[Videolib] Re: DVD security overlays

Fri, 17 Dec 2004 21:14:08 -0000 (UTC)


The problem with the security overlays lies not only in the installation,
I believe it is in the actual construction of the overlays themselves.
The ones we have seen have two metal strips running down the length of the
overlay. If you stop and think about the weighting of these overlays, as
the disc spins, it has an uneven distribution of weight. Think of a
merry-go-round with two kids sitting at the edges of the equipment. You
will have a faster spin on the side that contains the kids than you would
if it were equal distribution of weight. With the speeds that discs spin,
you can see where the laser would have trouble picking up on this
imbalance. DVDs are more susceptible to read problems caused by minor
imbalance than CDs. It is my opinion that the security strips shouldn't
be lengths, rather, they should be circular to have equal distribution.

Some DVD players are able to account for the change in spin speed and can
adjust for the imbalance. I am not sure if the discs are scratched, but
having any sort of scratches on the disc would definitely create
additional read problems for the laser. We do have clients that continue
to use the overlays. We test the repaired discs and it seems that once
the scratches are removed, the vast majority of the discs are returned to
play. Obviously re-scratching these discs may result in renewed problems
but at least this portion of the problem can be fixed.

One additional note, we have noticed that if pressed hard, the security
strips can disrupt the label of a disc. If the label side gets scratched
deep enough by these strips, it can permeate the foil layer. Once the
foil layer has been disturbed, no repair can be made to a disc. In short,
I would highly recommend you consider halting the addition of the security
overlays for your new discs and plan for another option for your disc

Hope this helps!
David Wright

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