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<div id="projectname">PortAudio
 <span id="projectnumber">2.0</span>
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<div class="title">Opening a Stream Using Defaults </div> </div>
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<div class="textblock"><p>The next step is to open a stream, which is similar to opening a file. You can specify whether you want audio input and/or output, how many channels, the data format, sample rate, etc. Opening a ''default'' stream means opening the default input and output devices, which saves you the trouble of getting a list of devices and choosing one from the list. (We'll see how to do that later.) </p>
<div class="fragment"><div class="line"><span class="preprocessor">#define SAMPLE_RATE (44100)</span></div>
<div class="line"><span class="preprocessor"></span><span class="keyword">static</span> <a class="code" href="structpaTestData.html">paTestData</a> data;</div>
<div class="line"></div>
<div class="line">.....</div>
<div class="line"></div>
<div class="line"> <a class="code" href="portaudio_8h.html#a19874734f89958fccf86785490d53b4c">PaStream</a> *stream;</div>
<div class="line"> <a class="code" href="portaudio_8h.html#a4949e4a8ef9f9dbe8cbee414ce69841d">PaError</a> err;</div>
<div class="line"></div>
<div class="line"> <span class="comment">/* Open an audio I/O stream. */</span></div>
<div class="line"> err = <a class="code" href="portaudio_8h.html#a0a12735ac191200f696a43b87667b714">Pa_OpenDefaultStream</a>( &stream,</div>
<div class="line"> 0, <span class="comment">/* no input channels */</span></div>
<div class="line"> 2, <span class="comment">/* stereo output */</span></div>
<div class="line"> <a class="code" href="portaudio_8h.html#a2f16d29916725b8791eae60ab9e0b081">paFloat32</a>, <span class="comment">/* 32 bit floating point output */</span></div>
<div class="line"> SAMPLE_RATE,</div>
<div class="line"> 256, <span class="comment">/* frames per buffer, i.e. the number</span></div>
<div class="line"><span class="comment"> of sample frames that PortAudio will</span></div>
<div class="line"><span class="comment"> request from the callback. Many apps</span></div>
<div class="line"><span class="comment"> may want to use</span></div>
<div class="line"><span class="comment"> paFramesPerBufferUnspecified, which</span></div>
<div class="line"><span class="comment"> tells PortAudio to pick the best,</span></div>
<div class="line"><span class="comment"> possibly changing, buffer size.*/</span></div>
<div class="line"> patestCallback, <span class="comment">/* this is your callback function */</span></div>
<div class="line"> &data ); <span class="comment">/*This is a pointer that will be passed to</span></div>
<div class="line"><span class="comment"> your callback*/</span></div>
<div class="line"> <span class="keywordflow">if</span>( err != paNoError ) <span class="keywordflow">goto</span> error;</div>
</div><!-- fragment --><p>The data structure and callback are described in <a class="el" href="writing_a_callback.html">Writing a Callback Function</a>.</p>
<p>The above example opens the stream for writing, which is sufficient for playback. It is also possible to open a stream for reading, to do recording, or both reading and writing, for simultaneous recording and playback or even real-time audio processing. If you plan to do playback and recording at the same time, open only one stream with valid input and output parameters.</p>
<p>There are some caveats to note about simultaneous read/write:</p>
<ul>
<li>Some platforms can only open a read/write stream using the same device.</li>
<li>Although multiple streams can be opened, it is difficult to synchronize them.</li>
<li>Some platforms don't support opening multiple streams on the same device.</li>
<li>Using multiple streams may not be as well tested as other features.</li>
<li>The PortAudio library calls must be made from the same thread or synchronized by the user.</li>
</ul>
<p>Previous: <a class="el" href="initializing_portaudio.html">Initializing PortAudio</a> | Next: <a class="el" href="start_stop_abort.html">Starting, Stopping and Aborting a Stream</a> </p>
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