title: what does mean 'A' of Acodec.cpp in Android Sources (in libstagefright)
body: <p>what does mean 'A' of <code>Acodec.cpp</code> in Android Sources (in <code>libstagefright</code>)  ???</p>
  
  <p>full path is below :</p>
  
  <pre><code>    android/frameworks/av/media/libstagefright/Acodec.cpp
  </code></pre>
  
  <p>please explain answer and background knowledge.</p>