IAMVideoAccelerator::GetBuffer method (videoacc.h)

Articolo
4/26/2023

[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The GetBuffer method gets a pointer to a compressed or uncompressed surface that was allocated for DirectX Video Acceleration (DXVA) decoding.

Syntax

HRESULT GetBuffer(
  [in]  DWORD  dwTypeIndex,
  [in]  DWORD  dwBufferIndex,
  [in]  BOOL   bReadOnly,
  [out] LPVOID *ppBuffer,
  [out] LONG   *lpStride
);

Parameters

[in] dwTypeIndex

Specifies the surface type:

To get a pointer to a compressed surface, specify one of the DXVA surface types defined in dxva.h.
To get a pointer to an uncompressed output surface, set this parameter to 0xFFFFFFFF.

The value 0xFFFFFFFF is valid only between calls to IAMVideoAccelerator::BeginFrame and IAMVideoAccelerator::EndFrame.

[in] dwBufferIndex

The zero-based index of the surface, within the pool of surfaces that were allocated for the specified surface type.

Compressed surfaces: To get the number of allocated surfaces for each surface type, call IAMVideoAccelerator::GetInternalCompBufferInfo.
Uncompressed surfaces: The buffer index must equal the dwDestSurfaceIndex member of the AMVABeginFrameInfo structure that was passed to the most recent IAMVideoAccelerator::BeginFrame call.

[in] bReadOnly

Specifies whether the decoder will write to the surface memory. For read-only access, specify TRUE. This might allow faster access to reference frames that are currently in use.

[out] ppBuffer

Receives a pointer to the surface memory. To get the size of the buffer in bytes, call the IAMVideoAccelerator::GetInternalCompBufferInfo method. The size is given in the dwBytesToAllocate member of the AMVACompBufferInfo structure that corresponds to dwTypeIndex.

[out] lpStride

Receives the surface stride, in bytes.

Return value

Returns an HRESULT value that depends on the implementation of the interface. HRESULT can include one of the following standard constants, or other values not listed.

Return code	Description
E_FAIL	Failure.
E_INVALIDARG	Argument is invalid.
E_NOTIMPL	Method is not supported.
E_POINTER	NULL pointer argument.
S_OK	Success.
VFW_E_INVALIDSUBTYPE	The decoder did not use a DXVA decoding type when it connected to the video renderer.
VFW_E_NOT_CONNECTED	The pins on the decoder and video renderer filters are not connected.

Remarks

If the filter's pins are not connected, the method returns VFW_E_NOT_CONNECTED.

This method locks and obtains access to a single buffer. Buffers are identified by type and by index within that type. The IAMVideoAccelerator::GetInternalCompBufferInfo method returns the number of surface types in its pdwNumTypesCompBuffers parameter. This number defines the valid range for dwTypeIndex. For each type, the dwNumCompBuffers member of the AMVACompBufferInfo structure gives the number of buffers, which defines the valid range for dwBufferIndex.

To release the buffer, call IAMVideoAccelerator::ReleaseBuffer.

Until all compressed buffers are released, it is possible that the calling thread will hold the Win16 lock or the DirectDraw lock.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	videoacc.h
Library	Strmiids.lib

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