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Given the recent articles on Blu Ray disk and HD-DVD, it may be helpful to discuss some technical considerations that may provide a contextual backdrop. This seventh in DVD articles will outline some of the various specifications of HD-DVDs.

Though format wars start over technical specifications, they wind up being decided by business considerations. Thus it was with the old Betamax versus VHS war between Sony and Panasonic during the late ’70s and early ’80s, and thus it remained between Blu Ray disc and HD-DVD more recently. By the end, there weren’t that many differences between the two, but the increasing lack of industry support fated HD-DVD to the status of historical footnote more than anything technological.

HD DVD-ROM, HD DVD-R, and HD DVD-RW all offer single-layer capacities of 15 GB and dual-layer capacities of 30 GB, while HD DVD-RAM has a single-layer capacity of 20 GB. In common with standard DVDs, an HD-DVD’s data layer is just 0.6mm below the surface so that it’s afforded some degree of protection from physical damage. The aperture of an HD-DVD pickup head is 0.1mm smaller than a standard DVD, which is 0.6mm. Thus, all HD-DVD players are backward-compatible with DVDs and CDs.

In common with previous optical disc formats, the HD-DVD supported several filing systems, including ISO 9660 and Universal Disk Format (UDF). All the HD-DVD titles ever released had used UDF 2.5, where multiplexed audio and video streams are stored in an EVO container format. Audio encoding is supported at up to 24-bit/192KHz stereo, or up to eight channels at 24-bit/96-KHz. Formats supported include linear or uncompressed PCM, Dolby Digital AC-3, Dolby Digital EX, Dolby Digital Plus, and Dolby TrueHD as well as DTS. Secondary soundtracks can also be available in DTS-HD High Resolution Audio or DTS-HD Master Audio. LPCM is also offered for audiophiles bent on the purest of high-fidelity experiences.

On the video side, HD-DVDs can use VC-1, AVC, or MPGEG-2 encoding, and are capable of displaying a broad range of resolutions from low-res CIF all the way to the HDTV formats of 720p and 1080i/p. Movies on HD-DVD are featured in a 1080-lined format while supplemental materials can be in 480i or 480p. Most releases were encoded in VC-1 by far, with the vast majority of the remainder using AVC.

As observed at the outset, many reasons exist to help explain the demise of an otherwise promising format, but almost certainly none are technical, as the specifications are about what is available with Blu Ray disk. Rather, it was the gradual loss of industry support that made the final determination.