Re-sizing DVD rips properly

[Tatsukun]

I have ripped the DVD to my HD and indexed it with DGIndex which reported it as 720x480 at 4:3 [2]. However, 720x480 is not 4:3 so I asked around some other places and was told various things such as:


Resize to 640x480
Resize to 654x486
Leave at 720x480 and use this (http://ps-auxw.de/cgi-bin/ar-calc.pl) to figure out SAR to set

#1 seems to be the most common answer, #2 just confuses me, and #3 feels most accurate but would result in a larger file size. It seems like when I do #3 the actual size is very close to 656x480 which isn't terribly off from #2. Is it worth encoding at 720x480 and setting SAR versus just encoding at 656x480? Most videos I have seen are just done in 640x480, but that doesn't necessarily mean it's correct so I was hoping someone could help clear this up for me.

Thanks.

[sneaker_ger]

If you resize to 640x480 or 654x486, you will lose horizontal resolution. Better to go with #3, though most people just use the following table for SAR instead of the complicated stuff on that website:
http://h9.abload.de/img/anamorph_sarqkx0r.png

It doesn't necessarily mean that it "would result in a larger file size", as bitrate can be arbitrarily chosen (within certain limits) by pretty much every encoder.

While not doing any resizing to keep the complete resolution, you may want to crop any black borders (this does not change the SAR).

[hello_hello]

What format are you wanting to convert to? Xvid/AVI or x264/MKV etc? Usually square pixels are used when converting to AVI (as most AVI capable DVD players only support square pixels) while when converting to x264/MKV anamorphic encoding is often used (which is basically encoding using the same shaped pixels as the DVD while setting the display aspect ratio to match). The idea behind the second method is you don't loose resolution as you do when resizing "down" to square pixels.
Where it gets confusing is there's two ways to resize a DVD which give you slightly different aspect ratios. Straight 4:3 resizing gives the DVD a 1.3333 (4:3) aspect ratio, while the official ITU resize method gives you around a 1.366 aspect ratio. Similarly two aspect ratios can be used for 16:9 DVDs. Then when you've picked the aspect ratio to use you've either got to resize it down to square pixels or set the output aspect ratio when converting etc.

Until you get your head around it, I'd recommend maybe using an encoder GUI which does the thinking for you. Or you can have a play with this resize calculator. http://www.mediafire.com/?09v9bldu9a6hm00 It's designed for calculating the cropping/resizing when converting to square pixels, although if you're setting the aspect ratio when encoding instead, it'll calculate that for you too.

As an example.... you'll see for DVD resizing there's an ITU option. Whether you select it or not will change the result. For example for 4:3 NTSC DVDs, with the ITU option de-selected, then 640x480 is a perfect resize. If you select the ITU option and still resize to 640x480 then you need to crop about 8 pixels from each side of the video in order not to distort the picture. If you don't crop, then 656x480 is the better fit.
Personally, I virtually never use ITU resizing as while it's the "official" way to resize a DVD, in my humble opinion very few of them use it.

Anyway, have a play with the calculator to see if it helps, or confuses you more. ;)

[Atak_Snajpera]

ripbot264 will do that for you using regular math rules. i'm also not big fan of so called itu resizing.

[Tatsukun]

Hello, thanks for the replies.

I am trying to use the x264/MKV format. In my AVS script I have cropped 4 pixels from both sides for a final resolution of 712x480. Using the calculator posted in my initial post this results in a (P)SAR of 4320/4739, which is very close to he 10/11 suggested by sneaker_ger.

So I guess I'll just take that 712x480 final video and set the SAR to 4320/4739 as suggested by the calculator. This will also end with the 1.366 aspect ratio you mentioned. The only thing I'm not sure about now, is do I resize back to 720x480 and then set the SAR, or leave it at 712x480?

If I misunderstood anything please let me know also. I'm not terribly new to encoding, I've just never bothered much with DVDs and perfect square ratios before.

[sneaker_ger]

The only thing I'm not sure about now, is do I resize back to 720x480 and then set the SAR, or leave it at 712x480?

Leave it at 712x480.