Aspect Ratio and Video Resize

[Russell_hq]

I have a PAL avi which is 640x352, so almost 16:9 and far from 4:3.

Having read the doom9 guide:
http://www.doom9.org/index.html?/mpg/cce270.htm

I tried it out and seems to produce fine results but got me thinking that I could do it the other way because doing it that way made a 4:3 DVD whereas my source is more 16:9.

PAL dvd is 720x576, 16:9 DAR flag would stretch this to 1024x576.

To scale up the width to 1024 I multiply by 1.6 so to scale up the height I multiply 352*1.6 to get 563.2. Round up to 564. So I need some black boarders. 576-564 = 12 Thus only bars of 6 pixels need to be added to the top and bottom.

So I write an avs script:

AviSource("F:\test.avi")
Lanczos4Resize(720,564)
AddBorders(0,6,0,6)

Then encode with a 16:9 DAR.

I can then use this to produce a proper 16:9 DVD. If I do it the doom9 way I have to make a 4:3 dvd to get a proper picture.

As a newbie to this, I may be missing some things so if someone would read over this and give some comments, I would be very greatfull.

[guns1inger]

You have missed some fundamentals along the way. The biggest thing you have missed is the fact that TV pixels are not square. On the PC, AVI files generally have a Pixel Aspect Ratio of 1:1 - i.e. square. Television pixels are not square, and each format and AR combination has a different pixel aspect ratio.

Have a look at either FitCD or Paranoia to see how these programs calculate their numbers. It's not quite as simple as you think.

[Mr_Odwin]

If the resize looks fine to you then that's all that matters really. Whenever I do stuff like that I open the avisynth script up in virtualdub and check it out. Also, you could try enooding just a small sample of the clip and test it out on your tv.

[Baldrick]

you can also use fitcd and let it calculate the resizing and make the avs script.

edit: guns1inger already mentioned it...

[Russell_hq]

Yeah, I tried out FitCD, but I like to know whats going on in the background instead of just trusting an application like this for resizing so when I couldn't figure out whey FitCD gave different numbers from my calculation I wanted to find out why

[guns1inger]

Have a read of this -> http://www.mir.com/DMG/aspect.html

Especially the Handy Reference Table. This was my key reference when I wrote my own resize app (see my sig)

The tip about using virtualdub to check your sript is a good one as well. You can right-click on the preview screen and change the aspect ratio to 4:3 or 16:9 to see how it will look with the correct pixel aspect ratios applied. Try to find some scenes with wheels or other round objects - you will soon know if you have distorted things.