Sub MFOverlayRect( _
   ByVal _pFrameOverlay As IMFFrame, _
   ByVal _pFrameMask As IMFFrame, _
   ByRef _pRect As MF_RECT, _
   ByVal _eMFOverlayFlags As eMFOverlayFlags, _
   ByVal _dblAlpha As Double, _
   ByVal _bsPropsList As String, _
   ByVal _bsAudioBufferID As String _
) 

void MFOverlayRect( 
   IMFFrame _pFrameOverlay,
   IMFFrame _pFrameMask,
   ref MF_RECT _pRect,
   eMFOverlayFlags _eMFOverlayFlags,
   double _dblAlpha,
   string _bsPropsList,
   string _bsAudioBufferID
)

procedure MFOverlayRect( 
    _pFrameOverlay: IMFFrame;
    _pFrameMask: IMFFrame;
   var  _pRect: MF_RECT;
    _eMFOverlayFlags: eMFOverlayFlags;
    _dblAlpha: Double;
    _bsPropsList: String;
    _bsAudioBufferID: String
); 

void MFOverlayRect( 
   IMFFrame* _pFrameOverlay,
   IMFFrame* _pFrameMask,
   ref MF_RECT _pRect,
   eMFOverlayFlags _eMFOverlayFlags,
   double _dblAlpha,
   BSTR* _bsPropsList,
   BSTR* _bsAudioBufferID
) 

Parameters

_pFrameOverlay

frame for overlay

_pFrameMask

frame mask

_pRect

rectangle for overlay

_eMFOverlayFlags

overlay flags

_dblAlpha

transparency: 0.0 - transparent (no mix), 1.0 - solid.

_bsPropsList

additional properties (for example, audio_gain)

_bsAudioBufferID

audio buffer's ID

Reference

IMFFrame Interface
IMFFrame Members