Analysis: The Future Of DVD (Part 1)

Unless you’ve been spending time with your head in a gopher hole, you’ve probably heard that we are now faced with two competing DVD “standards:" HD-DVD and Blu-ray. The quotation marks around the word "standards" are used to good effect. A “standard" is supposed to be a basis for comparison, a reference point against which other things can be evaluated. Well good luck with that. These two formats have very little in common with each other, let alone anything else. But I’m getting ahead of myself.

It All Began in the Land of Oz
Congress, in its infinite wisdom, has decided that we should all be watching digital TV. Exactly what the technical reason for that might be is something of a mystery, even to most members of congress. What they do know is that they’ll probably be able to sell the abandoned analog TV bandwidth for about $10 billion and Congress has rarely passed up an opportunity to find new ways to spend money. So, sometime in 2009 (probably), in the month of April (possibly), goodbye analog TV and Hello Digital!

Well, there’s no need to really worry. If you have an HDTV already, you’re set. Many current TVs are being sold with digital tuners. They won’t deliver digital pictures, but you’ll be able to receive digital signals. And, of course, if you’re a cable or satellite subscriber, you will continue to receive digital signals converted to analog for as long as your archaic TV should last.

Let me amend that last remark. There’s no need to really worry unless you’re a Cablevision subscriber and have noticed that the picture from NBC, which broadcasts in 1080i, looks like crap. In order to get that b-i-i-i-g picture into your itty-bitty analog screen, the cable company compresses the signal like an orange in a juicer. What emerges sometimes looks more like pulp than television — but that’s a rant for another day.

Size Matters
The problem with high definition television is that it’s high definition. The real meaning of that may have escaped you (especially those of you in gopher holes). A “true" HDTV signal has a 1920 x 1080 resolution. (You’ll see that "1080" suffixed by either an "i" for interlaced signal or a "p" for progressive scan.)

According to my trusty Excel spreadsheet, that’s 2,073,600 bits per frame. At 29.97 frames per second, that’s 223,724,851,200 (223.7GB) per hour. The average 1 hour TV show is actually somewhere between 41 and 43 minutes length without commercials but, even so, it’s plainly obvious that, even with compression, there’s no fitting a one hour HDTV broadcast on either a 4.7GB single layer or even a 8.5GB dual layer DVD of today. Those worked fine for analog TV’s 720 x 480 resolution (37,287,475,200 bits per hour, or about 3.7GB with MPEG-2’s 10:1 compression).

The solution? Bigger DVD discs! Physically they’re not bigger, they’re still the same 120mm/4.75" diameter size as the discs we know and love today. (Shame, too. I have a few hundred laser discs that could use some company.) They just have more capacity. HD DVD will be able to store 15GB, 30GB, or 45GB, depending on whether it’s a single, dual, or triple layer disc (respectively). For Blu-ray, that would be 25GB and 50GB for single and dual layer (respectively) and perhaps 75GB and even 100GB per disc if they can get triple and quad layer discs out of the lab. (Keep in mind that those numbers are fungible to a great degree. There is both science and brag built into them and, as the two camps jockey for world domination, there’s sometimes more of one than the other.)

So if the higher capacity discs are the same physical size as the current crop of low-capacity CD and DVD discs, how is it that they can hold so much more? The answer is the pits and we’ll be climbing into them next time. No need for pitons.

Bill O'Brien can be blamed for more than 2,000 articles on computers and technology topics. With his writing partner, Alice Hill, Bill co-authored "The Hard Edge," the longest-running (1992 to 2004) technology column penned by a techno duo. For more, go to www.technudge.com.