Hello i am trying to convert a ros2 topic which named “/serit” to a v4l2 virtual camera which named “/dev/video4”

i have writen this code

#include <opencv2/opencv.hpp>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/videodev2.h>
#include <rclcpp/rclcpp.hpp>
#include <sensor_msgs/msg/image.hpp>
#include <cv_bridge/cv_bridge.h>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
#include <errno.h>
#include <cstring>

using namespace std;
using namespace cv;

bool writeToV4L2VirtualCamera(cv::Mat& image, const char* device = "/dev/video4") {
    // Open the V4L2 device
    int fd = open(device, O_RDWR);
    if (fd == -1) {
        std::cerr << "Error: Could not open V4L2 device. Error code: " << errno << std::endl;
        return false;
    }

    // Get the current format of the device
    struct v4l2_format fmt;
    memset(&fmt, 0, sizeof(fmt));
    fmt.type = V4L2_BUF_TYPE_VIDEO_OUTPUT;
    if (ioctl(fd, VIDIOC_G_FMT, &fmt) == -1) {
        std::cerr << "Error: Could not get format. Error code: " << errno << std::endl;
        close(fd);
        return false;
    }

    // Print the current format
    std::cout << "Current format - Width: " << fmt.fmt.pix.width
              << ", Height: " << fmt.fmt.pix.height
              << ", Pixelformat: " << (char*)&fmt.fmt.pix.pixelformat
              << ", Field: " << fmt.fmt.pix.field << std::endl;

    // Convert the image to the format required by V4L2
    cv::Mat yuv_image;
    cv::cvtColor(image, yuv_image, cv::COLOR_BGR2YUV_I420);

    // Write the image data to the device
    size_t bufferSize = yuv_image.total() * yuv_image.elemSize();
    if (write(fd, yuv_image.data, bufferSize) == -1) {
        std::cerr << "Error: Could not write to V4L2 device. Error code: " << errno << " - " << strerror(errno) << std::endl;
        close(fd);
        return false;
    }  

    // Close the device
    close(fd);
    return true;
}

class ImageSubscriber : public rclcpp::Node {
public:
    ImageSubscriber() : Node("image_subscriber") {
        subscription_ = this->create_subscription<sensor_msgs::msg::Image>(
            "/serit", 10, std::bind(&ImageSubscriber::listener_callback, this, std::placeholders::_1));
    }

private:
    void listener_callback(const sensor_msgs::msg::Image::SharedPtr msg) {
        cv::Mat cv_image = cv_bridge::toCvCopy(msg, "bgr8")->image;

        // Specify new size directly
        cv::Size newSize(640, 480); // Example: resize to 640x480

        cv::Mat resizedImage;
        cv::resize(cv_image, resizedImage, newSize);

        if (!writeToV4L2VirtualCamera(resizedImage)) {
            std::cerr << "Error: Failed to write image to V4L2 device" << std::endl;
        }

        imshow("Image", resizedImage);
        waitKey(1);

        namedWindow("Image", WINDOW_KEEPRATIO);
    }

    rclcpp::Subscription<sensor_msgs::msg::Image>::SharedPtr subscription_;
};

int main(int argc, char* argv[]) {
    rclcpp::init(argc, argv);
    auto node = std::make_shared<ImageSubscriber>();
    rclcpp::spin(node);
    rclcpp::shutdown();
    return 0;
}

but it didn’t worked out

i got this error:

Current format - Width: 640, Height: 480, Pixelformat: YU12, Field: 1
Error: Could not write to V4L2 device. Error code: 22 - Invalid argument
Error: Failed to write image to V4L2 device

at every image that i am trying to convert

can you help me out please

onvert a ros2 topic which named “/serit” to a v4l2 virtual camera which named “/dev/video4”