VHS capture (through dvd recorder) in Composite or S-video ? (Avisynth comparison)

[Music Fan]

Hi,
I have to capture a Pal VHS with an Hauppauge PVR-150 (I do this with Virtual VCR in Lagarith yuy2) and I have 3 possible connections between VCR and PVR-150 ;
-direct connection ;
1) composite using a scart to composite adapter (only scart output on this VCR)

-standalone dvd recorder between VCR and PVR-150 ; dvd not recording of course, just switched on to let pass the signal to use its TBC better than PVR-150's TBC (especially on a Secam VHS I captured some time ago, maybe less useful with Pal) ; VCR connected with Scart to Dvd recorder (VCR probably sending a composite signal on scart), but 2 solutions for dvd output to PVR-150 ;
2) composite
3) s-video

I read that s-video was not very useful for VHS but also that sometimes, the Y/C separation could be best done by the player than by the capture card.
So I made tests ; I don't see any differences but as my eyes are not perfect, I'd like to be sure which is the best with this equipment.

Here are 3 extracts in Lagarith yuy2 ;
1) composite without dvd ;
http://www15.zippyshare.com/v/78102589/file.html
There is a little header problem with this video due to the Hauppauge filter used by VirtualVCR ; the framerate detected is 29.97 while it's actually 25 fps, just change it with Virtual Dub (video, framerate, source rate ... and save in direct stream copy).

2) composite with dvd ;
http://www58.zippyshare.com/v/63861223/file.html

3) s-video with dvd ;
http://www6.zippyshare.com/v/85808976/file.html

You can find Lagarith codec there ;
http://lags.leetcode.net/codec.html

Why do I ask it in Avisynth section ?
Because I'd like to know how to analyze these videos with Avisynth to measure precisely differences between these captures (if there are differences, I think to luma and chroma levels) to choose the best way to capture this VHS.
I will also need to filter this video but let's begin with the capture connection's question. ;)
:thanks:

[Guest]

You should use s-video as the luma and chroma are carried on separate wires and are not combined and thus do not require separation.

[Music Fan]

I know but for VHS things are different and s-video is not always recommended, that's why I said that the Y/C separation could be best done by the player than by the capture card.
Does anyone know how to analyze videos ?

[Asmodian]

With s-video the Y/C separation is done by the S-VCR not the capture card and sent separately so it doesn't cause interference with the luma information. Why would s-video not be recommended for VHS? My quick tests always looked much better using s-video but the Black Magic Intensity I was using doesn't have a great comb filter. I was capturing in uncompressed 10-bit 4:2:2. S-video is nice because you don't need a comb filter at all.

As I understand it, unless damaged, s-video is always better than composite.

"Analyze" is pretty vague.

[Music Fan]

Why would s-video not be recommended for VHS?
Because I read several times that VHS recorded video in a composite mode, Y and C are blended.
S-VHS record Y and C separately, thus a s-video cable is especially useful for S-VHS.
It means that for VHS, Y and C have to be separated by the capture card (if VCR connected in composite) or before, like I tried with the dvd burner used as intermediary.
And the quality of this separation varies from one device to another.
Topic on the same subject ;
http://forum.grassvalley.com/forum/showthread.php?t=1389

"Analyze" is pretty vague.
I got this answer on another forum ;
ColorYUV(analyze=true)
I tested but the results look very close and depend on the frames (values change from a frame to another), so it's hard to make a conclusion.
I cropped black borders ;
crop(16,2,-6,-24)

Don't forget that my question also concerns the TBC quality (you can compare both composite extracts).

[pandy]

Because I read several times that VHS recorded video in a composite mode, Y and C are blended.
S-VHS record Y and C separately, thus a s-video cable is especially useful for S-VHS.
It means that for VHS, Y and C have to be separated by the capture card (if VCR connected in composite) or before, like I tried with the dvd burner used as intermediary.


This is not true - Y and C in each color VCR are recorded separately - "The luminance (Y) and color (C) components of the composite video signal are recorded differently. Luminance, which is in effect the black and white picture with all the high resolution components but no color, is frequency modulated on a carrier at around 3.4 MHz. The deviation is about 1 MHz and the maximum frequency recorded on a VHS tape is a little over 5 MHz (Beta is slightly different and S versions of Beta and VHS extend some of these to achieve higher bandwidths. The color signal is separated from the composite video and is amplitude modulated on a 629 kHz carrier. This is called the "color under' system."

http://www.repairfaq.org/sam/vcrfaq.htm#vcrvhsvid
http://www.modeemi.fi/~leopold/AV/VideoFormats.html

main difference between S-VHS and VHS (except resolution) is fact that VHS VCR usually have no separate output for C and Y signal (S-Video) - S-VHS VCR can read VHS tape and S-Video providing Y and C will be better than CVBS.

