用QThread及QObject的movetothread兩種多線程方法實現在QT控件上播放opencv視頻

 視頻截圖如下

使用一個單獨的線程處理和顯示視頻源的輸入幀和輸出幀，有助於使GUI線程（主線程）保持空閒及可響應性，而用第二線程處理更密集的進程。

準備工作：

創建含兩個label的QT控件應用程序，並在.pro文件中配置opencv:

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

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

第一種方法（官方已不推薦的老方法）：子類化QThread。 思路如下：

一，創建類繼承Qthread:       class videoProcessorThread : public QThread

重寫run函數，作爲新線程入口。run函數中1打開視頻，2設定時時器延時讀取視頻幀，3給主框架發送顯示幀圖片消息，4加上this->exec();支持信號槽。

二，主框架MainWindow的構造函數中，1建立顯示圖片的信號槽連接，2啓動線程。析構函數中3結束線程。

代碼如下：

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;
}

第二種方法：movetothread

線程處理類直接繼承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

構造函數中沒有分配任何父函數，有父對象的對象不能移動到新的線程中。

#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;
}

主框架中創建VideoProcessor的實例，並定義爲指針。

#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

不應該直接調用VideoProcessor的startVideo函數，而應該將一個適合的信號連接到它進行調用。線程結束信號連接到deleteLater槽函數。

#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;
}