Recording YPbPr on VHS?

[jmac698]

Yep, it's true, you can record component on a consumer VHS. Of course you need to specially prepare the video to do it, and a computer to play it back as well.

So here is a crazy experiment you might find interesting. What I did was separate the colors into different tracks much like Betacam SP does. I also split the screen in half to double the resolution. By my calculations, I'm getting about 480x480 resolution here in 4:2:2 color resolution.

I've also discovered a way to record component video live onto a VCR, or with any capture card, with very simple equipment. I can also record/capture 480p component video with any capture card (with only composite in). This doesn't help eurpoeans with their SCART.

[jmac698]

Btw, I just came up with a way to do any avisynth processing live. This is great! Not only can I watch my component video encodings live, but I can calibrate to colorbars or do tweaks to video realtime, and then capture it. That really enchances the usability aspect.
Use iuVCS, go to filters, select ffdshow decoder, in ffdshow check avisynth, in that tab write your script.
For example just write one line, tweak(bright=-10, cont=1.1) you will see the tv input change instantly when you click Apply.
Very cool!

[admin]

What are the specs of the system you're running this on?

[jmac698]

AMD XP 2GHz, quite an old slow system. Basic tweaks are easily realtime.
I have a script which can overlay the measurements of colorbars realtime on the incoming video, and tell you the error. It can also automatically calibrate as best as it can with you not changiing any procamp settings.
I discovered somrething else too. The perfect procamp settings aren't really perfect. You can take advantage of the headroom you get from capture cards and make white 254 and black 0, and processing scales it back to the proper range.
What's the point of that, you ask? Well, as I discovered in my VCR comparison post, there are slight errors in the middle values of brightness being too bright and skewed, so I use a larger range which spreads out the errors, then when I shrink the range back again, the errors are shrunk too. The result: better linearity of the input.

I also discovered a way to generate true RF, composite, svideo, or component signal directly with your computer with nothing but a cable. I can now directly generate timebase errors and scientifically test timebase correctors, rf demodulators, etc.

Also I found out a feature of bt878 chipset called Ultralock, which seems to be a line TBC - I didn't know this was already built in to my capture card. I'll have to see how well it works. I never noticed that it cleaned up jitter that much, but maybe you just need a registry hack to turn it on - in which case this search for TBC just became trivial - wouldn't that be great news?

I also thought of a few ways to read the raw video signal, including the horizontal sync. This means a "true" software TBC may be possible! I just can't believe no one has done this yet. One way involves fiddling with GraphEdit and using a component called "Sample Grabber". Another way is mis-calibrating a chip register to shift the picture far over to the right, so that you can literally see the sync. You can actually read a blacker than black code of 0 here and use that as a basis for a simple straigtening of video.

Lots of new developments! This is what basic research gets you.

[admin]

Interesting stuff you're working on.

Quite a few things cooking here too -- details of which will become obvious throughout the year.
Stick around a while, and you'll notice the changes.

[themaster1]

Just found out this thread, If Jmac read this i'd love to hear more about your method to record "component" on a vcr

[jmac698]

Sure. I'm shocked to see this thread is 23 years old, and somehow I'm still alive!
I used a script to split the picture into 3 parts; the brightness and two aspects of the colour. These are then converted to greyscale pictures, and stacked vertically. What you see as a result, is a normal greyscale picture in the middle, and some strange squished versions above and below.
I did it this way, so that if all else fails, you can watch the video in black & white and use the "Zoom" setting of your TV to fill the screen, and it will look pretty normal.
However, if you apply the reverse script, you can add the colour back in real-time (using a tool called ffdshow).
The reason it looks better, is that greyscale is carried with much better resolution than colour signal is normally. You could say colour is about 40 pixels horizontally, which is shocking. Greyscale is, apparently, 480 pixels across. So, it's actually a better balance overall to encode of all it in the greyscale method.
If you ask, why wasn't TV invented in this way in the first place? Two reasons: First, it was designed to be compatible with the original greyscale method which came before it, and second, they would need some kind of "memory" of the signal in order to decode it, and that was difficult back then.
An invention did come eventually; that's where we have the Betacam SP system, which positioned the 3 parts together horizontally instead of vertically as I did, thus needing much less memory of the signal at a time.

