Different colors of recordable CDs and DVDs come from the combination of the reflective metal layer (gold or silver) and the dye used in the recording layer (cyanine [blue], phthalocyanine [clear], azo [dark blue], formazan [green], etc.). Judging DVD quality by color is like judging bell pepper quality by color (is yellow better than red or green?). You may find that some color discs seem to work better in some players, but you'll also find that there is little correlation between color and readability across multiple brands of disc. Other factors such as manufacturing quality and chemical formulation have much more of an effect on how well a disc records and plays back. Color does indicate longevity, since some dyes (such as phthalocyanine and azo) are more stable and last longer. See 3.12. Dual-layer recording is much trickier than single-layer recording. However, dual-layer recording techniques developed for Blu-ray (see 3.13) have been adapted for recordable DVD. Write-once (+R and -R) recordable DVD-9 discs, which hold almost double the amount of data or recording time (see 3.3), should show up around the end of 2004. Dual-layer rewritable discs are harder to get working, but they may show up a year or two later. Recordable drives will cost about the same as regular drives (since only firmware changes are required to record two layers) and the discs will cost between 1.2 to 3 times as much as single-layer discs. Philips first demonstrated dual-layer +R at CEATEC in Japan in October 2003. They expect the discs to be readable in about 70% of existing players and drives. Also in October, Pioneer announced a dual-layer version of -R, but they did not demonstrate it. Recordable discs come in different speed ratings (2x = twice standard write speed, 8x = eight times standard speed, and so forth). The speed ratings of blank discs match the speed ratings of drives (see 4.2). When faster drives become available, new discs are designed to work with the new drives as well as older drives. This means you should use discs that are rated at or above the speed of your drive. For example, if you have a 4x drive you should use 4x or faster discs, not 1x or 2x. Almost all home DVD video recorders use 1x drives, so any speed of discs should work. 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. Hardware acceleration must be turned off before screen capture will work. This makes some decoders write to standard video memory. Utilities such as Creative Softworx, HyperSnap, and SD Capture can then grab still pictures. Some player applications such as PowerDVD and the Windows Me player can take screenshots if hardware acceleration is turned off.
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