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by badlibrarian 219 days ago
Good lord the misinformation here.

VHS is a composite signal on the tape itself. Composite for sake of this thread means black and white detail plus color information. S-VHS has higher bandwidth in the luma (detail) but the same limited color bandwidth. And there are two audio standards. But there is no "RGB out."

At a minimum you want a device with S-Video out (it keeps the two signals on separate wires). You also need a time base corrector. These come in two forms. One is line-based sometimes built into DVD players. This is how Jason Scott at Internet Archive does it and it's wrong.

The other form of corrector requires a separate box and corrects each frame in full. Many boxes claim to be time base correctors but are not. They are "synchronizers" or amps. Don't buy until you understand the differences.

There are two time sources (not really clocks) in a VCR. The first is physical tape wobbling and stretching over a head that's spinning far faster than seems possible. Line TBC is a tiny buffer that reconstructs the sync of the luma on each line.

The other timing source is the overall signal sync. A proper TBC reconstructs this overall sync on a frame by frame basis and presents something sane to the capture card. Without it you'll drop frames silently, audio falls out of sync, and all the other crap that happens when you try to watch video older than an iPhone. Consumer video capture is total crap and you won't see it until you try to encode, edit, or watch it on a different device. And then you'll be very confused working back to the original problem.

But follow this careful path where you actually capture a clean, proper signal and feed it into even the cheapest Blackmagic box and you're good.

ChatGPT will walk you through this and seems to know more about proper ffmpeg settings than the developers themselves or 30,000 conflicting StackOverflow messages on the topic.

1 comments

You seem to know what you’re talking about. Could you recommend any devices that fit the requirements you outlined?
VHS-Decode did get a mention in these comments previously but probably beyond the reach (or patience) of even most hackers. But good information on decks and theory:

https://github.com/oyvindln/vhs-decode/wiki/

In the (original) spirit of this site, where people get curious and go off and solve impossible problems, I can point to this guy who gets it. He rants better than I do.

https://www.reddit.com/user/TheRealHarrypm

Read on for my rant if you care.

The last useful decks were built 25 years ago. Even then there's acres of bad advice on the internet, specifically around prosumer decks with built-in TBC that isn't sufficient to provide a proper signal to a modern video capture card.

So find any S-VHS deck that actually runs well, S-Video out into a external TBC. Blackmagic owns the cheap-but-great category for capture. Then ffmpeg to suit your storage budget.

Beyond that, things are so screwed up online around preservation technology and knowledge that my advice is to seek the services of a professional if the material is important. Or go ahead and DIY if you're just doing amateur stuff or you're a hoarder trying to justify your conditions. But try to refrain from posting your secret sauce; it likely isn't. Organize and post the videos instead. Most won't, because they know they look like shit and they can't handle the feedback.

I just did a quick Google search and found this on a formal preservation website: "This means that S-VHS tapes are playable in VHS decks but VHS tapes are not playable in S-VHS decks." https://psap.library.illinois.edu/collection-id-guide/videot...

Exactly backwards.

I don't think I've ever read an article about analog media of any type on the internet that didn't have me screaming at the screen.

I appreciate the reply. It does feel like most resources online are just the summary of 3 web searches and boom they’re an expert. Thanks for the links and info.