At 09:48 PM 1/29/2019 +0100, you wrote:
> My explanation is, that the original VHS was marked with copy
> protection, so the DVD recorder by legal reasons has to sustain the
> copy protection by creating an intentionally corrupted DVD file
> system (which is not readable from a computer) and additionally a
> corrupted vob stream, which is detected and forbidden to copy by
> legal DVD copy software.
This seems far fetched ("weit hergeholt"), at least in terms of
creating mixed progressive/interlaced content. Broken file systems and
streams: Yes, often.
My understanding of at least one VHS protection scheme was to record
the video with the horizontal/vertical sync pulses set very low to the
threshold for detection. The idea was that, if you made a copy, which
was lossy, the copy would not have detectable sync pulses and the
picture would appear scrambled.
I'm not sure how a DVD recorder would detect this, as opposed to a
VHS recording that was just of poor quality. But, if you suspect that
to be the case, you could certainly confirm it with a scope on the
output of the VHS player. For reference, a VHS tape of good quality
should give you typical voltage levels.
Eric
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