| Microsoft DirectX 8.1 (C++) |
Note In Microsoft Windows XP Home Edition and Windows XP Professional, the default video renderer is the Video Mixing Renderer Filter (VMR). On these operating systems, use of the Overlay Mixer is deprecated.
The Overlay Mixer filter is a video renderer designed specifically for DVD playback and broadcast video streams with line-21 closed captioning. The Overlay Mixer supports Video Port Extensions (VPEs), which enables it to work with hardware MPEG-2 decoders that send data directly to the graphics card rather than over the PCI bus.
The Overlay Mixer can be used in other scenarios where you have multiple input streams, but it does not perform any actual mixing or alpha blending of the overlaid graphics. It simply blits DVD subpictures and broadcast closed captioning graphics directly to the primary surface. For all other rendering scenarios, the Video Renderer Filter is preferred over the Overlay Mixer. Both renderers make use of Microsoft® DirectDraw® and overlay surfaces on the graphics card when these are available. The only difference is that the Overlay Mixer requires an overlay surface, whereas the Video Renderer can use other means of rendering video if an overlay surface is not available.
The Overlay Mixer uses the Video Renderer for window management. The Video Renderer connects to the Overlay Mixer's output pin.
Note In the following table, the media subtypes accepted on input pin 0 are entirely hardware dependent. There is no way for the Overlay Mixer to know in advance whether a particular subtype is supported, without attempting to create a DirectDraw surface. Therefore, the only way for an upstream filter to determine whether a particular subtype is supported is to attempt a connection using that subtype.
| Filter Interfaces | IAMOverlayFX, IAMVideoDecimationProperties, IBaseFilter, IDDrawExclModeVideo, IKsPropertySet, IMediaPosition, IMediaSeeking, IQualProp |
| Input Pin Media Types | Major Type: MEDIATYPE_Video Subtypes:
|
| Input Pin Interfaces | IAMVideoAccelerator, IKsPropertySet, IMemInputPin, IMixerPinConfig, IMixerPinConfig2, IOverlay (pin 0 only), IPin, IPinConnection, IQualityControl, IVPNotify, IVPNotify2 |
| Output Pin Media Types | MEDIATYPE_Video, MEDIASUBTYPE_Overlay |
| Output Pin Interfaces | IPin, IQualityControl |
| Filter CLSID | CLSID_OverlayMixer |
| Property Page CLSID | No property page. |
| Executable | qdvd.dll |
| Merit | MERIT_DO_NOT_USE |
| Filter Category | CLSID_LegacyAmFilterCategory |
Remarks
The Overlay Mixer uses destination color keying to mix video surfaces with overlays. It blits the color key and the subtitle or Line21 data to the primary surface, and sends the video to the overlay surface. The graphics card then composites the two surfaces into its frame buffer.
This filter is added to the filter graph automatically when applications use the IDvdGraphBuilder and ICaptureGraphBuilder2 interfaces to create the graph. The Filter Graph Manager will not automatically add the Overlay Mixer to the graph, because the filter's merit is MERIT_DO_NOT_USE. Game applications can use the Overlay Mixer in limited ways to add video to the game screen.
The Overlay Mixer 2 filter is identical to the Overlay Mixer, except for two distinctions: the Overlay Mixer supports the VIDEOINFO and VIDEOINFO2 format types, while the Overlay Mixer2 supports only the VIDEOINFO2 format type. Also, the Overlay Mixer 2 has a merit of MERIT_UNLIKELY, so the Filter Graph Manager might add it to the graph; for example, if the VIDEOINFO2 format type is required. This filter is primarily used in analog television graphs.
Applications can control certain behavior on the Overlay Mixer through its IMixerPinConfig2 interface, but application developers should never be concerned with the details of the mixer's internal workings. The following information is provided for the benefit of filter developers, and game developers who want to use the Overlay Mixer's DirectDraw Exclusive Mode: