Why are all my seek events ignored?

[Nikos Chantziaras]

I'm using QtGStreamer 1.2.0 (build against Qt 4.8.6) with GStreamer 1.4.5.

I'm trying to send a seek event to a pipeline to make the video play at 
half speed with:

   QGst::SeekEventPtr seekEv = QGst::SeekEvent::create(
     0.5,
     QGst::FormatTime,
     QGst::SeekFlagSegment,
     QGst::SeekTypeSet, 0,
     QGst::SeekTypeEnd, 0);

   pipeline->sendEvent(seekEv);
   pipeline->setState(QGst::StatePlaying);

But it gets ignored. The video plays at 100% speed. In fact, my bus 
message handler doesn't even receive a single QGst::MessageSegmentDone 
message.

I tried swapping the sendEvent() and setState() calls, but it doesn't 
change anything. (Both calls indicate success on return, btw.)

I'm using "playbin" for the pipeline, created with:

   QGst::ElementFactory::make("playbin")

The uri is an "appsrc://", in case that matters:

   pipeline->setProperty("uri", "appsrc://");