Overlay Mixer Internal Operations

The Overlay Mixer exposes an input pin for each incoming stream. Typically, there are three input pins: Pin 0 for video data and Pins 1 and 2 for line 21 and DVD subpicture data. Internally, the Overlay Mixer uses DirectDraw to render video. It creates a DirectDraw object with a primary surface comprising the entire desktop, and an overlay surface whose rectangle is defined by the size of the video stream connected to Pin 0. If the decoder does not specify a color key, the Overlay Mixer uses default color keys: dark gray for more recent graphics cards and magenta for older 256-color cards.

Note   The results are undefined if the decoder passes in two video streams to be rendered simultaneously in the same place on the overlay surface, as sometimes occurs with DVDs that contain both subpicture and line 21 streams. The video might flicker, or display only one of the streams.