Aspect Ratios 101

[wcndave2]

Thread you started triggered my curiosity - i don't understand why you willing to resize 704 to 768 in first place

If I don't, then the output will not play correctly. Don't worry, I am keeping a copy of the master source files.

- secondly 704 can't be properly resized to 768 - maximum active video line duration for PAL system is 52.3uS - if you sample your video with ITU601/656 compliant rate (13.5MHz) this gives you 706 pixels so you need to upsample 704 to something like 766 pixels ((704*768)/706)

Don't understand, it's clearly possible to resize to 768. In fact if you just throw the video into VLC, or on a TV, it will do that for you - if it can read the PAR which a lot of the time is not the case.

...isn't better to keep original pixel number and signal aspect ratio properly instead blindly resize one number to another especially that 768 pixels is unique for NTSC systems

As far as I know, 768 is the 704x12:11 so it's used in PAL

where active video line duration is 53.055uS and sampled with (NTSC) 4*Fsc you get 758 pixels (so it was rounded to nice binary 768 i.e. 48*16).

This why i asked for your sampling rate - if you don't know your sampling rate and reproduction sampling rate then perhaps it is better to not resize your source?

I have no idea where to get this from.

I am just a non-expert who wants to do the best job of converting some VHS, without a PhD in the subject.

I will actually upscale to 1440x1080 so that I can control that process instead of leaving it up to the device playing.

Telling QTGMC to do this slowly and carefully is going to be better than someone's mobile phone trying to upscale on the fly...

I got a JVC HR-S7722EK (SVHS) with built-in line TBC - to replace my crappy old panasonic.

I am using straightforward process via amarectv using Lagarith, then running via avisynth to remove sides, mask noise and scale, without making the DAR look shitty - within 0.09% seems fine to me.

The process is quick and (relatively) straightforward, and the result is very good.

I just didn't like that 704 seemed to make everyone wider than reality, whereas 720 seemed right.

However I now have the answer that 704 is correct (correct enough), so I will stick with that and assume that the DVDs (purchased) and my eyes are wrong instead!

Thanks for being curious!
Dave

[pandy]

The source is the same. The difference is you take max intervals, while I take standard/default.

Standard says 12uS (i.e. less visible pixels) and with allowed margin 300nS 11.7uS (more visible pixels).
For 12uS blanking interval, active video duration is 52 uS i.e. 702 pixels, for 12.05uS this is 701 pixels.
Normally when you programming digital encoder you maximize active video line duration to fit as much as possible pixels (as normally your source is 720 pixels wide) - 704 is closest compromise to satisfy MPEG-2 block size 16 ( 720 is 45 blocks and 704 is 44 blocks).

[wcndave2]

@wcndave2.
The consensus among "experts" is to store your captured video as is, without any alteration and using lossless codec.
Then, you take this video and convert it/crop it/mask it/whatever you want and watch it/send it to your friends and family, etc.
Why is that? Because today you think one way to process it, tomorrow another way, next year you will decide to upscale it using AI or whatever.
If you have your original capture, then you're good to go. But if it is gone, then it is gone...
Just a point of view...

100% agree

I will keep the lossless captures.

I want to convert it to 1080 (to avoid devices trying to do poor on the fly upscaling), and I just want the DAR to be correct.

Thanks again!

[pandy]

Don't understand, it's clearly possible to resize to 768. In fact if you just throw the video into VLC, or on a TV, it will do that for you - if it can read the PAR which a lot of the time is not the case.

Of course you can resize your source to any arbitrary size - problem is your display device (non PC as PC has own rules that usually can violate broadcast rules) - problem is even display organization - usually following or broadcast standards or being close as much possible.

...isn't better to keep original pixel number and signal aspect ratio properly instead blindly resize one number to another especially that 768 pixels is unique for NTSC systems

As far as I know, 768 is the 704x12:11 so it's used in PAL

Even if 768 is numerically correct then it is uncommon in video industry.

where active video line duration is 53.055uS and sampled with (NTSC) 4*Fsc you get 758 pixels (so it was rounded to nice binary 768 i.e. 48*16).

This why i asked for your sampling rate - if you don't know your sampling rate and reproduction sampling rate then perhaps it is better to not resize your source?

I have no idea where to get this from.

Your capture device may provide this information explicitly.

I am just a non-expert who wants to do the best job of converting some VHS, without a PhD in the subject.

