This is expected on your Vista, unfortunately. See the relevant post from the maintainer:
On Windows XP, Qt Multimedia uses DirectShow (and WMF for Windows Vista and later). The DirectShow plugin binary is not included in the Qt 5.0 package (only the WMF plugin is). You need to compile QtMultimedia yourself, or just the DirectShow plugin in qtmultimedia/src/plugins/directshow
... in the following report on the Qt issue tracker:
Qt 5.0 and QMediaPlayer failure on Windows XP
The steps to build it on your would be:
- grab the tarball
- unpack it
- move into the qtmultimedia folder
- run qmake -r
- (n)make
- (n)make install
Please make sure qmake is properly in your PATH before doing this.