Software TBC Solution?

[keller]

I've read all sorts of posts about fixing VHS crappyness with a hardware timebase corrector. I know it's a long shot, but is there ANY kind of software solution to this? If I understand correctly, the TBC takes the orginal, messy video signal, digitally figures out what it's really supposed to look like, and then sends it to the output cable. To me, this sounds like something that a filter or a software program should be able to do. Maybe it's just wishful thinking, but if I'm going to find an answer, it'll be here. Thanks to all in advance!

Keller

[txpharoah]

Wishful thinking.

[rgscout]

I've read all sorts of posts about fixing VHS crappyness with a hardware timebase corrector. I know it's a long shot, but is there ANY kind of software solution to this? If I understand correctly, the TBC takes the orginal, messy video signal, digitally figures out what it's really supposed to look like, and then sends it to the output cable. To me, this sounds like something that a filter or a software program should be able to do. Maybe it's just wishful thinking, but if I'm going to find an answer, it'll be here. Thanks to all in advance!

Keller

No my friend. Seems to be but the problem that comes with " VHS crappyness " ,as you say, cannot be corrected by a software solution because its related with source´s quality signal. And as you may know You can´t improve the processed quality of a video beyond the original one ( I mean if you put a a bad quality movie onto Virtualdub for example you cannot expect nothing better than the original " bad " ).
Oh well, will may ask: Why the " crappy vhs " appears so good in my TV set and so " crappy " on my computer. The answer to this is a complicated a little bit. Someone a long time ago posted here. The answer is related to the internal architeture of a TV set in comparison with the computers capture card. The way that TV set makes the image is very diferent to the computer due to eletronic circuits issues and thats why the TV doesn´t need any external device to make a good image in the screen ( may´be when I finish my Eletrical Eng. course in the college I can explain better, but up to now I think that is enough )
If your source signal quality is not so good, the capture card "won´t give you a chance" and blur up the image ( " crappy effect " ). That´s why TBCs and other kinds of corrector devices are needed.
I have several VHS tapes recorded in EP or LP speeds that have this kind of trouble. My old PANASONIC camcorder records only on SP mode... no problems for the capture card.

Sorry my bad english ( in sure that in portuguese I will write less and you understand more ) . I hope I could help.

Thanks.

[Nelson37]

Well, let's clarify a little. A TBC, or Time Base Corrector, does not in and of itself "improve" the signal in any way, although many devices which are also TBC's add additional circuitry to improve color saturation, etc. This secondary function can certainly be done in software, and is.

I must disagree with the statement that you cannot improve a bad video. You certainly can. While you could argue mathematically that missing info cannot be replaced, videos ARE NOT viewed mathematically. They are viewed by the human eye, and a simple, light noise filter will often result in a video that does indeed "look better" than the original.

Back to the original question, a TBC simply replaces the timebase information. There is software that is purported to do at least part of this function, such as PVAStrumento. While I have never gotten worthwile results from this program, and have seen few if any posts from anyone who has, the re-writing of this timebase info is absolutely POSSIBLE using software. For instance, you have 1 hour of audio and 1 hour of video which de-synchronize while playing, correcting the timebase might fix this problem. However, if both files were not of the same duration, one or the other would have to be manually stretched or compressed, no program could accurately "correct" such a problem, at least not currently.

[solarfox]

Oh well, will may ask: Why the " crappy vhs " appears so good in my TV set and so " crappy " on my computer. The answer to this is a complicated a little bit. Someone a long time ago posted here.

That would have been me. The reason why the same videotape can look OK on a TV set and lousy on a capture board is as follows:

A television set generates its image by sweeping its electron beam back and forth across the screen with electromagnetic deflection coils, using a "horizontal sweep" signal generated by a sawtooth oscillator. (I.E. it has an output that looks something like this: _/|_/|_/|_ ) While this oscillator is periodically reset by, or compared against, the horizontal-sync pulses on the incoming video signal, it spends most of its time free-running -- rather like the electronic equivalent of a spinning flywheel. And, like a flywheel, this oscillator has "inertia" (because of the expanding and collapsing magnetic fields in the coils, and in the high-voltage transformers that are part of the system) and tends to resist sudden changes in the signal timing -- so the picture tends to remain stable even if the signal timing drifts off for a few lines and then comes back into sync again. (This also applies to the vertical sweep as well, but usually the horizontal sweep is the worst offender when it comes to lousy, jittery pictures; vertical mis-timings generally just make the image roll.)

