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DVD Media Demystified
Posted Sep 1, 1999 - Eastman Software Positioning Paper [Sep 1999] Issue Print Version     Page 1of 1
  

Not all DVD media is created equal, and the differences go fairly deep—not only in terms of some brands being superior to others, but with regard to differences and gradations within the brands themselves. Everyone is familiar with the saying, "you get what you pay for." So why do people think that they are getting a bargain by buying some house imprint, cut-rate, or otherwise unknown brand of DVD? You are not getting a bargain. You may be saving 20 cents per disc, but if you add up having to re-burn a bad disc, re-label it, and inconveniencing your client by forcing them to return the bad DVD, you'll quickly lose that 20-cent savings and then some. Add in the damage to your reputation that delivering a poor-quality product will inevitably do, and the cost of a cheap DVD becomes something that you can't possibly put a price on.


The Price You Pay

Have you ever taken a minute to think about why some blank DVDs are expensive and some are cheap? Quality and consistency are the biggest factors. Companies like Taiyo Yuden, MAM-A, and Verbatim manufacture their own DVDs in their own factories where they have full control over the entire process. The DVDs manufactured this month are exactly the same as the ones manufactured last month. They also have done extensive testing to determine the predictive life, and Taiyo Yuden and Verbatim have given their products a 100-year life expectancy, according to their Web sites.

Lesser products have listed 25 years or nothing at all. There is a push in the federal government by the National Institute of Standards and Technology (NIST) to create a program (in conjunction with OSTA, the Optical Storage Technology Association) that would test all optical media to set standards to determine useable life. (Numerous institutions have done media longevity testing in the past, but never established standardized testing criteria, or yielded results that haven't themselves been widely criticized.)

In the world of event video, media longevity isn't some abstract issue any more than it is in corporations, libraries, and other institutions that archive "mission-critical" data. This disc-life thing is of great importance not only to our clients' cherished memories, but to the thousands of file cabinets full of records and data that are being archived to DVD by local and federal government agencies. Could you imaging gathering, producing, encoding, and archiving all of that data only to have it disappear in a few years?

Another key issue besides media longevity is media-player compatibility. According to research already done at NIST (www.nist.gov), media compatibility ranges from 80.5% to 100% (no names mentioned) for single-layer, write-once DVD media (don't get us started on double-layer—whatever the compatibility promises the media and drive manufacturers have made, none have been kept so far). Research also has determined that there is virtually no difference in compatibility between -R and +R media—again, it's really just a brand and within-brand issue at this point, rather than a format-specific one.

Sticking Points

Labels . . . paper or plastic? These days, using paper labels on DVDs should not be an option. There is very little margin for error with label positioning; even though there are good label applicators out there, even a slightly off-center or wrinkled label can create an imbalance that may cause wobble during playback and make a disc unplayable. What's more, the heat generated by many DVD players can cause labels to pucker and peel, which also renders the discs virtually useless. Combine that with the lower fault tolerances of newer, cheaper, off-brand DVD players—exactly the kind of players that are likely to balk at an imperfectly positioned DVD label—and they throw off the longevity predictions completely. All in all, using sticky labels is an extremely unwise business decision for anyone distributing work to clients on DVD. Many DVD manufacturers, such as Taiyo Yuden and Verbatim, have even placed notices on their Web sites stating that they do not support or recommend paper labels.

Pricing of coated DVDs is only a few cents more than branded DVDs. Printers that accept DVDs for direct surface labeling, such as the Casio CW-50, the Primera Z1, and the EventDV Reader's Choice-winning Epson Stylus Photo R200—which is also an all-purpose paper printer—can be had for just over $100. The new Lightscribe DVD recorders (introduced by Hewlett-Packard), which can print directly to a disc's surface in addition to burning data to disc (you have to flip the disc over after burning to access the printable side), present another option (see Hugh Bennett's review, March 2005, pp. 58-59). Considering that these new burners sell for only a small premium over non-Lightscribe drives, this is another cost-effective approach. Much as inkjet DVD label printers require inkjet-printable media, the Lightscribe burners also require certified Lightscribe-compatible media, which is now available (though perhaps not widely available) from most major DVD media manufacturers. These drives won't do the sort of bright, colorful labels that you can expect from inkjet models (though the sepia looks pretty good), but like inkjet surface printing, it's a much more durable and reliable approach than using sticky labels.

Built for Speed?

