IOverlay Interface

This interface provides information so that a filter can write directly to video memory while placing the video in the correct window position. It is implemented on the input pin of the video renderer and communicates with an upstream filter (typically a video decompressor) by calling that filter's IOverlayNotify methods to notify it of changes to the video window.

This interface has no relationship to the DirectDraw overlay capability. The Microsoft video renderer draws data it receives through the IMemInputPin interface, using DirectDraw overlays when available. This interface, used in place of IMemInputPin, is intended to provide notification support for any upstream filter that bypasses the renderer's drawing capabilities, but needs notifications of other display properties.

See the IOverlayNotify interface for more information on how the IOverlay and IOverlayNotify interfaces work together.

When to Implement

This interface is implemented on the DirectShow video renderer filter. It can also be implemented on replacement video renderer filters if desired. If doing so, implement this interface so that filters writing directly to the frame buffer or trying to position an overlay know where to display their video. To implement this interface, the renderer must be prepared to use methods on the IOverlayNotify interface of the filter doing the drawing, with notifications of video property changes.

The window-based renderer in DirectShow supports both IMemInputPin and IOverlay interfaces. These two interfaces are mutually exclusive. A filter chooses to use the IOverlay transport interface by providing a media type during connection that has a subtype of MEDIASUBTYPE_Overlay. After connection, it will be able to get and use successfully the IOverlay interface. If it connects with any other video formats (such as MEDIASUBTYPE_RGB8), trying to call through IOverlay returns VFW_E_NOT_OVERLAY_CONNECTION.

When to Use

Use the methods on this function from an upstream filter that must control video overlay properties and intends to handle the displaying of the video data itself. This typically is used by hardware video decoders that have an alternate connection to the video hardware.

Methods in Vtable Order

The following table shows the methods that appear in the Vtable beneath the standard COM methods inherited from IUnknown.

Method Description
GetPalette Retrieves the current palette.
SetPalette Sets the palette.
GetDefaultColorKey Retrieves the default color key.
GetColorKey Returns the identifier of the currently active color key.
SetColorKey Changes the color key.
GetWindowHandle Returns the window handle.
GetClipList Retrieves the clipping list.
GetVideoPosition Retrieves the current video source and destination rectangles.
Advise Sets up an advise link for the overlay events.
Unadvise Terminates the advise link.


DirectShow applications and DirectShow filters have different include file and link library requirements. See Setting Up the Build Environment for more information.

OS Versions: Windows CE 2.12 and later. Version 2.12 requires DXPAK 1.0 or later.

See Also

DirectShow Interfaces

Last updated on Wednesday, April 13, 2005

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