As far as the real-time recording of component video, that was a different method. Before the change to digital and HDMI, there used to be an analog connection called component (with 3 cables, often coloured as red, green, and blue). You still see these on old game consoles. I used a video amplifier to split the green signal into 3 copies, and to each copy I used a y splitter to combine the green signal with each of the blue and red signal, then the green signal on it's own. So in the end we have:
green, green+red, green+blue.
Electrically, the green/blue signals can vary +- some voltage, and the green voltage was usually somewhat higher and always +, so basically you get these weird greyscale pictures.
Now, record that in real-time to 3 VCRs and tapes.
To play it back, you have to reverse the operation. You need to find green minus (green+blue) = blue, etc.
I did that in software, and it did work.
There is some potential strain on the electronics when you connect two signals together because when red/blue goes - that means it's sucking electricity in to an output which is not normal!
There also is a problem with some colour combinations that mess up the signal.
But I did try it and got a recording of a DVD with a clear image.
It's easier to do it in pure software form. Instead of needing 3 VCR's, I made a video of greyscale which was 3x longer in length and recorded that to a single tape. To distinguish which frame, I had to put a little marker in the top line, much like a time code. It's not real time of course, but it's a way to archive a signal in higher quality on a primitive VHS tape.
You could maximize this further and even store digital data on a VHS, and there is a program that does that. Now that you can dump data to tape, you can use an compressed video (such as a video in MPEG format) and dump it to tape as a backup.
This method was invented before to some extent, with a type of digital audio recorder called a Sony PCM.
There are now programs to decode that kind of old signal too.

[themaster1]

Oh boy , i knew reopening this thread would lead to a can of worms, it's far and beyond what i expected héhé. One could say you did the extra mile to bypass A/V industry's shortcomings. I was hoping there is a simple & practical way to get component into a damned vcr but the good answer is there is none it appears.

I've read here one can do a mod on Sony's standard vcrs to force s-video in (quality being so-so i recall) , i guess i'll explore that path.

Before i forget: what about a RF generator (modulator) ? Say you link it directly from the source (Ypbpr or s-video) and then directly attach (with shielded cable) to the tuner (to limit noise i guess) of the vcr. Can you get a better picture than simple composite ?

Thank you Jmac

[jmac698]

Experimentalist that I am, I have compared the two methods. They looked about the same to me. In theory, a plain composite signal goes through less processing than going through a modulator, and I have no other reason to think a modulator is any better. But, I won't say it's really worse either.

It's interesting there's an S-VHS mod. I had an S-VHS machine, and it does look noticeably better. I think that's about the best you can do with a VCR, unless you find a Betamax ED, which I think is the equivalent to S-VHS.

[jmac698]

In case anyone reads this, I did finish all those experiments I was talking about. There is a thread called SoftwareTBC I posted in Doom9.
https://forum.doom9.org/showthread.php?t=162832

[dpalomaki]

Quote:

Sure. I'm shocked to see this thread is 23 years old, and somehow I'm still alive!

More like 13.5 years old. Is anyone still interested in recording component video sources to VHS tape, or even to S-VHS tape these days? The usual interest is best possible extraction of material already recorded on VHS and the the other legacy consumer analog formats.

[lordsmurf]

Quote:

Originally Posted by dpalomaki

More like 13.5 years old. Is anyone still interested in recording component video sources to VHS tape, or even to S-VHS tape these days? The usual interest is best possible extraction of material already recorded on VHS and the the other legacy consumer analog formats.

Strangely, yes, there are some who want to "hack" these old formats to support more data than was ever intended.

I find it to be a pointless and purely academic exercise, with no real-world value or usage to be had. But still, interesting, at least to read a few paragraphs about it, maybe a 5-minute Youtube video. It's interesting only to the nicheist of niches.

It's basically model rockets for adult EEs. As millennials often say, "it's because I can". Have at it! Enjoy!