Video Terminology Basics 101, Part 4 - Aspect Ratio
In this series of articles, I've been reviewing various tricky terms in video. Like any discipline, video has its own insider vernacular that sounds more complex to outsiders than it actually is. I've already covered two very different video terms related to "size": resolution and compression. Now it's time to talk about aspect ratio, something that often gets confused with size but has everything to do with shape.
(As with the previous topics I've covered, experts will tell you that it's a little more complicated than what I share below, and they're right, but the point of these articles is to clear up common misunderstanding, not to write a textbook. So, while a tad oversimplified, this should help clear things up for novices wanting basic familiarity with this topic.)
The best way to avoid confusion when hearing the term "aspect ratio" is to think of it as synonymous with shape, not size, and always a rectangular shape. So aspect ratio is the rectangular shape of a video. You may remember what a ratio is from math class, but as a quick refresher, ratios are ways to compare two terms relative to one another. In the video world they are always expressed with a colon between two digits. 4:3 and 16:9 are two common examples.
Since aspect ratio can best be imagined as the rectangular shape of a video, you likely already guessed that the two numbers represent the length and the width of the rectangle. The first number represents the length. The second represents the height. So a perfect square of video would be 1:1. The most common aspect ratio in video nowadays is 16:9. What 16:9 means is that for every sixteen horizontal units of length, there are always nine vertical units of height. This is independent of whether we're talking inches, feet or miles. In other words, the aspect ratio defines a locked-in rectangular shape, regardless of a video's size. Old TV aspect ratio was 4:3, which looked much more square than the wider 16:9 standard of today. This is why old sets have a very square shape and new flat screens have a much wider display.
When you go to a movie theater, you may have observed that in some cinemas, the black curtains move to the side just before the feature starts, effectively elongating the shape of the screen. This is to accommodate a wider aspect ratio that many movies are shot and projected in. The most common of these aspect ratios is 2.39:1, which is noticeable wider than 16:9. This is also why when you play back some movie trailers on a 16:9 shaped screen, like a iPhone 5 or newer laptop, there will sometimes be a black bar at the top and bottom of the video. This is simply because the wider 2:39:1 shape needs to be shrunk down to the 16:9 box it's playing in without being squished or stretched, thus the black bar on the top and bottom of some videos and the mysterious movement of the curtains at the multiplex.
As a quick recap, aspect ratio is the rectangular shape of a video, independent of its size. The first number stands for the length. The second number is the height. The bigger the first number (relative to the second), the wider the rectangle. In the final article, I'll talk about footage and hopefully clear up some of the confusion associated with it.
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