How to track people detected by hog descriptor - c++

Question

#include <iostream>
#include <opencv2/opencv.hpp>
using namespace std;
using namespace cv;
int main ()
{
VideoCapture cap("/opencv/images/people.avi");
if (!cap.isOpened())
return -1;
Mat img;
HOGDescriptor hog;
hog.setSVMDetector(HOGDescriptor::getDefaultPeopleDetector());
namedWindow("video capture", CV_WINDOW_AUTOSIZE);
while (true)
{
cap >> img;
if (!img.data)
continue;
vector<Rect> found, found_filtered;
hog.detectMultiScale(img, found, 0, Size(8,8), Size(32,32), 1.05, 2);
size_t i, j;
for (i=0; i<found.size(); i++)
{
Rect r = found[i];
for (j=0; j<found.size(); j++)
if (j!=i && (r & found[j])==r)
break;
if (j==found.size())
found_filtered.push_back(r);
}
for (i=0; i<found_filtered.size(); i++)
{
Rect r = found_filtered[i];
Point textOrg(r.x,r.y);
r.x += cvRound(r.width*0.1);
r.width = cvRound(r.width*0.8);
r.y += cvRound(r.height*0.07);
r.height = cvRound(r.height*0.8);
rectangle(img, r.tl(), r.br(), Scalar(0,255,0), 3);
putText(img, "human", textOrg,
FONT_HERSHEY_COMPLEX_SMALL, 0.8, Scalar::all(000), 1, CV_AA);
}
imshow("video capture", img);
if (waitKey(20) >= 0)
{ break;}
}
return 0;
}
above code can used to detect people in every frame using hog. But I want to track those people for action recognition.I hope to use dense optical flow for action recognition.Can I us hog descriptor for tracking or is there any other good method.