Qt and VLC
Well, we have a very easy howto for you: libVLC in Qt .
This will output the video inside the widget that you want using QWidget::winId() method.
This has been tested on Linux and Windows, using libVLC 0.9.9.
If you can't build your application easily, remember to install libvlc-dev or to use the SDK for windows from the .zip files of the releases!
Don't hesitate to complete this!