About DVD-Recordable Technology

I'm going to assume that most readers will be producing DVDs to record on DVD recorders, rather than for mastering at a DVD replication facility. If you're preparing a title for mastering and replication, I recommend reading DVD Authoring and Production, by Ralph LaBarge (CMP Books, 2001). If you're burning your own discs, read on.

How Much Video Can I Fit on My DVD?

As much as you want to, within a few basic parameters. MPEG-2 is a scalable technology, which means you can compress to any desired bitrate. For example, to fit one hour of video on a DVD, you might encode at 8 Megabits per second (Mbps); to fit 2 hours, at 4Mbps; or to fit 4 hours, at 2Mbps.

Of course, the video starts to look pretty awful below 4 to 5Mbps unless you have stellar source material and a top-of-the-line hardware VBR encoder (typically, only Hollywood movies can go this low and get away with it). Some encoders simply won't compress below a certain rate. There are other factors mitigating the number of minutes of video you can place on disc. If you want a quick look at the bitrate you'll need to fit between 60 and 120 minutes of video on a disc, flip to Table 8.2.

What's the Storage Capacity of DVD-Recordable Discs?

That depends upon the type of recorder you have, as shown in Table 8.1. However, let's start with the mastered discs, so you'll understand the advantage Hollywood enjoyed over most smaller producers until very recently. (There are five kinds of mastered discs; the three not mentioned here, DVD-10, DVD-14, and DVD-18, are rarely used and we're not going to concern ourselves with them here.)

Table 8.1. Capacity of mastered and recordable discs.

	Mastered Discs		Recordable Discs
Disc type	DVD-5	DVD-9	DVD±R/RW	Dual-Layer
Number of layers	1	2	1	2
Capacity	4.7GB	8.5GB	4.7GB	8.5GB
Video at 8Mbps (in minutes)	74	135	74	135

Mastered discs are mass-produced in a DVD replication facility, and most Hollywood DVDs that contain any kind of "extras" beyond the movie itself use the dual-layer DVD-9. Dual-layer discs contain data on two separate physical layers on a single side of the disc for a total disc capacity of 8.5GB. During playback, all set-top and computer DVD players first read the top data layer from the center of the disc outward. After reading all the content in the top layer, the player automatically refocuses and starts reading the bottom layer from the outside of the disc inward. This is called opposite track DVD, because the laser reads the two layers in opposite directions. The first layer has to contain at least as much content as the second layer so the laser can refocus without repositioning itself to make a seamless transition to the video on the second layer. You may notice a slight hiccup in the video when the player switches layers (although the latest players handle the layer break better than older players). Hollywood producers typically attempt to hide the break by placing it during a fade to black.

Some discs are designed to be read in the same direction on both layers, usually because the primary content of the disc is not a linear movie, but shorter video clips randomly accessed by the user. This is called parallel track; it's much less common, and always makes a player hiccup if read sequentially, because the laser has to refocus and reposition itself.

Industry Improvements

Until mid-2004, the maximum capacity of DVD-Recordable discs was 4.7GB, roughly 55 percent of the capacity of a mastered DVD-9. This huge difference started to become relevant to projects involving around 2 hours of video, because you had to drop the bitrate (and, thus, the quality) to squeeze the video onto the disc. For example, with 8.5GB of capacity, you can encode two hours of video at about 8.5Mbps, which should deliver absolutely flawless video quality. To fit 2 hours of video on 4.7GB, however, you'd have to encode at 4.7Mbps, a much lower rate that would visibly degrade the video.

In 2004, however, several vendors started to ship new DVD-Recordable drives that supported recording to dual-layer (DVD+R DL) discs with a storage capacity of 8.5GB, the same as a mastered DVD-9. Early adopters were punished with the usual incompatibility problems that plague most new formats, but the second-generation drives and discs improved matters considerably. Reviewing a first-generation drive, EMedia magazine reported about a 35 percent success rate in terms of playback of recorded dual-layer discs with consumer DVD players in June 2004. By September, second-generation drives were returning about a 65 percent success rate, which looks better, but still means you should proceed with caution. What's more, the price difference between single and dual-layer media remained quite large, with dual-layer media costing more than $15 per disc compared to less than $1 for recordable media in high quantities.

Surprisingly, the price difference between single-layer and dual-layer recorders isn't that significant. Since all dual-layer recorders can also record to single-layer recordable and rewritable discs, buying a dual-layer recorder is a no-brainer for all but the most thrifty. There is a risk that you may have to upgrade the firmware of the drive going forward, but generally it's fairly simple.

It's also worth noting that the terminology surrounding these discs and drives is fairly confusing. For all practical purposes, the two "competing" DVD-Recordable formats, DVD+R and DVD-R, are the same (see next section), but they're a little more divergent in the dual-layer scene than on the single-layer side. For one thing, as of November 2004, there are no dual-layer DVD-R discs or drives that will write them; dual-layer DVD-R isn't expected to see the light of day until sometime in 2005. The dual-layer discs you will find are "plus" family discs, called "DVD+R DL." And to make matters more confusing, they're officially known as "double-layer" discs, even though the accepted term for DVDs with two layers has been "dual layer" ever since DVD first appeared in 1997. If you're looking for a DL-capable drive or DL media, unfortunately, you'll have to keep your eye out for all of these terms.

Is There a Difference Between DVD-R/RW and DVD+R/RW?

The biggest current difference (as of late 2004) is that there are no dual-layer DVD-R products yet available. That said, there are many drives that support DVD-R/RW and DVD+R/RW, as well as DVD+R dual-layer (usually designated as DVD+R DL). Virtually all currently shipping DVD-Recordable drives support both the plus (+) and minus ( ) formats, although some of the older drives integrated into new PCs may only support one format or the other. Drives that support both single-layer standards double your media options, and improve your chances of producing a disc that will play on any given player (more on this in the next question). Since there is no price premium for drives that support both -R/RW and +R/RW, I would definitely recommend buying a drive that supports both formats, whether you're buying a single- or dual-layer recorder.

Will Discs Produced by My DVD Recorder Play on All DVD Players?

No. Compatibility appears to be improving, with some studies placing single-layer DVD-R and DVD+R compatibility well over 90 percent, but that still means that if you send your DVDs to 100 viewers, five to ten won't be able to play the disc. For this reason, when sending a disc, I always inform the recipient of the potential for compatibility issues, and tell them to contact me if this occurs.

You can minimize the risk of compatibility issues by:

• Using name-brand media. I use exclusively Verbatim and Ridata.

• Keeping the combined audio/video data rate below 8Mbps, since many players will sputter on media encoded at higher rates and burned to recordable media (go with 7Mbps to be truly conservative).

• Deliver your projects on DVD-R, not DVD-RW; disc/player compatibility is always better with write-once media than with rewritable media.

• Never apply paper disc labels on DVDs. Printing directly on the media with an inkjet or similar printer is fine.

I like DVD recorders that support both DVD-R/RW and DVD+R/RW because if I produce a disc in one format that won't play on a DVD player, I simply produce another using the other format. Invariably, the second disc is compatible with the player in question.