用QThread及QObject的movetothread两种多线程方法实现在QT控件上播放opencv视频

 视频截图如下

使用一个单独的线程处理和显示视频源的输入帧和输出帧，有助于使GUI线程（主线程）保持空闲及可响应性，而用第二线程处理更密集的进程。

准备工作：

创建含两个label的QT控件应用程序，并在.pro文件中配置opencv:

INCLUDEPATH += /usr/local/include \
               /usr/local/include/opencv \
               /usr/local/include/opencv2

LIBS += /usr/local/lib64/libopencv*

第一种方法（官方已不推荐的老方法）：子类化QThread。 思路如下：

一，创建类继承Qthread:       class videoProcessorThread : public QThread

重写run函数，作为新线程入口。run函数中1打开视频，2设定时时器延时读取视频帧，3给主框架发送显示帧图片消息，4加上this->exec();支持信号槽。

二，主框架MainWindow的构造函数中，1建立显示图片的信号槽连接，2启动线程。析构函数中3结束线程。

代码如下：

videoprocessorthread.h

#ifndef VIDEOPROCESSORTHREAD_H
#define VIDEOPROCESSORTHREAD_H

#include <QObject>
#include <QThread>
#include <QPixmap>
#include <opencv2/opencv.hpp>
using namespace cv;


class videoProcessorThread : public QThread
{
    Q_OBJECT
public:
    explicit videoProcessorThread(QObject *parent = nullptr);
    void showCamera();
    void stopVideo();

signals:
    void inDisplay(QPixmap pixmap);
    void outDisplay(QPixmap pixmap);

public slots:
private:
    void run() override;
    VideoCapture camera;
    Mat inFrame,outFrame;
    QTimer *timer;
};

#endif // VIDEOPROCESSORTHREAD_H

videoprocessorthread.cpp

 

#include "videoprocessorthread.h"
#include <QDebug>
#include "QTimer"

videoProcessorThread::videoProcessorThread(QObject *parent) : QThread(parent)
{

}

void videoProcessorThread::run()
{
    camera = VideoCapture("/home/jello/myprojects/images/bike.avi");

    double rate = camera.get(CV_CAP_PROP_FPS);
    int delay = 1000/rate;
    timer = new QTimer();
    connect(timer,&QTimer::timeout,this,&videoProcessorThread::showCamera);
    if(camera.isOpened())
    {
    timer->start(delay);
    this->exec();
    }
}

void videoProcessorThread::showCamera()
{
    camera >> inFrame;
    bitwise_not(inFrame, outFrame);

    emit inDisplay(
                QPixmap::fromImage(
                    QImage(
                        inFrame.data,
                        inFrame.cols,
                        inFrame.rows,
                        inFrame.step,
                        QImage::Format_RGB888)
                    .rgbSwapped()));
    emit outDisplay(QPixmap::fromImage(
                        QImage(
                            outFrame.data,
                            outFrame.cols,
                            outFrame.rows,
                            outFrame.step,
                            QImage::Format_RGB888)));
}

void videoProcessorThread::stopVideo()
{
    timer->stop();
    delete timer;
}

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "videoprocessorthread.h"

#include "videoprocessor.h"

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

protected:
    void closeEvent(QCloseEvent *event);

private:
    Ui::MainWindow *ui;
    videoProcessorThread processor;

//    VideoProcessor *processor1;
};

#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QCloseEvent>

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

    connect(&processor,
            SIGNAL(inDisplay(QPixmap)),
            ui->inVideo,
            SLOT(setPixmap(QPixmap)));

    connect(&processor,
            SIGNAL(outDisplay(QPixmap)),
            ui->outVideo,
            SLOT(setPixmap(QPixmap)));

    processor.start();

}

void MainWindow::closeEvent(QCloseEvent *event)
{
    processor.stopVideo();
    processor.quit();
    processor.wait();

    event->accept();
}

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

第二种方法：movetothread

线程处理类直接继承QObject

#ifndef VIDEOPROCESSOR_H
#define VIDEOPROCESSOR_H

#include <QObject>
#include <QPixmap>
#include "opencv2/opencv.hpp"
using namespace cv;

class VideoProcessor : public QObject
{
    Q_OBJECT
public:
    explicit VideoProcessor(QObject *parent = nullptr);
    void showCamera();

signals:
    void inDisplay(QPixmap pixmap);
    void outDisplay(QPixmap pixmap);

public slots:
    void startVideo();
    void stopVideo();

private:
    bool stopped;
    VideoCapture camera;
    Mat inFrame, outFrame;
    QTimer *timer;
};

#endif // VIDEOPROCESSOR_H

构造函数中没有分配任何父函数，有父对象的对象不能移动到新的线程中。

#include "videoprocessor.h"
#include <QTimer>

VideoProcessor::VideoProcessor(QObject *parent) : QObject(parent)
{

}

void VideoProcessor::startVideo()
{
    camera = VideoCapture("/home/jello/myprojects/images/bike.avi");
    stopped = false;

    double rate = camera.get(CV_CAP_PROP_FPS);
    int delay = 1000/rate;
    timer = new QTimer();
    connect(timer,&QTimer::timeout,this,&VideoProcessor::showCamera);

    if(camera.isOpened())
        timer->start(delay);
}

void VideoProcessor::showCamera()
{
    camera >> inFrame;
    bitwise_not(inFrame, outFrame);

    emit inDisplay(QPixmap::fromImage(
                       QImage(
                           inFrame.data,
                           inFrame.cols,
                           inFrame.rows,
                           inFrame.step,
                           QImage::Format_RGB888)));
    emit outDisplay(QPixmap::fromImage(
                        QImage(
                            outFrame.data,
                            outFrame.cols,
                            outFrame.rows,
                            outFrame.step,
                            QImage::Format_RGB888)));
}

void VideoProcessor::stopVideo()
{
    timer->stop();
    delete timer;
}

主框架中创建VideoProcessor的实例，并定义为指针。

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

#include "videoprocessor.h"

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    Ui::MainWindow *ui;

    VideoProcessor *processor1;
};

#endif // MAINWINDOW_H

不应该直接调用VideoProcessor的startVideo函数，而应该将一个适合的信号连接到它进行调用。线程结束信号连接到deleteLater槽函数。

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

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

    processor1 = new VideoProcessor();
    processor1->moveToThread(new QThread(this));

    connect(processor1->thread(),SIGNAL(started()),processor1,SLOT(startVideo()));
    connect(processor1->thread(),SIGNAL(finnished()),processor1,SLOT(deleteLater()));
    connect(processor1,SIGNAL(inDisplay(QPixmap)),ui->inVideo,SLOT(setPixmap(QPixmap)));
    connect(processor1,SIGNAL(outDisplay(QPixmap)),ui->outVideo,SLOT(setPixmap(QPixmap)));

    processor1->thread()->start();
}

MainWindow::~MainWindow()
{
    processor1->stopVideo();
    processor1->thread()->quit();
    processor1->thread()->wait();

    delete ui;
}