I think you need a
GStreamer and KGst.
I had a similar problem when installed AmaroK, it didn't found an installed GStreamer, so i just left it as is and use xine engine instead. (i am too lazy, yes..)
I don't tell you leave it as is... :wink:
Try to re-install GStreamer and it's plugins (find more info at project homepage). Bindings are KGst, you can find it at JuK's
homepage, look for two last entries in "Files" section in site menu.
If you get it to work - please, post it here.