cpython/Doc/lib/libsunaudio.tex

\section{\module{sunaudiodev} ---
         Access to Sun audio hardware.}
\declaremodule{builtin}{sunaudiodev}

\modulesynopsis{Access to Sun audio hardware.}


This module allows you to access the Sun audio interface. The Sun
audio hardware is capable of recording and playing back audio data
in u-LAW\index{u-LAW} format with a sample rate of 8K per second. A
full description can be found in the \manpage{audio}{7I} manual page.

The module defines the following variables and functions:

\begin{excdesc}{error}
This exception is raised on all errors. The argument is a string
describing what went wrong.
\end{excdesc}

\begin{funcdesc}{open}{mode}
This function opens the audio device and returns a Sun audio device
object. This object can then be used to do I/O on. The \var{mode} parameter
is one of \code{'r'} for record-only access, \code{'w'} for play-only
access, \code{'rw'} for both and \code{'control'} for access to the
control device. Since only one process is allowed to have the recorder
or player open at the same time it is a good idea to open the device
only for the activity needed. See \manpage{audio}{7I} for details.

As per the manpage, this module first looks in the environment
variable \code{AUDIODEV} for the base audio device filename.  If not
found, it falls back to \file{/dev/audio}.  The control device is
calculated by appending ``ctl'' to the base audio device.
\end{funcdesc}


\subsection{Audio Device Objects}
\label{audio-device-objects}

The audio device objects are returned by \function{open()} define the
following methods (except \code{control} objects which only provide
\method{getinfo()}, \method{setinfo()}, \method{fileno()}, and
\method{drain()}):

\begin{methoddesc}[audio device]{close}{}
This method explicitly closes the device. It is useful in situations
where deleting the object does not immediately close it since there
are other references to it. A closed device should not be used again.
\end{methoddesc}

\begin{methoddesc}[audio device]{fileno}{}
Returns the file descriptor associated with the device.  This can be
used to set up \code{SIGPOLL} notification, as described below.
\end{methoddesc}

\begin{methoddesc}[audio device]{drain}{}
This method waits until all pending output is processed and then returns.
Calling this method is often not necessary: destroying the object will
automatically close the audio device and this will do an implicit drain.
\end{methoddesc}

\begin{methoddesc}[audio device]{flush}{}
This method discards all pending output. It can be used avoid the
slow response to a user's stop request (due to buffering of up to one
second of sound).
\end{methoddesc}

\begin{methoddesc}[audio device]{getinfo}{}
This method retrieves status information like input and output volume,
etc. and returns it in the form of
an audio status object. This object has no methods but it contains a
number of attributes describing the current device status. The names
and meanings of the attributes are described in
\file{/usr/include/sun/audioio.h} and in the \manpage{audio}{7I}
manual page.  Member names
are slightly different from their \C{} counterparts: a status object is
only a single structure. Members of the \cdata{play} substructure have
\samp{o_} prepended to their name and members of the \cdata{record}
structure have \samp{i_}. So, the \C{} member \cdata{play.sample_rate} is
accessed as \member{o_sample_rate}, \cdata{record.gain} as \member{i_gain}
and \cdata{monitor_gain} plainly as \member{monitor_gain}.
\end{methoddesc}

\begin{methoddesc}[audio device]{ibufcount}{}
This method returns the number of samples that are buffered on the
recording side, i.e.\ the program will not block on a
\function{read()} call of so many samples.
\end{methoddesc}

\begin{methoddesc}[audio device]{obufcount}{}
This method returns the number of samples buffered on the playback
side. Unfortunately, this number cannot be used to determine a number
of samples that can be written without blocking since the kernel
output queue length seems to be variable.
\end{methoddesc}

\begin{methoddesc}[audio device]{read}{size}
This method reads \var{size} samples from the audio input and returns
them as a Python string. The function blocks until enough data is available.
\end{methoddesc}

\begin{methoddesc}[audio device]{setinfo}{status}
This method sets the audio device status parameters. The \var{status}
parameter is an device status object as returned by \function{getinfo()} and
possibly modified by the program.
\end{methoddesc}

\begin{methoddesc}[audio device]{write}{samples}
Write is passed a Python string containing audio samples to be played.
If there is enough buffer space free it will immediately return,
otherwise it will block.
\end{methoddesc}

There is a companion module,
\module{SUNAUDIODEV}\refstmodindex{SUNAUDIODEV}, which defines useful
symbolic constants like \constant{MIN_GAIN}, \constant{MAX_GAIN},
\constant{SPEAKER}, etc. The names of the constants are the same names
as used in the \C{} include file \code{<sun/audioio.h>}, with the
leading string \samp{AUDIO_} stripped.

The audio device supports asynchronous notification of various events,
through the SIGPOLL signal.  Here's an example of how you might enable 
this in Python:

\begin{verbatim}
def handle_sigpoll(signum, frame):
    print 'I got a SIGPOLL update'
pp
import fcntl, signal, STROPTS

signal.signal(signal.SIGPOLL, handle_sigpoll)
fcntl.ioctl(audio_obj.fileno(), STROPTS.I_SETSIG, STROPTS.S_MSG)
\end{verbatim}