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08-20-2011, 11:01 PM
jmac698 jmac698 is offline
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I have been working on various TBC techniques for sometime, mostly workarounds in rare cases. Finally I know a good technique to do software TBC that is fully general, with good results, and is simple to implement. Nothing written yet, but after about a year of thinking about this, there's progress

(admin might be interested in this).

Could be something in a few weeks, never know

the title restriction is really annoying.
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  #2  
08-20-2011, 11:06 PM
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Quote:
the title restriction is really annoying.
Well, titles are an important part of SEO, which in turn is important for helping people find accurate results when they search the web. When some goober puts down "help pls" as a title, that helps nobody. The title should describe the discussion that is about to take place, not reflect the txt message of a 14-year-old girl. So that's why that had to be put in place.

As far as the virtual TBC software goes...

I have some ugly footage, if you'd like to test with it. It's not horrible timebase errors, but just lots of little small ones that make the video crappy. If you're interested, I can send that to you. In fact, if you're able to find a corrective method sometime soon, I may even be able to pay you a few dollars for your assistance, since it would be something use on a for-pay project. A donation for your efforts. (The sample clip is from a non-private segment, a commercial from the recording.)

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  #3  
10-08-2011, 11:19 PM
jmac698 jmac698 is offline
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I have an update. I finally managed to tweak a capture card chip to give me the raw TV signal. That means I have access to the HSYNC just like a hardware TBC does, except now I can make a TBC purely in software, and it should work with most capture cards. Not only that, but I can get much higher resolution (1700 pixels) and all the lines (full 486 and also entire VBI). I can see closed captioning, VITC, teletext, laser disc frame/chapters, XDS, and all the other hidden data there.
I'm still working on it, but here's a picture:
http://screenshotcomparison.com/comparison/86066
Obviously I'm lining up that bright line, but I have a bad feeling that's not actually my HSYNC. I'm expecting more like a thick black line instead. That's probably why it's not working yet.
Anyone know what that bright line would be? I think the green line after it is the colorburst.
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  #4  
10-09-2011, 04:56 PM
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There's a chance I used to know what that was. You'd really have to research analog broadcasting and VCR/recording technology. Or find somebody that can remember everything off the top of their head in the post-analog era. This is all interesting, the attempt to create a software-based TBC, and I'm rooting for you, but I don't see it happening anymore than I foresee a cure to AIDS or cancer. It's an extremely complicated problem.

Please do keep reporting your status on this.

It would be awesome if you're someday able to create a filter that can resolve timing errors, even when original sync information has been discarded. Even more impressive will be if it's able to correct videos that have been abused a few times with re-encoding (Youtube uploads, for example).

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  #5  
10-16-2011, 12:30 AM
jmac698 jmac698 is offline
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It's getting much better,
http://www.sendspace.com/file/jdh9j9
That bright green line is actually not part of the video, so I was lining up to the wrong thing.
I now think that jitter has little to do with mechanical speed; it seems more related to video content.
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  #6  
10-19-2011, 04:05 PM
jmac698 jmac698 is offline
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Ok, I've finished my software TBC and it works. It was so simple, why didn't anyone do this before?
http://screenshotcomparison.com/comparison/88691

Next up is a TBC that works with 'baked in' jitter.

oh ya, lordsmurf should buy me lunch or something while he eats his words
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  #7  
10-19-2011, 04:30 PM
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Quote:
Originally Posted by jmac698 View Post
Ok, I've finished my software TBC and it works. It was so simple, why didn't anyone do this before?
http://screenshotcomparison.com/comparison/88691

Next up is a TBC that works with 'baked in' jitter.

oh ya, lordsmurf should buy me lunch or something while he eats his words
Thats because the "software" TBC is the same as a hardware line TBC, if you have access to the horizontal sync data its easy to correct. The 'baked in' jitter will be difficult to correct however since that horizontal sync data will have already been lost.
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  #8  
10-19-2011, 08:28 PM
jmac698 jmac698 is offline
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I don't think you need access to the hsync after all, it's just a matter of lining up two edges.
I realize baked in jitter is different, I have an approach for that that's known to work as well. Of course, if statement A is true then I don't need to use it anyway.
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  #9  
10-20-2011, 02:01 AM
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Quote:
Originally Posted by jmac698 View Post
oh ya, lordsmurf should buy me lunch or something while he eats his words
Proving me wrong would be most excellent.

