forked from auracaster/pyalsaaudio
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items. Argument parsing errors are reported with the methodname (minor improvement). Smallish documentation improvements. git-svn-id: svn://svn.code.sf.net/p/pyalsaaudio/code/trunk@23 ec2f30ec-7544-0410-870e-f70ca00c83f0
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<h2><a name="SECTION002430000000000000000"></a>
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<a name="mixer-objects"></a>
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<br>
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4.3 Mixer Objects
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</h2>
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<p>
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Mixer objects provides access to the ALSA mixer API.
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><span class="typelabel">class</span> <tt id='l2h-17' xml:id='l2h-17' class="class">Mixer</tt></b>(</nobr></td>
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<td><var></var><big>[</big><var>control</var><big>]</big><var>, </var><big>[</big><var>id</var><big>]</big><var>,
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</var><big>[</big><var>cardname</var><big>]</big><var></var>)</td></tr></table></dt>
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<dd>
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<var>control</var> - specifies which control to manipulate using this
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mixer object. The list of available controls can be found with the
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<tt class="module">alsaaudio</tt>.<tt class="function">mixers</tt> function. The default value is
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'Master' - other common controls include 'Master Mono', 'PCM',
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'Line', etc.
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<p>
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<var>id</var> - the id of the mixer control. Default is 0
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<p>
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<var>cardname</var> - specifies which card should be used (this is only
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relevant if you have more than one sound card). Omit to use the
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default sound card
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</dl>
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<p>
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Mixer objects have the following methods:
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-18' xml:id='l2h-18' class="method">cardname</tt></b>(</nobr></td>
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<td><var></var>)</td></tr></table></dt>
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<dd>
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Return the name of the sound card used by this Mixer object
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-19' xml:id='l2h-19' class="method">mixer</tt></b>(</nobr></td>
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<td><var></var>)</td></tr></table></dt>
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<dd>
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Return the name of the specific mixer controlled by this object, For
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example 'Master' or 'PCM'
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-20' xml:id='l2h-20' class="method">mixerid</tt></b>(</nobr></td>
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<td><var></var>)</td></tr></table></dt>
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<dd>
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Return the ID of the ALSA mixer controlled by this object.
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-21' xml:id='l2h-21' class="method">switchcap</tt></b>(</nobr></td>
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<td><var></var>)</td></tr></table></dt>
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<dd>
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Returns a list of the switches which are defined by this specific
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mixer. Possible values in this list are:
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<p>
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<div class="center"><table class="realtable">
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<thead>
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<tr>
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<th class="left" >Switch</th>
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<th class="left" >Description</th>
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</tr>
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</thead>
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<tbody>
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<tr><td class="left" valign="baseline"><volume capabilities>'Mute'</volume></td>
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<td class="left" >This mixer can be muted</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Joined Mute'</volume></td>
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<td class="left" >This mixer can mute all channels at the same time</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Playback Mute'</volume></td>
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<td class="left" >This mixer can mute the playback output</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Joined Playback Mute'</volume></td>
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<td class="left" >Mute playback for all channels at the same time</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Capture Mute'</volume></td>
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<td class="left" >Mute sound capture</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Joined Capture Mute'</volume></td>
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<td class="left" >Mute sound capture for all channels at a time</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Capture Exclusive'</volume></td>
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<td class="left" >Not quite sure what this is</td></tr></tbody>
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</table></div>
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<p>
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To manipulate these swithes use the <tt class="method">setrec</tt> or
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<tt class="method">setmute</tt> methods
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-22' xml:id='l2h-22' class="method">volumecap</tt></b>(</nobr></td>
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<td><var></var>)</td></tr></table></dt>
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<dd>
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Returns a list of the volume control capabilities of this mixer.
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Possible values in the list are:
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<p>
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<div class="center"><table class="realtable">
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<thead>
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<tr>
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<th class="left" >Capability</th>
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<th class="left" >Description</th>
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</tr>
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</thead>
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<tbody>
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<tr><td class="left" valign="baseline"><volume capabilities>'Volume'</volume></td>
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<td class="left" >This mixer can control volume</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Joined Volume'</volume></td>
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<td class="left" >This mixer can control volume for all channels at
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the same time</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Playback Volume'</volume></td>
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<td class="left" >This mixer can manipulate the playback volume</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Joined Playback Volume'</volume></td>
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<td class="left" >Manipulate playback volumne for all
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channels at the same time</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Capture Volume'</volume></td>
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<td class="left" >Manipulate sound capture volume</td></tr>
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<tr><td class="left" valign="baseline"><volume capabilities>'Joined Capture Volume'</volume></td>
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<td class="left" >Manipulate sound capture volume for all
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channels at a time</td></tr></tbody>
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</table></div>
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<p>
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-23' xml:id='l2h-23' class="method">getenum</tt></b>(</nobr></td>
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<td><var></var>)</td></tr></table></dt>
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<dd>
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For enumerated controls, return the currently selected item and
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the list of items available.
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<p>
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Returns a tuple <i>(string, list of strings)</i>.
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<p>
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For example, my soundcard has a Mixer called <i>Mono Output Select</i>.
