Public Overridable Sub PreviewEnable( _
   ByVal _bsChannelID As String, _
   ByVal _bEnableAudio As Integer, _
   ByVal _bEnableVideo As Integer _
) 

public virtual void PreviewEnable( 
   string _bsChannelID,
   int _bEnableAudio,
   int _bEnableVideo
)

public procedure PreviewEnable( 
    _bsChannelID: String;
    _bEnableAudio: Integer;
    _bEnableVideo: Integer
); virtual; 

public: virtual void PreviewEnable( 
   BSTR* _bsChannelID,
   int _bEnableAudio,
   int _bEnableVideo
) 

Parameters

_bsChannelID

channel ID. By default use empty string

_bEnableAudio

0 is to disable audio preview, 1 is to enable audio preview

_bEnableVideo

0 is to disable video preview, 1 is to enable video preview

Here is example of how to initialize a preview:

m_objPreview = new MFPreviewClass();
//Configure preview
m_objPreview.PreviewWindowSet("", panelPreview.Handle.ToInt32());
m_objPreview.PreviewEnable("", 1, 1);

Reference

MFPreviewClass Class
MFPreviewClass Members