Take frame after some millisecond

edit

You could do it e. g. this way:

System.loadLibrary(Core.NATIVE_LIBRARY_NAME);

VideoCapture videoCapture = new VideoCapture();
videoCapture.open(0);

...

Mat mat = new Mat();
Mat prevMat = null;
Mat diffMat = new Mat();

while( true) {

    // get frame
    videoCapture.read(mat);

    // difference
    if( prevMat != null) {
        Core.absDiff(mat, prevMat, diffMat);
    }

    // remember mat
    prevMat = mat.clone();

    // wait
    Thread.sleep(100);
}

The difference image is in diffMat.

Something like this will get you two images and save them to two matrixes then you can always pass them to functions from inside the loop for processing.

  VideoCapture stream(1);
  if(!stream.isOpened()){
    cout << "Video stream unable to be opened exiting.." << endl;
    exit(0);
  } 

  Mat img1, img2;

  namedWindow("curImg", CV_WINDOW_AUTOSIZE);

  int w_width = 200;
  int w_height = 75;
  int counter=0;
  int delay = 100; // delay in milliseconds

while(true){
    cap >> img;
    Mat frame = Mat(w_height, w_width, CV_8UC3, Scalar(255,255,255));

    if(counter%2 ==0){
      frame.coppyTo(img1);
    }else{
      frame.copyTo(img2);
    }

    imshow("curImg", frame);
    waitKey(delay);
    counter++;
 }