video device dimension

Fixrobert's icon

Sorry I've allready posted that question but got no answer so I try again (I realy bang my head againts that).

I wonder how I can get the exact dimensions (or, maybe, the ratio) of a video device (a camera...) with jit.qt.grab.
Quick time can do it when recording but I can't see any message or attribute (like @adapt, for jit.qt.movie) I could send to jit.qt.grab that allow automaticaly grab the video device dimensions.

any help greatly appreciated