mainwindow.h：

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <opencv2/core/mat.hpp>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    void on_playButton_clicked();

    void on_stopButton_clicked();

    void readFrame();

private:
    Ui::MainWindow *ui;
    cv::VideoCapture mCapture; // Video capture object for reading RTSP stream
    cv::Mat mFrame;   // Mat object to store the video frame
    bool mPlaying;   // Flag to indicate if video playback is in progress
};

#endif // MAINWINDOW_H


mainwindow.cpp：

cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QDebug>
#include <QTimer>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    // Set up VideoCapture object for reading RTSP stream
    //调节参数 取决于对视频流带宽要求以及本机性能 适点即可
    mCapture.set(cv::CAP_PROP_BUFFERSIZE,5);
    mCapture.open("rtsp://localhost:8554/unicast"); //修改RTSP地址

    if (!mCapture.isOpened())
    {
        qCritical() << "Failed to open RTSP stream.";
        return;
    }

    //初始化mFrame和mPlaying标记
    mPlaying = false;

    //设置Paly按钮为不可用状态
    ui->playButton->setEnabled(true);
    ui->stopButton->setEnabled(false);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_playButton_clicked()
{
    if (!mPlaying)
    {
        mPlaying = true;

        // 每20毫秒读取一帧并在QLabel显示该帧图像
        QTimer *timer = new QTimer(this);
        connect(timer, &QTimer::timeout, this, &MainWindow::readFrame);
        timer->start(20);

        //设置控件状态
        ui->playButton->setEnabled(false);
        ui->stopButton->setEnabled(true);
    }
}

void MainWindow::readFrame()
{
    if (mCapture.read(mFrame))
    {
        QImage frameImage((uchar*)mFrame.data, mFrame.cols, mFrame.rows, QImage::Format_RGB888);
        QPixmap framePixmap = QPixmap::fromImage(frameImage.rgbSwapped());
        // .rgbSwapped()因为OpenCV默认使用BGR，而Qt使用RGB，必须交换颜色通道才能正确地显示

        ui->videoLabel->setPixmap(framePixmap.scaled(ui->videoLabel->size(), Qt::KeepAspectRatio));
    }
}

void MainWindow::on_stopButton_clicked()
{
    if (mPlaying)
    {
        mPlaying = false;

        //停止计时器，断开信号/槽连接
        QObject::disconnect(this, &MainWindow::readFrame, nullptr, nullptr);

        //设置控件状态
        ui->playButton->setEnabled(true);
        ui->stopButton->setEnabled(false);

        //清除QLabel
        ui->videoLabel->clear();
    }
}