Why can't I get motion saliency to work in OpenCV C++?

Question

I'm trying to adapt code from this page: https://www.pyimagesearch.com/2018/07/16/opencv-saliency-detection/ , however that is written in Python and I'm trying to do it in C++. When I run my code it compiles, but all I see is a white screen and not any type of saliency detection going on. What's wrong?

cap.open(pathToVideo);
int frame_width = cap.get(CAP_PROP_FRAME_WIDTH);
int frame_height = cap.get(CAP_PROP_FRAME_HEIGHT);

while (true) {

    Mat frame;
    Mat salientFrame;
    cap >> frame;

    if (frame.empty()) {
        break;
    }

    Ptr<MotionSaliencyBinWangApr2014> MS = MotionSaliencyBinWangApr2014::create();
    cvtColor(frame, frame, COLOR_BGR2GRAY);
    MS->setImagesize(frame.cols, frame.rows);
    MS->init();
    MS->computeSaliency(frame, salientFrame);
    salientFrame.convertTo(salientFrame, CV_8U, 255);
    imshow("Motion Saliency", salientFrame);
    char c = (char)waitKey(25);
    if (c == 27)
        break;
}

cap.release();

Answer 1

The command Ptr MS = MotionSaliencyBinWangApr2014::create(); must be called before the loop. The method process video, not a single image.