[Music Fan]

This is not true - Y and C in each color VCR are recorded separately - "The luminance (Y) and color (C) components of the composite video signal are recorded differently. Luminance, which is in effect the black and white picture with all the high resolution components but no color, is frequency modulated on a carrier at around 3.4 MHz. The deviation is about 1 MHz and the maximum frequency recorded on a VHS tape is a little over 5 MHz (Beta is slightly different and S versions of Beta and VHS extend some of these to achieve higher bandwidths. The color signal is separated from the composite video and is amplitude modulated on a 629 kHz carrier. This is called the "color under' system."

http://www.repairfaq.org/sam/vcrfaq.htm#vcrvhsvid
http://www.modeemi.fi/~leopold/AV/VideoFormats.html
Thanks, interesting !
It means that a lot of people on several forums are wrong about that subject because all research I made (maybe not enough !) lead to the information that VHS record a composite signal.

main difference between S-VHS and VHS (except resolution) is fact that VHS VCR usually have no separate output for C and Y signal (S-Video) - S-VHS VCR can read VHS tape and S-Video providing Y and C will be better than CVBS.
Ok, but as my VCR does not have S-Video output but only SCART, and as the manual does not mention if this SCART can send a s-video signal, how to know what signal is sent on SCART to the dvd burner ? Could it be RGB ?
Let's admit that this is CVBS ; in this case I still have to know if the Y/C separation by the dvd is useful or not.
That's why I gave some extracts that can be analyzed.

[Guest]

Thanks, interesting !
It means that a lot of people on several forums are wrong about that subject because all research I made (maybe not enough !) lead to the information that VHS record a composite signal. You need to research original specifications and other technical materials, not the bloviations of random people on the internet.

Ok, but as my VCR does not have S-Video output but only SCART, and as the manual does not mention if this SCART can send a s-video signal, how to know what signal is sent on SCART to the dvd burner ? Could it be RGB ? SCART is capable of carrying composite, s-video, RGB, and YPbPr component. To determine which are actually present on your SCART connection, you can either examine a schematic for the VCR, or, if that is absent, look at the signals with an oscilloscope.

Let's admit that this is CVBS ; in this case I still have to know if the Y/C separation by the dvd is useful or not. Of course it is useful. How do you think your DVD recorder could avoid doing this separation?

[Music Fan]

SCART is capable of carrying composite, s-video, RGB, and YPbPr component. To determine which are actually present on your SCART connection, you can either examine a schematic for the VCR, or, if that is absent, look at the signals with an oscilloscope.
Ok, not simple, I don't have oscilloscope but I can search a schematic for the VCR (which is 15 years old).

Of course it is useful.
That's not so evident, especially if my VCR send only CVBS on its SCART. In this case, I have to choose between an Y/C separation by the card of before, by the dvd burner, but I need to know which one does it best.
Did you analyze my videos and saw differences ?

[Guest]

Without the schematics I can't know what you are getting through a DVD player interposed. How are you connecting the DVD player to the PVR? You'd have to have s-video or component to the PVR for this scenario to potentially improve things (if the DVD player Y/C separation is better than that of the PVR).

But can't you assess your test results yourself? Why do you need us to decide for you which appears better?

[Music Fan]

Without the schematics I can't know what you are getting through a DVD player interposed.
The first aim was to use its TBC.

How are you connecting the DVD player to the PVR?
I have the choice between CVBS and S-video and I try to know which one give the less damaged results in my configuration (and not only in absolute) and if S-video is useful or if my Hauppauge will handle better than the dvd recorder the CVBS signal coming from the VCR.

I do this capture for a friend (it's his wedding tape) and I wanna do it the best I can (with the equipment I have).

[Guest]

It's possible the interposed DVD could degrade the signal as well and so somewhat negate any improvement from the Y/C separation (assuming there is such an improvement). Anyway, assuming the VCR outputs only composite, it's clear that you must have an s-video from the DVD to the PVR to possibly gain anything. My eyes are probably worse than yours, so let's see if some others can comment on your captures. :sly:

[Music Fan]

Anyway, it's clear that you must have an s-video from the VHS to the DVD, and from the DVD to the PVR to possibly gain anything.
Actually, I'm convinced now (after what I read above) that S-video is the best output on a VCR when one has it (I mean to connect to a capture card having it and CVBS), but as mine has only Scart, the decision about this choice is more difficult to take.
Anyway, I continue my research about the VCR Scart's ouptut to know what signal passes through it (the VCR is a Sony SLV-E830 and the dvd recorder is a Philips DVDR-70 for those who wonder).

edit : I found SLV-E830's service manual, still have to read it ;
http://elektrotanya.com/sony_slv-e830.pdf/download.html

[sven_x]

You could record a still image like it is done here (http://www.engon.de/audio/grabber_en.htm) and then compare the output of that recording via s-video against SCART.

