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  15 <div class="title">Probing Device Capabilities </div>  </div>
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  17 <div class="contents">
  18 <div class="textblock"><p>A programmer may wish to query the available audio device capabilities before deciding which to use. The following example outlines how this can be done.</p>
  19 <div class="fragment"><div class="line"><span class="comment">// audioprobe.cpp</span></div>
  20 <div class="line"></div>
  21 <div class="line"><span class="preprocessor">#include &lt;iostream&gt;</span></div>
  22 <div class="line"><span class="preprocessor">#include &quot;<a class="code" href="RtAudio_8h.html">RtAudio.h</a>&quot;</span></div>
  23 <div class="line"></div>
  24 <div class="line"><span class="keywordtype">int</span> main()</div>
  25 <div class="line">{</div>
  26 <div class="line">  <a class="code" href="classRtAudio.html" title="Realtime audio i/o C++ classes.">RtAudio</a> audio;</div>
  27 <div class="line"></div>
  28 <div class="line">  <span class="comment">// Determine the number of devices available</span></div>
  29 <div class="line">  <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> devices = audio.<a class="code" href="classRtAudio.html#a747ce2d73803641bbb66d6e78092aa1a" title="A public function that queries for the number of audio devices available.">getDeviceCount</a>();</div>
  30 <div class="line"></div>
  31 <div class="line">  <span class="comment">// Scan through devices for various capabilities</span></div>
  32 <div class="line">  <a class="code" href="structRtAudio_1_1DeviceInfo.html" title="The public device information structure for returning queried values.">RtAudio::DeviceInfo</a> info;</div>
  33 <div class="line">  <span class="keywordflow">for</span> ( <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> i=0; i&lt;=devices; i++ ) {</div>
  34 <div class="line"></div>
  35 <div class="line">    info = audio.<a class="code" href="classRtAudio.html#a02d7ff44ad1d7eae22283a052f3dfda8" title="Return an RtAudio::DeviceInfo structure for a specified device number.">getDeviceInfo</a>( i );</div>
  36 <div class="line"></div>
  37 <div class="line">    <span class="keywordflow">if</span> ( info.<a class="code" href="structRtAudio_1_1DeviceInfo.html#a97573717ccb1e75a834a0a108cd6982d">probed</a> == <span class="keyword">true</span> ) {</div>
  38 <div class="line">      <span class="comment">// Print, for example, the maximum number of output channels for each device</span></div>
  39 <div class="line">      std::cout &lt;&lt; <span class="stringliteral">&quot;device = &quot;</span> &lt;&lt; i;</div>
  40 <div class="line">      std::cout &lt;&lt; <span class="stringliteral">&quot;: maximum output channels = &quot;</span> &lt;&lt; info.<a class="code" href="structRtAudio_1_1DeviceInfo.html#a81aaf488f8158ef55b1bb678f66feb7d">outputChannels</a> &lt;&lt; <span class="stringliteral">&quot;\n&quot;</span>;</div>
  41 <div class="line">    }</div>
  42 <div class="line">  }</div>
  43 <div class="line"></div>
  44 <div class="line">  <span class="keywordflow">return</span> 0;</div>
  45 <div class="line">}</div>
  46 </div><!-- fragment --><p>The <a class="el" href="structRtAudio_1_1DeviceInfo.html" title="The public device information structure for returning queried values.">RtAudio::DeviceInfo</a> structure is defined in <a class="el" href="RtAudio_8h.html">RtAudio.h</a> and provides a variety of information useful in assessing the capabilities of a device:</p>
  47 <div class="fragment"><div class="line"><span class="keyword">typedef</span> <span class="keyword">struct </span><a class="code" href="structRtAudio_1_1DeviceInfo.html" title="The public device information structure for returning queried values.">RtAudio::DeviceInfo</a> {</div>
  48 <div class="line">  <span class="keywordtype">bool</span> <a class="code" href="structRtAudio_1_1DeviceInfo.html#a97573717ccb1e75a834a0a108cd6982d">probed</a>;                           <span class="comment">// true if the device capabilities were successfully probed.</span></div>
  49 <div class="line">  std::string <a class="code" href="structRtAudio_1_1DeviceInfo.html#a24df596ab8d54f2eb540c7cf16212b3b">name</a>;                      <span class="comment">// Character string device identifier.</span></div>
  50 <div class="line">  <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> <a class="code" href="structRtAudio_1_1DeviceInfo.html#a81aaf488f8158ef55b1bb678f66feb7d">outputChannels</a>;           <span class="comment">// Maximum output channels supported by device.</span></div>
  51 <div class="line">  <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> <a class="code" href="structRtAudio_1_1DeviceInfo.html#a56247b458a937ae84d98ca9c4b243275">inputChannels</a>;            <span class="comment">// Maximum input channels supported by device.</span></div>
