插件中的QML和QtGStreamer

Question

I'm trying to prepare QML plugin to play video on embedded device in a way that other developers can use it without much hassle. However the way it is currently proposed requires almost always writing some C++ wrapper around your QML application. I'm refering to this example: http://gstreamer.freedesktop.org/data/doc/gstreamer/head/qt-gstreamer/html/examples_2qmlplayer_2main_8cpp-example.html

I would like to be able to have plugin and simply write:

import AwesomeVideoPlugin 1.0

Rect
{
    AwesomeVideo
    {
        width: 320 
        height: 240
        url: "./myvideo.avi" 
        // ... some minor stuff like mouse click handling, controls, etc.
    }
}

Currently QtGStreamer requires to provide videoSurface property to VideoItem. The only way to do this is to create and set context for additional property in rootContext(). And to create GraphicsVideoSurface I need QGraphicsView (QDeclarativeView fills this role).

Is it possible to:

1. Get QDeclarativeView from within QDeclarativeItem (to which I have only access from QML plugin) in a way that it can be later used to feed GraphicsVideoSurface? My guess is no - however I've found path QFraphicsItem::scene() ==> QGraphScene ==> QGraphScene::views() ==> QList of QGraphicsView - it looks like VERY bad programming but maybe somebody got it to work (I'm getting segfault)

2. Is there other way to provide video sink for QtGStreamer from within QDeclarativeItem ?

Greetz

Yatsa

Answer 1

I had the same question, but haven't come up with an elegant solution.

However, one thought would be to make the videosurface available via an accessor function from a sub-classed QApplication object.

This would, of course, mean that your plug-in depends on the application subclass having a getVideoSurface method, but it does remove the ugliness from the QML code.

class MyApp : public QApplication
{
    ....
     QGst::Ui::GraphicsVideoSurface *getVideoSurface() { return m_videosurface; }
}

 ...
int MyApp::init()
{
     m_viewer = new QDeclarativeView(); 
     m_viewer->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
     m_videosurface = new QGst::Ui::GraphicsVideoSurface(m_viewer);
}

MyVideoPlugin::MyVideoPlugin(QDeclarativeItem *parent) : QDeclarativeItem(parent)
{
    QGst::Ui::GraphicsVideoSurface *surface = ((MyApp*)qApp)->getVideoSurface();
}
...

Now the MyVideoPlugin element may be used without referencing an exported videosurface context item.