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<title>14.11 ossaudiodev -- Access to OSS-compatible audio devices</title>
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<H1><A NAME="SECTION00161100000000000000000">
14.11 <tt class="module">ossaudiodev</tt> --
Access to OSS-compatible audio devices</A>
</H1>
<P>
<A NAME="module-ossaudiodev"></A>
<p class="availability">Availability: <span
class="platform">Linux, FreeBSD</span>.</p>
<P>
<span class="versionnote">New in version 2.3.</span>
<P>
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.
<P>
<div class="seealso">
<p class="heading">See Also:</p>
<dl compact="compact" class="seetitle">
<dt><em class="citetitle"><a href="http://www.opensound.com/pguide/oss.pdf"
>Open Sound System Programmer's Guide</a></em></dt>
<dd>the official
documentation for the OSS C API</dd>
</dl>
<div class="seetext"><p>The module defines a large number of constants supplied by
the OSS device driver; see <code><sys/soundcard.h></code> on either
Linux or FreeBSD for a listing .</p></div>
</div>
<P>
<tt class="module">ossaudiodev</tt> defines the following variables and functions:
<P>
<dl><dt><b><span class="typelabel">exception</span> <tt id='l2h-4770' xml:id='l2h-4770' class="exception">OSSAudioError</tt></b></dt>
<dd>
This exception is raised on certain errors. The argument is a string
describing what went wrong.
<P>
(If <tt class="module">ossaudiodev</tt> receives an error from a system call such as
<tt class="cfunction">open()</tt>, <tt class="cfunction">write()</tt>, or <tt class="cfunction">ioctl()</tt>, it
raises <tt class="exception">IOError</tt>. Errors detected directly by
<tt class="module">ossaudiodev</tt> result in <tt class="exception">OSSAudioError</tt>.)
<P>
(For backwards compatibility, the exception class is also available as
<code>ossaudiodev.error</code>.)
</dd></dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4771' xml:id='l2h-4771' class="function">open</tt></b>(</nobr></td>
<td><var></var><big>[</big><var>device, </var><big>]</big><var>mode</var>)</td></tr></table></dt>
<dd>
Open an audio device and return an OSS audio device object. This
object supports many file-like methods, such as <tt class="method">read()</tt>,
<tt class="method">write()</tt>, and <tt class="method">fileno()</tt> (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.
<P>
<var>device</var> is the audio device filename to use. If it is not
specified, this module first looks in the environment variable
<a class="envvar" id='l2h-4773' xml:id='l2h-4773'>AUDIODEV</a> for a device to use. If not found, it falls back to
<span class="file">/dev/dsp</span>.
<P>
<var>mode</var> is one of <code>'r'</code> for read-only (record) access,
<code>'w'</code> for write-only (playback) access and <code>'rw'</code> 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.
<P>
Note the unusual calling syntax: the <em>first</em> argument is optional,
and the second is required. This is a historical artifact for
compatibility with the older <tt class="module">linuxaudiodev</tt> module which
<tt class="module">ossaudiodev</tt> supersedes. </dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4772' xml:id='l2h-4772' class="function">openmixer</tt></b>(</nobr></td>
<td><var></var><big>[</big><var>device</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
Open a mixer device and return an OSS mixer device object.
<var>device</var> is the mixer device filename to use. If it is
not specified, this module first looks in the environment variable
<a class="envvar" id='l2h-4774' xml:id='l2h-4774'>MIXERDEV</a> for a device to use. If not found, it falls back to
<span class="file">/dev/mixer</span>.
<P>
</dl>
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<LI><A href="ossaudio-device-objects.html">14.11.1 Audio Device Objects</a>
<LI><A href="mixer-device-objects.html">14.11.2 Mixer Device Objects</a>
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<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
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