How to find the GStreamer decoder plugin instance from Qt Phonon backend?

[wysota]

I just assumed that the decoder instance would be available in Phonon since Phonon basically wraps the GStreamer video playing pipeline and builds it from the standard GStreamer elements.

GStreamer is only one of the backends.

Therefore it should also have the decoder stored somewhere or at least have some GStreamer object that could be used to access the decoder plugin and it's interface.

That's surely the case but the whole point of Phonon is to hide those objects from the programmer and expose pure Qt API instead of platform-dependent quirks.