To avoid tearing images when refreshing the screen between frames, DirectDrawVideoPort objects can automatically flip their target overlay surfaces in response to VREF signals. To use this service, the target surface you set to the video-port object with the IDirectDrawVideoPort::SetTargetSurface method must be the first surface in a flipping chain of overlay surfaces. Then, to begin playing the video sequence, call the IDirectDrawVideoPort::StartVideo method, specifying the DDVP_AUTOFLIP flag in the dwVPFlags member of the associated DDVIDEOPORTINFO structure. The video-port object will flip to the next surface in the flipping chain for each VREF signal is receives. If the video port is interleaving fields, it will flip once for every two VREF signals it receives.
If you are using auto-flipping and want to direct VBI data to separate auto-flipped surfaces, you must have the same number of VBI surfaces as you do standard video surfaces.