File descriptor returned by
This ioctl is part of the video
overlay I/O method. Applications call
VIDIOC_OVERLAY to start or stop the
overlay. It takes a pointer to an integer which must be set to
zero by the application to stop overlay, to one to start.
On success 0 is returned, on error -1 and the
errno variable is set appropriately:
Video overlay is not supported, or the parameters have not been set up. See Section 4.2 for the necessary steps.