OpenCV VideoCapture with tcambin pipeline

This sample shows, how to use a GStreamer pipeline with our tcambin and set camera properties like exposure and gain. The pipeline string is passed to a cv::VideoCapture object.

#include <iostream>
#include <string>
#include <stdexcept>
#include "opencv2/opencv.hpp" 

/*
Helper function for formatted strings from
https://stackoverflow.com/questions/2342162/stdstring-formatting-like-sprintf
*/
template<typename ... Args>
std::string string_format( const std::string& format, Args ... args )
{
    int size_s = std::snprintf( nullptr, 0, format.c_str(), args ... ) + 1; // Extra space for '\0'
    if( size_s <= 0 ){ throw std::runtime_error( "Error during formatting." ); }
    auto size = static_cast<size_t>( size_s );
    std::unique_ptr<char[]> buf( new char[ size ] );
    std::snprintf( buf.get(), size, format.c_str(), args ... );
    return std::string( buf.get(), buf.get() + size - 1 ); // We don't want the '\0' inside
}

int main(int argc, char **argv) 
{
    std::string serial = "serial=41910044"; //Use the serial number of acamera or leave this string empty ("").
    std::string format = "BGRx";
    int width = 640;
    int height = 480;
    int fps = 30;

    // Create a string with some properties. Disable exposure and gain automatic and set a short
    // exposure time. If no properties are to be set, leave the string empty ("")
    std::string properties = "tcam-properties=tcam,ExposureAuto=Off,ExposureTime=3333,GainAuto=Off,Gain=0.0";

    // Create the pipleine.
    std::string pipeline = string_format("tcambin %s %s ! video/x-raw,format=%s,framerate=%d/1,width=%d,height=%d ! videoconvert ! appsink",
                                properties.c_str(), serial.c_str(), format.c_str(), fps, width,height);

    auto cap = std::make_unique<cv::VideoCapture>(pipeline.c_str(), cv::CAP_GSTREAMER);

    if (!cap->isOpened()) 
	{
        std::cout << "Error: Failed to open video capture device." << std::endl;
        return -1;
    }

    std::cout << "Press Esc key to end program." << std::endl;
 
    cv::namedWindow("Video Window",1);
    int key = 0;

    while(key != 27)
    {
        cv::Mat frame;
        *cap >> frame; // get a new frame from camera
        cv::imshow("Video Window", frame);
	key = cv::waitKey(10);
    }
	
    cv::destroyWindow("Video Window");
    std::cout << "End of Program." << std::endl;
 
    return 0;
}

This sample is inherited from the standard OpenCV VideoCapture sample. It is the GStreamer Pipeline, which is new.