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Using <i>amixer</i>, I get:
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<p>
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<div class="verbatim"><pre>
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$ amixer get "Mono Output Select"
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Simple mixer control 'Mono Output Select',0
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Capabilities: enum
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Items: 'Mix' 'Mic'
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Item0: 'Mix'
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</pre></div>
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<p>
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Using <tt class="module">alsaaudio</tt>, one could do:
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<div class="verbatim"><pre>
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>>> import alsaaudio
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>>> m = alsaaudio.Mixer('Mono Output Select')
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>>> m.getenum()
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('Mix', ['Mix', 'Mic'])
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</pre></div>
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<p>
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This method will return an empty tuple if the mixer is not an
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enumerated control.
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-24' xml:id='l2h-24' class="method">getmute</tt></b>(</nobr></td>
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<td><var></var>)</td></tr></table></dt>
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<dd>
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Return a list indicating the current mute setting for each channel.
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0 means not muted, 1 means muted.
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<p>
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This method will fail if the mixer has no playback switch
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capabilities.
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-25' xml:id='l2h-25' class="method">getrange</tt></b>(</nobr></td>
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<td><var></var><big>[</big><var>direction</var><big>]</big><var></var>)</td></tr></table></dt>
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<dd>
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Return the volume range of the ALSA mixer controlled by this object.
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<p>
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The optional <var>direction</var> argument can be either 'playback' or
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'capture', which is relevant if the mixer can control both playback
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and capture volume. The default value is 'playback' if the mixer
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has this capability, otherwise 'capture'
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<p>
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-26' xml:id='l2h-26' class="method">getrec</tt></b>(</nobr></td>
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<td><var></var>)</td></tr></table></dt>
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<dd>
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Return a list indicating the current record mute setting for each
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channel. 0 means not recording, 1 means recording.
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<p>
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This method will fail if the mixer has no capture switch
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capabilities.
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-27' xml:id='l2h-27' class="method">getvolume</tt></b>(</nobr></td>
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<td><var></var><big>[</big><var>direction</var><big>]</big><var></var>)</td></tr></table></dt>
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<dd>
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Returns a list with the current volume settings for each channel.
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The list elements are integer percentages.
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<p>
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The optional <var>direction</var> argument can be either 'playback' or
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'capture', which is relevant if the mixer can control both playback
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and capture volume. The default value is 'playback' if the mixer has
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this capability, otherwise 'capture'
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<p>
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-28' xml:id='l2h-28' class="method">setvolume</tt></b>(</nobr></td>
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<td><var>volume,</var><big>[</big><var>channel</var><big>]</big><var>,
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</var><big>[</big><var>direction</var><big>]</big><var></var>)</td></tr></table></dt>
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<dd>
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<p>
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Change the current volume settings for this mixer. The <var>volume</var>
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argument controls the new volume setting as an integer percentage.
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<p>
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If the optional argument <var>channel</var> is present, the volume is set
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only for this channel. This assumes that the mixer can control the
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volume for the channels independently.
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<p>
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The optional <var>direction</var> argument can be either 'playback' or
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'capture' is relevant if the mixer has independent playback and
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capture volume capabilities, and controls which of the volumes if
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changed. The default is 'playback' if the mixer has this capability,
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otherwise 'capture'.
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-29' xml:id='l2h-29' class="method">setmute</tt></b>(</nobr></td>
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<td><var>mute, </var><big>[</big><var>channel</var><big>]</big><var></var>)</td></tr></table></dt>
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<dd>
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Sets the mute flag to a new value. The <var>mute</var> argument is either
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0 for not muted, or 1 for muted.
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<p>
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The optional <var>channel</var> argument controls which channel is muted.
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The default is to set the mute flag for all channels.
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<p>
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This method will fail if the mixer has no playback mute capabilities
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</dl>
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<p>
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<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
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<td><nobr><b><tt id='l2h-30' xml:id='l2h-30' class="method">setrec</tt></b>(</nobr></td>
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<td><var>capture,</var><big>[</big><var>channel</var><big>]</big><var></var>)</td></tr></table></dt>
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<dd>
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Sets the capture mute flag to a new value. The <var>capture</var>
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argument is either 0 for no capture, or 1 for capture.
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<p>
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The optional <var>channel</var> argument controls which channel is
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changed. The default is to set the capture flag for all channels.
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<p>
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This method will fail if the mixer has no capture switch
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capabilities.
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</dl>
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<p>
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<b>A Note on the ALSA Mixer API</b>
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<p>
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The ALSA mixer API is extremely complicated - and hardly documented at
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all. <tt class="module">alsaaudio</tt> implements a much simplified way to access
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this API. In designing the API I've had to make some choices which may
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limit what can and cannot be controlled through the API. However, If I
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had chosen to implement the full API, I would have reexposed the
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horrible complexity/documentation ratio of the underlying API. At
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least the <tt class="module">alsaaudio</tt> API is easy to understand and use.
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<p>
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If my design choises prevents you from doing something that the
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underlying API would have allowed, please let me know, so I can
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incorporate these need into future versions.
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<p>
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If the current state of affairs annoy you, the best you can do is to
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write a HOWTO on the API and make this available on the net. Until
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somebody does this, the availability of ALSA mixer capable devices
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will stay quite limited.
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<p>
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Unfortunately, I'm not able to create such a HOWTO myself, since I
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only understand half of the API, and that which I do understand has
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come from a painful trial and error process.
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<p>
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<a class="sectref" rel="next" href="pcm-example.html">4.4 ALSA Examples</a>
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<span class="release-info">Release 0.4.</span>
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