In my opionion at VHS recorders the SCART output carries mostly only composite signal, RGB are not connected.

[Guest]

According to the service manual that ancient VCR has only composite out on the SCART connector.

Maybe you can borrow/purchase a better VCR for this.

[Music Fan]

Thanks for this information, you were fast ! On which page did you find that ? I searched (rapidly) but didn't see it.:o
I don't know anybody who has a better VCR than mine and as I don't capture a lot of VHS, I'm not gonna buy a new one just for a few tapes.
But now we know what signal arrives to the dvd, one problem solved.
Still have to see if there is a difference between dvd and capture card's CVBS treatment.

[Music Fan]

You could record a still image like it is done here (http://www.engon.de/audio/grabber_en.htm) and then compare the output of that recording via s-video against SCART.
Ok, I will read this.

[Guest]

Thanks for this information, you were fast ! On which page did you find that ? I searched (rapidly) but didn't see it.:o The specs at the start define the pins used and there is only one pin for the video out, so that's that. But it's also confirmed by looking at the schematic (schematic page 3-2).

Still have to see if there is a difference between dvd and capture card's CVBS treatment. Yes, it will be interesting to know your results.

[Music Fan]

The specs at the start define the pins used and there is only one pin for the video out, so that's that. But it's also confirmed by looking at the schematic (schematic page 3-2).
Wow, this schematic is chinese for me. Thanks, I wouldn't have found or understood this alone.

[ChiDragon]

You need captures of the same frames in order to compare your options. There is no reason to include VCR <cvbs> DVDR <cvbs> PVR-150 in the comparison though.

To compare the Y/C separation (comb filter), the most useful test footage has low movement and high spatial frequency (sharp definition).

[Music Fan]

You need captures of the same frames in order to compare your options.
That's what I did (at least for 2 of the 3 recordings, the other one was maybe recorded a few seconds before but the scene is the same).

There is no reason to include VCR <cvbs> DVDR <cvbs> PVR-150 in the comparison though.
Why not ? I'd like to compare them.

To compare the Y/C separation (comb filter), the most useful test footage has low movement and high spatial frequency (sharp definition).
Ok, and when I will have recorded this kind of footage, what script should I use to compare them ?

[wonkey_monkey]

This is not true - Y and C in each color VCR are recorded separately - "The luminance (Y) and color (C) components of the composite video signal are recorded differently. Luminance, which is in effect the black and white picture with all the high resolution components but no color, is frequency modulated on a carrier at around 3.4 MHz. The deviation is about 1 MHz and the maximum frequency recorded on a VHS tape is a little over 5 MHz (Beta is slightly different and S versions of Beta and VHS extend some of these to achieve higher bandwidths. The color signal is separated from the composite video and is amplitude modulated on a 629 kHz carrier. This is called the "color under' system."

I'm a bit clueless about analogue video, but isn't that still technically composite? It doesn't sound like two signals are being recorded on separate areas of tape.

David

[Music Fan]

Interesting remark.
It seems that understanding VHS's working is not so simple actually.

Anyway, I recall my main question : how to compare CVBS and S-video captures (and also 2 CVBS captures, one with dvd as intermediary) with Avisynth, except with ColorYUV(analyze=true) whose results are not easy to understand as Y/C levels are different in all pictures ?
The subquery concerned the Philips's TBC efficiency.

[Mounir]

There is a MSU tool called Noise estimation metric, you could use that to compare i suppose, have a look here:
http://www.compression.ru/video/quality_measure/metric_plugins/ne_en.htm

[StainlessS]

Perhaps built-in Compare() func could provide some measure of difference between clips (PSNR),
or then again, perhaps not. Just an idea.

EDIT: Retasked comparison with a Merge(A.blur(1.0),B.blur(1.0)) of both comparison clips.

