What is a Codec? Clarifying concepts

Speaking of multimedia terminology, there is a fairly widespread confusion between the concept of image and / or sound format and that of audio and / or video container format (also called multimedia container format) To finish bundling it, it is very common to refer to both with the term codec that does not express any of the two previous concepts.

The image, video, audio format… is the way in which this type of information is encoded so that it can be treated by computer, which includes both being able to store it and transmit it. That format, therefore, would be a series of rules to describe images and sound in a computer way; a mathematical model, if you want to see it that way.

A codec (or codec, with tilde, in its Spanish version) is a program that encodes or decodes multimedia information according to a certain format. Once the data is encoded, it can be processed, for example stored or transmitted. As you may have guessed, the word codec is an acronym formed by the English words coder and decoder: encoder and decoder in Spanish.

An audio / video container format (or multimedia container format) is a computer file structure according to which audio and / or video is stored or transmitted as well as information associated with them (such as subtitles or bookmarks) The same container You can include together (multiplexed) the different components (tracks) in a single document. It is very common to add an extension to the name of the documents (those few letters that are at the end of the name separated by a period) that usually refer to the type of document. If you are rigorous in establishing that extension, it can serve as a clue to know which container is the document.

Considering the above, we could say that the document «feature film.avi» is a container in AVI format that includes video in MPEG4 format encoded using the Xvid codec. As the orthodox version is a very long phrase, it is common, for example, to say colloquially that the document “short.avi” is an MPEG4: it is obvious that it is an AVI container and everyone will know what codec has installed in their system for what formats

Most of the time, when packaging the information according to a certain format, it is compressed, that is, it is transformed so that the resulting information requires less memory to be stored or less bandwidth when transmitted than the original information.

There are two ways to compress information, with or without losses. Lossless (or lossless) formats allow you to reconstruct the information as it was originally, before compressing, without any difference from the original. In most cases the lossless coding usually allows (much) less compression (takes up much more) and is reserved for the documents that are going to be edited, that is, that they are not final documents.

The most frequent image and sound coding is with losses (lossy) Of course, the coding system seeks to make these losses as less noticeable as possible, considering for this, for example, the movement (What changes the image between a frame and another) The level of quality-compression is usually configurable so you can choose the degree you want between occupying more and having more quality. In line with what has been said about lossless formats, it is not a good idea to code according to a material loss format that is going to be edited since the successive recompressions cause more and more quality information to be lost to images and sound. Do not compress again and again using a lossy format!

One moment, you said that it is better to encode the original material using a lossless format but also that it will take up more. Then I must give the button on my camera that records video without compression? For starters, unfortunately, it is quite rare for your camcorder to have that button (in those of taking pictures and in audio systems it is something that is usually possible) Only in some cameras you can do something like that, they will usually be professionals and of the highest range. On the other hand, be prepared to spend a lot of memory and quickly, since you will need to store a lot and at full speed. So, what should I do? Our advice is that you choose, if you can, the best possible quality, even with losses, for the images you are going to edit and suitable for those that do not require more editing than the “cut” assembly since, properly processed , does not have to be compressed again.