[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.
On playback, players will resize to the PAR of the display which usually is 1:1.

Cu Selur