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IAMVideoCompression::get_PFramesPerKeyFrame

  • Articolo
 
Microsoft DirectShow 9.0

IAMVideoCompression::get_PFramesPerKeyFrame

The get_PFramesPerKeyFrame method retrieves the rate of predicted (P) frames per key frame.

Syntax

  HRESULT get_PFramesPerKeyFrame(
  long *pPFramesPerKeyFrame
);

Parameters

pPFramesPerKeyFrame

[out] Pointer to a variable that receives the number of P frames per key frame. If the value is negative, the filter will use the default rate.

Return Values

Returns an HRESULT value.

Remarks

To determine if the filter supports this method, call the IAMVideoCompression::GetInfo method and check for the CompressionCaps_CanBFrame flag in the pCapabilities parameter. The GetInfo method also returns the default P-frame rate.

P frames are used in MPEG compression; in general, this property does not apply to other compression formats. For example, suppose a key frame occurs once every 10 frames, and there are three P frames per key frame. The P frames will be spaced evenly between the key frames. The remaining six frames are bidirectional (B) frames.

Requirements

Header: Declared in Strmif.h; include Dshow.h.

Library: Use Strmiids.lib.

See Also