convert VHS to DVD

[Tim]

On Tue, 2007-03-13 at 10:55 -0600, Guy Fraser wrote:
> I have a oscilloscope and developed a device that allows 
> me to view any specific line of video on it, and have 
> seen first hand what the macrovision protection is. There 
> is no doubt in my mind now why some movies would not track 
> properly on some VCRs. The signal varies in amplitude over 
> a few seconds which is what throws the AGC amuck, and when 
> at full brightness it has a higher "brighteness" that 
> a pure bright white signal "whiter than white" and the 
> signal pulses "blacker than black" even lower than the 
> sync pulses, which trows VHS tracking into conniptions.

I had a quick look at a DVD with it last night, the whiter than white
only went up to about 120IRE (for those unfamiliar with IRE, think of
that as 120% signal, where 100% is the maximum allowed).  Which oughtn't
to be a problem for most things, just those that go through an RF
modulator (110IRE being about the tops that you should attempt).  The
last time I looked at Macrovision on a VHS tape, ages ago, it went a lot
higher, much higher than reasonable, more like 150IRE-160IRE.  You'd
need white clipping circuitry to handle that, and it's usually only
present in recording circuitry.

The blacker than black goes all the way down to sync tip levels, on the
DVD, and that can cause problems in anything silly enough not to ignore
video signals during the vertical blanking period.  I haven't had a look
at that on other video sources.

In some cases, even the direct output from a VCR player is unusuable.
The syncs during the vertical blanking period have been crushed by the
extreme non-spec signal to about a third their normal amplitude.

> It is indeed an evil system 

It certainly is.  We had once looked at how to use a copyguarding
system, as we've one client obsessed that people pirate his recordings
and stop his sales.  But all evaluations showed that there was no way to
stop piracy, no way to ensure legit viewers would not be disturbed, and
we'd have to butcher our recorders to even attempt it.

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