    // The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
    /*

        This example shows how to use the correlation_tracker from the dlib C++ library.  This
        object lets you track the position of an object as it moves from frame to frame in a
        video sequence.  To use it, you give the correlation_tracker the bounding box of the
        object you want to track in the current video frame.  Then it will identify the
        location of the object in subsequent frames.

        In this particular example, we are going to run on the video sequence that comes with
        dlib, which can be found in the examples/video_frames folder.  This video shows a juice
        box sitting on a table and someone is waving the camera around.  The task is to track the
        position of the juice box as the camera moves around.
    */

    #include <dlib/image_processing.h>
    #include <dlib/gui_widgets.h>
    #include <dlib/image_io.h>
    #include <dlib/dir_nav.h>

    using namespace dlib;
    using namespace std;

    int main(int argc, char** argv) try
    {
        if (argc != 2)
        {
            cout << "Call this program like this: " << endl;
            cout << "./video_tracking_ex ../video_frames" << endl;
            return 1;
        }

        // Get the list of video frames.
        std::vector<file> files = get_files_in_directory_tree(argv[1], match_ending(".jpg"));
        std::sort(files.begin(), files.end());
        if (files.size() == 0)
        {
            cout << "No images found in " << argv[1] << endl;
            return 1;
        }

        // Load the first frame.
        array2d<unsigned char> img;
        load_image(img, files[0]);
        // Now create a tracker and start a track on the juice box.  If you look at the first
        // frame you will see that the juice box is centered at pixel point(92,110) and 38
        // pixels wide and 86 pixels tall.
        correlation_tracker tracker;
        tracker.start_track(img, centered_rect(point(93,110), 38, 86));

        // Now run the tracker.  All we have to do is call tracker.update() and it will keep
        // track of the juice box!
        image_window win;
        for (unsigned long i = 1; i < files.size(); ++i)
        {
            load_image(img, files[i]);
            tracker.update(img);

            win.set_image(img);
            win.clear_overlay();
            win.add_overlay(tracker.get_position());

            cout << "hit enter to process next frame" << endl;
            cin.get();
        }
    }
    catch (std::exception& e)
    {
        cout << e.what() << endl;
    }