A VCR or video-capture board, of course, doesn't have to worry about sweeping electron beams around, so their horizontal-sync circuits are built entirely differently. No deflection coils, no high-voltage transformers, or other devices whose expanding-and-collapsing electromagnetic fields would provide that "flywheel effect" to help stabilize the image when the sync signals drift off of their proper timing. Instead, they respond directly to each sync pulse as it occurs -- and if you feed it mis-timed pulses, the effect is a mis-timed picture. Your television set helps mask this effect because of the tendancy of its "electromagnetic flywheel" to smooth out sudden shifts in the sync pulses, but your video capture board can't do the same.

If your signal is this far out of whack, you may need a timebase corrector (TBC) to fix it. In a nutshell, TBC's work by recording the entire video signal into digital memory, including all of the sync pulses, then analysing the timing shifts on each line of video, realigning everything back to its proper timing, and outputting a newly-regenerated, properly-realigned signal.

Unfortunately, TBC's ain't cheap.

[txpharoah]

You guys keep forgetting the simple answer: a tv only sees part of the image, clipping off the sides. Computer resolutions are also 2x to 5x the size of the tv. You see more. It's that easy. Anything that looks decent on a monitor usually looks dang-near perfect on a tv.

[Limulus]

is there any device which only does do TBC without changing any colour or stuff as some devices are doing ? and...most important to me...is there a TBC advice for "normal" money which can handle NTSC AND PAL ? i am working with both formats and am not in the mood to spend much money twice only to be able to handle both formats if you know what i mean....

thanks for help

[miamicanes]

I'd argue that video capture cards are timebase correctors. Think about it... a TBC is really nothing more than a capture card with enough ram to buffer a couple of fields that and a DAC/modulator to reverse the process a moment later. It captures the field, possibly waits a fraction of a second if it's sync'ing to an external source, then outputs the field it captured a moment earlier (while capturing the next). Higher-end cards might have slightly more sophisticated hardware to compare its own timing reference to the timing hints it observes in the signal being captured so it can make adjustments if it notices some pattern of instability.

Take a look at ATI cards. If they didn't go out of their way to detect Macrovision, it would be largely irrelevant to them, because the thing Macrovision screws up is something they'd otherwise ignore anyway. More to the point, look at BT8x8 cards. I'm not sure about their newer cards, but I know their old cards are basically the vidcap equivalent of Winmodems -- the downside being that they take lots of CPU resources to capture, the upside being that just about any mischief Hollywood might enforce through hardware can be programmed around and ignored. I've heard that there are even apps for BT cards that can descramble non-digitally-scrambled cable TV channels (something that seems sound in theory, even if it's largely moot by now since analog scrambling is more or less consigned to the history books).

As for why software TBCs don't really seem to exist per se, I'd guess it's because actively marketing one would make you an easy target for Hollywood's lawyers: they'd be appealing as a product to consumers, who only need them occasionally and have a computer, but of little interest to professionals who use them a lot, because a TBC costs less than dedicating a whole computer to pretending to be one.

Strangely, I remember reading about a company that made a strange product that was basically a TBC on a PCI or ISA card. What made it strange is the fact that it only used the comptuer as a case and power source. The idea was that they could cut costs by leveraging the case and power supply the user presumably has already. It seemed like sound reasoning, but for some reason the company's cards STILL seemed to be outrageously expensive -- probably because they only sold their cards through exclusive dealers at full retail and had to compete with cards that might have cost more to manufacture being sold with minimal markup through buy.com and the like.

[disturbed1]

That card your talking about is Darim Mfilter. It comes in ISA and PCI flavors, and a black box. Includes TBC, plus filters for noise. The cost is $495 per internal card, outboard one is slightly more.

