用qt+opencv， 写一个电脑录屏的示例代码， 视频格式 h264

很高兴回答您的问题！以下是示例代码：

#include <QApplication>
#include <QWidget>
#include <QVBoxLayout>

#include <opencv2/core.hpp>
#include <opencv2/videoio.hpp>
#include <opencv2/imgproc.hpp>

#include <iostream>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QWidget w;

    // create a vertical layout to add the video widget
    QVBoxLayout *layout = new QVBoxLayout(&w);

    // open the default camera and check if it is available
    cv::VideoCapture cap;
    if (!cap.open(0)) {
        std::cerr << "Cannot open camera." << std::endl;
        return 1;
    }

    // set the codec for the output video
    int codec = cv::VideoWriter::fourcc('H', '2', '6', '4');

    // get the frame size from the camera
    int frame_width = static_cast<int>(cap.get(cv::CAP_PROP_FRAME_WIDTH));
    int frame_height = static_cast<int>(cap.get(cv::CAP_PROP_FRAME_HEIGHT));

    // create a video writer to save the recorded video
    cv::VideoWriter writer("output.avi", codec, 30, cv::Size(frame_width, frame_height), true);

    // start the loop to capture and record frames
    cv::Mat frame;
    while (true) {
        // capture a frame from the camera
        cap >> frame;

        // check if the frame is valid
        if (frame.empty()) {
            std::cerr << "Cannot capture frame." << std::endl;
            break;
        }

        // record the frame to the output video
        writer.write(frame);

        // convert the frame to a QImage
        cv::Mat rgb;
        cv::cvtColor(frame, rgb, cv::COLOR_BGR2RGB);
        QImage qimg(rgb.data, rgb.cols, rgb.rows, rgb.step, QImage::Format_RGB888);

        // create a QLabel to display the image
        QLabel *label = new QLabel(&w);
        label->setPixmap(QPixmap::fromImage(qimg));

        // add the label to the layout
        layout->addWidget(label);

        // update the widget to show the new label
        w.update();

        // wait for a key press or 10 ms
        if (cv::waitKey(10) >= 0)
            break;
    }

    // release the resources and exit
    writer.release();
    cap.release();

    w.show();
    return a.exec();
}

希望这能够帮助您解决问题。如果您还有其他问题，请随时问我！