change video framerate in c++

framedrop.cpp

#include <opencv2/opencv.hpp>

int main() {

    std::string inputVideoPath = "in_vid.mp4";    // Input video file
    std::string outputVideoPath = "out_vid.mp4";    // Output video file with the desired frame rate

    // Open the input video file
    cv::VideoCapture inputVideo(inputVideoPath);


    if (!inputVideo.isOpened()) {
          // Check if the input video opened successfully
        std::cerr << "Error: Could not open the input video file." << std::endl;
        return -1;
    }

    // input vid props
    double fpsInput = inputVideo.get(cv::CAP_PROP_FPS);
    int width = static_cast<int>(inputVideo.get(cv::CAP_PROP_FRAME_WIDTH));
    int height = static_cast<int>(inputVideo.get(cv::CAP_PROP_FRAME_HEIGHT));

    double fpsOutput = 24.0; 

    // VideoWriter object for the output video
    cv::VideoWriter outputVideo(outputVideoPath, cv::VideoWriter::fourcc('M', 'J', 'P', 'G'), fpsOutput, cv::Size(width, height));

    // Check if the output video opened successfully
    if (!outputVideo.isOpened()) {
        std::cerr << "Error: Could'nt open the output video file for writing." << std::endl;
        return -1;
    }

    // Convert the frame rate by dropping / dupes frames
    while (true) {
        cv::Mat frame;
        inputVideo >> frame;

        // Break the loop if the video is over
        if (frame.empty()) {
            break;
        }

        // Write frame to the output video
        outputVideo << frame;

        // delay to achieve wanted output frame rate
        int delay = static_cast<int>(1000.0 / fpsOutput);
        cv::waitKey(delay);
    }

  
  inputVideo.release();
    outputVideo.release();

    return 0;
}