mirror of https://github.com/python/cpython
436 lines
17 KiB
ReStructuredText
436 lines
17 KiB
ReStructuredText
:mod:`ossaudiodev` --- Access to OSS-compatible audio devices
|
|
=============================================================
|
|
|
|
.. module:: ossaudiodev
|
|
:platform: Linux, FreeBSD
|
|
:synopsis: Access to OSS-compatible audio devices.
|
|
|
|
|
|
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 anyway.
|
|
|
|
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
|
|
:c:func:`open`, :c:func:`write`, or :c:func:`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.
|
|
|
|
.. versionchanged:: 3.2
|
|
Audio device objects also support the context manager protocol, i.e. they can
|
|
be used in a :keyword:`with` statement.
|
|
|
|
|
|
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.
|
|
|
|
.. versionchanged:: 3.2
|
|
Mixer objects also support the context manager protocol.
|
|
|
|
|
|
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)
|
|
|