The current specifications for HD DVD-ROM and HD DVD-RW are version 1.0. The specification for HD DVD-R is currently at 0.9; the HD DVD-RAM specification is not yet finalized.
Disc structure
HD DVD-ROM has a single-layer capacity of 15 GB, a dual-layer capacity of 30 GB, and a 51 GB triple-layer disc (which uses slightly bigger 17 GB layers), approved in November 2007 by the DVD Forum[2]. Toshiba has declined to say whether the 51GB, triple-layer disc is compatible with existing drives and players. Specification 2.0 Part 1 (Physical Specification) for triple layer HD DVD has been approved in November 2007.[41]
HD DVD-R and HD DVD-RW has a single-layer capacity of 15 GB, a dual-layer capacity of 30 GB. The HD DVD-RAM has a single-layer capacity of 20 GB.[42] Like the original DVD format, the data layer of an HD DVD disc is 0.6 mm below the surface physically protecting the data layer from damage. The numerical aperture of the optical pick-up head is 0.65, compared with 0.6 for DVD. All HD DVD players are backward compatible with DVD and CD.
| Physical size | Single layer capacity | Dual layer capacity | Triple layer capacity |
|---|---|---|---|
| 12 cm, single sided | 15 GB | 30 GB | 51 GB (17 GB per layer instead of 15 GB) |
| 12 cm, double sided | 30 GB | 60 GB | 39 GB (HD DVD/DVD Twin-Format - HD-34 Double-Layer/DVD 5 Single-Layer) |
| 8 cm, single sided | 4.7 GB | 9.4 GB | |
| 8 cm, double sided | 9.4 GB | 18.8 GB |
File systems
As with previous optical disc formats, HD DVD supports several file systems, such as ISO 9660 and Universal Disk Format (UDF). Currently, all HD DVD titles use UDF version 2.5 as the file system.
Audio
HD DVD discs support encoding in up to 24-bit/192 kHz for two channels, or up to eight channels of up to 24-bit/96 kHz encoding.[43] For reference, even new big-budget Hollywood films are mastered in only 24-bit/48 kHz, with 16-bit/48 kHz being common for ordinary films.[citation needed]
All HD DVD players are required to decode linear (uncompressed) PCM, Dolby Digital AC-3, Dolby Digital EX, DTS, Dolby Digital Plus and Dolby TrueHD.[44] A secondary soundtrack, if present, can be stored in any of the aforementioned formats, or in one of the HD DVD optional codecs: DTS-HD High Resolution Audio and DTS-HD Master Audio.
For the highest-fidelity audio experience, HD DVD offers content-producers the choice of linear PCM, Dolby TrueHD and DTS-HD Master Audio. Due to the high-bandwidth requirements of linear-PCM, lossless audio on HD DVD movies has thus far been delivered in the lossless format Dolby TrueHD.
Video
The HD DVD format supports a wide variety of resolutions, from low-resolution CIF and SDTV, all video resolutions supported by the DVD-Video standard, and up to HDTV formats such as 720p, 1080i and 1080p.[43] HD DVD supports video encoded in MPEG2 which is what is used in DVDs as well as the new formats VC-1 and AVC which are more efficient. All movie titles released so far have had the feature encoded in 1080p, with most supplements in 480i or 480p. Almost all titles are encoded with VC-1, and most of the remaining titles encoded with AVC.
http://en.wikipedia.org/wiki/HD_DVD
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