Mixes frames - overlays _pFrameOverlay frame over this frame, the position is from top-left corner, for 4:2:2 images (e.g. UYVY) horizontal position is aligned by two (e.g. 21->20). By default audio gain is calculated based on overlay size and transparency or can be specified via 'audio_gain' props.

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
)