[FFmpeg-user] Meaning of ffprobe output

[Eric Wilde]

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