4X . . . 8X . . . 16X? How fast is fast? Everything is relative. Bet you didn't know that 8X is the fastest sustainable speed for a DVD recorder. 16X burners can only burn at 16X on the outer edge of a DVD. If you have ever timed a 16X burner, you will find that it is not even close to 16 times the speed of 1X DVD. DVD recorders use either partial constant angular velocity or zoned constant linear velocity to burn a disc. Essentially, what this means is that they achieve different burn speeds, gradually increasing burn speed over time as they record a disc.

Recording from the inner hub of a disc to the outer edge, if a drive spins at a constant speed, the write head is effectively moving faster at the outer edge because it's covering more territory on the disc (think of a figure skater doing a pirouette—as her body spins at a constant speed, her outstretched hand is actually traveling faster than her torso because it's covering a bigger circle in the same time). This is called constant angular velocity (CAV). CD and DVD players, which play back music or movies at a constant speed, actually have to spin at different speeds over the course of disc playback to achieve that constant speed. This is called constant linear velocity (CLV).

Because CD and DVD recorders aspire to higher speeds than drive mechanics will actually support in the strictest sense of how fast they can spin, they use variations on CAV to achieve higher recording speeds as the burn progresses. They vary their speed only slightly over the course of the burn so that the recording speed increases gradually or through a series of plateaus (i.e., the "zones" of "zoned constant linear velocity"). Partial CAV works in much the same way, although with fewer plateaus. With a 16X drive, the drive may start at 6X, then after 500 megabytes (MB) or so, move up to 8X, write at that speed for a while, then accelerate to 10X, and so forth, until it reaches maximum speed for the last 500MB or so of a full disc. Because the drives burn at maximum speed only at the outer edge of the disc, if you're not filling up the disc with data—say, if you're writing a 30-minute video that uses only 2.3 gigabytes (GB) instead of the disc's full 4.7GB—you'll never reach that maximum speed.

Plus, the faster you burn a disc, many argue, the less compatibility you will have. The biggest reason for this is that as new media brands and speeds emerge, it becomes less and less likely that the destination player has been tested—and tweaked, as necessary—to ensure compatibility with a particular new disc. If you are producing large numbers of DVDs, as you would for dance recitals or plays, compatibility becomes very important. 8X is OK (depending on who you talk to); I personally use 4X to be accepted by the maximum number of players (versus production speed).

On the subject of disc speed, you can use 8X media and record at 8X, 4X, 2X, or even 1X. And although drive manufacturers—who always seem to reach higher speeds before the media gets there—usually recommend a select group of discs that will support, say, 12X burning even though the discs are certified only for 8X burning, you'd be wise not to risk it. Never burn above the rated burn speed of the disc. It's not worth it. There also appear to be some issues with other players reading 8X media. If you have long-time clients who suddenly can't play your discs since you moved to 8X, find out which player they're using and check the Web for reported player/ media conflicts.

The mechanical speed that determines how fast a drive can record a disc at a given time is revolutions per minute (rpm). This is the same rpm we know from the days of vinyl records (33 rpm for LPs, 45 rpm for singles, 78 rpm if you go way, way back). In a conventional DVD player—or any DVD drive playing back a DVD movie—a DVD spins at between 570 and 1600 rpm at 1X, faster nearer the center of the disc. The spin speed changes over the course of the disc to maintain the data transfer speed. 16X recorders have spin speeds of 9210 to 25600 rpm (if sustainable).

Now, here is a bit of info. The maximum physical limit of the rotational speed of a DVD is 32,000 rpm. After that, problems of instability and balance arise. So, for all intents and purposes, 16X is the highest record speed that DVDs will see with the current technology (see sidebar, "DVD Tidbits"). That's why we've heard a number of drive manufacturers, such as Memorex, tell us that their 16X external burners (externals always come out later than internals) are the last model of DVD drive they'll make. After that, it's on to HD-DVD or Blu-ray. But we're not there yet, and that's a topic for another article.

Care and Feeding of DVDs

Want to maximize the life of your DVDs? There are some things that you can do to extend that life and advise your clients to do as well.
• Avoid extreme heat. Although heat normally does not affect CDs or DVDs, being plastic, they can warp. Warped discs cannot spin at 1600 rpm in a DVD player.
• Avoid sustained and bright light. Because these discs are optical media, they can be made useless by exposure to light. There is no written data on the brightness or length of exposure, but any sustained light will decrease the disc longevity. Keep DVDs in their cases.
• Although care of the bottom side of the DVD (or CD) is very important because the pickup laser has to "see" through this surface, the top surface is more important to the life of a disc. Any single penetration of the top surface will render the disc useless where a scratch on the bottom surface may cause a single glitch or may even be ignored (because of the interleaved manner in which data is written to the disc and the error correction capabilities of DVD players) due to a couple of dropped bits of information.

