Codec is a blended word, created by combining the words compress and decompress. The short version was defined to make the process of preparing digital media easier to talk about by using a single word to describe it. So basically it provides instructions on how to compress content and then decompress it so it can be viewed.
There have been many versions of codecs in the decades since it was first defined. Internet bandwidth has increased significantly, but so has the demand for HD video and audio streaming. This constant battle between demand and availability drives the creation of better technology to send more, better quality content in less space.
Audio and video have different codecs, even the final output is a single file. H.264, VP9, and H.265 are currently the most widely used video codecs. AAC and MPEG Audio Layer 2 are examples of audio codecs.
Codecs can be lossless or lossy. Lossless means that when a compressed file is decompressed, it contains all the original data. So no data is “lost” in the process. Lossy compression makes a file smaller by removing parts of the data. Usually the algorithms choose to remove duplicate data, or in other data that isn’t detectable by humans after it is decompressed.
File formats are not the same as codecs, though the terms are commonly misused that way. File formats are containers that may contain a variety of different codecs. For example, MP4 files contain both audio and video information, each compressed using different codecs.
It’s easy to remember the difference by knowing that the codec does all the work in preparing the data, and the container (file format) is just how it’s all bundled together.« Back to Glossary Index