  52 <div class="line">  <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> <a class="code" href="structRtAudio_1_1DeviceInfo.html#a3e8ad34c2d14e24293a0beafc26186e7">duplexChannels</a>;           <span class="comment">// Maximum simultaneous input/output channels supported by device.</span></div>
  53 <div class="line">  <span class="keywordtype">bool</span> <a class="code" href="structRtAudio_1_1DeviceInfo.html#a5365245e73ffe29a05734de4474acd58">isDefaultOutput</a>;                  <span class="comment">// true if this is the default output device.</span></div>
  54 <div class="line">  <span class="keywordtype">bool</span> <a class="code" href="structRtAudio_1_1DeviceInfo.html#a7c8aca084bd908799b6be5954b80def2">isDefaultInput</a>;                   <span class="comment">// true if this is the default input device.</span></div>
  55 <div class="line">  std::vector&lt;unsigned int&gt; <a class="code" href="structRtAudio_1_1DeviceInfo.html#afa65f5f92f66ce7aacd3ff35e11b230f">sampleRates</a>; <span class="comment">// Supported sample rates.</span></div>
  56 <div class="line">  <a class="code" href="RtAudio_8h.html#aafca92882d25915560018873221e44b8" title="RtAudio data format type.">RtAudioFormat</a> <a class="code" href="structRtAudio_1_1DeviceInfo.html#a23251b549b89b2fe04a57fcd7cb76ea4">nativeFormats</a>;           <span class="comment">// Bit mask of supported data formats.</span></div>
  57 <div class="line">};</div>
  58 </div><!-- fragment --><p>The following data formats are defined and fully supported by <a class="el" href="classRtAudio.html" title="Realtime audio i/o C++ classes.">RtAudio</a>:</p>
  59 <div class="fragment"><div class="line"><span class="keyword">typedef</span> <span class="keywordtype">unsigned</span> <span class="keywordtype">long</span> <a class="code" href="RtAudio_8h.html#aafca92882d25915560018873221e44b8" title="RtAudio data format type.">RtAudioFormat</a>;</div>
  60 <div class="line"><span class="keyword">static</span> <span class="keyword">const</span> RtAudioFormat  RTAUDIO_SINT8;   <span class="comment">// Signed 8-bit integer</span></div>
  61 <div class="line"><span class="keyword">static</span> <span class="keyword">const</span> RtAudioFormat  RTAUDIO_SINT16;  <span class="comment">// Signed 16-bit integer</span></div>
  62 <div class="line"><span class="keyword">static</span> <span class="keyword">const</span> RtAudioFormat  RTAUDIO_SINT24;  <span class="comment">// Signed 24-bit integer (lower 3 bytes of 32-bit signed integer.)</span></div>
  63 <div class="line"><span class="keyword">static</span> <span class="keyword">const</span> RtAudioFormat  RTAUDIO_SINT32;  <span class="comment">// Signed 32-bit integer</span></div>
  64 <div class="line"><span class="keyword">static</span> <span class="keyword">const</span> RtAudioFormat  RTAUDIO_FLOAT32; <span class="comment">// 32-bit float normalized between +/- 1.0</span></div>
  65 <div class="line"><span class="keyword">static</span> <span class="keyword">const</span> RtAudioFormat  RTAUDIO_FLOAT64; <span class="comment">// 64-bit double normalized between +/- 1.0</span></div>
  66 </div><!-- fragment --><p>The <code>nativeFormats</code> member of the <a class="el" href="structRtAudio_1_1DeviceInfo.html" title="The public device information structure for returning queried values.">RtAudio::DeviceInfo</a> structure is a bit mask of the above formats which are natively supported by the device. However, <a class="el" href="classRtAudio.html" title="Realtime audio i/o C++ classes.">RtAudio</a> will automatically provide format conversion if a particular format is not natively supported. When the <code>probed</code> member of the <a class="el" href="structRtAudio_1_1DeviceInfo.html" title="The public device information structure for returning queried values.">RtAudio::DeviceInfo</a> structure is false, the remaining structure members are undefined and the device is probably unusable.</p>
  67 <p>Some audio devices may require a minimum channel value greater than one. <a class="el" href="classRtAudio.html" title="Realtime audio i/o C++ classes.">RtAudio</a> will provide automatic channel number compensation when the number of channels set by the user is less than that required by the device. Channel compensation is <em>NOT</em> possible when the number of channels set by the user is greater than that supported by the device.</p>
  68 <p>It should be noted that the capabilities reported by a device driver or underlying audio API are not always accurate and/or may be dependent on a combination of device settings. For this reason, <a class="el" href="classRtAudio.html" title="Realtime audio i/o C++ classes.">RtAudio</a> does not rely on the queried values when attempting to open a stream. </p>
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