QuickTime for Java: A Developer's Notebook

Overlaying Video Tracks

When one video track is drawn on top of another, the top doesn’t necessarily have to obscure the bottom. QuickTime gives you the option of specifying a GraphicsMode to combine pixels from multiple video layers to create interesting effects.

How do I do that?

You can create a GraphicsMode object to describe the means of combining overlapping colors. To try it out, take the previous lab’s code and replace all the matrix stuff (after the foreTrack and backTrack are created, but before the MovieController is created) with the following:

GraphicsMode gm = new GraphicsMode (QDConstants.addMax,
                                  QDColor.green);
VisualMediaHandler foreHandler = 
  (VisualMediaHandler) foreTrack.getMedia( ).getHandler( );
foreHandler.setGraphicsMode(gm);
foreTrack.setLayer(-1);

Note

Run this example with ant run-ch08-composit-evideotracks.

When run, this sample program asks you to open two movies, then creates a new movie with video tracks from the source movies’ media, and combines the pixels of the foreground movie with the background, so the foreground appears atop the background. The result is shown in Figure 8-4.

What just happened?

Setting a GraphicsMode instructs QuickTime to apply a specific behavior to combine overlapping pixels. The GraphicsMode has a “mode” int, which indicates which kind of behavior to use, and a QDColor that is used by some behaviors to indicate a color to operate on. For example, you might use mode QDConstants.transparent and QDColor.green to make all green pixels ...