Saving data with dataWithPDFInsideRect: just makes a black pdf

I have a QTCaptureView and Im trying to save the view as a picture. So far I have this:

 NSRect rect = [outputView bounds];
 NSData *viewData = [outputView dataWithPDFInsideRect:rect];
 [viewData writeToFile:@"/test.pdf" atomically:YES];

but fo开发者_开发百科r some reason when I save instead of seeing a picture of my vie (iSight Camera) I see a black pdf file.

Thanks for any help

QTCaptureView isn't meant to be used in this way due to the way it is optimized. You'll need to do single-frame-grabbing the QTKit way: Creating a Single-Frame Grabbing Application.