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What is Aspect Ratio?

Aspect ratio expresses the proportional relationship between a frame’s width and height, using values such as 4:3 or 16:9. It describes shape independently of the frame’s pixel dimensions.

How Aspect Ratio works

A ratio reduces two frame dimensions to a proportional shape, so 1920×1080 and 1280×720 share the same geometry despite different resolutions. Display aspect ratio describes the visible frame, while pixel aspect ratio describes the shape of individual samples; confusing them can distort older video. Media pipelines use the value when deriving renditions, reserving layout space, and selecting crop or letterbox behavior.

Key facts

  1. Equivalent notations such as 16:9, 1.78:1, and a width divided by its height describe nearly the same frame shape, although rounded decimal forms can lose precision.
  2. Rotating an asset by 90 or 270 degrees swaps width and height and inverts the ratio without changing pixel count; a 180-degree rotation preserves the ratio, and arbitrary angles that expand the canvas change the frame shape differently.
  3. For video with non-square pixels, stored width divided by stored height is not necessarily the display ratio; sample-aspect metadata must be applied during presentation.

When Aspect Ratio matters

Use the ratio to size containers and choose whether an asset should be cropped, fitted, or padded. Changing width and height independently can stretch subjects or break layout assumptions.

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