A video capture driver passes DD_DXAPI_OPENVPCAPTUREDEVICE in the dwFunctionNum parameter of the DxApi function to open the device for video capture.

Input Parameters


Pointer to a DDOPENVPCAPTUREDEVICEIN structure that contains the relevant VPE object information required for the capture.

Output Parameters


Pointer to a DDOPENVPCAPTUREDEVICEOUT structure that contains the new capture handle.


A VPE capture device allows hardware video port data to be automatically bus mastered from the surface to a specified buffer. Opening the capture device determines which lines are to be captured. For example, for VBI, the capture driver may only be interested in the first 21 lines. If the capture driver wants to capture different regions to different buffers (for example, VBI and video to separate buffers), multiple capture devices can be created.

When a capture device is created, the kernel-mode video transport creates a queue for each device. The driver can later add buffers to this queue. Each time the hardware video port V-sync occurs, the kernel-mode video transport automatically initiates the correct bus masters from the frame buffer surface most recently filled by the hardware video port to the buffer in the queue. If you don't want to capture on every field, you can indicate this by setting the dwCaptureEveryNFields member of DDOPENVPCAPTUREDEVICEIN to something other than 1.

The hDirectDraw and hVideoPort members of DDOPENVPCAPTUREDEVICEIN specify the DirectDraw object and VPE object from which you want to capture. The dwStartLine and dwEndLine members indicate which lines are to be captured. The dwStartLine member is relative to the start of the surface (0 is the first line) and dwEndLine is inclusive (setting dwStartLine and dwEndLine to 0 causes the first line to be captured).
The driver must also specify a callback that is called when the capture device becomes unusable due to the VPE object being released at user mode. The pContext member of DDOPENVPCAPTUREDEVICEIN contains a value that is passed if the pfnCaptureClose callback function is ever called.

If the ddRVal member of DDOPENVPCAPTUREDEVICEOUT is set to DD_OK, the output from this function identifier is a new DirectDraw capture handle. This new handle must be used on all subsequent calls that reference this capture device.

This function identifier can only be called from PASSIVE_LEVEL.



Ddkmapi.h (include Ddkmapi.h)

See also




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