Fastest way to render a VideoFrame?

Zack

I have a grabber card, where I receive my video frames.
I have all the code to grab the frames.
Now I want to render the frame. How can I do this efficient for Qt-Desktop?
With QML it was easy, using the "VideoOutput" node.

But where is the C++ equivalent for this, because I don't want to use QML atm.
I saw QVideoWidget, but this seems to be only plug able to a MediaPlayer...
So what to do here? Has anybody a small code snippet for me?

SGaist

HI,

How did you do it for QML ?

Zack

Here is my simplified code for the Grabber:
The grabber object will be exposed to the QML engine.
It has a property called: videoSurface, this is required from the VideoOutput element in QML.

class grabber : public QObject
{
    Q_OBJECT

    Q_PROPERTY(bool capture READ is_capturing WRITE set_enable_capturing)

    //! This property is needed to connect a VideoOutput with this grabber.
    Q_PROPERTY(QAbstractVideoSurface* videoSurface READ get_video_surface WRITE set_video_surface)
    
    QAbstractVideoSurface* get_video_surface() const;
    void set_video_surface(QAbstractVideoSurface* s);

    QAbstractVideoSurface* m_video_surface;
};

Somewhere in grabber.cpp I just update the video surface when I get a new video frame from the grabber.

connect(m_grabber.get(), &matrox_grabber::new_video_frame, this, [this](const QVideoFrame& frame)
    {
        if (m_video_surface)
            m_video_surface->present(frame);
    });

My matrox_grabber has all the logic to retrieve frame and put it into a QVideoFrame.

And here is the QML file:

# Main.qml
import QtQuick 2.3
import QtQuick.Controls 1.2
import QtQuick.Window 2.2
import QtMultimedia 5.9

import divas.components 1.0
ApplicationWindow {
 id: window
  visible: true
  Grabber {
    id: matrox
  }
  
   VideoOutput {
        source: matrox;
        anchors.centerIn: parent;
        width: parent.width;
        height: parent.height;
        }

}

SGaist

I usually wrote that kind of backend as QCamera plugins which makes it simpler to integrate with both C++ and QML

IIRC, you might be able to avoid that by implementing a QMediaObject subclass that provides the adequate interface basically grabber should become a QMediaObject. However I'm not sure whether you can then just call bind on your QVideoWidget from your grabber instance.

r2d3

@SGaist Hello Samuel, do you have any pointer to a doc on how to create QCamera plugins ?

SGaist

Hi, sorry, no I don't. I went it hardcore style and looked at the various camera backend implemented by Qt. You'll see that it's not that complicated to put together.