Open source VHS: how would you do it?

That video is not at all like VHS! It has none of the characteristic artifacts of a VHS recording. About the only thing is the 4:3 aspect ratio which was also used in the VHS days.

Here is a random video that I got when searching for "vhs recording" on YouTube:

You can find many others.

Look at the horizontal glitches and the overall video resolution. Also apparent in many VHS-to-digital video transcriptions is an area at the top or bottom where some lines are permanently pulled sideways or jittering.

Apologies.

My memory of my youth is short, and full of errors. :(

I did once briefly look at tape & paper storage to see if it were viable, but the amount of data storable that way is worth more or less nothing, and the input/output bandwidth abysmal. You could calculate it easily enough.

For magnetic tape's multitrack alternative google Tefi cartridges.

NT

Well you got the Ha-ha part right. Tape is the worst thing ever. You're better off cutting the data to a vinyl record like an LP. (33 1/3)

Stamped CDs and DVDs should last forever, but not burned ones. However they have come out with some extremely long life ones though you need a special burner to use them.

That's time base errors due to differences in the recording and playback machines or tape stretch. It should go through a time base corrector before conversion.

But you'll never get rid of the edges it puts on everything or the effect of the COMB filters which shifts the chroma toward the bottom of the screen.

My tape archive has fared better than my DVD archive. But, requires periodic maintenance.

Long time ago for Amiga 500 Video Backup System existed. Recording on VHS was done directly from composite out and reading via RS-232 and small circuit that if I remember rember was just an Op-amp ( or comparator). Took about minute to archive a floppy (800kB). I used to build "converters" for it; if dig deep enough might find schematics but not any time soon as my boxes with old stuff are 300 miles away.

Marcin

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but the amount of data storable that way is worth more or less nothing, an d the input/output bandwidth abysmal. You could calculate it easily enough.

My memory of the figures is hazy... this may be a bit approximate.

IIRC PAL VHS did 240 line resolution with similar horizontal resolution, so one got about 240/625 lines or that squared x 6MHz as a rough data rate = 0.88MHz. Now subtract sync pulses, flyback time & trim the picture edge s and you might get say 0.5 - 0.6MHz. Allow for massive redundancy of 10x - you'll need it - gets you about 50kHz data rate in & out.

50kHz x 3hrs = 540megabits or 67Mb. And yes, with a standard transport it 'll take 3 hours to record or play that. Not too impressive.

Tape is reliable/durable if splices are avoided, meaning tape ends are clam ped without leaders. That drops max rewind speed of course. But they're alw ays a little bit fragile.

Going to grooves as in a 33 or a tefi is a bad move, you then can't get muc h above audio for your data transfer rate. It also makes writing data diffi cult, the discs/tapes become WORM.

NT

The recorders used precision machined heads. Few would have the required skill.

Sylvia.

The signal was transferred through a rotary signal transformer as well.

Finding an old VHS recorder and rehabilitating it would be a couple of orders magnitude easier than making one.

--sp

--
Best regards,  
Spehro Pefhany 
Amazon link for AoE 3rd Edition:            http://tinyurl.com/ntrpwu8

Still not very practical. There are probably a few high end five motor deck s out there that do not use belts that actually still work.

But the main reason disks took over is that there is no physical contact an d therefore no wear. Every time you play a tape it gets worn out and so do the heads. With CDs, every time you play a burned one the LASER does actual ly degrade the signal just a little bit, but not stamped CDs. However, the plastic does degrade over time. When it is not transparent enough for that LASER to focus it is over.

Anyway, tape is another concern. I wonder if anyone is making any more. I g ot a nice big reel of Ampex R2R tape just opened last year and the oxide co mes off it so fast that it is unusable. With a helical scan system, you bea t on the tape much more.

As much as I would like to have a reel to reel because I like the looks of it and the sound quality is extremely good, and I could get one off my budd y, a really nice four track Teac, tape is so ridiculously expensive it just ain't worth it in light of the fact I got DVD burners in my computers.

Somewhere in DC they have the original Constitution in a thing filled with pure nitrogen. It has lasted a while but one day it will also be gone. (alo ng with the shit stains from them wiping their ass with it) Nothing lasts f orever. They got those new DVDs supposed to last billions of years, but who is going to be around to complain if they don't ?

