How do I smooth feature trajectories of lkdemo

edit

I've to smooth feature trajectories of Lucas Kanade and for that purpose, its possible to apply low pass filter to x and y coordinates of the tracked feature points in lkdemo. I got thee understanding of applying low pass filter to image in opencv but I can't get it in lkdemo. What I've tried is completely wrong in my opinion. Please guide me so that I can solve m issue. My trial is given as:

void conv2(vector<vector<Point2f>> src, int kernel_size)
{
    vector<vector<Point2f>> dst;
    Mat kernel;
    kernel = Mat::ones(kernel_size, kernel_size, CV_32F) / (float)(kernel_size*kernel_size);

    /// Apply filter
    filter2D(src, dst, -1, kernel, Point(-1, -1), 0, BORDER_DEFAULT);
    //namedWindow("filter2D Demo", CV_WINDOW_AUTOSIZE); imshow("filter2D Demo", dst);
}

and then at the end of main function of lkdemo,

conv2(pointsFrame, 3);

waitKey(0);

return 0;
}