Errors: undefined reference to cv::VideoCapture::VideoCapture()

Arev

cv::VideoCapture:

This is a class from the OpenCV library used for capturing video from camera devices or video files. It provides methods to open, read, and manage video streams.
By declaring cap as static, it's accessible across all instances of the class, and there will be only one instance of it throughout the program execution.

jsulm

@Arev I did not ask what it is, I asked whether your app starts if this line is not there.

Arev

@jsulm

Oh sorry, I created another test app and added that line that nothing in the app depended on and it didn't work and didn't cause any problems, but without that line the app works.

jsulm

@Arev said in Errors: undefined reference to cv::VideoCapture::VideoCapture():

0xc0000135

This error code means: STATUS_DLL_NOT_FOUND
Looks like the cv libs are not found when starting your app. How do you start it? From QtCreator?

Arev

@jsulm

I can share code
This is my .pro

QT += quick

CONFIG += c++11
QT_DISABLE_DEPRECATED_BEFORE=0x060000  

SOURCES += \
        main.cpp \
        opencvimageprovider.cpp \
        videostreamer.cpp

RESOURCES += qml.qrc

QML_IMPORT_PATH =

QML_DESIGNER_IMPORT_PATH =

qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

HEADERS += \
    opencvimageprovider.h \
    videostreamer.h \

win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/ -llibopencv_videoio450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_calib3d450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_core450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_dnn450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_features2d450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_flann450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_gapi450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_highgui450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_imgcodecs450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_imgproc450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_ml450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_objdetect450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_stitching450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_photo450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_video450.dll
win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/-llibopencv_videoio450.dll

INCLUDEPATH += $$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/include
DEPENDPATH += $$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/include

win32: LIBS += -L$$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/x64/mingw/lib/ -llibopencv_core450.dll

INCLUDEPATH += $$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/include
DEPENDPATH += $$PWD/OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/include

Main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "opencvimageprovider.h"
#include "videostreamer.h"
#include <QQmlContext>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;

    qRegisterMetaType<cv::Mat>("cv::Mat");

    VideoStreamer videoStreamer;

    OpencvImageProvider *liveImageProvider(new OpencvImageProvider);

    engine.rootContext()->setContextProperty("VideoStreamer",&videoStreamer);
    engine.rootContext()->setContextProperty("liveImageProvider",liveImageProvider);

    engine.addImageProvider("live",liveImageProvider);

    const QUrl url(QStringLiteral("qrc:/main.qml"));

    engine.load(url);

    QObject::connect(&videoStreamer,&VideoStreamer::newImage,liveImageProvider,&OpencvImageProvider::updateImage);

    return app.exec();
}

VideoStreamer.h

#ifndef VIDEOSTREAMER_H
#define VIDEOSTREAMER_H

#include <QObject>
#include <QTimer>
#include <OpenCV-MinGW-Build-OpenCV-4.5.0-with-contrib/include/opencv2/opencv.hpp>
#include <QImage>
#include <iostream>
#include <QThread>


static cv::VideoCapture cap;


class VideoStreamer: public QObject
{
    Q_OBJECT
public:
    VideoStreamer();
    ~VideoStreamer();

public:
    void streamVideo();
    QThread* threadStreamer = new QThread();
    void catchFrame(cv::Mat emittedFrame);

public slots:
    void openVideoCamera(QString path);

    void streamerThreadSlot();

private:

    cv::Mat frame;
    QTimer tUpdate;

signals:
    void newImage(QImage &);

    void emitThreadImage(cv::Mat frameThread);
};

#endif // VIDEOSTREAMER_H

VideoStreamer.cpp

#include "videostreamer.h"

VideoStreamer::VideoStreamer()
{
    connect(&tUpdate,&QTimer::timeout,this,&VideoStreamer::streamVideo);

}

VideoStreamer::~VideoStreamer()
{
    cap.release();
    tUpdate.stop();
    threadStreamer->requestInterruption();
}

void VideoStreamer::streamVideo()
{

    if(frame.data)
    {
        QImage img = QImage(frame.data,frame.cols,frame.rows,QImage::Format_RGB888).rgbSwapped();
        emit newImage(img);
    }
}

void VideoStreamer::catchFrame(cv::Mat emittedFrame)
{
    frame = emittedFrame;
}

void VideoStreamer::openVideoCamera(QString path)
{
    if(path.length() == 1)
    cap.open(path.toInt());
    else
    cap.open(path.toStdString());

    VideoStreamer* worker = new VideoStreamer();
    worker->moveToThread(threadStreamer);
    QObject::connect(threadStreamer,SIGNAL(started()),worker,SLOT(streamerThreadSlot()));
    QObject::connect(worker,&VideoStreamer::emitThreadImage,this,&VideoStreamer::catchFrame);
    threadStreamer->start();

    double fps = cap.get(cv::CAP_PROP_FPS);
    tUpdate.start(1000/fps);
}

void VideoStreamer::streamerThreadSlot()
{
    cv::Mat tempFrame;

    while (1) {
        cap>>tempFrame;
        if(tempFrame.data)
            emit emitThreadImage(tempFrame);

        if(QThread::currentThread()->isInterruptionRequested())
        {
            cap.release();
            return;
        }

    }
}

OpencvImageProvider.h

#ifndef OPENCVIMAGEPROVIDER_H
#define OPENCVIMAGEPROVIDER_H


#include <QObject>
#include <QImage>
#include <QQuickImageProvider>

class OpencvImageProvider : public QObject, public QQuickImageProvider
{
    Q_OBJECT
public:
    OpencvImageProvider(QObject *parent = nullptr);

    QImage requestImage(const QString &id, QSize *size, const QSize &requestedSize) override;

public slots:
    void updateImage(const QImage &image);

signals:
    void imageChanged();

private:
    QImage image;
};

#endif // OPENCVIMAGEPROVIDER_H

OpencvImageProvider.cpp

#include "opencvimageprovider.h"

OpencvImageProvider::OpencvImageProvider(QObject *parent) : QObject(parent), QQuickImageProvider(QQuickImageProvider::Image)
{
    image = QImage(200,200,QImage::Format_RGB32);
    image.fill(QColor("black"));
}

QImage OpencvImageProvider::requestImage(const QString &id, QSize *size, const QSize &requestedSize)
{
    Q_UNUSED(id);

    if(size){
        *size = image.size();
    }

    if(requestedSize.width() > 0 && requestedSize.height() > 0) {
        image = image.scaled(requestedSize.width(), requestedSize.height(), Qt::KeepAspectRatio);
    }
    return image;
}

void OpencvImageProvider::updateImage(const QImage &image)
{
    if(!image.isNull() && this->image != image) {
        this->image = image;
        emit imageChanged();
    }
}

jsulm

@Arev You did not answer my question

Arev

@jsulm
Yes, from Qt creator

Arev

@jsulm

In the .pro file I have not added these two lines

CONFIG += link_pkgconfig
PKGCONFIG += opencv4

could this be the reason?
And after adding I get this problem:

opencv4 development package not found

SGaist

@Arev hi,

Are you sure about the pkgconfig package name ? If so, where is its .pc file located ?

Arev

@SGaist said in Errors: undefined reference to cv::VideoCapture::VideoCapture():

.pc

what is .pc file (
I do not have that file, where can I get

SGaist

@Arev it's the pkgconfig configuration file. Each library / framework can provide it (or you can create your own).