Quantcast Would QTGMC be adding jitter? - digitalFAQ Forum
  #1  
01-19-2021, 11:54 PM
aussieskier aussieskier is offline
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I've been tackling a stubborn video from a VHS-C camcorder and the interlacing is sending me in circles. Normally I leave things interlaced and handle that at playback, but that has with glaring combing on the edges here.

That leads me to cleaning it up in avisynth with QTGMC, but when I do and leave it at doubled frame rate, it seems to introduce (or maybe just accentuate?) jitter in the capture. It's noticeable on playback, but also when you progress through frame by frame in virtualdub.

When I selecteven() the output, it doesn't seem to have that effect, although I do get some ghosting on the edges.

Attached are three samples to illustrate. One as captured, one with QTGMC at 59.97, and another with QTGMC at 29.97. They are in need of levels and color work, but I turned all that off to isolate QTGMC for the moment. Just using basic qtgmc(preset="faster") nothing fancy.

Is there something I'm missing with QTGMC, or should I be tackling this another way in avisynth? Is this an error in the underlying capture that's just being accentuated by the deinterlacing?

Thanks!


Attached Files
File Type: avi sample.avi (17.15 MB, 12 downloads)
File Type: avi sample_withqtgmc-29.avi (15.22 MB, 8 downloads)
File Type: avi sample_withqtgmc-59.avi (30.11 MB, 9 downloads)
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  #2  
01-20-2021, 02:02 PM
scharfis_brain scharfis_brain is offline
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make a comparison of gtgmc() with bob()

I suspect that the fields are not aligned.
That's nothing QTGMC is going to fix for you.
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  #3  
01-20-2021, 03:39 PM
hodgey hodgey is offline
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Looks like you deinterlaced with the wrong field order, what was your full script?
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  #4  
01-20-2021, 07:07 PM
aussieskier aussieskier is offline
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Thanks all.

As far as comparing QTGMC vs Bob, it is the same result as far as movement between fields/frames.

Regarding the script. I've reduced it down to the following and still seeing the same.

Code:
AviSource("D:\Videos\sample.avi")
ConvertToYV12(interlaced=true)
AssumeTFF()
QTGMC(preset="faster")
ConvertToRGB32(matrix="Rec601")
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  #5  
01-20-2021, 08:20 PM
hodgey hodgey is offline
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Try with
Code:
avisource("blah.avi")
swapfields()
AssumeTFF()
ConvertToYV12(interlaced=true)
QTGMC(preset="faster")
ConvertToRGB32(matrix="Rec601")
The fields seem to be swapped for whatever reason.
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The following users thank hodgey for this useful post: aussieskier (01-20-2021)
  #6  
01-20-2021, 09:22 PM
aussieskier aussieskier is offline
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Excellent. That seems to have addressed the issue. Thanks for the assist!

It looks like the underlying problem is the "swap fields" option was on in the virtualdub capture settings. Must have hit it by accident. oops.
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