High definition showdown
Blu-ray is not the last word in high definition movie distribution. It will be challenged by HD DVD, the official Standard of the DVD forum.

The continuing increase in size of the average TV or other display is not without its drawbacks.

For sure, everything else being equal, a bigger picture is better. There are a lot of people who are perfectly happy with a large TV picture, regardless of quality.

The healthy sales of horrid low resolution 42” plasma TVs attest to this.
But the negative aspects of this shouldn’t be ignored. There are two primary ones.

First, a larger picture makes for a fuzzier picture. What might look razor sharp on a 76cm screen can be noticeably soft on a 127cm plasma display, and especially on a 250cm projection screen. Second, to the extent that there are defects in the recording, these become more obvious when the display is larger.

That’s where high definition video comes in.

True high definition
Now there are a few, ahem, definitional issues with ‘high definition’. I’m not sure quite what possessed the British Government, but when it came to mandating high definition TV, it declared not one but three Standards: 1080i, 720p and 576p.

This last Standard should not be regarded as high definition at all, since it is precisely the same resolution as standard PAL TV, otherwise known as 576i. The only difference is that with 576p, both fields constituting a frame are sent in one fiftieth of a second, rather than one twenty-fifth of a second as occurs with 576i. With film sourced material, the same frame is shown twice, so the net result is the same. With video material originally captured with a 576p camera, there will be an improvement in motion smoothness. But that isn’t really high definition.

What is truly high definition is providing more detail in each frame than our standard PAL system, and this is delivered only by 720p and 1080i. We now have 1080i HD broadcast on some stations (the others use merely 576p to meet their legal obligations). But the real boon for the home entertainment lover will appear later this year, or perhaps early next year, with the introduction of high definition movies distributed on optical disc.

HD DVD
As pointed out in the last issue of Connected Home Solutions, there will be two competing formats for this disc: Blu-ray and HD DVD. Here we shall look closely at HD DVD.
HD DVD is primarily a development of the Japanese electronics giant, Toshiba. As with Blu-ray, it has been created to deliver true high definition video in 1080i format. That is, its resolution will be 1920 x 1080 pixels.

The video will be compressed, likewise, similarly to Blu-ray DVD, with disc manufacturers being able to encode the video with MPEG2, the same as that used with DVDs; or with VC-1 Advanced Video Codec, a variation of the video compression algorithms used in Microsoft Windows Media; or with MPEG-4 AVC High Profile.

Both of these last two are later and consequently more advanced developments than MPEG2. They permit higher compression levels than MPEG2 with the same quality of video being retained, or improved quality by using the same space on the disc. As always, tradeoffs will need to be made between the amount of compression and other material (such as special extras) recorded on the disc.

Just as with DVDs the audio can comply with several different Standards – Dolby Digital, DTS, MPEG2 and PCM. But some more have been tossed into the collection: Dolby Digital Plus, Dolby Digital TrueHD and DTS HD. More on these in a moment.

HD DVD pros
HD DVD has two things going for it in the forthcoming battle with Blu-ray DVD, and potentially a third.

First, it is the official high definition Standard of the DVD Forum. That is the body that controls the Standards for DVD video, DVD audio, DVD-R and DVD-RW. Its might shouldn’t be underestimated, but eventually the bulk of consumers will decide which one will succeed.

Second, for the moment it is easier to make HD DVD discs than Blu-ray ones. The reason is the physical structure of the discs. Both types of discs have a total thickness of 1.2mm. But HD DVD has a transparent plastic layer that is 0.6mm thick – just the same as CDs and DVDs – while Blu-ray’s transparent layer is only 0.1mm thick. That means that considerably more tooling is required to convert from CD or DVD manufacture to Blu-ray than is required for HD DVD.

Third, this difference in layer thickness may give HD DVD the edge in durability. When it was first developed, Blu-ray discs were actually supplied in caddies for their protection. For consumer use, new materials have been developed for the transparent layer which are said to be one hundred times more scratch resistant, so caddies are no longer used.

Still, HD DVDs could be assembled using a similar tough material (such as that used in TDK’s premium recordable discs) providing even better durability. And it remains to be seen how the thin layer on Blu-ray discs will cope with Disk Wizard-type repairs, which rely on fine abrasion to polish the surface.

HD DVD cons
But not everything is in HD DVD’s favour when compared to Blu-ray. The very fact that the data layer has been buried 0.6mm into the disc rather than 0.1mm means that the data cannot be stored as compactly. Consequently a single layer HD DVD has a capacity of 15GB, compared to Blu-ray’s 25 to 27GB.

Both formats provide for multiple data layers, so we can expect to see 30GB and 50GB forms respectively, with even higher capacities provided if required in the future.

In addition, Blu-ray was largely developed by Sony, which also owns the Columbia and TriStar film studies, and their large, high quality back catalogues, so it may be quite a while before we see these titles becoming available in HD DVD format.

However, both formats use the same laser light wavelengths in their read-heads: 405 nanometres. So we should not be surprised if eventually dual format HD DVD/Blu-ray players become available. Both types of players will provide support for DVDs and CDs from the start.

The new Dolby Digitals
Like DVD, HD DVD has a speed limit: the maximum rate at which data can be extracted from a disc. For DVD that’s just over 11Mbps.

HD DVD more than triples that to 36.55Mbps.
Using MPEG2 format, truly high quality HD requires between 20 and 25Mbps (most 1080i HD broadcasts only deliver around 12Mbps). The newer compression systems need lower data extraction rates for the same quality. That leaves quite a bit of room for audio. (The other constraint is, of course, disc space.)

Both Dolby Digital and DTS, in their seemingly never ending quests to dominate movie sound, have come up with new formats for even better sound quality. The very best ones will be Dolby Digital TrueHD and DTS HD.

Unlike the systems used on current DVDs, these are ‘lossless’ systems. That means that absolutely none of the audio data is thrown out on the grounds that you won’t hear it anyway. That’s the answer to an audiophile’s dreams.

Since they aren’t lossless, they cannot deliver the extreme compression offered by their traditional counterparts. Instead they can manage compression rates of around 2:1. Both offer up to eight channels of sound and could require over 10Mbps of data transfer capacity.

Their use is likely to be limited to music-heavy discs, such as the forthcoming 2004 Phantom of the Opera, which in the US release uses Dolby Digital TrueHD.

For regular movies, HD DVDs will typically use Dolby Digital Plus. This also supports up to eight channels and can use bitrates of up to 6Mbps. By way of comparison, the highest bitrate for Dolby Digital as used on DVDs is less than 0.5Mbps, and for DTS is around 1.5Mbps (most DTS discs use half this rate).

But Dolby Digital Plus seems to have standard Dolby Digital 5.1 built in, so that if you have an existing home theatre receiver it will remain compatible, albeit without the higher quality.