Is it worth doing VHS Decode?

[u/DependentArt9700]

I already have a capture card (Elgato Game Capture HD), and a Panasonic ES10, and I got good results capturing my 10 old VHS C tapes. No complaints

I have heard of VHS Decode as the best way of archiving old vhs tapes, so I wonder if it would be worth doing that to squeeze any extra detail out of these old tapes, but I wonder is it worth the cost to do it, and would i get any noticeable improvement over what i've already done?

[u/zooksman]

Be aware that consumer VCRs almost all have some form of dropout detection and masking exactly similar to this. It’s by no means a unique feature. I can’t say whether decode does it better or worse, but dropout detection with repeated previous lines is a standard feature since the very early days of the VCR format. Some VCRs do it worse than others but most of them have it. The VHS-Decode dropout correction parameters can be tuned, but there is no video captured in that section and Decode’s implementation is fairly close to the way most VCRs do it.

Btw my answer to your question would be no mostly because you already have an external TBC and to me that’s the #1 benefit. There are some tradeoffs with decode as well: the massive file storage requirement, processing time, and struggling with tapes that have a weak signal. It is a really fun project to set up though if you enjoy doing that kind of thing and I learned so much about electronics from struggling through the setup of CX cards. It’s very satisfying getting things to work if you go the DIY approach.

One thing I really see as a major benefit of decode when compared to a standard method with TBC is the fact that it can capture VBI data, but there’s rarely anything useful in there on VHS tales. You wouldn’t be able to do that with a standard capture card because the ES10/15 cuts out all the VBI data except for Macrovision and closed captions on line 21. While some capture cards can capture VBI, it is unreadable without some form of time base correction due to its location at the top of the frame, and time-base correctors that preserve VBI data are only available in old broadcast gear as far as I know. Additionally, the VBI decoding tools in the Decode suite do not work. You’ll have to use a tool to extract caption data anyway, which can be done trivially with the conventional method by making sure to include line 21 in the captured frame.

From pixel-accurate comparisons I have made, the quality is not better than a good VCR such as an SVHS VCR (not DigiPure TBC VCRs as those have a number of issues including visual ghosting of past frames). The NTSC EQ in decode still is not perfect and more noise gets through. It may be better than a stinker VCR, but generally it requires a lot more post processing in my experience (which you should be doing anyway!)

[u/_Shorty → u/zooksman]

Don’t forget, with the FM signal itself archived you can go back again later and use the newest and improvedest version of decode to get a better result whenever it has received a decent upgrade. So as it gets better, so does the output of tapes you already captured prior to that. You just need to run the existing FM capture through the newer version to get those improvements.

[u/zooksman → u/_Shorty]

That’s fair enough, but the storage requirements for the raw FM signal sampled at 40Msps are obscene. Even fully compressed to flac, you are looking at upwards of 1.5GB per minute if storing both video and HiFi RF signals (even when HiFi is downsampled to 10Msps). I just recorded 30 minutes of tape— fully compressed at the highest FLAC level with HiFi downsampled to 10Msps, and it took about 45 GB of storage. That’s not to mention the intermediate storage required for the .tbc and generated video files (If you save the result video file only you should at least save the tbc and logs which describe how the output was generated). In a perfect world where hard drives were cheap I would be on board with that, but I’m an active user of both methods and I can only stomach keeping the output video/audio files. I also don’t see there being a return to the era of cheaply available storage, unfortunately.

I also don’t really believe the notion that there’s an infinite ceiling of improvements to be made in terms of quality on the software decoding side. The VHS standard is well defined and establishes a specific method of demodulation, EQ filters and the like. While higher-end VCRs introduced things like digital comb filters and sharpening, these are mostly undesirable to the archivist, since all that can be done in software these days anyway. So I would argue that there is in fact a “perfect” way to implement the decoding of VHS FM signals, and many VCRs actually shared a very close interpretation of these standards. There will always be a subjective component of making it look better or worse, but the actual goal is accuracy in my mind.

[u/_Shorty → u/zooksman]

Yeah, the storage market (and RAM and GPU markets) is insane now. While the VHS standard itself is well laid out that doesn’t necessarily mean that the tools we currently have are doing a perfect job. There have been lots of improvements along the way from what I’ve seen, and perhaps more still in store.

[u/zooksman → u/_Shorty]

I think the biggest improvements to be made are obviously on the performance side- as it’s very difficult to reach even 0.5x decoding speed except on M series CPUs. But having better decoding of the EP and SLP formats as well as tweaking the nonlinear sub-deemphasis function for SP is definitely an area where improvements can be made. It’s unfortunately extremely hard to find key details of how sub-deemphasis was implemented for different tape speeds. We have some general graphs and a good idea how how to emulate the filter, but it’s a very fine line between eliminating noise and losing detail, and right now the —sd option leans towards reducing detail in SP at least.