title: ALSA: How can I send audio through both headphone and speaker
body: <p>I need to control the audio output device at run time :</p>
  
  <pre><code>1) Main Speaker only
  2) Headphone Only
  3) Headphone + Main Speaker both together
  </code></pre>
  
  <p>My application take run time decision to switch among above combinations. What ALSA API should I use for above purpose.</p>
  
  <p>(I use Linux 3.0, ALSA, C, TI tlv320aic3x , ARM).</p>