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Video Terminology Basics 101, Part 3 - Compression

In the last article I talked about video "size" and how that tricky word refers to both video image size (called resolution) and video file size. File size is closely tied to the topic of this week's article: compression. Compression, like most basic video terminology, is actually somewhat simple, but can seem a little confusing at first.

When a video guy talks about making a video file "smaller", most of the time this is in reference to the file size, not the resolution. Compression is how one decreases the file size of a certain piece of video content. The advantages of this, while once huge, are diminishing slowly as technology improves and computers get faster. But, for at least the foreseeable future, compression is still a big and relevant topic, especially when talking about video content tailored for streaming on the Web.

The issue of compression arises out of what a video really is in its basic form: a series of images played back at a certain rate to create the illusion of movement. A good way to think of it is a film reel with a bunch of images—in film they're called frames—played back at a specific rate. The trouble is that for a long video that's a lot of frames. Video ranges between 24 and 30 frames per second. So a single minute of footage can be 1800 or more individual images. An hour is over 100,000 images! And a single digital image can be pretty large as far as file size goes. In a basic sense, that's what uncompressed video is: a sequence of independent images played back at a defined rate, and it can make for massive files just because of the sheer number of frames.

This creates a problem because uncompressed files are so big that they don't play back well on slower computers, they take forever to transmit digitally, and take up a massive amount of hard drive space. So the need quickly arose for far smaller files of the same content while somehow not compromising the quality of the footage. That's essentially what compression is. It's making a big file small with the goal of reducing the visual quality (how it looks to the human eye upon playback) as little as possible. In the early days, compression was lousy, but nowadays it's pretty remarkable. A compressed file can be created that is only a tiny fraction of the original uncompressed file size and yet looks indistinguishable to most viewers.

Here's another fancy word for you: codec. A codec is the math magic used to pull off a certain type of compression. It doesn't matter how, it's just good to know that it does. Today, among video professionals, this has been nearly standardized to H.264 (though H.265 may overtake it). It doesn't matter to you what those letters and numbers stand for, all that matters is that H.264 is a great way to make a very large file turn into a very small file and still look really good and play back smoothly.

Hopefully, if you didn't know anything about video compression, this will give you some idea of the basics. The next article in this series will about aspect ratio, another tricky area of video that people often find a little confusing.

Filed Under: general

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