[FFmpeg-user] Meaning of ffprobe output

Carl Zwanzig cpz at tuunq.com
Tue Jan 29 23:36:27 EET 2019

On 1/29/2019 1:16 PM, Eric Wilde wrote:
> 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.

That fits my memory, too. There was also macrovision, which IIRC added extra 
analog pulses to mess with the recorder's AGC circuits. Been a long time 
since I've thought about this.

> 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.  

Digital capture of any analog tape source, especially VHS, without at least 
a proc-amp (TBC would be better) in line will give rather-less-than-optimal 
results. Capturing the composite signal just compounds the problems (as 
opposed to using Y/C or component).


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