Phonon can't play the video

[leegoe]

Hello, everybody!
I have written a program use Qt and Phonon to play a AVI video. But when I run this program, it can not play the video, and it output some messages:

Setting new source
New source: QUrl( "file:///home/lp.avi" )
Transitioning to state "ready"
State change
Moving from "null" 0 to "ready" 1
Transitioning to state "ready"
Transitioning to state "ready"

Does anybody know what is the problem?

My system is Fedora16, and I have installed gstreamer-plugins.

[leegoe]

I make the example playvideo of the <<Advanced Qt Programming>> book's source code, and it also has this problem. Is there any way to fix it???