Avisynth script to fix poor VHS-C tracking?

[Benthony]

I've had no luck resolving tracking issues on a handful of VHS-C tapes. Strangely the ones recorded from 2005-2009 (yes my family used tapes that recently lol) suffer the worst from their tracking issues, while the ones before then don't experience them at all. The afflicted tapes will experience sporadic, rapid vertical roll where there is a gap of at most ~40 pixels of black space between the top and bottom of the frame. De-interlaced, a frame of the video where the issue is experienced looks something like this

1.png

Some frames will also push the image up, while not wrapping far enough to make the top visible on the bottom.

Switching from my old vcr to a JVC 9500U has done little to improve this. The stabliziation/calibration settings turned on will fight against the issue, at the expense of distorting/warping the image in different, equally detrimental ways. (for reference, my capture setup is Windows XP Integral Edition -> AmaRec 3.10 -> ATI USB 600 -> ES10 -> HR-9500U)

If I can't fix this, I would like to make an Avisynth script that will go frame-by-frame and simply detect if the bottom of the frame has been pushed up by a black bar ~20-40 pixels in height, and re order the parts of the frame so the bottom part goes on the bottom and the top part goes on the top. If there isn't a top part, then that frame would simply move whatever image there is to the bottom and leave the black bar on top. So something like Attachment 1 would be corrected to this

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The end result would be a black bar running up and down a stable image as opposed to a headache-inducing unstable image. Would that totally resolve the issue? No, but provided it isn't possible for Avisynth to fill in those black bars using information from surrounding frames, I suppose that would be a good enough fix for the time being.

[Benthony]

If I could be a bit more specific:

The JVC player makes the issue less severe in the sense that I'm not seeing total vertical roll, just an isolated frame of misalignment every so often and a little jitter. However, that happens more frequently than the rolling did on my older setup. So I guess a script that would just replace a frame whose contents exceed x amount of solid black with a null/dupe frame would also suffice.