I've tried to use -wid with a QT Widget and it doesn't work, "X11 Bad access", i don't know how to fix this, i'm writing a kpart and with -wid option it didn't work, so i've decided to swallow it, first by window name, then by pid that's unique. Sadly, mplayer doesn't set the _NET_WM_PID, so KWin can't find it.