IWMWriterFileSink3::SetUnbufferedIO method (wmsdkidl.h)

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4/26/2023

[The feature associated with this page, Windows Media Format 11 SDK, is a legacy feature. It has been superseded by Source Reader and Sink Writer. Source Reader and Sink Writer have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use Source Reader and Sink Writer instead of Windows Media Format 11 SDK, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The SetUnbufferedIO method specifies whether unbuffered I/O is used for the file sink. You can improve performance by using unbuffered I/O for writer sessions with a high bit rate and a long running time.

Syntax

HRESULT SetUnbufferedIO(
  [in] BOOL fUnbufferedIO,
  [in] BOOL fRestrictMemUsage
);

Parameters

[in] fUnbufferedIO

A BOOL that specifies whether to use unbuffered I/O.

[in] fRestrictMemUsage

A BOOL that specifies whether memory usage should be restricted. Passing True for this parameter severely limits the size of the buffers used to prepare data for unbuffered writing. This limitation usually counteracts any performance gains from using unbuffered I/O.

Return value

The method returns an HRESULT. Possible values include, but are not limited to, those in the following table.

Return code	Description
S_OK	The method succeeded.
NS_E_INVALID_REQUEST	The header has already been written.

Remarks

This method enables the application to override the writer's decision about whether to use unbuffered I/O.

If you want to use unbuffered I/O, you must call this method before writing the header of the file.

This method dynamically allocates a set of buffers to prepare data for unbuffered writing. The size of these buffers is dependent upon the amount of available physical memory.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only],Windows Media Format 9 Series SDK, or later versions of the SDK
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	wmsdkidl.h (include Wmsdk.h)
Library	Wmvcore.lib; WMStubDRM.lib (if you use DRM)

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