How to use QVideoSink in QML in Qt6

Question

I created my own video sink inherited from QVideoSink in Qt 6. And I want to show content of this sink in QML side. How can I do it?

VideoOutput QML type has videoSink property, but it's read only..

Answer 1

The output elements such as the VideoOutput and the QVideoWidget have a QVideoSink so you should not create one but write over that QVideoSink:

#ifndef PRODUCER_H
#define PRODUCER_H

#include <QObject>
#include <QPointer>
#include <QVideoSink>
#include <QQmlEngine>
#include <QTimer>

class Producer : public QObject
{
    Q_OBJECT
    QML_ELEMENT
    Q_PROPERTY(QVideoSink* videoSink READ videoSink WRITE setVideoSink NOTIFY videoSinkChanged)
public:
    Producer(QObject *parent=nullptr);
    QVideoSink *videoSink() const;
    void setVideoSink(QVideoSink *newVideoSink);
    Q_INVOKABLE void start();
signals:
    void videoSinkChanged();
private:
    QPointer<QVideoSink> m_videoSink;
    void handleTimeout();
    QTimer m_timer;
};

#endif // PRODUCER_H

#include "producer.h"

#include <QImage>
#include <QPainter>
#include <QSize>
#include <QVideoFrame>

#include <QRandomGenerator>
#include <QDateTime>

Producer::Producer(QObject *parent):QObject(parent)
{
    m_timer.setInterval(500);
    connect(&m_timer, &QTimer::timeout, this, &Producer::handleTimeout);
}

QVideoSink *Producer::videoSink() const
{
    return m_videoSink.get();
}

void Producer::setVideoSink(QVideoSink *newVideoSink)
{
    if (m_videoSink == newVideoSink)
        return;
    m_videoSink = newVideoSink;
    emit videoSinkChanged();
}

void Producer::start()
{
    m_timer.start();
    handleTimeout();
}

void Producer::handleTimeout()
{
    if(!m_videoSink)
        return;
    QVideoFrame video_frame(QVideoFrameFormat(QSize(640, 480),QVideoFrameFormat::Format_BGRA8888));
    if(!video_frame.isValid() || !video_frame.map(QVideoFrame::WriteOnly)){
        qWarning() << "QVideoFrame is not valid or not writable";
        return;
    }
    QImage::Format image_format = QVideoFrameFormat::imageFormatFromPixelFormat(video_frame.pixelFormat());
    if(image_format == QImage::Format_Invalid){
        qWarning() << "It is not possible to obtain image format from the pixel format of the videoframe";
        return;
    }
    int plane = 0;
    QImage image(video_frame.bits(plane), video_frame.width(),video_frame.height(), image_format);
    image.fill(QColor::fromRgb(QRandomGenerator::global()->generate()));
    QPainter painter(&image);
    painter.drawText(image.rect(), Qt::AlignCenter, QDateTime::currentDateTime().toString());
    painter.end();

    video_frame.unmap();
    m_videoSink->setVideoFrame(video_frame);
}

#include <QGuiApplication>
#include <QQmlApplicationEngine>


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

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

import QtQuick
import QtQuick.Window
import QtMultimedia

import com.eyllanesc.multimedia

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    Producer{
        id: producer
        videoSink: videoOutput.videoSink
    }
    VideoOutput{
        id: videoOutput
        anchors.fill: parent
    }
    Component.onCompleted: producer.start()
}

_{The complete example can be found here.}