QMediaPlayer setVideoOutput locks up user interface

gmparker2000

I took the mdi example from qt examples as a starting point. I created my own mdi child window called "VideoMdiChild".

VideoMdiChild *MainWindow::createMdiChild()
{
    VideoMdiChild *child = new VideoMdiChild;
    mdiArea->addSubWindow(child);
    return child;
}

This video mdi child uses a form that contains a video widget. The video widget contains a QMediaPlayer. When I open the video mdi child it locks up the entire user interface until I resize the window. Once resized, the menu becomes usable again. The toolbar is also unresponsive until I tear it off and place it somewhere else.

If I remove the line "_mediaPlayer->setVideoOutput(videoWidget);" from the following code, then things work properly. Of course this means that the video is not rendered.

VideoWidget::VideoWidget(QWidget *parent) :
    QWidget(parent)
{
    _mediaPlayer = new QMediaPlayer(
                this
                , QMediaPlayer::VideoSurface);

    QVideoWidget *videoWidget = new QVideoWidget;
    _mediaPlayer->setVideoOutput(videoWidget);

    QBoxLayout *layout = new QVBoxLayout;
    layout->addWidget(videoWidget);
    setLayout(layout);

   ...
}

Am I doing something obviously wrong? I tried 5.11.2, 5.11.1, and 5.9.7. They all exhibit the same behavior.

Qt 5.11.2 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 5.3.1 20160406 (Red Hat 5.3.1-6)) on "xcb"
OS: Ubuntu 18.04.1 LTS [linux version 4.15.0-42-generic]

Architecture: x86_64; features: SSE2 SSE3 SSSE3 SSE4.1 SSE4.2 AVX AVX2

gmparker2000

So it looks like it turned out to be related to display scaling in KDE. If you set the scale to an even number like 2 then there are no problems. I had changed the scaling to 1.7. I have it set to 2 now and the problem appears to be gone.

SGaist

Hi,

Do you have the same behavior if you use your distribution provided Qt ?

gmparker2000

So it looks like it turned out to be related to display scaling in KDE. If you set the scale to an even number like 2 then there are no problems. I had changed the scaling to 1.7. I have it set to 2 now and the problem appears to be gone.

SGaist

Thanks for sharing your findings !