save image sequence to mp4 file, and read them back, see discussion here: https://stackoverflow.com/questions/76106625/what-is-the-best-way-to-save-an-image-sequence-with-different-time-intervals-in

save_image_sequence.cpp

#include <opencv2/opencv.hpp>

using namespace cv;

int main() {
    int width = 640;
    int height = 480;
    int fps = 30;
    int num_frames = 100;
    Scalar black(0, 0, 0);
    Scalar white(255, 255, 255);
    int font = FONT_HERSHEY_SIMPLEX;
    double font_scale = 1.0;
    int thickness = 2;

    VideoWriter writer("output.mp4", VideoWriter::fourcc('M', 'P', '4', 'V'), fps, Size(width, height));

    for (int i = 0; i < num_frames; i++) {
        Mat frame = Mat::zeros(height, width, CV_8UC3);
        putText(frame, std::to_string(i), Point(width / 2 - 50, height / 2), font, font_scale, white, thickness);
        writer.write(frame);
    }

    writer.release();

    return 0;
}

Here is the code to read back the mp4 file, and save the images with the file name as the index. You can see the for "00.jpg", it shows "0" in the image, so it works correctly.

#include <opencv2/opencv.hpp>
#include <string>

using namespace cv;

int main() {
    std::string video_path = "output.mp4";
    VideoCapture cap(video_path);

    if (!cap.isOpened()) {
        std::cerr << "Error opening video file" << std::endl;
        return -1;
    }

    int i = 0;
    Mat frame;
    while (cap.read(frame)) {
        std::string file_path = std::to_string(i);
        file_path = std::string(2 - file_path.length(), '0') + file_path + ".jpg";
        imwrite(file_path, frame);
        i++;
    }

    cap.release();

    return 0;
}

There is a warning when I save the mp4 file, the warning is below:

OpenCV: FFMPEG: tag 0x5634504d/'MP4V' is not supported with codec id 12 and format 'mp4 / MP4 (MPEG-4 Part 14)'
OpenCV: FFMPEG: fallback to use tag 0x7634706d/'mp4v'