1. Video ratios: Aspect ratio is defined as the ratio of width to height of an image.
4:3 For every 4 inches wide you would have 3 inches high.
16:9 For every 16 inches wide you would have 9 inches high and so on.
The ratio has to be defined to make shapes fit into different and distinct mediums, such as computer, movies, television and camera screens.
Aspect Ratio
Uses
TVs
4:3
1.33:1
Standard Channels
Old TVs
16:9
1.77:1
HD Channels
The majority of HDTVs
21:9
2.35:1
Most movies
Very few TVs

2. History of the 4:3 Aspect Ratio
The 4:3 aspect ratio has been around since 1940's and 1950's.
A television that has an aspect ratio of 4:3 is often referred to as being NTSC, or pan and scan.
Most analogue cable channels still broadcast in 4:3.

3. History of the 16:9 Aspect Ratio
The 16:9 aspect ratio is a product of movie producers.
They wanted to find a way to make their movies bigger and better to attract more customers.
The widescreen format of the 16:9 aspect ratio allows users to view a bigger picture compared to the 4:3 aspect ratio.
The 16:9 aspect ratio also enhances the quality of the image by allowing for bolder backdrops and scenery.
The 16:9 aspect ratio is not as wide as you would see in a cinema, but it is close.

4. Difference in Television Watching
Both the 4:3 aspect ratio and 16:9 aspect ratio are popular today.
A 4:3 aspect ratio produces a more box-like picture, because the screen is only slightly wider than it is high.
A 16:9 aspect ratio produces a widescreen, or letterbox, picture. If you are watching only analogue cable, a 4:3 aspect ratio is for you. A 16:9 ratio is the standard aspect ratio of HD televisions, so you need a television that is compatible with the 16:9 aspect ratio to benefit from a high definition picture.