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11-28-2023, 10:24 AM
aramkolt aramkolt is offline
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Hello all, one of the most visually annoying things I've come across so far in my hardware experiments are line dropouts - even with the more professional decks - really all they do is repeat the last known good line if the RF signal level drops below a certain level.

Older TBCs on the other hand that had DOC ports I believe would store the prior frame and replace the line with one from a prior frame which would probably be more visually accurate. Has anyone actually ever tried to feed a rack mount TBC with a DOC port the RF signal to see if that changes how dropouts are addressed? I believe DOC outputs were pretty standard on say Umatic or higher end formats, but I don't see why the RF stream from a VHS player couldn't be presented to it in the same way - this would basically be the same sort of RF tap that VHS-decode uses, but I am unclear if the RF amplitude would be high enough for the TBC to "see" and it could require some sort of amplification maybe.

I also feel like there should be a software way to "detect" covered up line dropouts (since it will be an exact repeated line from the one above it) and then go and replace that with say an averaged one from the frame before and after. I am not aware of such a software but am curious if anyone has heard of such a thing.

I did see an example where it appears that avisynth was able to vastly improve a sample here, but they don't explain how it was actually done:

Doing some basic looking into this seems to bring up this (DePulse): http://avisynth.nl/index.php/DePulse but I'm curious if anyone has actually used it or has an example clip with a more detailed process. I also am guessing you'd need a way to bypass the VCRs internal dropout compensation so that you actually do get "static" that Depulse can "see".

Does anyone know how that avisynth dropout correction works as shown in that YouTube video or if feeding an older TBC's DOC port with RF from the VCR produces a similar effect? I get there are disadvantages to rack mount TBCs, but in certain situations where there's a lot of line dropouts, this could be very beneficial to some clips if they actually work that way. Could also be that some capture cards address dropouts natively maybe?
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Someday, 12:01 PM
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11-28-2023, 10:33 AM
aramkolt aramkolt is offline
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Here's some more restoration techniques they use over at CMRG Ditital Video Restoration - according to the comments it's all functions of Avisynth, quite impressive, though no idea how you'd decide what to do for what problems: https://www.youtube.com/watch?v=VHck630Z5kk
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12-04-2023, 03:36 PM
Winsordawson Winsordawson is offline
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Avisynth can handle most if not all of these types of issues. For the first video of a car museum, Stab in Avisynth can be used to stabilize the shaky footage, although I always use Premiere Pro for that purpose as it is easier.

I have never found much luck with DePulse, but I would try other filters like KNLMeansCL and SpotLess. SpotLess is slower and may remove more dropouts, but also more detail. However, this video only has a limited amount of dropouts that may be fixed first with RemoveDirtMC called several times. Then followed by a light use of KNLMeansCL
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