|Microsoft DirectX 9.0|
There are certain kinds of video that the Video Renderer filter cannot display by itself. In these situtations, the Video Renderer must work with the Overlay Mixer filter. The Overlay Mixer manages the rendering, while the Video Renderer manages the video window. The Overlay Mixer is needed in the following situations:
The Capture Graph Builder's RenderStream method inserts the Overlay Mixer whenever needed. If you are building the graph without using the Capture Graph Builder, however, you must check for each of these situations and insert the Overlay Mixer yourself.
Important If the device has a VP pin, you must connect the Overlay Mixer even if you do not need preview functionality in your application. With a video port, the capture device always sends the video data to the hardware overlay, so the Overlay Mixer is always needed.
The Video Mixing Renderer filters (VMR-7 and VMR-9) both support interlaced video, and are able to mix closed caption bitmaps onto the primary video. If you are using the VMR for those scernarios, then you do not need to use the Overlay Mixer. The VMR-9 does not support VP pin connections. The VMR-7 supports VP pin connections through the Video Port Manager filter. However, you may find that some drivers do not work correctly with the Video Port Manager. For that reason, the Overlay Mixer is still recommended for VP pins.