title: MAC OS X: Set external USB camera resolution with AVCaptureSession's sessionPreset doesn't work
body: <p>I am trying to set the camera's resolution for the capture session using this:</p>
  
  <pre><code>[session setSessionPreset:AVCaptureSessionPresetLow];  // or any others resolutions
  </code></pre>
  
  <p>It doesn't seem to make any difference.  It always uses the highest resolution the camera can offer.  This is a UVC compliant USB camera and wasn't made by Apple.</p>
  
  <p>Question: Can setSessionPreset apply to external USB non-Apple camera?  Or my problem is something else?</p>
  
  <p>Edit:
  I also tried this test:</p>
  
  <pre><code>if ([session canSetSessionPreset:AVCaptureSessionPresetLow])
  {
      NSLog(@"can presetlow");    // this part got called.
      [session beginConfiguration];
      session.sessionPreset = AVCaptureSessionPresetLow;
      [session commitConfiguration];
  }
  else
  {
      NSLog(@"no, can't presetlow");
  }
  </code></pre>
  
  <p>Bounty question:  How to set the camera resolution in this case?</p>