QML Desktop Streaming

[mark.lt]

Hi, I have the following problem: I need to capture part of the desktop, specifically of the second monitor, given an x, an y, the width and the height. My question is: is it possible to stream a part of desktop and show it inside a box in a qml project.
My first thought is to somehow find a c++ function that allows to do screenshot of my second monitor and after importing it inside qml I would call it like every 0.2 seconds with Timer to do screenshot and show it in a box in QML.

Thank you.

[GrecKo]

You can use QScreen::grabWindow for that.

To use that in QML, you could feed this in a VideoOutput.

To do that you would have to put your QObject derived class instance as the source of the VideoOutput : http://doc.qt.io/qt-5/qml-qtmultimedia-videooutput.html#source-prop
Your class needs to have a Q_PROPERTY(QAbstractVideoSurface* videoSurface READ videoSurface WRITE setVideoSurface NOTIFY videoSurfaceChange)

In your setVideoSurface method, you need to call the start method of QAbstractVideoSurface with a correct format (your size and the pixelformat, pixelformat should be QVideoFrame::Format_ARGB32 for desktop I guess).

And then when you want to update the VideoOutput (via a QTimer for example), you call the present method of QAbstractVideoSurface with a QVideoFrame you constructed from the QPixmap you got in QScreen::grabWindow.

[mark.lt]

Thank you for the instructions, I'm new to all of this so I hope to get to the bottom of this :D

[mark.lt]

Hi, I need some help. I really don't have idea how to do it. This is what I have done so far:
videostream.h

#ifndef VIDEOSTREAM_H
#define VIDEOSTREAM_H
#include <QObject>
#include <QAbstractVideoSurface>

class videoStream: public QObject
{
    Q_OBJECT
    Q_PROPERTY(QAbstractVideoSurface* videoSurface READ videoSurface WRITE setVideoSurface NOTIFY videoSurfaceChange)

public:

    explicit videoStream(QObject *parent = nullptr);
    QAbstractVideoSurface* videoSurface();
    void setVideoSurface(const QAbstractVideoSurface &videoSurface);
    void updateScreen();

signals:
    void videoSurfaceChange();

private:
    QAbstractVideoSurface* m_videoSurface;
};

#endif // VIDEOSTREAM_H

videoStream.cpp

#include "videostream.h"
#include <QVideoSurfaceFormat>
#include <QSize>
#include <QGuiApplication>
#include <QWidget>
#include <QWindow>

videoStream::videoStream(QObject *parent):
    QObject(parent)
{

}
QAbstractVideoSurface* videoStream::videoSurface()
{
    return m_videoSurface;
}

void videoStream::setVideoSurface(const QAbstractVideoSurface &videoSurface)
{
    QVideoSurfaceFormat* qvideosurfaceformat;
    qvideosurfaceformat=new QVideoSurfaceFormat(QSize(800,600),QVideoFrame::Format_ARGB32);

    videoSurface.start(&qvideosurfaceformat);

}

void videoStream::updateScreen(){
    QScreen *screen = QGuiApplication::primaryScreen();
    if (QWindow *window = QWidget::windowHandle())
        screen = window->QWindow::screen();
    if (!screen)
        return;

    m_videoSurface->present(screen->grabWindow(0));
}

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "videostream.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    qmlRegisterType<BackEnd>("videostream", 1, 0, "VideoStream");

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

main.qml

import QtQuick 2.9
import QtQuick.Window 2.2
import QtMultimedia 5.9
import videostream 1.0

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

    VideoStream{
        id:video_stream
    }

    Rectangle {
        width: 800
        height: 600

        VideoOutput {
            id: videoOutput
            source: video_stream.videoStream
            anchors.fill: parent
        }
    }
Timer {
        interval: 500; running: true; repeat: true
        onTriggered: video_stream.updateScreen
  }
}

A part from errors with these lines

videoSurface.start(&qvideosurfaceformat);

if (QWindow *window = QWidget::windowHandle())

m_videoSurface->present(screen->grabWindow(0));

I have no idea what should I do

[mark.lt]

Nevermind, thanks anyway. I simply solved it by using QScreen::grabWindow inside QQuickImageProvider and with a Timer inside QML I request and show the image every 33ms to have 30 frames per second of the screen.