questions in GMM...

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Can anybody figure out what's going on with the code? I am using opencv310

 #include <opencv2\opencv.hpp>
#include <iostream>  
#include <string>  
using namespace cv;


int main(int argc, char** argv)
{
    std::string videoFile = "1.avi";

    VideoCapture capture;
    capture.open(videoFile);

    if (!capture.isOpened())
    {
        std::cout << "read video failure" << std::endl;
        return -1;
    }


   Ptr<BackgroundSubtractorMOG2> subtractor;

    cv::Mat foreground;
    cv::Mat background;

    cv::Mat frame;
    long frameNo = 0;
    while (capture.read(frame))
    {
        ++frameNo;

        std::cout << frameNo << std::endl;

        // 运动前景检测，并更新背景  
        subtractor->apply(frame, foreground, 0.001);

        // 腐蚀  
        cv::erode(foreground, foreground, cv::Mat());

        // 膨胀  
        cv::dilate(foreground, foreground, cv::Mat());



        cv::imshow("video", foreground);
        cv::imshow("background", background);


        if (cv::waitKey(25) > 0)
        {
            break;
        }
    }



    return 0;
}