I have some homemade barbecue sauce here, if needed. Maybe I can cut a steak to read "TBC".

Make a working software TBC that fixes some videos I have, and I'll definitely look at sending you something.
Take the whole family out to a small feast.

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  #10  
10-20-2011, 02:26 AM
jmac698 jmac698 is offline
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But I did - did you see the screenshot? I guess you mean the baked in kind then?
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  #11  
10-20-2011, 02:50 AM
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I need something for already-existing digital videos. We can even say it's an interlaced MPEG-2 from a DVD recorder, to keep it easy.

Youtube videos may be too many generations removed from the source to even be fixed again. There's a limit to bake-in, before the error starts to replace the actual image. I would imagine your typical poorly-converted progressive MP4/FLV files are not going to make for good candidates of repair. Would that be an accurate assessment?

Is this dedicated software, or leveraging Avisynth?

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  #12  
10-20-2011, 04:39 AM
jmac698 jmac698 is offline
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I have a lot of ideas floating in my head so let's be clear.

The method to work on digital/baked jitter I'll call 'intrinsic dejitter'. I have the algorithm worked out but it would take a week to implement. I don't think there can be too much jitter, but working with compressed progressive digital video I think does impact the algorithm, but it's too far to speculate yet. This method has *no* requirements and lines up structures in the video. It's the holy grail.

What I've been doing in the last week is replace a hardware TBC with a capturecard+software. It's nothing exciting to professionals as they already have this ability but - it might work in these cases:

-Black borders visible in digital version
-Analog tape available but capture didn't have complete black borders or none - if you could re-capture with tweaked drivers, you can access black borders and then it can be processed.
-It's an avisynth solution, I could make it standalone if need be, possibly integrated in a capture program/utility.

There is something innovative I've done however, as far as I can tell no one has gotten my approach to work this well so far, and also I found a way to tweak drivers to view the hsync and vbi, which has it's own possibilities. I also think my software TBC can be slightly better quality than a hardware box in terms of it's processing precision, since I can use high quality algorithms for the line shifting (which implies interpolation). Finally there's loads of possibilities for further basic research, which I think will lead to something.

I think it just takes R&D to beat this thing, it's hard work and not for everyone, and I think others would just give up unless it showed immediate practical results. For the potential benefits I think it's worth it.

Fixed the bugs.
http://screenshotcomparison.com/comparison/88810

New comparison http://screenshotcomparison.com/comparison/88873
It shows to me that hsync does give better result.
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  #13  
10-25-2011, 04:37 AM
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I'm watching with great interest, even if I don't post any feedback.

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  #14  
10-29-2011, 02:11 PM
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Me too! This is all very cool. I'm wondering if it would be possible to apply these same methods to fixing the issue caused by JVC VCR TBCs where a tape playing back with the TBC engaged occasionally causes the picture to shift up and then down (usually about four frames, first shifted +2 to +4 pixels above the X axis, down -1 or -2 below it, and then back up to 0) and the interlaced frames are smudged together and/or "mangled". Once I get my new computer up and running, I'll see about posting an example.

I often find myself going back and identifying these errors later, and then re-doing all of those individual parts with the TBC off (and possible with an ES-10 hooked up, since having the TBC off may introduce other issues), while matching the color with the original with my proc-amp.

