Slow Video in Object Tracking Script using OpenCV - c++

Question

I wrote a short routine in openCV and C++ to track objects with a webcam. The webcam formulation was speedy with no lag, but before leaving work for the weekend, I recorded a typical sequence to use as a test template while I work until Monday. This and the corresponding change in code somehow make the video play back in really slow motion. Here is the code, opening "Test.avi", ~20 seconds long instead of running a constant stream off of the webcam:
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include <vector>
using namespace cv;
using namespace std;
Mat drawBoundingBoxes (Mat canvasImage, vector<vector<Point>> contours);
int main(int argc, char** argv[])
{
Mat frame;
Mat back;
Mat fGround;
BackgroundSubtractorMOG2 bGround;
bGround.nmixtures = 3;
//bGround.nShadowDetection = 0;
bGround.fTau = .5;
VideoCapture cap;
cap.open("Test.avi");
if (!cap.isOpened())
{
cout << "Can't open video" << endl;
return -1;
}
vector<vector<Point>> contours;
namedWindow("video", CV_WINDOW_AUTOSIZE);
while (true)
{
static int count = 1;
cap >> frame;
if (frame.empty())
break;
bGround.operator()(frame, fGround);
bGround.getBackgroundImage(back);
erode(fGround, fGround, Mat(), Point(-1,-1), 2, BORDER_DEFAULT);
dilate(fGround, fGround, Mat(), Point(-1,-1), 10, BORDER_DEFAULT);
if (count > 50)
{
findContours(fGround, contours, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_NONE);
drawContours(frame, contours, -1, Scalar(239,255,0), 2);
drawBoundingBoxes(frame, contours);
}
imshow("video", frame);
if(waitKey(30) >= 0)
break;
count++;
}
return 0;
}
Mat drawBoundingBoxes (Mat canvasImage, vector<vector<Point>> contours)
{
vector<Rect> boundRect(contours.size());
for (int i=0; i<contours.size(); i++)
{
boundRect[i] = boundingRect(contours[i]);
rectangle(canvasImage, boundRect[i], Scalar(153,0,76), 2, 8, 0);
}
return canvasImage;
}
Any ideas? Memory Leak somewhere? Thanks,
-Tony

Answer 1

I believe your recorded video has a higher framerate than that your PC can process real time. It's not a problem with a webcam as it just drops the frames. You could try to decrease the delay in the waitKey() procedure and see if that helps.