It's impossible to create another pipeline with d3dvideosink after disposing
the previous one due to some problem in d3dvideosink. The message is: "Unable
to register Direct3D hidden window class".
I've evaluated the problem and it's that UnregisterClass() in working thread is
called before DestroyWindow() and UnregisterClass() does nothing.
https://bugzilla.gnome.org/show_bug.cgi?id=722622