EDIT: Ignore, just another Brainlesss Stainlesss idea :(

[Music Fan]

Thanks guys, I'm gonna have look at this.
Except ColorYUV(analyze=true), I was also told about Histogram ;
http://avisynth.org.ru/docs/english/corefilters/histogram.htm

[ChiDragon]

Why do you want a machine to tell you which is better? Capture a scene or test pattern with appropriate content and look with your eyes.

That's what I did (at least for 2 of the 3 recordings, the other one was maybe recorded a few seconds before but the scene is the same).

If you say so. I'm not going to spend my time cutting them to match.

Why not ? I'd like to compare them.

Because there's no way the recombined and reseparated capture is better than the S-Video capture.

[Music Fan]

Why do you want a machine to tell you which is better? Capture a scene or test pattern with appropriate content and look with your eyes.
As I already said, I don't see differences because I don't have good eyes.
Even with very good eyes, some things are hard to do without tools (hardware or software), for example calibration.

Because there's no way the recombined and reseparated capture is better than the S-Video capture.
I'm not sure to understand what you mean, I just made tests with extracts and still have to capture the entire VHS.

[Music Fan]

I tested Histogram(mode="levels") which shows very similar results between S-video and Composite captures.
I also tests ColorYUV(analyze=true), here are the results on a frame (S-video on left, Composite on right) ;

http://nsa33.casimages.com/img/2013/10/08/131008103948453956.jpg

and another ;

http://nsa33.casimages.com/img/2013/10/08/131008104607644499.jpg

And finally I tested Compare(clip1, clip2, "", "compare.log") on the exact same portion of video (15 frames), here is the log : clip1 (= clip_filtered) is Composite, clip2 (= clip_original) is S-video ;

Comparing channel(s) YUV

Mean Max Max
Absolute Mean Pos. Neg.
Frame Dev. Dev. Dev. Dev. PSNR (dB)
-----------------------------------------------------
0 2.0545 -1.3906 51 -74 37.6727
1 2.0336 -1.4016 35 -62 37.8019
2 2.0766 -1.3972 55 -61 37.5089
3 1.9896 -1.3571 43 -54 38.0099
4 2.0342 -1.3658 36 -46 37.6620
5 1.9665 -1.3317 40 -47 38.0741
6 2.0110 -1.3624 42 -45 37.8413
7 2.0702 -1.3564 42 -49 37.4747
8 2.0049 -1.3173 50 -63 37.8216
9 2.0380 -1.3558 32 -40 37.6822
10 2.0190 -1.4192 40 -44 37.8700
11 2.0492 -1.4073 36 -38 37.7398
12 2.0689 -1.3935 39 -48 37.5861
13 2.0683 -1.4123 53 -43 37.6493
14 2.0834 -1.3746 37 -38 37.5346



Total frames processed: 15

Minimum Average Maximum
Mean Absolute Deviation: 1.9665 2.0379 2.0834
Mean Deviation: -1.4192 -1.3762 -1.3173
PSNR: 37.4747 37.7286 38.0741
Overall PSNR: 37.7253

And the reverse (clip1 is S-video, clip2 is Composite) ;

Comparing channel(s) YUV

Mean Max Max
Absolute Mean Pos. Neg.
Frame Dev. Dev. Dev. Dev. PSNR (dB)
-----------------------------------------------------
0 2.0545 +1.3906 74 -51 37.6727
1 2.0336 +1.4016 62 -35 37.8019
2 2.0766 +1.3972 61 -55 37.5089
3 1.9896 +1.3571 54 -43 38.0099
4 2.0342 +1.3658 46 -36 37.6620
5 1.9665 +1.3317 47 -40 38.0741
6 2.0110 +1.3624 45 -42 37.8413
7 2.0702 +1.3564 49 -42 37.4747
8 2.0049 +1.3173 63 -50 37.8216
9 2.0380 +1.3558 40 -32 37.6822
10 2.0190 +1.4192 44 -40 37.8700
11 2.0492 +1.4073 38 -36 37.7398
12 2.0689 +1.3935 48 -39 37.5861
13 2.0683 +1.4123 43 -53 37.6493
14 2.0834 +1.3746 38 -37 37.5346



Total frames processed: 15

Minimum Average Maximum
Mean Absolute Deviation: 1.9665 2.0379 2.0834
Mean Deviation: +1.3173 +1.3762 +1.4192
PSNR: 37.4747 37.7286 38.0741
Overall PSNR: 37.7253

I don't really know how to read (interpret) these results.:confused: What do you think of this ?

[ChiDragon]

As I already said, I don't see differences because I don't have good eyes.

You said your eyes aren't perfect. So you actually have an uncorrected vision problem?

