IPreFetchOffset::SetPreFetchOffset method (portcls.h)

The SetPreFetchOffset method sets the prefetch offset, which is the number of bytes of data separating the write cursor from the play cursor in a DirectSound output stream.

Syntax

void SetPreFetchOffset(
  [in] ULONG PreFetchOffset
);

Parameters

[in] PreFetchOffset

Specifies the prefetch offset size in bytes.

Return value

None

Remarks

A WavePci miniport driver calls the SetPreFetchOffset method to specify the prefetch offset of a hardware-accelerated DirectSound output stream.

The prefetch offset is the number of bytes of data separating the write cursor from the play cursor in the audio device's hardware buffer:

• The write cursor specifies the buffer position into which a DirectSound application can safely write the next sound sample.
• The play cursor specifies the buffer position of the sound sample that is currently being played by the audio device.

For information about using SetPreFetchOffset to control a DirectSound stream's prefetch offset, see Prefetch Offsets.

Requirements

See also

IMiniportWavePciStream::GetPosition

IPortWavePciStream::GetMapping

IPreFetchOffset

KSAUDIO_POSITION

KSPROPERTY_AUDIO_POSITION