DVD burners at ceatec: inside looking out

Computer Technology Review, April, 2004 by Gordon Merit

Let's get this out of the way quickly: Few burner manufacturers are making a lot of money even as the number of manufacturers and volumes swell. They all have dual formats. Cheap no-name and brand name manufacturers are moving rapidly to deliver higher speed products. The burners are cheap ... getting cheaper. Your challenge is always to buy intelligently taking into consideration manufacturer's reputation, software bundles and commitment to customer support. Then focus on only using quality media, not the stuff that saves you a few cents.

And so the story ends? Nope. Just when you thought life would settle down and you could focus on mastering your video software, the burner and media camps have set out to meet your insatiable appetite for capacity.

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The great thing about going to CEATEC (a trade show held in Japan) is that you get to see all the newest and greatest fun techie toys. It took a lot of willpower to stay away from the do-everything cell phones that will be available in the Pacific Basin and Europe but we were on a mission: to focus on the future of DVD storage and video production.

The good news for readers is that within 12 months:

* The burner and media manufacturers will be able to double the capacity of the recordable DVD discs giving us 8.5GB of capacity on a single side (currently to get more than 4.7GB on a disc double-sided media was used)

* The new media will store four hours of DVD-quality video or 16 hours of VHS quality

* The discs can be played by the majority of the players in use today.

The bad news is:

* It will require new DVD burners

* We will still have two formats ( /-) to contend with

* Neither side seems willing to compromise

For the sake of space, we are going to divide the dual-layer discussion into two parts: burners and media.

Quick Background

After a lifespan of ten years, the CD-ROM finally got the facelift it required to take it into the next century when the standard for DVD was finally agreed on during 1996.

The movie companies immediately saw a big CD as a way of stimulating the video market, producing better quality sound and pictures on a disc that costs considerably less to produce than a VHS tape. Using MPEG-2 video compression (the same system that is used for digital TV, satellite and cable transmissions), it is quite possible to fit a full-length movie onto one side of a DVD disc. The picture quality is as good as live TV and the DVD-Video disc can carry multi-channel digital sound.

All writable DVD formats include a set of specifications that define a media's physical layer that enables the media to be read. The application layer specification deals with the content. Motion pictures are typically released on replicated ROM media (the physical layer) and authored using the DVD-Video format (the application layer).

The DVD-Video format is essentially a publishing format for one-time-only mastering. Today there are four flavors of DVD:

* DVD-5 is a single-sided single-layered disc with 4.7GB

* DVD-9 is a single-sided double-layered disc offering 8.5GB

* DVD-10 is a 9.4GB dual-sided single-layered disc

* DVD-18 will deliver 17GB on a dual-sided dual-layered disc

A single-sided (DVD-5) DVD-Video disc was designed to hold a typical feature-length movie, which averages 133 minutes. For a dual-layer disc (DVD-9) capacity increases to 240 minutes (see Figure1).

DVD's data layer is right in the middle so that the disc can be double-sided. As a result, the laser assembly of a DVD-ROM drive is more complex than the CD-ROM to enable it to read from both CD and DVD media. Early drives used a pair of lenses on a swivel but current designs use dual optical pickup lasers optimized for CD (780nm wavelength) and DVD (650 nm).

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Some DVD movies have taken advantage of double-sided discs by putting a version formatted for a normal TV or monitor with a 4:3 aspect ratio on one side and a widescreen version formatted for 16:9 aspect ratio on the other. But most of today's DVD movies take advantage of the dual-layer, single-sided media, which until now was only produced by professional replicators/duplicators. Pits on both layers of the DVD-9 layers are 10% longer than on a DVD-5 or DVD-10 disc. Each layer is molded in one substrate, the two are joined using an optically transparent bonding layer and the replicators print the discs in the conventional way (see Figure 2).

There are two ways of writing the DVD data layers: parallel track path (PTP) and opposite track path (OTP). The refection film of the first layer is semi-transparent and the bonding agent is transparent, providing instant access from the first to the second layer. They provide seamless continuous playback from the two layers.

In PTP discs, both layers read from the inside of the disc to the outside, whereas in an OTP disc the outer layer reads from the inside to out and then back in for the inner layer. This allows the drive to read both layers almost continuously, with only a short break to refocus the pickup lens. This is especially useful for DVD movies, where long playtime without interruption is needed.