#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>

using namespace cv;
using namespace std;

int main() {
VideoCapture stream1(0);   //0 is the id of video device.0 if you have only one camera.

if (!stream1.isOpened()) { //check if video device has been initialised
    cout << "cannot open camera";
}

//unconditional loop
while (true) {
    Mat cameraFrame;
    stream1.read(cameraFrame);
    imshow("cam", cameraFrame);
    if (waitKey(30) >= 0)
        break;
}
system("pause");
return 0;
}

VideoCapture stream1("video.avi");
stream1.read(cameraFrame);

if (waitKey(30) >= 0)
     break;

if( (char)waitKey(10) == 'q' )
     break;