c++ - 使用 QT6 在 QVideoWidget 上绘制 QVideoFrame

Question

我想用 QT6 逐帧处理网络摄像头的流。我在网上查过，但由于 QTMultimedia 使用 QT6 进行了大量修改，而且由于 QT6 非常新，所以所有可用的文档/问题都已过时。

因此，为了实现我的目标，我使用了一个 QMediaCaptureSession，并在 QMediaDevices::defaultVideoInput() 上设置了摄像头。我通过使用 m_session.setVideoOutput(ui->videowidget); 将 QMediaCaptureSession 的视频输出设置为 QVideoWidget 来检查这是否有效，它工作正常，除了我无法处理帧(基本上，它在 QVideoWidget 上呈现我的网络摄像头)。

现在，据我对文档的理解，要处理帧，我必须使用 QVideoSink here和 there .所以我用 m_session.setVideoSink(&mysink); 替换了 m_session.setVideoOutput(ui->videowidget);，其中 mysink 是一个 QVideoSink.

然后，因为我想处理帧，所以我将 mysink 的 videoFrameChanged 信号连接到我想要的函数 processVideoFrame做两件事:

1. 处理当前帧
2. 在 UI 上呈现结果，最好是在 ui->videowidget
上

这就是我苦苦挣扎的地方。 我不明白如何使用paint function类 QVideoFrame 以在 QVideoWidget 上呈现处理后的帧。更准确地说:

• 我不明白应该如何实例化 QPainter。我尝试了一个简单的 new QPainter(ui->videowidget) 但它以 QWidget::paintEngine: Should no longer be called 异常结束并且没有呈现任何内容
• 我不明白 QVideoFrame::paint 的第二个参数 rect 的实际含义是什么？

我做了一个MWE，代码在下面。

mwe_videosinkpainting.h

#ifndef MWE_VIDEOSINKPAINTING_H
#define MWE_VIDEOSINKPAINTING_H

#include <QMainWindow>
#include <QMediaCaptureSession>
#include <QMediaDevices>
#include <QCamera>
#include <QVideoSink>
#include <QPainter>

QT_BEGIN_NAMESPACE
namespace Ui { class MWE_VideoSinkPainting; }
QT_END_NAMESPACE

class MWE_VideoSinkPainting : public QMainWindow
{
    Q_OBJECT

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

private slots:
    void processVideoFrame();


private:
    Ui::MWE_VideoSinkPainting *ui;

    QVideoSink mysink;
    QMediaCaptureSession m_session;
    QScopedPointer<QCamera> m_camera;
};
#endif // MWE_VIDEOSINKPAINTING_H

mwe_videosinking.cpp

#include "mwe_videosinkpainting.h"
#include "ui_mwe_videosinkpainting.h"

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

    m_camera.reset(new QCamera(QMediaDevices::defaultVideoInput()));
    m_session.setCamera(m_camera.data());
    //m_session.setVideoOutput(ui->videowidget);

    connect(&mysink, &QVideoSink::videoFrameChanged, this, &MWE_VideoSinkPainting::processVideoFrame);

    m_session.setVideoSink(&mysink);
    m_camera->start();
}

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

void MWE_VideoSinkPainting::processVideoFrame()
{
    QVideoFrame videoframe = mysink.videoFrame();
    if(videoframe.map(QVideoFrame::ReadOnly))
    {
        //This is the part I'm struggling to understand and achieve
        videoframe.paint(new QPainter(ui->videowidget), QRectF(0.0f,0.0f,100.0f,100.0f), QVideoFrame::PaintOptions());
        videoframe.unmap();
    }
}

main.cpp

#include "mwe_videosinkpainting.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MWE_VideoSinkPainting w;
    w.show();
    return a.exec();
}

ui_mwe_videosinkpainting.h(只是为了让您拥有完整的代码，它对问题没有任何值(value))

#ifndef UI_MWE_VIDEOSINKPAINTING_H
#define UI_MWE_VIDEOSINKPAINTING_H

#include <QtCore/QVariant>
#include <QtMultimediaWidgets/QVideoWidget>
#include <QtWidgets/QApplication>
#include <QtWidgets/QGridLayout>
#include <QtWidgets/QHBoxLayout>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QMenuBar>
#include <QtWidgets/QStatusBar>
#include <QtWidgets/QWidget>

QT_BEGIN_NAMESPACE

class Ui_MWE_VideoSinkPainting
{
public:
    QWidget *centralwidget;
    QGridLayout *gridLayout;
    QVideoWidget *videowidget;
    QHBoxLayout *horizontalLayout;
    QMenuBar *menubar;
    QStatusBar *statusbar;

    void setupUi(QMainWindow *MWE_VideoSinkPainting)
    {
        if (MWE_VideoSinkPainting->objectName().isEmpty())
            MWE_VideoSinkPainting->setObjectName(QString::fromUtf8("MWE_VideoSinkPainting"));
        MWE_VideoSinkPainting->resize(800, 600);
        centralwidget = new QWidget(MWE_VideoSinkPainting);
        centralwidget->setObjectName(QString::fromUtf8("centralwidget"));
        gridLayout = new QGridLayout(centralwidget);
        gridLayout->setObjectName(QString::fromUtf8("gridLayout"));
        videowidget = new QVideoWidget(centralwidget);
        videowidget->setObjectName(QString::fromUtf8("videowidget"));
        horizontalLayout = new QHBoxLayout(videowidget);
        horizontalLayout->setObjectName(QString::fromUtf8("horizontalLayout"));

        gridLayout->addWidget(videowidget, 0, 0, 1, 1);

        MWE_VideoSinkPainting->setCentralWidget(centralwidget);
        menubar = new QMenuBar(MWE_VideoSinkPainting);
        menubar->setObjectName(QString::fromUtf8("menubar"));
        menubar->setGeometry(QRect(0, 0, 800, 21));
        MWE_VideoSinkPainting->setMenuBar(menubar);
        statusbar = new QStatusBar(MWE_VideoSinkPainting);
        statusbar->setObjectName(QString::fromUtf8("statusbar"));
        MWE_VideoSinkPainting->setStatusBar(statusbar);

        retranslateUi(MWE_VideoSinkPainting);

        QMetaObject::connectSlotsByName(MWE_VideoSinkPainting);
    } // setupUi

    void retranslateUi(QMainWindow *MWE_VideoSinkPainting)
    {
        MWE_VideoSinkPainting->setWindowTitle(QCoreApplication::translate("MWE_VideoSinkPainting", "MWE_VideoSinkPainting", nullptr));
    } // retranslateUi

};

namespace Ui {
    class MWE_VideoSinkPainting: public Ui_MWE_VideoSinkPainting {};
} // namespace Ui

QT_END_NAMESPACE

#endif // UI_MWE_VIDEOSINKPAINTING_H

Answer 1

答案很简单:您可以使用 setVideoSink 和 setVideoOutput。

我在 OP 中给出的代码很好，您只需取消注释 setVideoOutput(ui->videowidget); 的 mwe_videosinking.cpp 并调用 setVideoSink 在调用 setVideoOutput

之前