Synchronization of remotely originating video signals to a standardized frequency is assured on a field-by-field basis. The video signals are digitized, multiplexed and stored in fields in accordance with their horizontal and vertical sync signals. A reading out of storage, demultiplexing and reconversion to video signals at the standardized frequency on a field-by-field basis allows a real time presentation to standard equipments at a standardize rates. - definition of TBC

A software solution would be quite difficult to do. If your capping at 30 fps, the software would need to process the video at 60 fps. Read in at 30 fps, resync along vertical and horizontal, then write at 30 fps at the same time. That's a large task to accomplish

An ATI capture card includes nothing but a $5 Brooktree chip and a $5 Philips TV tuner , hardly worthy of a TBC. Even the Conexant 878a Fusion is only $11. No company would market a low cost chip such as these with a hardware TBC. That would turn their $50-70 retail priced TV Wonders into at least $175 retail priced cards. The DSP's that do the TBC functions aren't exactly cheap. Talking only real TBC with both H-Sync and V-Sync, not just a stabilizer. No capable effects, as that would raise costs even higher.

Of course people like you and I would gladly buy these cards, but since ATI markets the bulk of their products to Walmart, it's hard to justify the price increase for a built in device that 75% of the intended market have no clue about. We all know how educated Circuit City and Best Buy sales people are, imagine one trying to explain what a TBC does correctly.

Production cost increase with sales decrease, not a wise business move.

[davideck]

miamicanes - you may be thinking of the datavideo TBC-100. It is a full frame TBC on a pci card that grabs power from the PC. I am currently using the datavideo TBC-3000 with a Haupaugge PVR-250, and the TBC has helped considerably. I believe that one of the main reasons is that the TBC provides stable, uninterrupted, and properly shaped sync and burst signals regardless of what happens at its input. Tape dropouts, mistracking, record gaps, etc. were all upsetting my PVR-250. Sometimes the audio and video would get out of sync. These issues have not occurred since I added the TBC. I can now reliably capture a two hour SVHS tape without any problems. As far as I am concerned, the TBC is worth the price (about $250 for a TBC-100).

[Cornucopia]

miamicanes-
thank you for providing a well thought out explanation. others could learn a thing or two from you.

for those noobies tracking this thread, some more info:
TBC's include 4 sections...

1. ProcAmp or Processing Amplifier is the thing which allows you to adjust the Setup/Gain/ChromaSaturation/ChromaPhase (otherwise known as BlackLevel-Contrast / WhiteLevel-Brightness / Color Vividness / Hue-Tint). This can be and is often done in software already, though usually on output, not so much on input.

2 & 3. Frame Store and Frame Sync are two items that work together to make sure the picture is displayed cleanly and evenly.
If your source video pictures are coming off the tape unevenly like this:

[].....[]....[]......[]......[].....[]....[].....[]

these sections will be stored (either line-by-line or frame-by-frame) and lined up with a reference-either an internal crystal or externally gen-locked to a house bars/black/genlock box. then the signal will look like this:

[].....[].....[].....[].....[].....[].....[].....[]

4. Waveform Restorer, which strips the pulses which precede each field and generates a clean, synthetic new pulse in it's place.

#4 is done with capping to computer, just by the nature of the digital storage of pictures--all that is stored is just the visual frame and a few additional hidden lines that might include timecode, closed-captioning, and a macrovision flag. Some TBC's retain these additional lines, some strip them out, others will give you the choice. There is also variety in the capture card realm.

#2 and 3 are only halfway done upon capture and playback. The part that works well is the playback, since it spits out full stored pictures at the exact rate given by the internal crystal sync on the video card. Capturing well is hampered by the fact that regular capture cards "expect" a well-formed regular signal and aren't set up to receive something that's non-standard. If the spot where it expects the top left pixel to be is not there because the waveform is skewed, it'll digitize whatever it finds at that point (usually noise) and that will be what you get from then on. OR it will drop frames or stop capturing.

Hope that doesn't add to the confusion..
Scott