VHS capturing and resizing for correct AR

[kangarooster]

Hi,
I've been reading a little about capture width, sample frequency and aspect ratios and have a question:

Is resizing necessary for HDTV playback or does it only apply when for non-square pixel, e.g. SDTV, playback?

[jagabo]

It depends. DVD and SD Blu-ray have fixed size frames so you have no choice but to encode anamorphically. If you're making MKV, MP4, AVI, etc. files for playback with a media player you can go either way. Encode at the captured frame size (720x576 or 704x576) and set aspect ratio flags that tell the player how to display the video, or resize to a frame size that matches the aspect ratio of the source and encode with square pixels. If your player(s) don't support AR flags for media files you'll have to resize.

[KarMa]

I'm going to guess this VHS is 4:3, so currently I go with the ITU 4:3 AR of 1.367. So for my NTSC VHS tapes I capture at 720x480, then in avisynth I resize it to 656x480 (480 x 1.367 = 656). From there I crop off the black bars on the left and right side, usually giving me something close to 640 x 480. I also crop off tape noise at the bottom or top, making it less than 480.

An aspect ratio of 1.367 is also what you would use for PAL, but would need to be resized to 788 x 576. I don't work with PAL but would guess there would be black bars to crop off on the left and right side. Giving you something like 768x576.

[LMotlow]

Right. Then you encode it as DVD or BluRay? I think you'd better give the noob more details. He might not own a video server setup or a bunch of external hard drives for playing square pixel video formats. He might just own only a DVD player, has no BD player, or maybe he still has good visual discrimination and doesn't want to watch video only on a computer. I know that you don't use mainstream playback methods, so you might want to warn kangarooster before you talk him into major video surgery.

AT 720x480 4:3, the displayed image in most devices is closer to 1.37:1, not 4:3. Of course there's always the possibility that the original source really should be displayed at 4:3, and a lot also depends on the real proportions of the original image and the size of the side borders, which vary. You should also warn very seriously against resizing interlaced noisy VHS video or randomly cropping without checking colorspace specs, and caution that resizing has a certain quality loss, or his videos might end up looking as damaged as yours.

[kangarooster]

Thank you for your replies. I own a BD/DVD-player.

I am in the process of digitizing PAL VHS tapes (non commercial - recorded by my dad, so I guess it's 4:3?) . My capture device captures at 720x576. Let say my capture width is 51.85 µs, which would give me 13.5*52.59=710 pixels captured. Now since I am capturing at 720 pixels, these 710 pixels will get stretched and mess up my AR, right? So in order to compensate for this, I should add 10 pixels, making the resolution 730x576, then resize back to 720x576 to squeeze back to the original AR. Is this correct? Or maybe I could instead crop some pixels and resize to 704x576 instead?

I will post the avisynth file:

SegmentedAVISource("path_to_file\file.avi")
(Trim(xx,yy)++.... #some trims)
Cnr2("xxx", 4, 5, 255) #Chroma noise reduction
ChromaShift(C=-6)
Letterbox(0, 8) #Remove head switching noise
#Noise reduction for interlaced video
SeparateFields()
odd=SelectOdd.Convolution3D (1, 32, 128, 16, 64, 10, 0)
evn=SelectEven.Convolution3D (1, 32, 128, 16, 64, 10, 0)
Interleave(evn,odd)
Weave()
AddBorders(5, 0, 5, 0, $000000) #adding borders, 5 left and 5 right
BicubicResize(720, 576) #resizing back again
#colors
saturation_v = 1.5
cv = - (1-saturation_v)*256
ColorYUV(off_y=-28, gain_y=42, cont_u=0, cont_v = cv, opt="coring")
#VideoScope("both", true, "U", "V", "UV")

[Skiller]

Let say my capture width is 51.85 µs, which would give me 13.5*52.59=710 pixels captured. Now since I am capturing at 720 pixels, these 710 pixels will get stretched and mess up my AR, right?

Yes, that would be the case if your capture window is indeed 51.85 µs which I highly doubt (where did you get that number from?). It's almost certainly 53.333 µs, so 720 px = 53.333 µs and no distortion.

If you are not sure you can always hook up a DVD-player to your capture device, play a test card (preferably) and capture it via S-Video or Composite and then compare the capture to the source on the DVD.

[kangarooster]

Let say my capture width is 51.85 µs, which would give me 13.5*52.59=710 pixels captured. Now since I am capturing at 720 pixels, these 710 pixels will get stretched and mess up my AR, right?

