IVideoFrameStep::Step method

The Step method causes the filter graph to step forward by the specified number of frames.

Syntax


HRESULT Step(
   DWORD    dwFrames,
   IUnknown *pStepObject
);

Parameters

dwFrames

Specifies the number of frames to skip. If dwFrames is 1, the graph steps forward one frame. If dwFrames is a number n greater than 1, the graph skips n - 1 frames and shows the nth frame.

pStepObject

Pointer to an interface on the filter that will control the stepping operation, or NULL. Specify NULL to perform the frame stepping using the renderer filter in the graph. If non-NULL, the object must implement the IKsPropertySet interface and support the AM_KSPROPSETID_FrameStep property. (For more information, see Frame Stepping Property Set.) If the graph includes a custom filter that implements the frame stepping, pStepObject can specify a pointer to that filter.

Return value

Returns an HRESULT. Possible values include the following.

Return codeDescription
S_OK

Success.

VFW_E_FRAME_STEP_UNSUPPORTED

Frame stepping is not supported.

E_INVALIDARG

The pStepObject parameter is invalid.

 

Remarks

When the step operation is complete, this method sends an EC_STEP_COMPLETE event notification to the filter graph manager, which will pass it to the application's event loop and set the filter graph to a paused state.

The frames step in real time, which means that if the movie is playing at 30 frames per second, calling IVideoFrameStep::Step with dwFrames set to 60 would take 2 seconds to execute. All methods in this interface are asynchronous, so control returns to the application immediately.

Requirements

Minimum supported client

Windows XP [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]

Header

Strmif.h (include Dshow.h)

Library

Strmiids.lib

See also

Error and Success Codes
IVideoFrameStep Interface

 

 

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