[netsharc]

Windows has this too. Something to do with sending the video data directly to the graphics card, and the graphics card doing the decoding of the MPEG data, and replacing the color (which is usually green) with the video image before outputing to the screen.

So if you're playing a video and you open a web page, and the webpage has the same green color, it looks like there's a hole on the browser window and you can see the video playing "behind" it.

[akx]

This isn't probably really used much these days, but yeah, it was/is called Overlay mode.

The graphics card isn't necessarily decoding the MPEG data (though that could have been an option in the olden days too), but it is likely scaling it and spitting it out in the given-colored pixels faster than you could've done with just software back in the days.

The AVS visualizer for Winamp also supported this; if you set the overlay color to black, you could have all of the black text on your desktop be very, very funkily animated.