QuickTime 2.5 adds support for combining images using alpha channel graphics modes. This allows two images to be combined using a soft edged matte, such as generated by many graphics and 3D rendering applications.
The example movie file, "David's Lost", shows a background video track combined with a title video track. The alpha channel of the title track is being used to control how the title is drawn over the video track. Using MoviePlayer's "Get Info" dialog, you can experiment with different graphics modes to see how the alpha channel effect works.
You are not limited to just having static titles drawn using the alpha channel. If you have a video or animation clip that contains an alpha channel, QuickTime 2.5 can combine this with other video or animations in the same way as the example movie file.
QuickTime supports several different ways of interpreting the alpha channel. The most common is "Straight Alpha". This is what is used in the example movie file. QuickTime also supports "Straight Alpha Blend" which allows for the alpha channel to be made more transparent. Try applying the "Straight Alpha Blend" mode and then changing the color in MoviePlayer's "Get Info" dialog. QuickTime also supports "Pre-multiplied with white" and "Pre-multiplied with black" alpha channel graphics modes for specialized graphics applications.
