opencv/highgui.go
func (capture *Capture) RetrieveFrame(streamIdx int) *IplImage {
	rv := C.cvRetrieveFrame((*C.CvCapture)(capture), C.int(streamIdx))
	return (*IplImage)(rv)
}
func (capture *Capture) RetrieveFrame(streamIdx int) *IplImage {
	rv := C.cvRetrieveFrame((*C.CvCapture)(capture), C.int(streamIdx))
	return (*IplImage)(rv)
}
/* get the frame grabbed with cvGrabFrame(..)
This function may apply some frame processing like
frame decompression, flipping etc.
!!!DO NOT RELEASE or MODIFY the retrieved frame!!! */