Yes, that would be the case if your capture window is indeed 51.85 µs which I highly doubt (where did you get that number from?). It's almost certainly 53.333 µs, so 720 px = 53.333 µs and no distortion.

If you are not sure you can always hook up a DVD-player to your capture device, play a test card (preferably) and capture it via S-Video or Composite and then compare the capture to the source on the DVD.

I just made that number up. But for the sake of argument, if i capture at 51.85 µs, would my solution be correct?

Where do I get hold of a test card? My player has an USB port. Can I play it from a flash drive or do I have to burn a DVD (i don't have any DVD disks at the moment, maybe SVCD is OK?)?

[Skiller]

Let say my capture width is 51.85 µs, which would give me 13.5*52.59=710 pixels captured.

Where does the 52.59 come from if you assume your capture window has a width of 51.85 µs?

13.5 × 51.85 ≈ 700

So if your capture window has a width of 51.85 µs you would capture 700 pixels and then these would be erroneously stretched to the requested capture resolution of 720.



To correct for that...
720 × (53.333 ÷ 51.85) ≈ 740.6

You can then correct this by padding to 741 and resizing back to 720. But that's all theoretically speaking. I'm quite sure you don't need to do any of that.

I just made that number up. But for the sake of argument, if i capture at 51.85 µs, would my solution be correct?

No, not for 51.85 µs (as demonstrated above). It would be correct for 52.59 however.

720 × (53.333 ÷ 52.59) ≈ 730.2

Can I play it from a flash drive or do I have to burn a DVD

If you player can properly playback an otherwise DVD compliant MPEG or VOB file at 720x576 via USB then it should be fine.

maybe SVCD is OK?)?

SVCD would be 480x576, so not very appropriate because this involves the player possibly interferring by internally resizing or adjusting it's DAC clock. If you burn a non-standard SVCD at 720x576 that would be OK, and you player is most likely not going to have any problem with that.

[kangarooster]

Oh, I am sorry about 52.59, I mixed up some numbers in my head.

Thank you for your answer.

If you player can properly playback an otherwise DVD compliant MPEG or VOB file at 720x480 via USB then it should be fine.

That would be 720x576 in my case (PAL), right?

I tried doing like the guide here: http://www.doom9.org/index.html?/capture/capture_window.html

However when I use my USB drive I get large black bars on the sides, see this image:

Original image:


So I guess I have to burn it after all

[KarMa]

What does your 720x576 capture look like? Can you post a picture of one of the frames from your dad's recordings or anything really.

[kangarooster]

What does your 720x576 capture look like? Can you post a picture of one of the frames from your dad's recordings or anything really.

Sure.



To be honest, even if "need" to resize, I wouldn't probably see any difference, but I want to do it properly

[KarMa]

Use the ITU 4:3 PAL DAR settings to help with getting the perfect aspect ratio for VHS. Then just crop the black bars off.

A NTSC VHS TAPE (The image is the raw 720x480 capture)


After using the ITU 4:3 NTSC DAR, and then cropping down from 656x480 to 640x480 (still need to deal with the head noise)

[kangarooster]

Use the ITU 4:3 PAL DAR settings to help with getting the perfect aspect ratio for VHS. Then just crop the black bars off.

A NTSC VHS TAPE (The image is the raw 720x480 capture)
*IMG*

After using the ITU 4:3 NTSC DAR, and then cropping down from 656x480 to 640x480 (still need to deal with the head noise)
*IMG*

Thanks.

I assume what you've done is suitable on an HDTV considering your AR calls for square pixels? I capture raw at 720x576, so I am forced to lower my vertical resolution in order to achieve 4:3.

When I open the software the input DAR is set to 5:4 (i guess because I capture at 720x576). Then I changed to ITU 4:3 PAL. After cropping I noticed that I could only use 702 as the highest horizontal resolution, I guess because I cropped off 18 pixels. Now I am stuck.. which resolution should I resize to? The highest possible resolution (for even numbers) would be 696x522 for 4:3 AR. Should I choose this then add black borders to get a DVD friendly resolution, e.g. 704x576?

[KarMa]

MeGui by default tries to stop people from upscaling, I only recently found how to allow upscaling in MeGui without just editing the script manually. Makes life easier in cases like yours.

Click on the Config button

[kangarooster]

Thank you KarMa!