At worst, it ends up being about 50 to 100 frames of video over the course of say a two-hour tape, but the time to fix that and edit them back in is monumental. If it could be fixed in software after the fact (with just the slight penalty to quality due to having to re-encode it that frame) then it would save me lots and lots of time. If it could analyze a video stream and correctly detect AND correct those sorts of errors, it would be a miracle, but just even being able to correct them as long as I know where they are would be a godsend. That's certainly something I'd be willing to pay for.
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  #15  
10-29-2011, 02:36 PM
jmac698 jmac698 is offline
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That shouldn't be too hard. I'm in the middle of some other things though. Let me know when you got a sample.
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  #16  
10-29-2011, 05:13 PM
robjv1 robjv1 is offline
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Quote:
Originally Posted by jmac698 View Post
That shouldn't be too hard. I'm in the middle of some other things though. Let me know when you got a sample.
Sure! I need to go snatch my other hard drive from my broken computer as well. Probably be about a week, so take your time. I'll get a really representative sample.
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  #17  
11-01-2011, 05:53 PM
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Time for another update.

This is an experiment to answer the questions, what would a perfectly calibrated VHS look like? What are the effects of tape, VCR, and capture card on noise, jitter, linearity, and frequency response?

To answer the questions, custom software was designed and test recordings carefully measured. The resulting technologies advance calibration far beyond the test patterns on typical test DVD's. In essence, practically every measurable aspect of analog capturing can be optimized to the fullest. These experiments are just beginning, but included is one example of it's use.

How this video was created

First, the video was separated into it's component values (Y, Pb, Pr). Each image was recorded separately as a frame. It was also anamorphically squeezed.

Next, a special alignment signal was added to the video.

Upon playback, custom software aligned the video to within .1 pixel. While theoretically perfect, the processing was affected by noise and distortion in the video.

Then the component frames were merged into a color composite. The anamorphic video was unsqueezed. Finally the levels were perfectly stetched between the resulting black/white points.

The resulting video has only these distortions remaining:
-noise
-frequency response
-levels non-linearity
-some banding was introduced by the levels adjustment
-various other minor effects

Commentary on the Video
The video is fairly blurry as can be expected from VHS. The image is quite stable, but one can see a slight movement in the edges of the colorbars. This can probably be eliminated by further work in the software. The noise level is quite good for VHS. Sometimes there is line jitter as the video exceeded the range of the software (this can be corrected too).
Finally, the bottom lines of the video look normal. In fact in the orignal, it was badly slanted and had head switching noise. This part is normally cutoff, but now we don't need to!

Further possibilities

HD
With this technique, pixel-perfect video can be recorded. This brings the possibility of recording HD resolution. To do so, we would separate the HD image into 3x2 tiles or more. Then each tile is recorded as a separate image. The tiles are then stacked back together upon playback, increasing resolution 6 times. The only downside, is that the video takes 6 times as much tape!

The perfect alignment enables this technique because otherwise, it would be difficult to piece the tiles together, as the borders would be wiggling into each other (due to jitter) resulting in obvious artefacts.

Noise reduction
We could also record the video twice, and average the noise upon reconstruction. If this were done without alignment, the result would get much blurrier, as the two copies would be overlapping each other.

Perfect linearity
Currently when you record brightness levels of 128,129,130 etc. we get back 128, 130, 130 for example, as the mid-tones are a little brighter than they should be. Though these levels can be adjusted, there will be some banding as half of the mid-tone values have disappeared. There could be a scheme of HDR where the shadows and highlights are recorded as separate frames.

Frequency Response
Another test signal (frequency sweep) could be recorded to determine frequency response. This can easily be undone with an FFT.

Other methods of encoding video
The alignment would be critical for other methods of recording video. For example the video could be recorded as it's 2d FFT. In this case, mis-alignment would ruin the results, possibly resulting in severe ringing effects.

Measuring VHS Parameters
Further test signals could determine the ideal noise profile of each VCR/Tape combination, the jitter performance of a VCR/TBC/Capture card, frequency response, linearity, etc.

Using the VCR model to improve normal captures
Once we have an ideal model of these parameters, it can be used to tune normal VHS captures to the highest quality. For example, a plain grey image with ideal noise can be provided for use with the well-known Neat Video noise reduction program. The frequency response profile can be used for sharpening. The linearity profile can be used, with debanding, to improve the brightness curve (although this is usually adapted to user preference anyhow).

