About aspect ratios
An aspect ratio describes the proportional relationship between a rectangle's width and height. Common ratios include 16:9 (widescreen video), 4:3 (traditional TV and monitors), 1:1 (square), and 3:2 (35mm film). The simplified ratio is found by dividing both dimensions by their greatest common divisor (GCD).
To scale an image or video, keep the ratio constant: new height = original height x (new width / original width).