Quantcast What is the actual PAR of HuffYUV files captured from VHS tapes with VC500? - digitalFAQ Forum
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  #1  
02-25-2021, 09:29 AM
rokoko32 rokoko32 is offline
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Since capturing with Virtualdub there is no PAR data in the saved lossless HuffYUV file’s header.
I read somewhere:
“AVI capture video file does not have display aspect ratio (DAR) information embedded in its data. Nor does un-encoded video have a pixel-shape aspect ratio (PAR).”

I want to encode my VHS captured HuffYUV files using Hybrid. VHS captures done with Diamond VC500 using Virtualdub, 720x576.
Since there is no PAR data in capture file header, Hybrid does not know what to use and sets PAR 1:1, and that is not correct.

Hence, Input PAR has to be set manually.
The big question what is the right PAR value for that particular VC500 + Virtualdub combination:
1. 1150:1053 (ITU-R 601)
2. 12:11
3. 16:15 – this on is more close to DAR 4:3, since 4/3 = 1.3333 and (720/576) * (16/15) = 1.3333.
And 16:15 this is the value that is set in to DV avi file header if capturing with Canopus ADV100

Lordsmurf and others, curious what values are you using to get most accurate not distorted picture?
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  #2  
02-25-2021, 11:16 AM
latreche34 latreche34 is offline
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All the info is already here you just need to do some reading:
Masking edges. Aspect ratio.
AVI to MP4 frame size, rectangle vs. square pixels?
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  #3  
02-25-2021, 12:17 PM
rokoko32 rokoko32 is offline
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Thanks for pointing out those links.
The info per links is suggesting to:

The fist link: "The proper way of doing it is to crop to 704x480 (704x576 PAL/SECAM)"
I am not sure if this is the best idea to crop active pixels, removing active image content.

The second link also does not explain the SAR for 720x576, it shows some SAR values, also generic formula SAR = 4:3 x (V resolution : H resolution).

That is not 100% accurate, the active image area very depends on the actual HW equipment used to do the capture.
No guarantee that cropping to 704x576 will result to an image with no distortions.
(There were links in this forum pointing to this information.).

I seen cropping suggestions for an analog capture and 702x576, and 711x576 and etc.


This is why I am asking for the real life practical use data, applicable for VC500 capture device.
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  #4  
02-25-2021, 12:26 PM
lollo2 lollo2 is offline
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Display Aspect Ratio = Pixel Aspect Ratio * Storage Aspect Ratio

PAR Pal Standard = 1.066

Analog capture of video PAL 4:3 at 720 x 576 --> DAR = 4:3, SAR = 720 / 576 = 5:4

(Check: PAR = DAR / SAR = (4 / 3) / (5 / 4) = 16 / 15 = 1.066)


Do not crop, mask!
crop(crop_left,crop_top,-crop_right,-crop_bottom)
...
addborders(crop_left,crop_top,crop_right,crop_bott om)

Last edited by lollo2; 02-25-2021 at 12:38 PM.
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  #5  
02-25-2021, 12:54 PM
rokoko32 rokoko32 is offline
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Ok, agree.
Still in doubt.
That "PAR Pal Standard = 1.066" is applicable for a generic already encoded (MPEG-2 based for example) content.

For an analog capture there is ITU-R BT.601 that defines a standard sampling rate for both 625/50 and 525/59.94 video signals. That ITU-R 601 defines PAR = 1150/1053. It is just a little bit, by 2.5% different from 1.066.

Watching a circle shape on TV, PC screen it is difficult to catch , measure such small difference.
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  #6  
02-25-2021, 01:09 PM
lollo2 lollo2 is offline
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Correct.
I posted the "generic" PAR ignoring ITU.
The exact PAR according to ITU-R BT.601 is 1150/1053 for 4:3 PAL and 4600/3159 for 16:9 PAL.
I always use "generic" PAR.
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  #7  
02-25-2021, 01:25 PM
rokoko32 rokoko32 is offline
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If I will keep captured size 720x576 (do not crop to 704x576) and apply that bizarre PAR 1150/1053 I will get quite accurate, not distorted encoded frame, correct?
This is what most people do whit their captured VHS ?
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  #8  
02-25-2021, 02:37 PM
rokoko32 rokoko32 is offline
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Looks like it is not quite that simple.

For my VHS video achieve I have done two sets of captures, one with VC500 and one with Canopus ADV100.
I checked Canopus generated DV avi file, from same VHS tape. This one has the PAR data in the header, Hybrid shows PAR = 1.067, corresponding PAR 16:15.
Which one is correct 16:15, or 1150/1053?
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  #9  
02-25-2021, 08:39 PM
traal traal is offline
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Being analog, it's all subjective.

I just mask out the head switching noise, center the image, set the Display Aspect Ratio to 4:3, and call it good.
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  #10  
02-25-2021, 09:33 PM
latreche34 latreche34 is offline
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Quote:
Originally Posted by rokoko32 View Post
Thanks for pointing out those links.
The info per links is suggesting to:

The fist link: "The proper way of doing it is to crop to 704x480 (704x576 PAL/SECAM)"
I am not sure if this is the best idea to crop active pixels, removing active image content.

The second link also does not explain the SAR for 720x576, it shows some SAR values, also generic formula SAR = 4:3 x (V resolution : H resolution).

That is not 100% accurate, the active image area very depends on the actual HW equipment used to do the capture.
No guarantee that cropping to 704x576 will result to an image with no distortions.
(There were links in this forum pointing to this information.).

I seen cropping suggestions for an analog capture and 702x576, and 711x576 and etc.


This is why I am asking for the real life practical use data, applicable for VC500 capture device.
I don't know if you are trying to re-invent the wheel or what, Per D1 standard every capture card has a width of 720 pixels, 16 being a safety margin because camera's sensors back in the day were not positioned in the same location, So the active video area is 704 not 720.
As to the aspect ratio, it is calculated based on 704x480 not 720x480 and I already demonstrated it here.
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