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Does dual-layer DVD disc work in all players?

A dual-layer disc has two layers of data, one of them semi-transparent so that the laser can focus through it and read the second layer. Since both layers are read from the same side, a dual-layer disc can hold almost twice as much as a single-layer disc, typically 4 hours of video.

Many discs use dual layers. One layer only a few replication plants could make dual-layer discs, but most plants now have the capability. The second layer can use either a PTP (parallel track path) layout where both tracks run in parallel for independent data or special switching effects, or an OTP (opposite track path) layout where the second track runs in an opposite spiral; that is, the pickup head reads out from the center on the first track then in from the outside on the second track. The OTP layout, also called RSDL (reverse-spiral dual layer), is designed to provide continuous video across both layers. When the laser pickup head reaches the end of the first layer it changes focus to the second layer and starts moving back toward the center of the disc. The drive with dual-layer capability accesses the second layer by shining the laser through the first semitransparent layer.

The DVD specification requires that players and drives read dual-layer discs. Some discs are designed with a "seamless layer change" that technically goes beyond what the DVD spec allows. This causes problems on a few older players.

In some DVD players, the layer change can exhibit a noticeable pause, up to several seconds. This caused some viewers to worry that their dual-layer DVD discs were damaged or defective, with the end result that studios began listing a standard message explaining the dual-layer DVD pausing effect on all dual-layer DVD disc packaging.

All players and drives also play double-sided discs if you flip them over. No manufacturer has announced a model that will play both sides, other than a few DVD jukeboxes. The added cost would be hard to justify since discs can hold over 4 hours of video on one side by using two layers. Pioneer LD/DVD players can play both sides of a laserdisc, but not a DVD.

Tags: DVD, DVD disc, DVD player