title: setPreviewCallback() and setPreviewCallbackWithBuffer()
body: <p>I have a code that accesses the stream of frames from front camera and pushes them to the processing to background thread. Right now I'm not using any buffers at all and everything works (on my phone).</p>
  
  <p>So the question how <code>setPreviewCallback()</code> is different from <code>setPreviewCallbackWithBuffer()</code> for this particular task?</p>