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<title>14.11.2 Mixer Device Objects </title>
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<H2><A NAME="SECTION00161120000000000000000"></A><A NAME="mixer-device-objects"></A>
<BR>
14.11.2 Mixer Device Objects
</H2>
<P>
The mixer object provides two file-like methods:
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4792' xml:id='l2h-4792' class="method">close</tt></b>(</nobr></td>
<td><var></var>)</td></tr></table></dt>
<dd>
This method closes the open mixer device file. Any further attempts to
use the mixer after this file is closed will raise an IOError.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4793' xml:id='l2h-4793' class="method">fileno</tt></b>(</nobr></td>
<td><var></var>)</td></tr></table></dt>
<dd>
Returns the file handle number of the open mixer device file.
</dl>
<P>
The remaining methods are specific to audio mixing:
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4794' xml:id='l2h-4794' class="method">controls</tt></b>(</nobr></td>
<td><var></var>)</td></tr></table></dt>
<dd>
This method returns a bitmask specifying the available mixer controls
(``Control'' being a specific mixable ``channel'', such as
<tt class="constant">SOUND_MIXER_PCM</tt> or <tt class="constant">SOUND_MIXER_SYNTH</tt>). This
bitmask indicates a subset of all available mixer controls--the
<tt class="constant">SOUND_MIXER_*</tt> constants defined at module level. To determine if,
for example, the current mixer object supports a PCM mixer, use the
following Python code:
<P>
<div class="verbatim"><pre>
mixer=ossaudiodev.openmixer()
if mixer.controls() & (1 << ossaudiodev.SOUND_MIXER_PCM):
# PCM is supported
... code ...
</pre></div>
<P>
For most purposes, the <tt class="constant">SOUND_MIXER_VOLUME</tt> (master volume) and
<tt class="constant">SOUND_MIXER_PCM</tt> 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, <tt class="constant">SOUND_MIXER_VOLUME</tt> does not
exist.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4795' xml:id='l2h-4795' class="method">stereocontrols</tt></b>(</nobr></td>
<td><var></var>)</td></tr></table></dt>
<dd>
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
<tt class="method">controls()</tt> to determine which).
<P>
See the code example for the <tt class="method">controls()</tt> function for an example
of getting data from a bitmask.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4796' xml:id='l2h-4796' class="method">reccontrols</tt></b>(</nobr></td>
<td><var></var>)</td></tr></table></dt>
<dd>
Returns a bitmask specifying the mixer controls that may be used to
record. See the code example for <tt class="method">controls()</tt> for an example of
reading from a bitmask.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4797' xml:id='l2h-4797' class="method">get</tt></b>(</nobr></td>
<td><var>control</var>)</td></tr></table></dt>
<dd>
Returns the volume of a given mixer control. The returned volume is a
2-tuple <code>(left_volume,right_volume)</code>. 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.
<P>
Raises <tt class="exception">OSSAudioError</tt> if an invalid control was is specified,
or <tt class="exception">IOError</tt> if an unsupported control is specified.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4798' xml:id='l2h-4798' class="method">set</tt></b>(</nobr></td>
<td><var>control, (left, right)</var>)</td></tr></table></dt>
<dd>
Sets the volume for a given mixer control to <code>(left,right)</code>.
<code>left</code> and <code>right</code> 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.
<P>
Raises <tt class="exception">OSSAudioError</tt> if an invalid mixer control was
specified, or if the specified volumes were out-of-range.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4799' xml:id='l2h-4799' class="method">get_recsrc</tt></b>(</nobr></td>
<td><var></var>)</td></tr></table></dt>
<dd>
This method returns a bitmask indicating which control(s) are
currently being used as a recording source.
</dl>
<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
<td><nobr><b><tt id='l2h-4800' xml:id='l2h-4800' class="method">set_recsrc</tt></b>(</nobr></td>
<td><var>bitmask</var>)</td></tr></table></dt>
<dd>
Call this function to specify a recording source. Returns a bitmask
indicating the new recording source (or sources) if successful; raises
<tt class="exception">IOError</tt> if an invalid source was specified. To set the current
recording source to the microphone input:
<P>
<div class="verbatim"><pre>
mixer.setrecsrc (1 << ossaudiodev.SOUND_MIXER_MIC)
</pre></div>
</dl>
<P>
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<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
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