First, I'd have to ask why not just use layouts properly instead of using constructs such as "ui->verticalLayout_3->setGeometry(QRect(2,2,event->size().width(),event->size().height()));" ? There's no need for this kind of code on a well designed ui.

Next, Phonon isn't a magic media player. It requires and depends on back ends to do some of its work (like the rendering of audio), and these back ends depend on what your trying to play. You may wish to check the codecs on the development machine compared to the machine your trying to get it to work on.