IMediaObject::GetInputSizeInfo method (mediaobj.h)

Article
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 It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation.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 GetInputSizeInfo method retrieves the buffer requirements for a specified input stream.

Syntax

HRESULT GetInputSizeInfo(
        DWORD dwInputStreamIndex,
  [out] DWORD *pcbSize,
  [out] DWORD *pcbMaxLookahead,
  [out] DWORD *pcbAlignment
);

Parameters

dwInputStreamIndex

Zero-based index of an input stream on the DMO.

[out] pcbSize

Pointer to a variable that receives the minimum size of an input buffer for this stream, in bytes.

[out] pcbMaxLookahead

Pointer to a variable that receives the maximum amount of data that the DMO will hold for lookahead, in bytes. If the DMO does not perform lookahead on the stream, the value is zero.

[out] pcbAlignment

Pointer to a variable that receives the required buffer alignment, in bytes. If the input stream has no alignment requirement, the value is 1.

Return value

Returns an HRESULT value. Possible values include those in the following table.

Return code	Description
DMO_E_INVALIDSTREAMINDEX	Invalid stream index.
DMO_E_TYPE_NOT_SET	Media type was not set.
S_OK	Success.

Remarks

The buffer requirements may depend on the media types of the various streams. Before calling this method, set the media type of each stream by calling the IMediaObject::SetInputType and IMediaObject::SetOutputType methods. If the media types have not been set, this method might return an error.

If the DMO performs lookahead on the input stream, it returns the DMO_INPUT_STREAMF_HOLDS_BUFFERS flag in the IMediaObject::GetInputStreamInfo method. During processing, the DMO holds up to the number of bytes indicated by the pcbMaxLookahead parameter. The application must allocate enough buffers for the DMO to hold this much data.

A buffer is aligned if the buffer's start address is a multiple of *pcbAlignment. The alignment must be a power of two. Depending on the microprocessor, reads and writes to an aligned buffer might be faster than to an unaligned buffer. Also, some microprocessors do not support unaligned reads and writes.

Requirements

Requirement	Value
Target Platform	Windows
Header	mediaobj.h (include Dmo.h)
Library	Dmoguids.lib

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