4.4 Why can't I take a screenshot of DVD video? Why do I get a pink orblack square?
Description
This article is from the DVD Formats FAQ, by jtfrog@usa.net (Jim Taylor) with numerous contributions by others.
4.4 Why can't I take a screenshot of DVD video? Why do I get a pink orblack square?
Most DVD PCs, even those with software decoders, use video overlay hardware
to insert the video directly into the VGA signal. This an efficient way to
handle the very high bandwidth of full-motion video. Some decoder cards,
such as the Creative Labs Encore Dxr series and the Sigma Designs Hollywood
series, use a pass-through cable that overlays the video into the analog
VGA signal after it comes out of the video display card. Video overlay uses
a technique called colorkey to selectively replace a specified pixel color
(often magenta or near-black) with video content. Anywhere a colorkey pixel
appears in the computer graphics video, it's replaced by video from the DVD
decoder. This process occurs "downstream" from the computer's video memory,
so if you try to take a screenshot (which grabs pixels from video RAM), all
you get is a solid square of the colorkey color.
Some decoders write to normal video memory. In this case, utilities such as
Creative Softworx, HyperSnap, and SD Capture can grab still pictures. Some
player applications can also take screenshots.
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