Den mandag den 15. august 2016 kl. 22.35.33 UTC+2 skrev snipped-for-privacy@gmail.com:

cks out there that do not use belts that actually still work.

and therefore no wear. Every time you play a tape it gets worn out and so d o the heads. With CDs, every time you play a burned one the LASER does actu ally degrade the signal just a little bit, but not stamped CDs. However, th e plastic does degrade over time. When it is not transparent enough for tha t LASER to focus it is over.

got a nice big reel of Ampex R2R tape just opened last year and the oxide comes off it so fast that it is unusable. With a helical scan system, you b eat on the tape much more.

f it and the sound quality is extremely good, and I could get one off my bu ddy, a really nice four track Teac, tape is so ridiculously expensive it ju st ain't worth it in light of the fact I got DVD burners in my computers.

h pure nitrogen. It has lasted a while but one day it will also be gone. (a long with the shit stains from them wiping their ass with it) Nothing lasts forever. They got those new DVDs supposed to last billions of years, but w ho is going to be around to complain if they don't ?

another future problem will finding equipment that can actually play those DVDs or what ever it will be, the myriad of different codecs and even worse DRM could make that a nightmare

years ago I saw an article on how the national TV station was still working on transferring old tapes to modern media, there was one semiretired guy t hat knew how to run the tape machine and there was only two still existing one of them used for spares

-Lasse

The tensioning, tilting of the drum, correction of azimuth due to tape variation, and such, are relatively hard to do. So is the manufacture of read heads for close contact with the tape. Two for stereo, two for video, one for control, not sure about VHS HiFi.

So, I'd leave those technologies out. The VHS scheme didn't have any frame memory, it had to operate real-time; we don't. So, I'd scan to a buffer, repeatedly, then analyze.

A T120 tape holds 247 meters, half a minute or so of video per meter. Hold the tape against a transparent medium that exhibits Faraday rotation, use polarized light to scan it (lasers, maybe galvanometers, image sensors, the whole works) to read the magnetic field. Patch together scan data and read out the audio tracks, the video tracks, and the 'control signal' tachometer track. VHS HiFi will take some extra work, though.

cks out there that do not use belts that actually still work.

belt drive decks should be workable. For smaller belts you can use statione ry rubber bands, so it's not costly to re-belt.

got a nice big reel of Ampex R2R tape just opened last year and the oxide comes off it so fast that it is unusable.

Fit a wiping pad to keep loose oxide off the heads & record the data to som ething else.

IIRC the read head on vhs/beta didn't touch the tape, it flew above the sur face. The tapes seemed to take it no problem, even years after VHS was obso lete.

f it and the sound quality is extremely good, and I could get one off my bu ddy, a really nice four track Teac, tape is so ridiculously expensive it ju st ain't worth it in light of the fact I got DVD burners in my computers.

h pure nitrogen. It has lasted a while but one day it will also be gone. (a long with the shit stains from them wiping their ass with it) Nothing lasts forever. They got those new DVDs supposed to last billions of years, but w ho is going to be around to complain if they don't ?

that might be what makes them last a billion years :)

For archival a real key is simplicity of data extraction. Extracting data f rom a 78 is easy without any original equipment. Doing the same with bluray once the bluray players are all gone will likely be prohibitive. Time, lac k of killed personnal & thus cost will prevent it being done.

NT

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It's a damn mess is what it is. Better quality is achieved with four video heads, the ones for SP being wider then the ones for EP. The video carrier is about 4.2 MHz and the chroma is about 629 KHz. The chroma also goes thro ugh a phase rotation to reduce crosstalk between the tracks. They used four phases and a COMB filter to reject the unwanted signal, as it does bleed b eing a lower frequency.

There is a difference between a discrete six head hifi and a DA hifi, and t hey will not track each other right. The audio and video will not peak at t he same point on the tracking control because the DA heads (later models) d o not have an offset between SP and EP speeds, and the hifi heads are somet hing like 30 degrees away.

The hifi signal is depth multiplexed by using a larger gap head. It records deeper into the oxide and because of the larger gap is not picking up the higher video carrier. I remember that the azimuth of the two normally opera ting video heads is offset to reduce crosstalk, I think 7 degrees (?) but I don't remember about the hifi heads.

The whole damn thing was a mess, and hifi noticeably degraded the video qua lity. Bets hifi not so much because with their bigger head drum they had ba ndwidth to spare and didn't even require separate hifi heads. I had a few a nd the performance was noticeably better, even on old TVs. However most bet as were an incredible bitch to align.

