title: Remove channels from PCM
body: <p>I have extended "libtinyalsa" (a very small version of ALSA) with a method to resample in- &amp; outgoing PCM-audio (with libresample, e.g. from 48 kHz to 44.1 kHz).</p>
  
  <p>Now I would like to extend it with a "downMixing" (is that the right word?) method.</p>
  
  <p>I have 5.1 channel PCM and just need 2 channel stereo audio (left &amp; right):</p>
  
  <ul>
  <li>is "downMixing" the right word?</li>
  <li>how can I do this in C?</li>
  </ul>
  
  <p>I have no real knowledge about C and PCM - simple answers would be really welcome.</p>
  
  <p>With kind regards &amp; thanks in advance!</p>