I just have one or two more things to add:
First, the word anamorphic comes from photographic film, where it means something that isn't stored in the correct way, but is distorted in one way or another. With this definition
ALL DVD's are anamorphic.
Secondly, MPEG has defined two more DAR as valid for MPEG-2 streams. These are
20:9 and
PAR=1. The later would be the MPEG equivalent of AVI's way of defining aspect ratio as width/height. The former on the other hand is more interesting. We all know that 4:3 and 16:9 is movie formats used on the silver screen long before TV (and DVD) . But 20:9? If you look at
IMDB you will find less than 100 DVD's with aspect ratio between 2.00:1 and 2.34:1. Why not use 2.35:1 as this is the most common format? Simply because it should be easy to convert between formats!
20:9 = (16:9) * (5:4) MPEG actually states that these formats are used so it shall be possible to just drop lines and add letterboxing in order to change between formats.
Code:
From\To 4:3 16:9 20:9
4:3 x 1/4V 2/5V
16:9 1/4H x 1/5V
20:9 2/5H 1/5H x
x= No change.
k/mV= Drop Vertical lines (
k lines dropped out of every
m) and add black bars at the sides
k/mH= Drop Horizontal lines (
k lines dropped out of every
m) and add letterboxing at top/bottom.