Between all these problems, as well as drum wear which screws with the alig nment in ways that cannot be completely fixed, my recommendation about vide o tape is just get it running and rip it to your PC or DVD burner. Then put it away and don't wear it out anymore in case you lose the disks or your h arddrive fails.

Even belts are ridiculous now. A belt kit used to be like five bucks, try t en times that now and that was last year FOR A CASSETTE DECK !

variation,

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o heads, the ones for SP being wider then the ones for EP. The video carrie r is about 4.2 MHz and the chroma is about 629 KHz. The chroma also goes th rough a phase rotation to reduce crosstalk between the tracks. They used fo ur phases and a COMB filter to reject the unwanted signal, as it does bleed being a lower frequency.

they will not track each other right. The audio and video will not peak at the same point on the tracking control because the DA heads (later models) do not have an offset between SP and EP speeds, and the hifi heads are som ething like 30 degrees away.

ds deeper into the oxide and because of the larger gap is not picking up th e higher video carrier. I remember that the azimuth of the two normally ope rating video heads is offset to reduce crosstalk, I think 7 degrees (?) but I don't remember about the hifi heads.

uality. Bets hifi not so much because with their bigger head drum they had bandwidth to spare and didn't even require separate hifi heads. I had a few and the performance was noticeably better, even on old TVs. However most b etas were an incredible bitch to align.

ignment in ways that cannot be completely fixed, my recommendation about vi deo tape is just get it running and rip it to your PC or DVD burner. Then p ut it away and don't wear it out anymore in case you lose the disks or your harddrive fails.

ten times that now and that was last year FOR A CASSETTE DECK !

Cassette decks can usually be done with regular stationery rubber bands. So me types last well, some don't. But you get 99 free spares in the pack.

NT

I wouldn't. At least not for money. Things that don't last are bad news, an d some them the disassembly to change the belts is no trivial matter.

I tell people "No, I don't want to do it right, I just don't want to do it again". Like if I paint something for you, there is only a warranty if I pi ck the paint. That would be Benjamin Moore. That is in the best class off p aints. Down a shelf is like Sherwin Williams and the high end Sears that ev eryone thinks is so great but it isn't. At the bottom we got like Glidden a nd Walmart brand, though I have not used it I assume it is the cheap stuff. However, Walmart has surprised me with good quality on occasion. But I mea n like the paint that was six bucks a gallon at Kmart. Part of the reason g ood paint costs ten times that is it has more titanium dioxide in it. Cheap paint cannot match the look of it, plus it is durable. You prep a wall rig ht and but Benny Moore Aquaglow (IIRC) on it, after it dries for a week you can literally scrub it with steel wool ad it ain't coming off.

Also when doing wiring. Yeah, one time I bought a box of elcheapo light swi tches. Brand new, and by the time the drywall was up I had to replace three of them. When I got the call, the contractor (I worked for him this time b ut he has worked for me as well) sounded like he thought it was my fault. W ell I showed him, bad switch, no continuity when turned on. From now on it' s Leviton. And I won't replace any Federal Pacific. The box gets torn out a nd replaced either with Square D QO or GE if the customer wants it a bit ch eaper. But Square D QO series is seriously top of the lie, in fact I think better than Seimens which is pretty damn good.

Now the nature of a DC coupled audio amp makes it possible for bad outputs to blow other parts. What do you think I am going to do ? I really don't wa nt to have to do it again.

If you are over like 50 years old, put the good belts in the tape deck and it is likely you will never have to change them again. With rubber bands th en gotta get the thing apart and not lose any screws or little gears and wh atnot, not break any of the brittle plastic parts in the process, and unles s you screw thepro way you wear out the holes.

By that I mean when you stick the screw in the hole you turn it backwards u ntil it drops. That means it goes into the threads already there rather tha n making new ones. In plastic, you only get so many chances it you do that. In fact things are so flimsy now I no longer use an electric screwdriver o r drill, at least during reassembly.

Oh, and that won't work for the capstan belt. It is supposed to flat. Using a rubber band the speed will be off and you'll have so much wow and flutter that it might make you dizzy.

No-one would for money. So what. If you're fixing your own it's normally fine, like I said.

not usually.

I cba discussing the rest. Everyone knows the options.

NT