DAR & SAR question

[thetoof]

Ok, this may be basic, but what I saw here confused me : http://mewiki.project357.com/wiki/MeGUI/Aspect_Ratio_Signalling_in_AviSynth_Scripts

Isn't 4:3's DAR 1.3333333 ?
480*(4/3)=640 while 480*1.3672=656.256

Or is it that when there is a 16px pillarboxing, the DAR is 1.3672 (so 1.333 after cropping) and where there is no pillarboxing, it is already 1.333??

What about 16:9? Is there something special for this too?

All this is meant to feed the proper SAR to meGUI.

:confused:
Thanks for your input.

[Wilbert]

from that page:
DAR = 1.3672 # suppose we know the input is ITU 4:3

[thetoof]

Sorry for my lack of knowledge, but I don't know what this implies.

[Nightshiver]

It's the national encoding standard, or more specifically, Studio Encoding Parameters of Digital Television for Standard 4:3 and Wide-Screen 16:9 Aspect Ratios. Also, read this (http://www.pcmag.com/encyclopedia_term/0,2542,t=ITU-R+BT601&i=45512,00.asp)

[thetoof]

Yes, I know it's a standard, but what I don't get is why DAR is higher than 4/3 when it's "ITU".

[Wilbert]

We have had countless discussions about that in the past. See for example: http://forum.doom9.org/showthread.php?t=111102&highlight=ITU

[thetoof]

Thanks for the link... looks like I'm up for some good reading. My bad for not doing a proper research in the other sub-forums.

[Alex_ander]

One more useful link:
http://lipas.uwasa.fi/~f76998/video/conversion/

I personally think it's a bad practice to calculate basing on artificial values like 'pixel aspect ratio' and other numbers with several digits. Those numbers were derived from clear proportions 4:3 or 16:9 plus standard picture resolution numbers 704x480(576). Using those you'll calculate anything easily without overloading your memory with a collection of new numbers. Quite enough to know pixel numbers and which of the 2 ways they will be shown.
The difference with ITU is that it sets ~704 pixels (in theory 702 for PAL) instead of 720 for digitizing the active part of analog line and this limited part of image corresponds to displayed 4:3 or 16:9 image. Nothing is said there about storage of 4:3 or 16:9 image, but (sadly) general practice is that an mpeg image stored as 720x480(576) is treated as image with blank vertical fields and 16x480(576) of the stored pixels are thrown away as if it were 704x480(576) which is just an extension to mpeg storage standard for DVD. However there are devices/authored works ignoring this difference.

[EuropeanMan]

What exactly is tearing?

[thetoof]

http://en.wikipedia.org/wiki/Page_tearing

However... I don't really get why this question belongs to this thread.