IOCTL_VIDEO_QUERY_NUM_AVAIL_MODES IOCTL (ntddvdeo.h)
Returns the number of video modes supported by the adapter and the size in bytes of the video mode information, which can be used to allocate a buffer for an IOCTL_VIDEO_QUERY_AVAIL_MODES request. Miniport drivers are required to support this nonmodal request.
The miniport driver returns the number of modes in a VIDEO_NUM_MODES structure in the VRP OutputBuffer.
If the miniport driver successfully returns the mode count, it sets the Information member of the STATUS_BLOCK structure to sizeof(VIDEO_NUM_MODES); otherwise, the miniport driver sets this member to zero.