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HD-DVD: truce or stalemate? |
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Gadgets & Computers -
Computers
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HD-DVD: truce or stalemate? How do the standards battling to be the High Definition optical disc of the future compare? James Morris investigates
The competing camps in rewriteable DVD technology have never really settled their differences. Instead, multi-format drives have arrived, which could accommodate both the -R and +R discs, and some handle DVD-RAM as well. So the consumer now has far less to worry about. But now that the next generation of optical formats is approaching production, we could be set for yet another conflict.
Although Blu-ray Disc (BD) is widely considered technically the better of the two options, HD-DVD will arrive first. So consumers will yet again be faced with a tough choice.
Technically speaking, there’s not as much separating BD and HD-DVD as you would at first assume. Both formats are made possible by blue lasers with a lower wavelength than the red laser currently used with standard DVD rewriteable formats. This red laser operates at a wavelength of 658nm, while” both BD and HD-DVD use a blue beam with a wavelength of 405nm.
The differences are in the media used and numerical aperture of the lens. Both HD-DVD and BD media are 1.2mm thick, as are DVDs and CDs, but the two formats use totally different cover layer sizes. HD-DVD sandwiches two 0.6mm layers together, but BD puts a much thinner 0.1mm layer over a thicker l.l mm one. This allows the laser to be more tightly focused on the disc surface for smaller spot sizes, in turn making it possible to pack a greater density of data onto the disc. This is one reason why BD can fit more data per layer (25GB) than HD-DVD (15GB).
But the thin layer requires a new manufacturing process with a hard coating, because otherwise media would be far too fragile for everyday use, and would need a caddy. In contrast, HD-DVD discs can be manufactured in modified DVD media plants, as the specification is much closer to today’s DVDs.
To help with the finer focusing, BD uses a higher numerical aperture of 0.85 than HDDVD, which uses 0.65 lenses. The latter, again, is closer to the 0.6 numerical aperture used by current DVD technology.
However, reports emerged in May that the DVD format war may be reaching an entente cordiale before battle even commences. Toshiba, which backs HD-DVD, and Sony, the force behind BD, have been in talks for several months. The latest from the Japanese Nihon Keizai Shimbun newspaper implied that a new format blending both standards might be on the cards. With software from Toshiba and BD’s 0.1mm-layer technology, the new format would replace both BD and HD-DVD.
However, media companies such as Maxell are still developing HD-DVD recordable discs, and Sony’s Ken Kutaragi has recently described the chances of unification as “almost none”. So the conflict hasn’t been settled just yet.
High Definition video: another theatre of conflict
There’s more confusion over the actual format of the video to be stored on the discs than with the physical media for HD opticals. Both BD and HD-DVD currently support at least three video file types. MPEG-2 was specified from the beginning with HD video support, so it’s no surprise that it’s a prime contender.
Windows Media Video 9 has already made a name for itself as a High Definition format via www. wmvhd.com. VC-l, a codec based on WMV9, is another possibility on both Blu-ray and HD-DVD. So is H.264, the Advanced Video Coding MPEG-4 enhancement which promises even better quality at even lower data rates. Apple has added H.264 to its QuickTime has joined Blu-ray to go with it.
However, as MPEG-2 is the format used by broadcasters, recordable discs currently only support this type of video file. Digital broadcasts, including HD, would be captured and copied straight to disc in the same way as current digital TV tuners capture the MPEG-2 broadcast stream.
With so many video formats vying for attention on pre-recorded discs, the media wars are clearly just half the story. Even if BD and HD-DVD do settle their differences and come up with a hybrid format based on the best of both worlds, consumers could still be faced with a confusing array of choices. We could find that some movies can be bought in more than one HD video format, despite the underlying discs being the same.
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