Well I suspect you can't work this issue out by Qt API, i.e. keep your app cross-platform.
I see the libvlc.dll problem is in that it has dependencies in the same directory(C:\Program Files (x86)\VideoLAN\VLC) which is not a part of default dll search paths.
To make your app looking more cross-platform I would suggest you to call SetDllDirectory WinAPI and then load libvlc by using QLibrary:
Qt Code: 
  1. #if defined( Q_WS_WIN )
  2.       SetDllDirectory( L"C:\\Program Files (x86)\\VideoLAN\\VLC" );
  3. #endif
  4.  
  5.       QLibrary lib( "libvlc" );
  6.  
  7.       if ( lib.load() )
  8.       {
  9.         qDebug() << "libvlc loaded";
  10.       }
  11.       else
  12.       {
  13.         qDebug() << "libvlc not loaded";
  14.       }
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