What is dual layer disc? Can I play it on my PC?

Mar 30th, 2010 by dvdxplayer 16,151 views |Comments Off

Dual-layer disc is a kind of disc which has two layers of data, the first layer is semi-transparent so that the laser can go through it and read data on the second layer. Since both layers are readable from one side, a dual-layer disc can hold almost twice as much data as a single-layer disc, typically 4 hours of video.

Initially only a few replication plants could make dual-layer discs, now it is available almost everywhere. 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 layer change can occur anywhere in the video; it doesn’t have to be at a chapter point. There’s no guarantee that the switch between layers will be seamless. The layer change is invisible on some players, but it can cause the video to freeze for a fraction of a second or as long as 4 seconds on other players. The “seamlessness” depends as much on the way the disc is prepared as on the design of the player. The advantage of two layers is that long movies can use higher data rates for better quality than with a single layer. See 1.27 for more about layer changes.

Dual-layer discs have three paticular features: 1) the gold color, 2) a menu on the disc for selecting the widescreen or fullscreen version, 3) two serial numbers on one side.

Players and drives of your computer are two major factors that decide whether a dual-layer disc is readable or not. There are very few units that have problems with dual-layer discs–this is a design flaw and should be corrected for free by the manufacturer. 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.

All players and drives can 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. (Early discs used two sides because dual-layer production was not widely supported. This is no longer a problem.)

Reference: http://www.dvddemystified.com/dvdfaq.html#1.18(Reedited)
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