About DirectDraw Video-Port Extensions

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DirectDraw has been extended to include the DirectDrawVideoPort object, which takes advantage of video-port technology and provides its services through the IDDVideoPortContainer and IDirectDrawVideoPort interfaces.

DirectDrawVideoPort objects do not control the video decoder, because it provides services of its own, nor does DirectDraw control the video source; it is beyond the scope of the video port. Rather, a DirectDrawVideoPort object represents the video port itself. It monitors the incoming signal and passes image data to the frame buffer, using parameters set though its interface methods to modify the image, perform flipping, or carry out other services.

The IDDVideoPortContainer interface, which you can retrieve by calling the IDirectDraw4::QueryInterface method, provides methods to query the hardware for its capabilities and create video-port objects. You create a video-port object by calling the IDDVideoPortContainer::CreateVideoPort method. Video-port objects expose their functionality through the IDirectDrawVideoPort interface, enabling you to manipulate the video-port hardware itself. Using these interfaces, you can examine the video-port's capabilities, assign an overlay surface to receive image data, start and stop video playback, and set hardware parameters to manipulate image data for cropping, color control, scaling, or shrinking effects.

DirectDraw video-port extensions provide for multiple video ports on the same machine by allowing you to create multiple DirectDrawVideoPort objects. There is no requirement that multiple video ports on a machine be identical — each port is separately enumerated and configured separately, regardless of any hardware differences that might exist.

In keeping with the general philosophy of DirectX, this technology gives programmers low-level access to hardware features while insulating them from specific hardware implementation details. It is not a high-level API.

 Last updated on Thursday, April 08, 2004

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