HD-DVD compatable?

[NThomas76207]

if HD-DVD can be played back in a standard DVD player, and Blu-ray is capable of playing DVDs couldent a Blu-ray device play a HD-DVD???

[Marwin]

You got it backwards. DVDs can be played in a HD-DVD player, but not the other way around.

It sounds more likely that Blu-ray will be able to support HD-DVDs than the other way around at least (because they already have to support both 0.1mm and 0.6mm protection/cover layers). However, there are a lot of differences between Blu-ray and HD-DVD, both with the physical and logical/application specifications, so it won't be done easily.

[Blu-Wave]

Part of the confusion may be because there are two versions of HD-DVD, one based upon blue laser technology, which can support up to 30GB spread over two layers, and a red laser version, HD-DVD9, which uses very low bitrates to provide high definition on an 8.54GB two layer disc.
Red laser HD-DVD9 can be played on DVD players which have been designed to decode the (non DVD) signal and which support the potentially higher data rates required - for example, DVD drives in modern PCs which support the Windows Media 9 set of codecs can play back this type of video given an appropriate display and graphics card.

In contrast, blue-laser based HD-DVD (and Blu-ray) have much narrower tracks and smaller "pits" than DVD and so cannot be read by a standard DVD player or drive. Whilst the blue laser in an HD-DVD/Blu-ray machine can be used to read single-layer DVDs, it cannot reliably read dual-layer discs, and so a second red laser is required by both HD-DVD and Blu-ray to achieve backwards compatibility with DVDs. To ensure maximum compatibility with CDs as well, a third infra-red laser is used in blu-ray machines to read (and potentially write to) them, and accordingly Sony and Philips have developed three-laser optical heads which will be productionised over the next year or so.

Using a red laser, HD-DVD9 offers 8.54GB spread over two layers and a maximum data transfer rate of 9.6Mbps, whilst single layer HD-DVD-ROM is 15GB and single layer BD-ROM 25GB, with a maximum transfer rate of 36Mbps. What does this mean in practice? In recent tests of the latest version of MPeg4, which goes by the exciting name of H.264/AVC FRExt and is reported elsewhere on this site, at a resolution of 1920 by 1080 pixels progressive scanned at 24 frames per second, an average video data rate of 16Mbps was required to achieve similar to or better than the performance of MPeg2 at 24Mbps with difficult (noisy film) material, 12Mbps with general material and 8Mbps with computer-generated imagery. This doesn't include sound, but compressed DD/DTS 5.1 would add around 0.5Mbps whilst lossless 5.1 is around 4.5Mbps. H-264/AVC FRExt is very similar to VC9 - the algorithm set behind WMV9, so this is also relevant to Microsoft's considerations - except note that currently virtually all of Microsoft's claimed 1920 by 1080p24 demo material is actually encoded at 1440 by 1080p24 resolution. :roll:

Anyway, at the minimum (computer-graphics) rate of 8Mbps with compressed DD or DTS5.1, HD-DVD9 can store around 2 hours of material, with general material this drops to 1.5 hours whilst with "difficult" material it falls again to one hour - so realistically one either requires computer-generated films of two hours or less or switching to 1280 by 720p2 resolution (going from over two megapixels to less than one megapixel). Coincidently, Microsoft is pushing 720p very hard in other areas such as broadcasting, and unlike the 1080p24 demos, the 720p24 demos are true 1280 by 720p24 resolution.

... and what about blue laser HD-DVD at 15GB? At the general purpose 12Mbps, with DD/DTS5.1, it can hold around 2h 40m, whilst at 16Mbps it can hold around 2h - 1h 40m with lossless 5.1. Blu-ray, with 25GB in a single layer, can hold 4h 30m at 12Mbps with DD/DTS5.1, 3h 20m at 16Mbps with DD/DTS5.1, 2h 40m at 16Mbps with lossless 5.1, 2h 30m with lossless 10.2, 2h 15m with lossless 14.2 and 2h with lossless 22.2 (sound system as used in Ultra High Definition Video [UHDV], with 10 speakers at ear level, 9 above, 3 below and 2 subwoofers). Blu-ray appears to have the advantage - and unlike HD-DVD9 which is already at two layers, both Blu-ray and HD-DVD can potentially double their capacity to achieve 30GB and, in the case of Blu-ray, 50GB, if required. However, where blue laser HD-DVD probably needs to double its capacity up to 30GB in order to compete with 25GB single-layer Blu-ray, most 1080p24 material can fit comfortably on 25GB with lossless 7.1 audio, but the option of using two-layer BD-ROMs for extended films, etc. is still there.

Note that as Marwin commented, it is also more likely that Blu-ray machines could be built to support HD-DVD, because they already have 0.1mm/0.85NA technology for Blu-ray, 0.6mm/0.6NA technology for DVD compatibility and 1.2mm/0.45NA technology for CD compatibility anyway, whilst HD-DVD machines have no 0.1mm/0.85NA technology and so can't easily support Blu-ray. Accordingly, Sony are currently developing a computer drive which can read CDs, DVDs, BDs and HD-DVDs (AODs). :?

[NThomas76207]

Ok, that makes it alot clearer. But on some forum today somewone posted that Sony has developed a Blu-ray player WITH another head to playback HD-DVD (kinda like switching between DVD&CD) Is that even possable concidering that Sony may not have the rights to develop HD-DVD (being a Blu-ray founder).

Then again, Sony helped Develop the DVD+ format while still making dual format burners (DVD+/-RW)

[Blu-Wave]

... Sony is also in the chair for Consumer Electronics in the DVD Forum ...

Also note that all forms of BD were designed from the outset to support multi-layer recording, so dual-layer 50GB and quad-layer 100GB BD-ROMs will be possible (at additional cost).