if successful; raises :exc:`IOError` if an
+   invalid source was specified.  To set the current recording source to the
+   microphone input::
+
+      mixer.setrecsrc (1 << ossaudiodev.SOUND_MIXER_MIC)
+