Qt: QVideoWidget doesn't show up and disables all buttons within application OR extremely slows down the application

Question

To make it clear the question is: Why, when I add a QVideoWidget to my application, all buttons become not clickable, the scrollbars don't work, and the comboboxes as well become not clickable? Is QVideoWidget disabling those functionalities? Or is that maybe (like I read in this SO question ) QVideoWidget is extremely slowing down my application, just by being added to the application?

Now the details: I really hope someone can help me with this. I'm trying to place a QvideoWidget into my desktop application with the following code (nothing special, just like in the tutorials):

// ...
// more code above for other things...
// main video-player widget
video_widget = new QVideoWidget;
video_widget->setMaximumHeight(100);    // I could set any size here...this is not the point
video_widget->setMinimumHeight(100);
video_widget->setStyleSheet(STYLE_WIDGET_BG); // same background as the other widgets...
video_widget->setMaximumWidth(100);
video_widget->setMinimumWidth(100);
media_player = new QMediaPlayer(0, QMediaPlayer::VideoSurface);
TV_V_LAYOUT_MAIN_2->addWidget(video_widget);    // #define TV_V_LAYOUT_MAIN_2 ui.lvl_4_tv2_h_1 --> this a layout inside another layout...
media_player->setVideoOutput(video_widget);
return; // this function is called inside the MainWindow constructor

So there are the situations:

1) Without adding the videowidget, everything works fine...

2) As soon as I add the QVideoWidget with the code above: app overview

What happens? The video player doesn't show up in any way. There should be at least the gray background like the other widgets, but nothing. Yet the buttons position lowers, so I guess the player was inserted...The problem is: all buttons (and I mean ALL buttons within my application ) are disabled. So are the comboboxes and the scrollbar . By disabled I mean, when you click them, it doesn't normally "animate" like when a button is cliked, and the scrollbar doesn't scroll...

By the way the QVideoWidget is not places into the same layout as the buttons below. You can see the layout hierarchy here: Layouts with Qt Designer

I guess I'm missing something very simple. Anyone got the solution for me?

INFO: I'm programming with Visual Studio 2013 with Qt Add-In; I use only standard libraries; gstreamer is included in the project as well (nothing implemented yet).

OLD EDIT: it may be that the inserting of the video-widget extremely slows down the application , therefore giving the illusion that the scrollbar and the buttons don't work, just because it takes a lot of time for them to process the user interaction. Is this possible? Any solution for that?

Answer 1

Got the solution: If your QVideoWidgets or QMediaPlayers extremely slow down your application, all you have to do, if you haven't yet, is to move all (or just the nedeed) Qt dll's into your project folder.

That's very basic, I know, yet that was my problem. Now it works like heaven.