can not display a video with qml sink within qwidgets layout

[JoeCFD]

I am trying to use qml sink inside a qwidget and play video with a gstreamer pipeline. When I start to play the video, I get the following error:

error Could not initialize window system
Debugging info: gstqtsink.cc(309): gst_qt_sink_change_state (): /GstGLSinkBin:glsinkbin0/GstQtSink:sink

Pure qml code works fine.

Did anyone have the similar problems before? I know it is not a good idea to mix qml with qwidgets. Unluckily, I do not have other choices for now.

Qt 5.15.2 + Ubuntu 18.04 + gstreamer 1.14
Qt 5.15.3 + Ubuntu 22.04 + gstreamer 1.22

[JoeCFD]

@JoeCFD got a test case and it works.
https://github.com/zt-luo/QuickWidgetPlayer

[SGaist]

Hi,

How did you implement it ? Using a QQuickWidget ?

[JoeCFD]

@SGaist Thanks for your reply. I tried both.

class MyWidget: public QQuickWidget
{
};

MyWidget::MyWidget( QWidget * parent ) : QQuickWidget( parent )
{
    setWindowFlags( Qt::FramelessWindowHint | Qt::WindowTitleHint );
    auto vbox_layout = new QVBoxLayout( this );
    vbox_layout->setContentsMargins( 0, 0, 0, 0 );

    QUrl source("qrc:res/StreamingRect.qml");

    m_quickView = new QQuickView;
    m_quickView->setResizeMode( QQuickView::SizeRootObjectToView );
    m_quickView->setSource( source );
    m_currentRootObject = m_quickView->rootObject();
    
    m_quickWidget = QWidget::createWindowContainer( m_quickView );
    vbox_layout->addWidget( m_quickWidget );

    if ( m_currentRootObject ) {
        m_currentRootObject->setProperty( "m_height", size().height() );
        m_currentRootObject->setProperty( "m_width", size().width() );
        m_currentRootObject->setProperty( "m_visible", true );
    }
}

[SGaist]

@JoeCFD why did you subclass it ? The usual way is to simply use it to display your QtQuick content and then integrate the widget within another one.

[JoeCFD]

@JoeCFD
I make a simple case and display it in the main. Eventually I will add it to my app. I would like to make sure the sink works fine. StreamingRect.qml has a qml sink and it is added to the pipeline without any issue. The same qml file is used in a pure qml app and works fine.

int main( int argc, char * argv[] )
{
    auto app = new QApplication( argc, argv );
    app->setStyle( "Fusion" );

    QSize size( 800, 600 );
    auto streamer = new MyWidget ( nullptr );
    streamer->resize( size );
    streamer->setVisible( true );

    return app->exec();
}

[SGaist]

The issue here is that rather than using QQuickWidget as a qml container, you create a second QML container widget that you put on top of it.

[JoeCFD]

@SGaist I tried to use QWidget as well. I need to put it somewhere in the layout of my app anyway later.

[SGaist]

@JoeCFD what happens is you only use QQuickWidget in your main function ?

[JoeCFD]

@SGaist Tried it and got the exactly same errors:

error Could not initialize window system
Debugging info: gstqtsink.cc(309): gst_qt_sink_change_state (): /GstGLSinkBin:glsinkbin0/GstQtSink:sink

More error output:
0:00:00.412321063 11575 0x555f6545be00 ERROR qtglwidget qtitem.cc:336:initWinSys: 0x555f657c5a20 failed to retrieve wrapped context (NULL)
0:00:00.412390280 11575 0x555f6545be00 ERROR playbin gstplaybin2.c:5444:activate_group:<playbin0> failed to activate sinks

[JoeCFD]

@JoeCFD got a test case and it works.
https://github.com/zt-luo/QuickWidgetPlayer