title: How to send Audio through SoundCard Output channels 1/2 and 3/4 in PortAudio Callback function?
body: <p>Here is my simple callback. PA detects my soundcard with 8ins/8outs. I would like to send audio stream to output channels like 1/2 and 3/4 simultaneously. How can I do this in the callback? Thanks         </p>
  
  <pre><code>int audioCallback ( const void* input, void* output, unsigned long samples,
                         const PaStreamCallbackTimeInfo* timeInfo, PaStreamCallbackFlags statusFlags, void* userData)
      {
          const float *in = ( const float*)input;
          float *out = (float*)output;
  
          paTestData *data = (paTestData*)userData;
  
  
          for (int i = 0; i &lt; samples; ++i)
          {
  
              *out++ = *in++; // left Channel(1)
              *out++ = *in++; // right Channel(2)
  
          }
  
  
          return paContinue;
      }
  </code></pre>