HD-DVD

HD-DVD is a format developed and backed by the open DVD Forum. Formerly known as the DVD Consortium, it's the same body officially responsible for the adoption of the DVD format over a decade ago. HD-DVD is perhaps the less technically advanced of the two formats, though arguably the easier and less expensive to manufacture and support. Like BlueRay, HD-DVD uses a 405nm blue-light laser, but with a smaller numerical aperture of .65 and a lower data transfer rate of 36.55 Mbit/s. This constrains the storage capacity of HD-DVD to 15GB per layer, as opposed to 25GB per layer for BlueRay. The capacity difference further widens when you talk about dual layer discs with the formats supporting 30GB and 50GB respectively. Toshiba has announced a new triple layer disc format for HD-DVD sporting 17GB per layer for a maximum of 51GB of storage, though it's important to note this new esoteric format may or may not be supported on any currently shipping HD-DVD players.

Beyond the physical medium differences, things get a lot more similar between the two formats. HD-DVD supports MPEG2, the old standard video codec used in DVD movies as well as the newer MPEG4 derivatives, AVC, VC-1, and h.264. Currently most HD-DVD content is encoded with the VC-1 implementation of MPEG4. Though MPEG2 is supported, it's significantly larger file sizes make it an unlikely format to be widely used in the future. Audio codec choices are significantly varied, with support for Linear PCM, DTS HD, Dolby Digital, Dolby Digital Plus, and MPEG Layer 3 audio.

Actual playback times at standard definition (480p) resolutions are 13.8 hours and 5.4 hours at high definition (1080p) resolutions on a dual layer disc. Note these are maximum's and not necessarily what you will see all the time, due to the different codecs available and optimizations that can be made. One interesting difference from BlueRay is HD-DVD's support of HD encoded dual layer DVD-ROM, which allows about 2 hours of high definition content on the same physical medium we use today for DVD.

HD-DVD utilizes a form of copy protection known as AACS, or Advanced Access Content System. Though significantly more difficult to defeat than the CSS system used on DVD, it appears AACS is already crumbling as a protection scheme (no shock there), with HD-DVD content already slowly beginning to appear on line for download. HD-DVD also support a method of digital watermarking in an HD-ROM's audio track, which allows players to detect the presence of copied discs. HD-DVD also support HDCP, or High-bandwidth Digital Content Protection. If HD-DVD discs are flagged with what is known as the Image Constraint Token or ICT Flag, any high definition content being played back on a non HDCP supporting display gets automatically down sampled to a much lower resolution of 960x540. Though this might seem to bode badly for those who have already invested in HD displays (many of which till recently not supporting HDCP), as a whole most entertainment companies are at least for now not enabling the ICT flag on HD-DVD content.

Currently HD-DVD has a fairly significant level of industry support. Industry giants like Toshiba, Sanyo, NEC, Intel and Microsoft are major backers of this format. Entertainment industry giants like Universal Studio's, Paramount, Warner, and HBO also are major backers. Interestingly enough the format also has significant support from the pornography industry as well, as was the case with VHS during the historic VHS vs Betamax war of old. Toshiba was first out of the gate with a high definition player, and currently has the most models of players available. Perhaps the cheapest way to get into HD-DVD currently is courtesy of Microsoft with their HD-DVD drive add on for their XBOX360 console, at around $200 (not counting the cost of an XBOX360 itself).

Let's move on, and take a look at BlueRay...