I'd start by installing VLC and ensuring that the VLC core library can be found somewhere on the path specified in your LIBS variable along with the VLC-Qt stuff.
LIBS += -L$$quote{c:/Path to the/VLC-Qt} -lvlc-qt -lvlc-qt-widgets
LIBS += -L$$quote{C:/Program Files/VLC} -lvlccore
LIBS += -L$$quote{c:/Path to the/VLC-Qt} -lvlc-qt -lvlc-qt-widgets
LIBS += -L$$quote{C:/Program Files/VLC} -lvlccore
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You will probably need to adjust the path and/or library name (I am guessing).
Beyond that, it is generally helpful if you post information on what you have done and what the entire error messages are.
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