HD DVD

HD DVD (High Definition DVD, 高清晰度数字多功能光盘) is an optical disc format designed for high-definition audio and video and high-capacity data, promoted by companies such as Toshiba and NEC and endorsed by the DVD Forum. The physical specifications, file system, and video application standards for its read-only discs were finalized in the mid-2000s, and the first consumer-grade players hit the market in 2006. HD DVD subsequently competed with Blu-ray for dominance in the high-definition disc format market; commercial distribution quickly came to an end after Toshiba announced in 2008 that it would discontinue its player and recorder business.

The discs retained a 120-millimeter diameter and a structure consisting of two 0.6-millimeter substrates bonded together; the data layer depth was similar to that of DVDs, so some existing DVD manufacturing equipment could be retrofitted for production. The reading system used a blue-violet laser with a wavelength of approximately 405 nanometers, increasing capacity through a smaller spot size and denser tracks. Single-layer read-only discs have a capacity of 15 GB, while dual-layer discs have a capacity of 30 GB; Toshiba also demonstrated and promoted a 45 GB triple-layer structure, but it did not become a common mass-produced format on the market.

Recordable discs support MPEG-2 Video, VC-1, and H.264/AVC, with common program resolutions including 1920×1080 and 1280×720. Audio formats include linear PCM, Dolby Digital Plus, Dolby TrueHD, DTS, and extended formats, with the specific combination determined by the disc’s production. HD DVD’s advanced content system employs an interactive framework based on technologies such as XML and ECMAScript, enabling menus, picture-in-picture, internet connectivity, and additional features; some early discs also used a simpler standard content mode.

The file and application systems are built upon the evolution of the DVD specification, but HD DVD does not involve writing high-definition video files directly to standard DVDs. Official discs must comply with specific disc, file system, video, and navigation specifications, and require HD DVD-compatible optical drives and decoders. There were also non-standard or limited-capacity methods on the market that wrote HD DVD video structures onto standard red-laser DVDs; such discs do not have the 15 GB or 30 GB physical structure of HD DVD and have different compatibility characteristics. Both HD DVD and Blu-ray use blue-violet lasers, but they differ in terms of data layer placement, disc capacity, application formats, and interaction systems; standard playback devices cannot read the other format’s discs. A few manufacturers have released players or computer drives that support both formats simultaneously, but this involves integrating two sets of compatibility capabilities into a single device, rather than achieving interoperability between the two disc standards.

HD DVD-ROM is used for factory-pressed read-only content, while HD DVD-R offers write-once capability. There were also rewritable specifications and a concept for dual-format discs combining DVD and HD DVD content. Due to the format’s relatively short lifespan, actual releases primarily consisted of 15 GB and 30 GB pre-recorded discs. Programs already released still require corresponding hardware for playback; the later Ultra HD Blu-ray has no format succession or backward compatibility with HD DVD.