ROS2 CV2 imshow and publish in the same loop fails

Question

I attempted to publish and display an image from a video using cv2 and ros2. Although the code compiled successfully, running it consistently resulted in a memory allocation failure. Could someone clarify the reason for this failure? Interestingly, when I comment out the section of code responsible for displaying an image, the publishing process works correctly, allowing me to observe the output in rviz. Conversely, if I comment out the code responsible for publishing the image and retain the code for displaying a frame, it successfully creates a window and displays frames without any issues.

Ubuntu 22.04 ROS2 Humble OpenCV 4.8 built from source with cuda support

void Video::loadVideo(const std::string &video_path)
{

    cv::VideoCapture cap(video_path);

    if (!cap.isOpened())
    {
        RCLCPP_ERROR(this->get_logger(), "Failed to open the video file: ");
        return;
    }

    cv::Mat frame(cv::Size(1280, 720), CV_8UC3);
    while (rclcpp::ok())
    {
        cap >> frame;

        if (frame.empty())
            break;

        sensor_msgs::msg::Image::SharedPtr msg =
            cv_bridge::CvImage(std_msgs::msg::Header(), "bgr8", frame).toImageMsg();

        _img_pub->publish(*msg.get());

        // cv::imshow("Frame", frame);
        // cv::waitKey(1);

        // char c = (char)cv::waitKey(25);
        // if (c == 27)
        //     break;

    }
}

when I uncomment

    cv::imshow("Frame", frame);
    cv::waitKey(1);

I get something like:

  what():  OpenCV(4.8.0-dev) /home/oskar/opencv/opencv/modules/core/src/alloc.cpp:73: error: (-4:Insufficient memory) Failed to allocate 62285023075440 bytes in function 'OutOfMemoryError'

Thanks in advance

Solution:

cv::VideoCapture cap(video_path); -> cv::VideoCapture cap(video_path, cv::CAP_FFMPEG);