Performing Custom Video Mixing in Script

This topic applies to Windows XP only.

The Video Control works closely with the DirectShow Video Mixing Renderer filter (VMR). The VMR enables C++ developers to create powerful mixing effects by implementing custom compositors. Script-based applications can invoke and run this custom compositor through the Video Control, and also use the default capabilities of the VMR to perform effects such as overlaying an alpha-blended bitmap on the video frame. One limitation of script applictions running in Microsoft® Internet Explorer® is that they cannot save a captured frame to disk, since these applications cannot access the file system.

Some settings on the VMR must be made before the application calls Build or Run (in other words, before a filter graph is constructed). One such setting is whether the VMR should reduce the size of the native video before attempting to process it. (This is useful when viewing HDTV on a monitor that is set to a lower resolution.) To pre-configure the VMR, enumerate the MSVidVideoRendererDevices collection and get the one MSVidVideoRenderer item that it contains. Call its methods to configure it, and then set this object as the active renderer before calling Build or Run. For more information, see MSVidVideoRenderer and Using the Video Mixing Renderer.