daveo(Competent) posted this on Thursday, 22nd March 2001, 13:04
This topic has been niggling me for a while now.
How does the DVD have multiple layers?
How does the machine distinguish between the different layers?
How do you tell if a disc has multiple layers?
I think there was one layer change on my R4 Ronin disc, the screen went blank for half a second - there were no other pauses like this in the rest of the film.
It doesn`t bother me, but just being inqusitive I would like to know.
RE: DVD Layer Change
montydeno(Harmless) posted this on Thursday, 22nd March 2001, 13:22
Most DVD movie discs have a single-sided dual layer configuration, meaning there are two layers on the `bottom side` of the DVD (the side without the movie title and so on).
The first layer is able to hold 4.7GB of data which is seldom enough for a high quality 2hr long MPEG2 encoded movie. So a second layer is introduced which can hold an additional 3.8GB of data. The first layer is semi transparent and gold in color. (that`s why our two-layered DVD movie disc looks like a gold disc but yet not quite) And the second layer which is hidden, is silver in color. The two layers are bonded together by a unique Ultra-voilet adhesive bonding method.
Now coming to the layer change issue here. When the laser reaches the end of the first layer, it increases in power slightly in order to penetrate the first layer which is semi-transparent and begins to read the second layer. This layer change would introduce a slight pause to the movie and the duration varies from around half a second to a second on most players.
One thing i like to point out is that, this layer-change-pause is usually not noticeable on DVD-ROM drives. When you play a dvd movie on a reasonably fast computer with a 4x or better DVD-ROM drive, the layer change is almost seamless. This might be due to the fact that computer systems have comparatively better data buffering.
