Aspect ratio, bars, cropping, resizing

[Kangiten]

Greetings, everyone :)

I want to convert one of my DVDs to Xvid using VirtualDubMod. The problem is that the box of the DVD doesn't specify the exact display aspect ratio of the movie (just 16/9).
What I want to do is to crop the black bars and then resize the movie to a proper aspect ratio. Therefore, I have a couple of questions

1) Should I crop before resizing or resize before cropping ?
2) Is there a way or tool for determining the exact aspect ratio of the film ? If not, should I just use "16/9" as aspect ratio (and crop the entire image area to fit it ?)

Am I totally wrong ? Does it even make sense ? :D

I apologize if these questions have been answered before.

Thanks for any input.

[killingspree]

hi and welcome to the forum
1) crop befor resizing
2) well apart from determining the right AR you should primarily see that you get at least a mod 16, even better a mod 32 resolution. this is required for effective mpeg4 encoding. it will always a slight aspect error, but in a range where you won't even be able to recognise it!

as a general hint i would recommend you to first try to use gordianknot, befor you do the whole process manually. it pretty much takes care about the AR problems for you and let's you familiarize with the process...

even easier would of course be AutoGK but it won't let you take a close look at what is happening behind the curtains.

hth
steVe

[jggimi]

A DVD doesn't have square pixels. It has a fixed resolution (720x480/576), and will have a Display Aspect Ratio of either 4:3 or 16:9. But films have all sorts of aspect ratios. So DVD producers will add letterboxing to produce a DVD with either a 4:3 or 16:9 DAR.

When we convert these to .avi, we typically resize with square pixels. As long as we trim letterboxing away, and get the Display Aspect Ratio right, then our .avi files will have correct aspect ratios.

However, as Steve mentioned, we usually resize to values divisible by 32 or 16, to maximize video compressibility and to preclude problems with some video cards. This limited resizing can introduce small, usually unnoticable errors in aspect ratio. GK will show you that aspect error.

If you want to check the original aspect ratio of a film, you can look it up at The Internet Movie Database (www.imdb.com), and then click on the "technical specs" link.