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A codec is a device or
computer program In imperative programming, a computer program is a sequence of instructions in a programming language that a computer can execute or interpret. In declarative programming, a ''computer program'' is a Set (mathematics), set of instructions. A comp ...
which encodes or decodes a
data stream In connection-oriented communication Connection-oriented communication is a network communication mode in telecommunications and computer networking, where a communication session or a semi-permanent connection is established before any useful ...
or
signal In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image processing, images, and scientific measurements. Sig ...

signal
. ''Codec'' is a
portmanteau A portmanteau (, ) or portmanteau word (from "portmanteau (luggage) A portmanteau is a piece of luggage Baggage or luggage consists of bags, cases, and containers which hold a travel Travel is the movement of people between distant ...

portmanteau
of coder/decoder. In electronic communications, an endec is a device which acts as both an encoder and a decoder on a signal or data stream, and hence is a type of codec. ''Endec'' is a
portmanteau A portmanteau (, ) or portmanteau word (from "portmanteau (luggage) A portmanteau is a piece of luggage Baggage or luggage consists of bags, cases, and containers which hold a travel Travel is the movement of people between distant ...

portmanteau
of encoder/decoder. A coder or encoder encodes a data stream or a signal for transmission or storage, possibly in
encrypted In cryptography, encryption is the process of Code, encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can ...

encrypted
form, and the decoder function reverses the encoding for playback or editing. Codecs are used in
videoconferencing Videotelephony, sometimes also referred to as video teleconference or videoconferencing, comprises the technologies for the reception and transmission of audio signal, audio-video signals by users in different locations, for communication betwee ...
,
streaming media Streaming media is multimedia Multimedia is a form of communication that combines different such as , , , , or into a single interactive presentation, in contrast to traditional mass media which ...
, and
video editing Video editing is the manipulation and arrangement of video Video is an electronic Electronic may refer to: *Electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and ...
applications.


History

In the mid-20th century, a codec was a device that coded analog signals into digital form using
pulse-code modulation Pulse-code modulation (PCM) is a method used to Digital signal (signal processing), digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio ap ...
(PCM). Later, the name was also applied to software for converting between digital signal formats, including
compander After compressing, before expanding In telecommunication Telecommunication is the transmission of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defi ...
functions.


Examples

An
audio codecAn audio codec is a device or computer program capable of encoding or decoding a digital data stream (a codec A codec is a device or computer program which encodes or Decoding methods, decodes a data stream or signal. ''Codec'' is a portmanteau of ...
converts analog audio signals into digital signals for transmission or encodes them for storage. A receiving device converts the digital signals back to analog form using an audio decoder for playback. An example of this are the codecs used in the sound cards of personal computers. A
video codec A video codec is software Software is a collection of Instruction (computer science), instructions that tell a computer how to work. This is in contrast to Computer hardware, hardware, from which the system is built and actually performs the ...
accomplishes the same task for video signals. An
Emergency Alert System The Emergency Alert System (EAS) is a national warning system in the United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primar ...

Emergency Alert System
unit is usually an endec, but sometimes just a decoder. When implementing the
Infrared Data Association Infrared via USB The Infrared Data Association (IrDA) is an industry-driven interest group that was founded in 1993 by around 50 companies. IrDA provides specifications for a complete set of protocols for wireless infrared communications, and t ...
(IrDA) protocol, an endec may be used between the UART and the optoelectronics.


Compression

In addition to encoding a signal, a codec may also compress the data to reduce transmission bandwidth or storage space. Compression codecs are classified primarily into
lossy In information technology, lossy compression or irreversible compression is the class of data compression, data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to r ...
codecs and
lossless Lossless compression is a class of data compression In signal processing Signal processing is an electrical engineering subfield that focuses on analysing, modifying, and synthesizing signals such as audio signal processing, sound, image ...
codecs. Lossless codecs are often used for archiving data in a compressed form while retaining all information present in the original stream. If preserving the original quality of the stream is more important than eliminating the correspondingly larger data sizes, lossless codecs are preferred. This is especially true if the data is to undergo further processing (for example
editing Editing is the process of selecting and preparing written language, written, photographic, Image editing, visual, Audio engineer, audible, or Film editing, cinematic material used by a person or an entity to convey a message or information. T ...

editing
) in which case the repeated application of processing (encoding and decoding) on lossy codecs will degrade the quality of the resulting data such that it is no longer identifiable (visually, audibly or both). Using more than one codec or encoding scheme successively can also degrade quality significantly. The decreasing cost of storage capacity and network bandwidth has a tendency to reduce the need for lossy codecs for some media. Many popular codecs are lossy. They reduce quality in order to maximize compression. Often, this type of compression is virtually indistinguishable from the original uncompressed sound or images, depending on the codec and the settings used. The most widely used lossy data compression technique in
digital media Digital media means any media (communication), communication media that operate with the use of any of various encoded machine-readable data formats. Digital media can be created, viewed, distributed, modified, listened to, and preserved on a di ...
is based on the
discrete cosine transform A discrete cosine transform (DCT) expresses a finite sequence of data points In statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics ...
(DCT), used in compression standards such as
JPEG JPEG ( ) is a commonly used method of lossy compression In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represe ...

