GetCurrentImage的MSND说明，暂记

IBasicVideo::GetCurrentImage 

Microsoft DirectShow 9.0

IBasicVideo::GetCurrentImage

The GetCurrentImage method retrieves the current image waiting at the renderer.

Syntax

HRESULT GetCurrentImage(
  long *pBufferSize,
  long *pDIBImage
);

Parameters

pBufferSize

[in, out] Pointer to a variable that contains the size of the buffer that the caller is passing in. If pDIBImage is NULL, this parameter receives the required buffer size.

pDIBImage

[out] Pointer to a buffer where the complete image will be stored in device-independent bitmap (DIB) format. Cast the pointer to a long pointer type.

Return Values

Returns an HRESULT value.

Remarks

The Video Renderer filter and the Video Mixing Renderer (VMR) implement this method differently.

Video Renderer only:

This method fails if the renderer is using DirectDraw acceleration. Unfortunately, this depends on the end-user's hardware configuration, so in practice this method is not reliable.

Pause the Video Renderer before calling this method. Otherwise, the method returns VFW_E_NOT_PAUSED. Make sure that the pause operation has completed by calling IMediaControl::GetState; if the pause operation has not completed, the GetCurrentImage method returns E_UNEXPECTED. Depending on what data the source filter has available, the video renderer is not guaranteed to service this request. If no image is available, it returns E_FAIL.

Video Mixing Renderer only:

This method is reliable regardless of whether the VMR is using DirectDraw acceleration and regardless of the current graph state (running, stopped, or paused).

Video Renderer and Video Mixing Renderer:

To obtain the required buffer size to hold the image, call this method with a NULL pointer in the pDIBImage parameter. The method returns the required buffer size in the pBufferSize parameter. Allocate a buffer of that size and call the method again, with pDIBImage pointing to the buffer. On the second call, use pBufferSize to specify the buffer size. If the buffer is too small to hold the complete image, the method returns E_OUTOFMEMORY.

If the method succeeds, the buffer is filled with the entire DIB image, including the BITMAPINFOHEADER structure, plus any palette entries and bit masks as defined in the Win32 BITMAPINFO structure. The format of the image depends on the type provided by the source filter, and cannot be specified in advance.

Requirements

  Header: Dshow.h.

Library: Quartz.dll