Cannot add Multimedia Widgets to Qt Creator C++ project

[Cazzaniga]

Hi,
I am trying to compile and run the official Media Player Example in Qt:
http://doc.qt.io/qt-5/qtmultimediawi...r-example.html
for a Raspberry Pi running Raspbian Jessie. I still have no success: when I build the project, the following error appears:

:-1: error: Unknown module(s) in QT: multimedia multimediawidgets

:-1: error: Unknown module(s) in QT: multimedia multimediawidgets

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I installed "sudo apt-get install qtmultimedia5-dev" but without any success. Is it the right module to install?
My Qt should be up to date, and I don't know where the problem can be. Could anyone help please?
Thanks!