Well... seem you are very detailed on aspect ratio and reproduction accuracy - normally i would say this is standard engineer approach and PhD is not required.

I just didn't like that 704 seemed to make everyone wider than reality, whereas 720 seemed right.

However I now have the answer that 704 is correct (correct enough), so I will stick with that and assume that the DVDs (purchased) and my eyes are wrong instead!

Thanks for being curious!
Dave

Why 704 and 720 exist ? I already provided some explanation - normally 704 is between maximum (706) and minimum (702) number of visible pixels.
All my feedback is based on sampling rate 13.5MHz (so most common, widely accepted digital TV standard).
Good luck with your quest for perfect aspect ratio.

[Sharc]

704 (rather than 702 or 706 or some odd fractional value in between) was selected because it is an integer multiple of 16 ("mod16") which was driven by mpeg2 encoding/compression based on 16x16 macroblocks. A practical implementation constraint.

[wcndave2]

Even if 768 is numerically correct then it is uncommon in video industry.

This is very true, it's not an option in Premiere Pro for example (preset option). However without that I can't get square pixels, and there's a large range of devices and software that don't read PAR...

Well... seem you are very detailed on aspect ratio and reproduction accuracy - normally i would say this is standard engineer approach and PhD is not required.

I want the best outcome for the minimum effort, so definitely an engineer approach!! I used to be an electronics engineer decades ago, and I know I would get caught up in everything, when all I really want it is a good outcome without too much thinking

[_Al_]

pandy is always glitching and responding from another virtual universe, which runs in parallel with ours, but yet, things feel different and you will never be able to understood that one, so just let it glitch ...

[wcndave2]

pandy is always glitching and responding from another virtual universe, which runs in parallel with ours, but yet, things feel different and you will never be able to understood that one, so just let it glitch ...

Like I asked my garage to show me how to change tyres and they said "first of all we need to understand the chemical composition and behaviour of the rubber..."

Seriously though, when people give too much detail, it's normally because they are super passionate about a subject, which is good. One has to be careful it doesn't put noobs off though!

[CaptureCraft]

@wcndave2. Could you check your messages?

[pandy]

pandy is always glitching and responding from another virtual universe, which runs in parallel with ours, but yet, things feel different and you will never be able to understood that one, so just let it glitch ...

Should i bother with opinion expressed by person suffering Dunning Kruger effect mixed with illusory superiority syndrome...?

[pandy]

This is very true, it's not an option in Premiere Pro for example (preset option). However without that I can't get square pixels, and there's a large range of devices and software that don't read PAR...

768 is fine but automatically you are limited to HD capable decoders - SD limit is 720 pixels and something above is reserved for HD and higher resolutions decoders - i would find bit odd limiting possibility to watch SD content only to HD capable equipment but wise people says: "not my circus and not my monkeys"

Good luck.

[VWestlife]

The easiest thing to do is just keep it in its native rectangular-pixel resolution and let the player take care of converting it to square pixels and upscaling it as needed. Even a 20-year-old copy of Windows Media Player or QuickTime Player can do this just fine, so it's no sweat.

[dellsam34]

After a lot of captures and a lot of experimenting with different processing scenarios I learned 3 lessons which I know some will disagree, but this is what works for me:

- I always keep a master copy of the captures that are worth revisiting.

- I crop the junk, Not worth keeping for me, I first crop in the ratio of 704:480 for NTSC, 704:576 for PAL/SECAM, If there is still junk on one dimension I'll cut a little bit into the active area of the other dimension in an effort to respect the AR, Too much cutting into the active area? I apply the 3% max AR distortion rule to save the active area, trust me you won't visually see the distortion.

- I never resize SD to another SD resolution, Minimum HD, where I can set my final AR, and no more than one resize at any given time.

I use to be very picky about the exact AR, but after seeing a lot of captures of me and other people I prefer to have a clean frame than watching a nasty border flickering along the video or an ugly tiny black border surrounding the frame, This is just my personal preference which I'm aware some may disagree.

Note on de-interlacing: Some suggest de-interlacing before cropping/masking, some say do it after, I haven't experimented with this to make my own decision, I just got the habit to do it before cropping.

[lollo]

I do not understand why 43 posts on the subject. Everything needed is in post #2:

• crop 720x576 to 704x576, mask head switching noise (and eventually dirty on the top) and add 4:3 DAR.

end of the story.

If the player supports the flag, cropping instead of masking is an option (specifying PAR 12/11, called SAR in ffmpeg)