Hi Erfan,

from OpenCV doc:

device – id of the opened video capturing device (i.e. a camera index). If there is a single camera connected, just pass 0.

Bests

#include

#include

#include "opencv2/core/core.hpp"

#include "opencv2/features2d/features2d.hpp"

#include "opencv2/nonfree/features2d.hpp"

#include "opencv2/highgui/highgui.hpp"

#include "opencv2/nonfree/nonfree.hpp"

using namespace cv;

using namespace std;

int main(int argc, char* argv[])

{

int method = 0;

VideoCapture cap(-1); // open the video file for reading

if ( !cap.isOpened() ) // if not success, exit program

{

cout