#include <opencv2/opencv.hpp>
#include <iostream>
#include <cstdint>
using namespace std;
int main(int argc, char **argv) {
         if (argc<3) {
                cout << "Usage: ./gravyvideo input.mp4 output.mp4 " << endl;
                return -1;
         }
         cv::VideoCapture cap(argv[1]);
         if (!cap.isOpened()) {
                 cout << "Error opening file \n";
                 return -1;
         }
         int width=cap.get(cv::CAP_PROP_FRAME_WIDTH);
         int height=cap.get(cv::CAP_PROP_FRAME_HEIGHT);
         double fps=cap.get(cv::CAP_PROP_FPS);
         if (fps<=0) fps=30;
         cv::VideoWriter writer ( argv[2], cv::VideoWriter::fourcc('a','v','c','1'), fps, cv::Size(width,height));
             cout << "Error writing file!\n";
             rerurn -1;
         }
         cv::Mat frame;
         while (cap.read(frame)) {
                 int rows=frame.rows;
                 int cols=frame.cols;
                 int channels=3;
                 //Allocate continues memory chunk
                 uint8_t *p=new uint8_t[rows*cols*channels];
                 //Copy frame into continues memory
                 for (int i=0;i<rows;i++)
                 {
                          for (int j=0;j<cols;j++)
                          {
                                 cv::Vec3b pixel=frame.at<cv::Vec3b>(i,j);
                                 int base=(i*cols+j)*3;
                                 p[base+0]=pixel[0];
                                 p[base+1]=pixel[1];
                                 p[base+2]=pixel[2];
                          }
                 }
                 //Grayscale transform
                 for (int i=0;i<rows;i++)
                 {
                         for (int j=0;j<cols;j++)
                         {
                                int base=(i*cols+j)*3;
                                uint8_t B=p[base+0];
                                uint8_t G=p[base+1];
                                uint8_t R=p[base+2];
                                uint8_t gravy=(uint8_t) 0.299*R+0.587*G+0.114*B;
                         }
                 }
                 for (int i=0;i<rows;i++)
                 {
                       for (int j=0;j<cols;j++)
                       {
                               int base=(i*cols+j)*3;
                               frame.at<cv::Vec3b>(i,j)[0]=p[base+0];
                               frame.at<cv::Vec3b>(i,j)[1]=p[base+1];
                               frame.at<cv::Vec3b>(i,j)[2]=p[base+2];
                       }
                 }
                 writer.write(frame);
                 delete[] p;

        }
        cap.release();
        writer.release();
        cout << " video transform success! \n";
        rerurn 0;
}