addCallbackbuffer was used

I check addCallbackBuffer().
addCallbackBuffer() registers the buffer to use OnPreviewFrame(). OnPreviewFrame() was registered setPreviewCallbackWithBuffer().

First, caculate the buffer size. frame_size is the buffer size.
example. width = 800 and height = 400, PreviewFormat is NV21 , frame_size is 576000 byte.

Camera.Parameters param = _camera.getParameters();
int imgformat = param.getPreviewFormat();
int bitsperpixel = ImageFormat.getBitsPerPixel(imgformat);
int byteperpixel = bitsperpixel / 8;
Camera.Size camerasize = param.getPreviewSize();
int frame_size = ((camerasize.width * camerasize.height) * bitsperpixel) / 8;

prepare callback function. If you process video image, you use data to received by callback.

private Camera.PreviewCallback mPreviewListener = new Camera.PreviewCallback() {
 @Override
 public void onPreviewFrame(byte[] data, Camera camera) {
  Log.d("camera", "onPreviewFrame size=" + data.length);
     //outputFile(data);//ファイル取得する関数
       //_camera.addCallbackBuffer(data);//バッファを再利用する
 }
};

register callback.

_camera.setPreviewCallbackWithBuffer(mPreviewListener);

register the buffer. If register the buffer, callback function is called soon.

byte[] frame = new byte[frame_size];
_camera.addCallbackBuffer(frame);

My source code is here.