computing average image of N webcam images crashes sometimes

edit

Hey guys, I wanted to write a program which takes N live webcam images, calculates an averaged-image out of it and saves the average image as a jpg. I'm passing the filename and the number N of images to be averaged as parameters. First I thought everything is working fine with my code, but sometimes the program crashes during runtime (I'm calling the exe via LabVIEW). I'm not changing N, only the filename-number is incremented by 1 for each call, so I don't think that's the issue. It crashes about 1 time in 25 calls but it's nor really reproducible when. With crashing I mean the window freezes, and is greyed out by Windows and I get the promt that the program isn't responding.

Here is my code:

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include "opencv2/highgui/highgui.hpp"
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>

using namespace cv;
using namespace std;

int main(int argc, char* argv[])
{
    string outputfilename;
    int NMean; // number of images to take mean values of

    if (argc == 2)
    {
        outputfilename = argv[1];
        NMean = 100;
    }

    else if(argc > 2)
    {
        outputfilename = argv[1];
        istringstream ss(argv[2]);
        ss >> NMean;
    }

    else
    {
        outputfilename = "newframe.jpg";
        NMean = 100;

    }

    VideoCapture cap(0);

    if (!cap.isOpened())
    {
        cout << "Cannot open the video cam" << endl;
        return -1;
    }

    double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH);
    double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT);

    cout << "Frame size : " << dWidth << " x " << dHeight << endl;

    cap.set(CV_CAP_PROP_FRAME_WIDTH, 1280);
    cap.set(CV_CAP_PROP_FRAME_HEIGHT, 1024);

    namedWindow("WebcamImage",CV_WINDOW_AUTOSIZE);

    Mat frame;
    Mat meanImage(1024, 1280, CV_32FC3, cv::Scalar(0));

    for (int i=0; i<NMean; i++)
    {

        bool bSuccess = cap.read(frame); // read a new frame from video

        if (!bSuccess) //if not success, break loop
        {
             cout << "Cannot read a frame from video stream" << endl;
             break;
        }

        imshow("WebcamImage", frame);
        accumulate(frame, meanImage);

       if (waitKey(30) == 27)
       {
            cout << "esc key is pressed by user" << endl;
            break;
       }
    }

    meanImage = meanImage / NMean;
    meanImage.convertTo(meanImage,CV_8UC3);
    imwrite(outputfilename.c_str(),meanImage);

    cap.release();
    destroyWindow("WebcamImage");

    return 0;

}

I noticed that during a crash the averaged image is still saved. So the error must occur after the last imwrite (I also tried to put destroyWindow in front of break; but it didn't help).

What could be the issue? Thanks a lot and best regards!