Further work
There are many aspects to VHS recordings. We can further examine tint/saturation errors, contamination between luma/chroma levels, chroma placement, and other various linear/non-linear shifts within and between signals.

Before anyone says so, yes it's completely useless to come up with better ways of recording to VHS. However if I were working in a TV studio 30 years ago I'm sure I would've come up with a scheme to preserve old TV Shows and today I'd be recovering them

Anyhow, it's all part of the basic research. The practical aspect that could result from this is a measured, scientifically ideal way of restoring VHS recordings, in new ways. It can also lead to a better explanation/theories of various problems like color distortions, head switching noise, jitter, etc. Finally it can be used to rate the performance of tapes/VCR's/capture cards etc.

Example of my ideal TBC performance
http://screenshotcomparison.com/comparison/91487
You'll see some aliasing, that's due to a simple resizer to fix the jitter. On VHS you'd never notice.

This is pretty neat, and probably the first time anyone has seen such a comparison (well, rare anyhow).
It's color bars in normal VHS vs a component format I made up, on the same tape. Basically it's an excellent comparison in apples vs apples of the color resolution of VHS. The luma looks exactly the same between screenshots. You can see the color resolution is something like 20 pixels!
http://screenshotcomparison.com/comparison/91499
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  #18  
11-02-2011, 01:46 AM
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WARNING: The Sendspace.com link was displaying a false "download here" ad that would download malware.

Please attach files to the forum, do not use "file sharing" services because this is a known problem on those shady sites. I downloaded what I thought was your "setup.exe" for a TBC program, but it was malware caught by MalwareBytes. Even the best of us can be tricked by some of this malicious crap.

All images/etc related to the thread are archived long-term this way, too. Those silly "sharing" sites delete data after a few months.

Thanks for understanding.

The intended download "ideal TBC.zip" has been added to this post.


Attached Images
File Type: jpg sendspace-malware.jpg (44.4 KB, 24 downloads)
Attached Files
File Type: zip ideal TBC.zip (2.15 MB, 71 downloads)

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  #19  
11-02-2011, 08:08 AM
jmac698 jmac698 is offline
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Sorry about that I have noscript and noflash installed and don't even see what you're talking about. Though I didn't give it much thought, I had assumed that my file would exceed the size restrictions. Most videos are too large to put on a forum.
Anyhow, if I can find a simple and malware free site, would that be acceptable should I have a larger video? If it's not much different than a plugin download link, that should be acceptable.

About the file, I've been getting some comments and non-experts are a little confused about what I'm doing. To be clear, the video is a capture from a VHS. The capture has been processed in 3 ways; 1 levels adjustment to perfect black/white 2 dejitter *based on an embedded test signal* 3 decoding "component mode"
-the dejitter here only works with the special test signal embedded during recording, and is not in any way a general TBC
-the component mode is something I made up, I just record 3 b/w frames for each original frame; the frames represent luma, pb, and pr. This completely bypasses the color of VHS and has the resolution of VHS luma for each color channel.

Again, the point of the video is just a fun experiment *however*, it's also a demonstration of the embedded dejitter algorithm. The practical use of this algorithm is to measure the jitter of VCR's in various conditions, and to rate the performance of real TBC's or capture cards etc. I plan to make a 2nd generation copy of this tape and list statistcs of actual jitter, i.e. exactly how many pixels it moves and any patterns. This is just basic research to help me make a better *real, practical software TBC*
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  #20  
11-03-2011, 07:52 AM
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You can attach files to the forum: up to 8MB RAR or ZIP files for Free Members. So just do that.
Dropbox is good for larger files.

Premium Members can attach 16MB.
Site Staff 32MB. We can also add files to FTP, if needed.

And then I'd like to see the before/after images side by side, not just as rollover. Maybe do your rollover, but also attach both images to posts, so they're archived here as well. I was looking into some rollover before/after scripting for the site last night. I found something, but it has to be manually implemented into site pages or forum posts. I'm working on it (won't be a fast addition).

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