Frequently Asked Questions
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Q: What is HD DVD?A: The basic idea behind High-Definition DVD (HD-DVD) is simple - it looks like a DVD and acts like a DVD, but it holds more information. A DVD holds about two hours of standard definition video, but an HD-DVD can hold about 48 hours. You can play a regular DVD on a high-definition display, but the disc does not take advantage of the display's extra resolution.
An HD-DVD player is very similar to a DVD player, but it has a few notable differences. An HD-DVD uses the same principles - it contains a bumpy layer that reflects light from a laser to a sensor, creating a digital signal. HD-DVDs are exactly the same size as DVDs (120 millimeters in diameter and 1.2 millimeters thick). But three important differences allow them to hold quite a bit more information than DVDs:
The color of the laser may seem like a trivial change to make. But the shorter wavelength of the blue-violet laser is what allows HD-DVDs pits to be smaller and arranged closer together. In other words, it allows the disc to have a much narrower track pitch. Regular DVDs have a track pitch of 0.74 micrometers, and HD-DVDs have a track pitch of 0.40 micrometers. This is like the difference between writing with a fine-tipped pen and a magic marker.
The other big difference between DVDs and HD-DVDs involves how the information on the disc is compressed. Most DVDs use MPEG-2 compression. HD-DVDs can use MPEG-2, but they typically use the more efficient MPEG-4, which allows higher video quality with a smaller file size. HD-DVDs can also use VC-1 (or Windows Media) compression.
Finally, because of general improvements in the technology, an HD-DVD player can read information from the disc and deliver it to the TV about three times as fast as a DVD player can. It can also send the signal to an HDTV digitally using a High Definition Multimedia Interface (HDMI), preventing the quality loss that conversion to analog causes.