I'll bet that almost everyone out there that provides DVDs to their clients has heard this: "The DVD that I got from you doesn't play in my DVD player but I don't have a problem with movies that I buy or rent." What is your response? Here is what you can tell your client: Commercial DVD movies are manufactured in the millions and are created from different materials, and by a different process (stamping) from what is known as Recordable DVDs or DVD±R. Some DVD players were not designed to play DVD-R or DVD+R media, especially older machines. Most newer players have been engineered to play DVD±R videos, but you should look for the terms DVD-R or DVD+R right on the box to be sure that that particular player will play your recordable DVD.

What you should know: DVD±R discs have four things in common with the stamped DVDs that deliver commercially released movies: diameter, thickness, storage capacity, and very similar (but not identical) reflectivity, which puts them within the acceptable range of the read lasers that "read" data off of DVDs in DVD players. Beyond that, they're not really the same animal. Unfortunately, not even the old/new dichotomy works for determining which players will play which discs. In the early days of DVD ('97-'99), DVD players were significantly more expensive than they are now ($250 and up). While part of the issue was economies of scale, another significant difference between today's DVD players and the earlier models is that as new manufacturers came into the game determined to churn out cheaper players, they began cutting corners, and lowered engineering standards. Believe it or not, many older players are more likely to play back the new double-layer DVD+R DL discs that increase DVD storage by almost four gigabytes; testing has proved this.

Another issue that affects all DVD players vis-a-vis recordable DVD media—but cheaper, newer players in particular—is the bitrate at which you encode your video. (This is only a media deficiency inasmuch as it's true of all recordable media, but doesn't affect video written to stamped media at the replication plants that the Hollywood studios use to press their DVDs.) Encode too high—like 8 megabits per second (Mbps) or higher, in many cases—and many players will choke and sputter on the video, particularly the newer, off-brand, $50-or-less models. Sturdier vintage players rarely have this problem, but to be on the safe side, always encode at 7Mbps or less, regardless of what you think (or your encoding program tells you) it will do to video quality. Those extra megabits aren't worth the risk that the disc won't play when your client sits back to watch it in her living room.

DVD-R vs. DVD+R

First, there was DVD-R, a DVD Forum-approved standard produced by Pioneer, which debuted at roughly the same time as DVD itself (late 1997), although it wasn't widely used until 4-5 years later. At that time there was another set of companies that called themselves the DVD+RW Alliance that encouraged end users to hold off on purchasing any DVD-R products because they were developing their own standard that would blow DVD-R out of the water. Just about the time DVD-R recorders became cheap enough (sub-$1,000) to attract more general interest—in late 2001—the first DVD+R/RW drives came out, and the "format war" was on.

This "war" still exists with some people. Though it used to be a VHS vs. Beta type of conflict, the battle lines are less prominent and fading fast. Because of recording differences, the compatibility of these totally different formats used to be a major issue and a total pain in the backside for most event video producers who wanted to supply their clients with DVDs. The big problem was that one type of drive wouldn't burn the other type of media, and you essentially had to choose one format or the other when you bought a drive. If you bought a DVD-R drive, you had to be very careful not to buy DVD+R media, and vice versa. After about 18 months of this nonsense, Sony (one of the original +R/RW backers) got the peace talks going by releasing a drive that recorded in both formats. Pioneer followed suit, and the war was over. It's hard to find a recorder these days that doesn't support both formats.

But there always has been (and maybe always will be) a difference of opinion about which format has the best compatibility. I'm going to settle the argument here and now: it doesn't make any difference. Most DVD players on the market today play either format equally well. As we go back to older players, the DVD-R format has a slight edge in the compatibility game only because of the greater number of DVD players that have been manufactured and sold that complied with the specs of the DVD Forum (DVD-R). That said, the DVD+R group pulled off a nice bit of misdirection when they first introduced their drives and media: by setting a Book Type of DVD-ROM (Book Type is one of the internal designations that helps a DVD player identify a disc), DVD+R discs were able to trick DVD players that predate the format into believing that they were seeing something familiar, so they were able to read discs they would have balked at otherwise.

