HD DVD is a redundant high-density optical disc format that was designed for storing data and high-definition video. It was proposed to be the successor to the standard DVD format. However, after the abandonment by Toshiba, the HD DVD Promotion Group was dissolved in 2008.
Also known as High-Definition/Density DVD, it employs a blue laser with a shorter wavelength. This enables it to store about three and a half times as much data per layer as the standard DVD format. The single-layer capacity of HD DVD-ROM, HD DVD-R and HD DVD-RW is 15 GB and the dual-layer capacity is 30 GB.
The data layer of an HD DVD is 0.6 mm below the surface. This is done to protect the data layer from damage. The numerical aperture of the optical pick-up head is 0.65 and the HD DVD players are backward compatible with CD and DVD. It supports several file systems like Universal Disk Format and ISO 9660. The titles use UDF version 2.5 as the file system where a multiplexed audio and video streams are stored in EVO container format.
For two channels, the format supports encoding in up to 24-bit/192 kHz, or up to eight channels of up to 24-bit/96 kHz. These players decode uncompressed linear PCM, Dolby Digital EX, Dolby Digital, Dolby Digital Plus, DTS, Dolby TrueHD and E-AC-3. The format offers the choice of LPCM, DTS-HD Master Audio and Dolby TrueHD for highest-fidelity audio experience.