which Qt version are you using and which QtVomp version?
The version on google works last time I compiled it with 4.3, but the current 5.x won't compile as Phonon is not longer part of Qt.
Maybe you can try to compile with Phonon from KDE, VLC is anyway the best backend to use.
I'm not working on QtVomp anymore. The reason I stopped developing is the unsure future of Phonon.
Last time I compile QtVomp it wasn't working anymore due to changes in the mediastream format from Vomp. I have an "ugly" patch to get SD signals working, but HD is not working with it.