Qt Mobility using Gstreamer CPU Usage

[goli]

I am trying to use Qt Mobility to run video on embedded linux system.
when I use the gstreamer directly (gst-launch playbin2 uri=file://video-file.avi) the CPU is ~20%,
but when I use the QtMobility(Video element of QtMultimediaKit) the CPU is ~100% usage.
I see from the outputs that the qt use the gstreamer, but it's not efficient.

Any idea what is wrong here?