test.cpp

#include <opencv2/opencv.hpp>
#include <iostream>
#include <thread>
#include <chrono>

using namespace cv;
int main()
{
    Mat frame;
    VideoCapture cap;

    int deviceID = 2; // Select the ID of the USB camera we want - 0 = default
    int apiID = CAP_V4L2; // ??

    cap.open(deviceID, apiID); // Opens selected cam using selected API
    
    // Error if fail to open cam
    if (!cap.isOpened()) {
	    std::cerr << "ERROR! Unable to open camera\n";
	    return -1;
    }
    std::cout << "Sleep" << std::endl;

    std::this_thread::sleep_for(std::chrono::milliseconds(500));

    std::cout << "Starting to grab (??)" << std::endl;

    while (true)
    {
	    cap.read(frame); // I think this reads *into* the frame?
	    // Break on err
	    if (frame.empty())
	    {
		    std::cerr << "ERROR! Blank frame grabbed\n";
		    break;
	    }
	    // Show image
	    imshow("Live", frame);

	    // Break if key pressed (??)
	    if (waitKey(5) >= 0)
		    break;
    }
    return 0;
}