In addition, the DVD+R group is the only format that has a substantial dual-layer market presence. Dual layer DVD-R is on the way, but given the still-disappointing compatibility results that plague DVD+R DL (and it's been out for a year now), I don't recommend putting too much stake in either format.

For an extensive, technical discussion of all these issues and more, check out Hugh Bennett's white paper, "Understanding Recordable & Rewritable DVD," which is available free of charge on OSTA's Web site at www.osta.org/technology/dvdqa.

DVD Tidbits

• If you have a DVD duplicator that uses DVD±R drives, you may find that it will allow you to duplicate only in the same format as the master. +R in the player, +R in the recorders; and -R in the player, -R in the recorders. This is not always the case; it depends on the logical formatting of the source disc—that is, how the video data was recorded and structured on the disc. Discs that were written on set-top (that is, TV-attached, rather than computer-hosted) DVD recorders, are written in DVD-VR or DVD+VR format, which differ somewhat from DVD-Video in the way the data is recorded on the disc. DVD-Video discs written to DVD+R and DVD-R are functionally identical, and will pose no problem for duplication, regardless of which kind of source and destination media you use (i.e., you can write from DVD-R to DVD+R and vice versa, and in a multi-disc tower duplicator, you can even write to a mixed set of source discs from both camps). But DVD+VR and DVD-VR discs (that is, VR discs written to +R and -R discs, respectively), have fundamental logical differences that prevent inter-format copying. So if you originally recorded the disc on a set-top player, or wrote it in VR format in a consumer DVD authoring tool that allows a VR option, you have to be careful about making sure your source and destination media match. But it won't be a problem if you use computer DVD recorders to burn your master and stick with the trusty DVD-Video format.

• DVDs with two hours of video on them, duplicated at 4X, take only about 14.5 minutes to record. Wait, isn't that 8X? No, and here is why. DVD duplicators copy data, not video and not audio. Therefore, regardless of how much video is on a DVD, a duplicator sees sees a maximum of 4.7GB of data and copies it at the rated speed.

• Writing on your DVD (or CD) can be hazardous to its health. Using a hard-tipped writing instrument (pen or pencil) can penetrate the top layer of the DVD and emboss or destroy the reflective surface of the DVD (the next layer down), rendering the DVD useless. Felt tip pens aren't much better. Many use inks that contain alcohol which will attack the top layer of the DVD over time and bingo, no data. There are some pens that are marketed as "DVD/CD friendly," as are Sharpie brand markers.

• How a recordable optical disc is created is the top surface, the reflective surface, the dye, and the bottom layer. Replicated discs have a mask that replaces the dye layer. This mask is a laser cut sheet that has holes, known as pits and lands, which correspond to the burn marks of a recorded disc. These sheets can be manufactured by the thousands or even millions in a fraction of the time of burning discs. Once the mask is cut, it's sandwiched between plastic discs (with the reflective layer), and you have a DVD.

• Recording to the edge of a DVD (to full capacity) can decrease compatibility. It has been determined at NIST in testing that 38 of 50 errors took place in the outer 10% of DVDs tested and that that percentage increased dramatically in the outer 5%. The ability of most players to ignore bit errors outside this "edge area" was found to be approximately 98%.

• DVD-R "Authoring" Media—You may at some point in your DVD media shopping come across DVD-R for Authoring Media. It's substantially more expensive than "General" DVD±R media, and rarely available in quantity. Is this a superior-quality disc? Maybe, but that won't help you—unless you bought a Pioneer DVD-R "Authoring" drive, which records at 1X or 2X to DVD-R (only) and costs much more than today's general run of $100-$200 DVD burners, you can't use it.

• DVD-RAM: although not compatible with most DVD-ROM drives and DVD-Video players, DVD-RAM has the most recording features. It is somewhat like a removable hard disk and used for large-capacity storage. Computer-based and standalone DVD recorders that are emblazoned with the "Multi-Write" symbol support both DVD-R/RW and DVD-RAM. Miniature DVD-RAM discs are used in DVD camcorders from Hitachi and others.

Companies Mentioned in This Article

Casio, www.casio.com
Epson America, www.epson.com
Hewlett-Packard Company, www.hp.com
Lightscribe, www.lightscribe.com
Memorex, www.memorex.com
National Institute of Standards and Technology, www.nist.gov
Optical Storage Technology Association, www.osta.org
Primera Technology, www.primera.com
Sony Electronics, www.sel.sony.com
Taiyo Yuden, www.t-yuden.com
Verbatim, www.verbatim.com



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