TUTORIAL: LEARN MORE ABOUT IT

HIGH DEFINITION DVD: WHAT’S THAT ALL ABOUT?

by Peter H. Putman, CTS                                                                                 HDTVexpert Home

If you haven’t heard yet, high definition DVDs are coming to a store near you next year. And of course, there’s a format war in the works between the two proposed standards – Blu-Ray, which is led by a consortium of 13 major manufacturers including Sony, Panasonic, HP, and Dell; and HD DVD, led by Toshiba and NEC (recently joined by Sanyo).

Those readers who remember the DVD video and audio format wars are already groaning, “Why can’t these folks get their act together and just come up with a single format?” After all, we now have DVD-R/-RW, DVD+R/+RW, DVD-RAM, and DVD-ROM. Will the evolving high-def DVD market be déjà vu all over again?

Last October, I attended the AVS Forum Home Theater Cruise for the first time. This 7-day cruise through the western Caribbean on Royal Caribbean Cruise Lines featured a broad range of panel discussions and presentations of interest to home theater enthusiasts.

One panel in particular (which turned out to be the best, in my opinion) covered the emerging high-definition DVD standards.

To be sure, both sides made compelling case for their proposed standards. Blu-Ray, which uses a short wavelength blue-violet laser pickup (hence the name) will offer 27 GB of capacity on a single-layer DVD and 54 GB on a dual-layer DVD. That’s enough for 2+ hours and 4+ hours of HDTV programming, respectively, assuming 9 GB per hour and MPEG-2 encoding.

The HD DVD format also employs a blue laser, but employs much of the existing manufacturing process for regular DVD. It claims capacities of 15 and 30 GB for read-only and rewriteable versions and (supposedly) offers considerable manufacturing cost savings over the ‘from scratch’ Blu-Ray format. 

Table 1: Blu-Ray and HD DVD Compared

Source: www.Blu-Ray.com

However, the differences between the formats and the alliances being formed to support one or the other aren’t what I found interesting. Rather, it was the news that both DVD formats will support MPEG-2, MPEG-4, AVC (H.264), and VC-1 (Windows Media 9) video encoding.

For those readers who are still getting their feet wet with HDTV, one of the biggest problems (if not THE biggest) is juggling the bit rate with MPEG-2 encoding to achieve a reasonable compromise between HD picture quality and transmission efficiency. MPEG-2 has certainly done a yeoman job with standard-definition video (480i or 576i), but there is plenty of evidence that it is straining to keep up with HD content.

Consider this: The “pipes” for MPEG-2 are already tight as it is. Off-air HDTV can’t use anymore than 18.5 – 19 Mb/s data rates; the 6 MHz channel size is capped at 19.39. Empirical results show that multicasting HD with other SD programs and chopping the HD bit rate down has a noticeably adverse effect on picture quality, particularly on larger (40” and up) TV screens.

Cable system operators use a different modulation scheme to pack two HD programs into a single 6 MHz digital cable channel with a 38.8 Mb/s data rate, adding a pair of SDTV channels to fill out the package. But they have finite channel capacity and can’t afford the luxury of higher bit rates. Satellite operators are also constrained by the cost of transponders; so precious bits are used for as many programs as possible, not for enhancing picture quality.

JVC’s languishing D-Theater (D-VHS) HDTV tape format has a maximum bit rate of 25 Mb/s for showing 1080i encoded movies, but requires special tape players and has not been able to penetrate the mainstream consumer markets.

The answer is a more efficient codec, and that’s where MPEG-4 AVC and VC-1 come in. Both systems are relatively new and both promise to cut the required bit rate for HD in half. (Yes, you read correctly, by half.)

That means an HD program could be encoded at 8-9 Mb/s and SD programs at 1-2 Mb/s, yet still provide the same image quality that MPEG-2 is capable of. Public demos of VC-1 have already been going on for several months (Both AVC and VC-1 were demo’ed at NAB 2004) and several VC-1 high-definition DVDs have been released by Microsoft, including Step Into Liquid, Terminator 2, To The Limit, and Stormchasers.

Given that MPEG-2 is over a decade old but universally supported (now, who among you still doesn’t have a DVD player yet? Come on, ‘fess up!), there’s a bit of a dilemma here. For a still-evolving high-definition disc playback and recording format, the decision to support more advanced codecs is a win-win for everyone. But the existing broadcasting/cable/satellite structure is still stuck with an MPEG-2 infrastructure for the time being.

The Advanced Television Systems Committee (ATSC) is currently investigating AVC and VC-1 for digital TV broadcasting. SMPTE recently standardized VC-1, and there has been talk of HD satellite broadcaster VOOM moving to VC-1 encoding to free up transponder space. But giving up tried-and-true MPEG-2 will be a tricky, time-consuming and expensive process.

To be sure, MPEG-2 picture quality issues would never have come up if television screens had stayed in the 20” to 30” range – it’s a lot harder to spot compression artifacts on smaller screens, particularly with interlaced programming and the typical viewing distances of seven feet or more.

But TV screens are getting bigger as prices drop, and it’s not a stretch to say that the ‘standard’ TV size for the home will probably be between 30” and 42” in the not-too-distant future. Not only that, the optimum viewing distance for HDTV is nominally 3.1 times the screen height. In essence, your TV screen gets bigger and you sit closer to it.

If there are quantization errors such as macro blocking and compression problems such as mosquito noise, it’s a sure bet that cable and satellite operators (not to mention TV stations) will get plenty of phone calls complaining about picture quality. Anyone who has watched standard-definition digital cable on a 50-inch rear-projection LCD or DLP TV knows very well what I’m talking about.

Hence, the argument can be made that a more efficient video codec must evolve and go hand-in-hand with HDTV program distribution. Right now, HD program content providers are faced with a Hobbesian choice and must decide whether bit rate, bandwidth, or bucks (as in $$$) are most important to them. If it’s the last two (and it usually is), then picture quality is inevitably sacrificed.

By parsing the bit rate in half, content providers now have more breathing room and may be able to satisfy all three requirements – deliver lots of HD programming at affordable rates while maintaining the best picture quality, and add additional channels/program streams on top of all that.

The Blu-Ray and HD DVD camps won’t have to make these hard decisions; they’ve already future-proofed their systems for advanced codecs (and by the way, both standards also support Dolby Digital +, DTS++, and MLP audio codecs, too!). Plus, they have plenty of breathing room with the proposed 36 Mb/s data rates – twice that of the ATSC standard.

The only thing remaining is to decide who wins the high-def DVD format war, and Toshiba is already announcing it will release HD DVD players in early 2005 with software expected to follow. Blu-Ray member Sony says a player/recorder won’t be available until late 2005 or early 2006, although Sony and Panasonic already have models available for sale in Japan.

Either way, the door has been opened for the introduction of more advanced, HD-friendly video codecs into the mainstream consumer market. How much longer before cable, terrestrial, and satellite HDTV programmers follow suit?

Copyright ©2004 Peter H. Putman / Access Intelligence

This article appears in the January 2005 issue of Studio Monthly magazine.