@Override
 public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
   Log.d(TAG, "Surface Changed Callback");
   final Camera camera = NgnCameraProducer.getCamera();
   try {
     myProducer.startCameraPreview(camera);
   } catch (Exception exception) {
     Log.e(TAG, exception.toString());
   }
 }
 @Override
 public int stop() {
   return myProducer.stopCallback();
 }
 @Override
 public int pause() {
   return myProducer.pauseCallback();
 }
 @Override
 public int start() {
   return myProducer.startCallback();
 }
 @Override
 public int prepare(int width, int height, int fps) {
   return myProducer.prepareCallback(width, height, fps);
 }