Dear Maintainer,

The kwin effects KCM provides, for some effects, a button that looks like it should show
a video preview. Hitting that button makes the corresponding row in the effects configuration
really large, but nothing else happens. The result looks rather ugly, and not like it has been
intended.

On stdout/stderr, I see:

  defaultServiceProvider::requestService(): no service found for - "org.qt-project.qt.mediaplayer"

So maybe there's some dependency missing here? In any case, these buttons should either work,
or they should be hidden.

Kind regards,
Ralf