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What is a codec? – clearly explained

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Codecs are crucial to the quality and efficiency of data encoding. In this practical tip we explain exactly what a codec is.

What is a codec? – 10 facts

The following information will help you understand what a codec is. The following example shows the differences between format, encoder, and decoder and shows how quality and efficiency depend on the codec.

-A codec is a combination of encoder and decoder.
-The objective of a codec is usually to reduce the amount of data for transmission or storage.
-Codecs are used in particular for audio, video and image data, as well as for text compression and encryption.
-In the audio sector there are special codecs for voice or music. -Video and graphics codecs are specially designed for comics / cartoons and real pictures / movies.
Lossy data reduction primarily uses psychophysical tricks to inaccurately encode those parts of image and sound that humans can barely or barely perceive.
-The most popular audio codecs are FLAC and MP3, where FLAC specifies both the format and the codec. MP3 is a codec for audio in MPEG I or MPEG II format.
-The MP3 decoder side is standardized by Fraunhofer and can be obtained without a license. However, the encoder is paid. Therefore, many use the free LAME encoder.
-G.722.2 and Full Rate (FR) voice codecs are used especially in telephony.
-The most popular video codecs are H.265 for UHD TV, DivX and XviD in MPEG-4 Part 2 and H.264 for QuickTime.
-Often various encoded formats like MP3 and JPG are combined into one container file, for example in AVI, MKV, MP4 and FLV.

A simple codec example

The principle of a codec is clarified with an example. An abbreviation codec reduces typed text to abbreviated text and uses it to generate typed text:

-Format: Your digital font format might dictate how all the letters and characters you use are encoded in binary.
-You define the type of encoding in a specification, for example, the rule that each character consists of 8 bits. To do this, write a table showing which bit sequence is assigned to which letter or character.
-Codec: You can now create an abbreviation codec to convert typed text into font formatted abbreviated text.
-To do this, your codec must specify which words will be abbreviated and how, for example, through a set of rules, a large list of abbreviations or a combination.
Encoder – An encoder can now convert typed text to abbreviation format using the rules and directory.
Decoder: a decoder can convert it to written text.
-The efficiency of data reduction is highly dependent on your codec.
-If you only created a directory with three abbreviations, most of the texts will not be noticeably shorter. Compression is low.
-If your list of abbreviations is huge, the device that is going to encode and / or decode the text must have a large memory and a high reading speed.
-However, if you set up a smart set of rules for encoding, your codec is ideally small and the end device doesn’t have to do a lot of computing or reading work.
-If a word can be abbreviated in more than one way, that’s fine. A good encoder would use the most efficient abbreviation.
-However, if an abbreviation can have multiple meanings, you have lost information. This will probably render your codec unusable.
-However, if only the words that you know you are omitting were abbreviated ambiguously, you would have invented a lossy psychophysical encoding. This takes advantage of the fact that you do not visually perceive every existing word optically.
-This idea is not entirely false. Because, as this example shows, we don’t necessarily read exactly what is written.

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How do the audio and video codecs work?

For what purposes and how are codecs used?

Let’s start with the analysis of the name that is the result of the union of two words CODer and DECoder. In fact, through the codecs it should be possible both to decode multimedia, audio or video files, as well as to create them.
In reality, codecs do not always allow file creation and the reason is often legal or commercial in nature.

Its internal functioning is usually very complex, due to
to the nature of the processing they must perform. While the
The purpose is to allow the expansion capacity of the different players, so that they can see or let us listen to the content of the files written in a format that they did not understand at the time of their launch.

Regardless of the file format, the content is always the same, that is, a movie or audio, intended to be played.
So it was decided to introduce an additional software layer between the file and the player, which filters access to the file itself and that
always makes the player “see” the same type of object even if the file format varies.

In order to use codecs, you first need to know
its existence, which is why in Windows systems there are
parts of the log file, which collect information
on the different multimedia filters installed. Generally, your
Interaction with players is done through COM interfaces.
Simply put, when we tell our favorite player to open a media file, it will do nothing more than retrieve the list of installed codecs and try to open the file with
each. If one of the codecs is successful, the player will use it
to show us or listen to the file.

As we have seen, its use is completely transparent for the user and is completely managed by the player. Some players even manage the installation of the necessary codecs. However, it is also possible to install them manually. On Windows systems, codecs that use COM technology are generally in the form of DLLs that must be registered, a procedure that involves entering all public interfaces of the codec in the registry file.
To do this, you need to run the command
“Regsvr32 <dll name>” while uninstalling it
just add the “/ u” option to the first command.

Other operating systems use some interprocess communication mechanism other than COM, but the structure does not change. That is, it is always a filter to access the file.

The existence of different formats and related CODECs arises for technical and commercial reasons. Different multimedia companies usually prefer to define their own encoding formats, to optimize their use by their applications.
And in addition to this, by defining their own format, they are not obliged to pay user licenses
. This mainly applies to file generation; in fact, many codecs are simply decoders.

In this way, companies can add read support for various formats to their applications at no additional cost, while using their proprietary format for saving.

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.