[INFO] About pixel aspect ratios,..

[Selur]

We differentiate between three types of aspect ratio:
Display Aspect Ratio (DAR): the aspect ratio of the image as displayed.  ('4:3', '16:9', '16:11',...)
Storage Aspect Ratio (SAR): which is the ratio of pixel dimensions.  ('720:480','720:576','1920:1080')
Pixel Aspect Ratio (PAR): which is ratio of the pixels themselfes.  ('1:1', see below tables)

Here's how these three relate to each other: SAR × PAR = DAR
Meaning: If you multiply the shape of the pixels with their dimensions you get the display aspect ratio.

Since in video and image processing people can't make it simple there have been a lot of pixel aspect ratios definitions over the years, since the most common you will encounter are either the MPEG-4, ITU-R 601 or Generic defined values I will only list these:

MPEG-4:  (common for MPEG-4 based content)

DAR	PAL	NTSC
4:3	12/11	10/11
16:9	16/11	40/33

ITU-R 601:  (common for analog content)

DAR	PAL	NTSC
4:3	1150/1053	38800/42651
16:9	4600/3159	155200/127953

Generic:  (common for MPEG-2 based content)

DAR	PAL	NTSC
4:3	16/15	8/9
16:9	64/45	32/27

and the most common as pixel aspect ratio: Square Pixel 1:1, which means that the DAR and the PAR are the same.

Side note:
Is content is encoded with a pixel aspect ratio that is not 1:1 it's called anamorphic.
A good read about the topic is The Ultimate Guide to Anamorphic Widescreen DVD (forDummies!) by Bill Hunt from The Digital Bits.

Cu Selur