func NewFileCapture(filename string) *Capture {
	filename_c := C.CString(filename)
	defer C.free(unsafe.Pointer(filename_c))
	cap := C.cvCreateFileCapture(filename_c)
	return (*Capture)(cap)
}
func NewFileCapture(filename string) *Capture {
	filename_c := C.CString(filename)
	defer C.free(unsafe.Pointer(filename_c))
	cap := C.cvCreateFileCapture(filename_c)
	return (*Capture)(cap)
}
/* start capturing frames from video file */