Pixel Aspect Ratio — Video resolution of 1440×1080 considered a widescreen format 16:9 ?

Camcorders sometimes offer to record video in 1440×1080 besides of full HD 1920×1080 mode.
Both can deliver an outcome of a 16:9 (widescreen) frame aspect ratio.

Confusing is that 1440 divided by 1080 results in: 1.33333333333 which is the classic 4:3 (~1.3333333) format but definitely not 16:9 widescreen (1.7777777777778).

The explanation:

Besides of the Frame Aspect Ratio the pixel aspect ratio is the important thing.

Pixel Aspect Ratio == pixel width (x) in relation to pixel height (y)

Pixels can be square or rectangular: a square pixel has the aspect ratio of 1:1 (aka 1) but a rectangular pixel can be anything else.

In the case of the 1440×1080 resolution we have RECTANGULAR pixels which are wider than high, to be precise, their pixel aspect ratio is 1.333333333 : 1.

Multiply 1440 with 1.3333333 == 1920

Multiply 1080 with 1.0 == 1080

So you get a frame aspect ratio of widescreen 16:9 (1920×1080) — done with rectangular pixels.

Details:

How is the pixel aspect ratio calculated?

You need to know the video resolution (widthVideo by heightVideo) and the frame aspect ratio, defined by width x and height y ( xF:yF ). F is here just a symbol for frame.

The formular is:

(xF * heightVideo) / (yF * widthVideo) == Pixel-Aspect-Ratio X / Pixel-Aspect-Ratio Y

In our example we have a resolution of 1440 by 1080

and

a frame aspect ration of 16:9

(16 * 1080) / (9 * 1440) == 4 / 3 which is : ~1.333333 / 1 which results in a pixel aspect ratio of decimal : ~1.333333

Modern digital world computer screens and HD televisions

On Computer screens and in digital processing pixels are in general SQUARE. Only for conversion scenarios software is able to deal or output rectangular pixels.

Modern HD TV’s use fortunately square pixels and therefore a video that was rendered for a computer screen should display normal on a TV screen. However, if the TV screen is older and/or uses rectangular pixels then your video would either be displayed stretched or squished OR the TV displays it in between black bars on top/bottom or left/right.

Let’s define following general rules:
if an image has 640×480 pixels then those pixels are all square pixel.

IMAGES: if an image has 640×480 pixels then those pixels are all square pixel.

DIGITAL VIDEO:

Full HD 1920×1080 video uses also square pixels.

HDV 1440×1080 video uses rectangular pixels with an ratio of 1.333333.

TV:

Modern digital HDTV 1080p uses square pixels.

Older digital TV (non-HD) uses rectangular pixels.

PAL, NTSC, SECAM: those are ANALOG TV systems and they do not use pixels but analog signals in an interlaced manner.

Glossary: some video editing terms

Pixel Aspect Ratio == pixel width (x) in relation to pixel height (y)

Frame Aspect Ratio is also called Display Aspect Ratio. The term Frame describes in the photography and video world a single picture, i.e. the area of what you see in a picture. A photographer ‘frames’ a motif, i.e. decides how much of the motif will be seen on the picture. Imagine that you hold an empty picture frame in front of you and look through it.