VideoOutput QML的自定义源属性

Question

为VideoOutputQML对象提供自定义帧源到底需要做什么？

VideoOuput本身是否QAbstractVideoSurface向“源” 提供类的实例 ？

Qt5文档说了有关提供此问题的以下内容：

如果要扩展自己的C ++类以与VideoOutput互操作，则可以为基于QObject的类提供mediaObject属性，该属性公开具有可用QVideoRendererControl的QMediaObject派生类，也可以为基于QObject的类提供可写videoSurface属性可以接受基于QAbstractVideoSurface的类，并且可以遵循正确的协议向其提供QVideoFrame。

根据以下文档，我执行了以下操作：

1. 我implmented我自己的类myFrameProvider来源于QObject具有可写的videoSurface属性。
2. 使一个类连接到以下类，该类将帧发送到myFrameProvider。
3. 实例化myFrameProvider类，并使其在与“ VideoOutput”小部件相同的QML上下文中可访问。

之后-每当访问“ videSurface”属性时，我都会遇到段错误。我应该设置自己的视频界面属性吗？

Answer 1

在遇到类似问题时，我偶然发现了您的问题。不久之后，我找到了一个对我有用的解决方案。即使您的问题比较老，并且您可能继续前进，我也想分享我的答案，以帮助其他人。

我在QT文档的“使用低级视频帧”部分中找到了答案。在那里发布的那段代码作为起点非常有用，但是我必须对其进行修改，以使其正常运行。一个最小的工作示例如下所示：

FrameProvider.h

#include <QObject>
#include <QAbstractVideoSurface>
#include <QVideoSurfaceFormat>

class FameProvider : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QAbstractVideoSurface *videoSurface READ videoSurface WRITE setVideoSurface)


public:
    QAbstractVideoSurface* videoSurface() const { return m_surface; }

private:
    QAbstractVideoSurface *m_surface = NULL;
    QVideoSurfaceFormat m_format;

public:


    void setVideoSurface(QAbstractVideoSurface *surface)
    {
        if (m_surface && m_surface != surface  && m_surface->isActive()) {
            m_surface->stop();
        }

        m_surface = surface;

        if (m_surface && m_format.isValid())
        {
            m_format = m_surface->nearestFormat(m_format);
            m_surface->start(m_format);

        }
    }

    void setFormat(int width, int heigth, int format)
    {
        QSize size(width, heigth);
        QVideoSurfaceFormat format(size, format);
        m_format = format;

        if (m_surface) 
        {
            if (m_surface->isActive())
            {
                m_surface->stop();
            }
            m_format = m_surface->nearestFormat(m_format);
            m_surface->start(m_format);
        }
    }

public slots:
    void onNewVideoContentReceived(const QVideoFrame &frame)
    {

        if (m_surface)
            m_surface->present(frame);
    }
};

main.qml

import QtQuick 2.9
import QtQuick.Controls 2.2
import QtQuick.Controls.Material 2.2
import QtMultimedia 5.4
import com.yourcompany.FrameProvider 1.0

ApplicationWindow {
    objectName: "mainWindow"
    visible: true
    width: 640
    height: 480

    FrameProvider{
        objectName: "provider"
        id: provider
    }

    VideoOutput {
        id: display
        objectName: "display"
        anchors.top: parent.top
        anchors.bottom: parent.bottom
        width: parent.width
        source: provider
    }
}

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>

 int main(int argc, char *argv[])
{
    // initialize the qml application engine
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;

    //register the custom control to the qml application engine
    qmlRegisterType<FameProvider>("com.yourcompany.FrameProvider", 1, 0, "FrameProvider");

    // start the view
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
    {
    return -1;
    }

    // find your custom control
    QObject *rootObject = engine.rootObjects().first();
    Qobject *display = rootObject->findChild<QObject *>("display");
    auto provider = qvariant_cast<FameProvider *>(display->property("source"));

    // Create your custom frame source class, which inherits from QObject. This source is expected to have the following public fields and signals:
    // - int width
    // - int height
    // - int format (following QVideoFrame::PixelFormat)
    // - signals: void newFrameAvailable(const QVideoFrame &frame);
    CustomFramesource source;

    // Set the correct format for the video surface (Make sure your selected format is supported by the surface)
    provider->setFormat(source.width,source.height, source.format);

    // Connect your frame source with the provider
    QObject::connect(&source, SIGNAL(newFrameAvailable(const QVideoFrame &)), provider, SLOT(onNewVideoContentReceived(const QVideoFrame &)));

    // run the app
    int retVal =  app.exec();

    return 0;
}

MWE来自我的实际代码，因此未经测试。我希望它无论如何都能运行并显示所有需要的步骤。