Image is Everything
Most people would agree that DVDs look great. So why do we need a new disc format? Here's one excellent reason: both Blu-ray and HD DVD discs have enough capacity to contain high-def video versions of movies. To put this in perspective, the picture from a DVD is made up of around 345,000 discrete picture elements, or pixels. But the images in the HD DVD or Blu-ray high-def versions of that same movie can have more than 2 million pixels - a fivefold increase in resolution!
High data-transfer rates don't only deliver remarkably crisp images. They also give both formats the potential to deliver more solid, stable-looking high-def pictures than those on cable, satellite, and broadcast TV. While broadcast HDTV channels send data at 19 megabits per second (Mbps) and DVD maxes out at 10 Mbps, the maximum data-transfer rate for HD DVD is 36 Mbps, while Blu-ray can go up to 48 Mbps.
Also, along with standard MPEG-2 compression (the format currently used for DVD authoring and HDTV broadcasting), both HD DVD and Blu-ray support MPEG-4 AVC and Microsoft's VC1 compression. These advanced codecs were designed with high-def in mind and are much more efficient than MPEG-2.
It will be up to individual studios to decide what combination of compression scheme and data-transfer rate ultimately works best for its releases. Sony Pictures, for example, has committed to sticking with MPEG-2 in its initial Blu-ray titles, claiming better image quality at the 18 Mbps data rate they've settled on for those discs. (See "Tech Talk: MPEG-2 vs. MPEG-4?," for more on this.)
Beyond mere specs, another reason why it's time for high-rez discs is that more and more regular people - not just early adopters and gearheads - are upgrading their old tubes to swanky new HDTVs. According to the Consumer Electronics Association, U.S. sales of digital TVs and related products in 2005 increased 60% over 2004. It might be easy to get high-def programming via broadcast, cable, and satellite TV, but the number of high-def movies in circulation has been pretty limited. HD DVD and Blu-ray are about to change all that.
Both Blu-ray and HD DVD players will put out signals in the standard Dolby Digital and DTS formats. But there's new audio excitement brewing, with Dolby Digital Plus debuting on both formats. DD Plus is an enhanced version of Dolby Digital, able to deliver up to 7.1 discrete audio channels as well as higher audio data rates (3 Mbps on HD DVD and up to 4.7 Mbps on Blu-ray).
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