As I see it there are two possible advantages of running your video through the DVD recorder:

Could have a better comb filter (Y/C separation)
Could clean up wiggling lines


For the first it's easier to compare (http://www.techpowerup.com/reviews/NVIDIA/PureVideo/images/PureVideo-24.jpg) using a DVD test pattern. For the second you could find a scene where the camera is still and there are vertical lines, if that ever happens on the tape.

Both effects are pretty obvious to see when there is an improvement (with appropriate content), and none of the analyzing filters you ran would be particularly helpful to measure them.

[turbojet]

If you are looking for an opinion the pictures on the left are superior in every way to my 20/20 eyes (is that perfect?). The right looks over-saturated, look at the back of the neck on the guy on the right and the left cheek of the lady on the right. The edges are cleaner on the left, look at right elbow of the guy on the right. Left picture also has more detail look at the fingers on the left hand of the woman on the right. PSNR also agrees but that doesn't matter much. Your eyes may differ.

[Music Fan]

Thanks for these answers !

my 20/20 eyes (is that perfect?)
Eagles have better eyes, but for a human I guess it's near perfection ;)
Now that you mention the saturation problem, I see it, but I have to admit I don't see very well differences on fingers and elbow. A little bit but I'm perhaps influenced by your analyze.
Anyway, the saturation problem justify I choose S-video.
And as I have to return the dvd recorder to its owner today, I don't have time anymore to make further tests.

So you actually have an uncorrected vision problem?
It's corrected by glasses but even with them, I remarked in some situations I didn't see details as well as some others.

[pandy]

I'm a bit clueless about analogue video, but isn't that still technically composite? It doesn't sound like two signals are being recorded on separate areas of tape.

David


Nope, two signal are recorded at the same time but on different frequencies (thus you can say that this is frequency multiplexing).
Chrominance is recorded in native way (as chrominance itself is AM/PM modulated) on "low" frequency, luminance is converted to FM signal and later recorded on different frequency (or rather part of spectrum) such signal is combined and feed trough write amplifier to write head (usually this is one head - combined head write/read).

This is same principle as radio - multiple radio station at the same time if each of them use different part of spectrum.

---

I've check schematics for this Sony SLV-E830 and you can easily recognize that Y and C are separate signals up to point where they are combined as CVBS and feed to video output - oscilograms clearly show this principle (there are visible colorbar signal with two part - L signal is for example on pin 25 of the IC201, where C signal is on pin 48 of the IC201.
So this VCR can be modified to provide Y/C signals.

I don't know any of the of VCR with RGB output as this require CVBC decoder (NTSC/PAL/SECAM) - there is no added value to have such decoder in VCR as required decoder already exist in TV.

[Ghitulescu]

I know but for VHS things are different and s-video is not always recommended, ...
VHS is not different from eg S-VHS in how it records the signals.
However, if you detach the concepts of VHS from the S-Video ...
.... s-video is not always recommended ...then you might be right.

S-Video is not always recommended. The reason is that the signal has no synch, and in studios, where the cables are quite long compared to home use, any difference in length between the two cables could cause an error.

[Music Fan]

Thanks for your explanations.

this VCR can be modified to provide Y/C signals
Interesting. Do you believe it requires modifications (adding and/or removing electronic components) or there are just some weldings to do ?

[pandy]

Thanks for your explanations.


Interesting. Do you believe it requires modifications (adding and/or removing electronic components) or there are just some weldings to do ?


Yes, for sure it require modifications, perhaps adding same video buffers but this should be not complicated - if basic principle is that C and Y are recorded as independent signal paths and later they need to be combined before output them as CVBS then outputting separately Y and C is possible and doable.

Probably some schematics for VCR is required, also datasheet for R/W video processor can be nice but even with scope some optimal source of signal can be found and used.

(im considering only to add Y/C output as this can be most important for us - to capture and process digitized video data).

I can imagine even further step as whole digital processing by capture video head baseband and DSP such digitzed signal to restore particularly precious recordings but this is out of scope for this topic definitely.

[Music Fan]

Yes, for sure it require modifications, perhaps adding same video buffers but this should be not complicated - if basic principle is that C and Y are recorded as independent signal paths and later they need to be combined before output them as CVBS then outputting separately Y and C is possible and doable.

Probably some schematics for VCR is required, also datasheet for R/W video processor can be nice but even with scope some optimal source of signal can be found and used.
Ok, not so easy for me, and I should find the same buffer.

I can imagine even further step as whole digital processing by capture video head baseband and DSP
I don't understand very well what you mean. What would be different compared to my current capture method ?