JPEG
images,
H.26x The Video Coding Experts Group or Visual Coding Experts Group (VCEG, also known as Question 6) is a working group of the (ITU-T) concerned with video coding standards. It is responsible for standardization of the "H.26x" line of video coding sta ...
and
MPEG The Moving Picture Experts Group (MPEG) is an alliance of working groups established jointly by International Organization for Standardization, ISO and International Electrotechnical Commission, IEC that sets standards for media coding, includ ...

MPEG
video, and
MP3 MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio Digital audio is a representation of sound recorded in, or converted into, Digital signal (signal processing), digital form. In digital a ...

MP3
and
AAC AAC may refer to: Aviation * Advanced Aircraft Advanced Aircraft Corporation is an aircraft manufacturer based in Carlsbad, California. History AAC bought out Riley Aircraft in 1983 in aviation, 1983. Products The firm has specialised in conve ...
audio. Smaller data sets ease the strain on relatively expensive storage sub-systems such as
non-volatile memory Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data. Examples of non-volatile ...
and
hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device On a reel-to-reel tape recorder (Sony TC-630), the recorder is data storage equipment and the magnetic tape is a data stora ...

hard disk
, as well as write-once-read-many formats such as
CD-ROM A CD-ROM (, compact disc read-only memory) is a pre-pressed optical compact disc The compact disc (CD) is a digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital ...

CD-ROM
,
DVD The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electr ...

DVD
and
Blu-ray Disc The Blu-ray Disc (BD), often known simply as Blu-ray, is a digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electronics is a field of elec ...

Blu-ray Disc
. Lower data rates also reduce cost and improve performance when the data is transmitted, e.g. over the internet.


Media codecs

Two principal techniques are used in codecs, pulse-code modulation and
delta modulation A delta modulation (DM or Δ-modulation) is an and conversion technique used for transmission of voice information where quality is not of primary importance. DM is the simplest form of (DPCM) where the difference between successive samples is e ...
. Codecs are often designed to emphasize certain aspects of the media to be encoded. For example, a digital video (using a
DV
DV
codec) of a sports event needs to encode motion well but not necessarily exact colors, while a video of an art exhibit needs to encode color and surface texture well. Audio codecs for cell phones need to have very low
latency Latency or latent may refer to: Science and technology * Latent heat, energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process * Latent variable, a variable that is not directly observed but inferred i ...
between source encoding and playback. In contrast, audio codecs for recording or broadcast can use high-latency audio compression techniques to achieve higher fidelity at a lower bit-rate. There are thousands of audio and video codecs, ranging in cost from free to hundreds of dollars or more. This variety of codecs can create compatibility and obsolescence issues. The impact is lessened for older formats, for which free or nearly-free codecs have existed for a long time. The older formats are often ill-suited to modern applications, however, such as playback in small portable devices. For example, raw uncompressed
PCM audio Pulse-code modulation (PCM) is a method used to Digital signal (signal processing), digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio ap ...
(44.1 kHz, 16 bit stereo, as represented on an audio CD or in a .wav or .aiff file) has long been a standard across multiple platforms, but its transmission over networks is slow and expensive compared with more modern compressed formats, such as Opus and MP3. Many
multimedia Multimedia is a form of communication that combines different such as , , , , or into a single interactive presentation, in contrast to traditional mass media which featured little to no interaction fr ...

multimedia
data streams contain both
audio Audio most commonly refers to sound In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion ( ...

audio
and
video Video is an electronic Electronic may refer to: *Electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active d ...

video
, and often some metadata that permits synchronization of audio and video. Each of these three streams may be handled by different programs, processes, or hardware; but for the multimedia data streams to be useful in stored or transmitted form, they must be encapsulated together in a container format. Lower
bitrate In telecommunications Telecommunication is the transmission of information by various types of technologies over , radio, , or other systems. It has its origin in the desire of humans for communication over a distance greater than that ...
codecs allow more users, but they also have more distortion. Beyond the initial increase in distortion, lower bit rate codecs also achieve their lower bit rates by using more complex algorithms that make certain assumptions, such as those about the media and the packet loss rate. Other codecs may not make those same assumptions. When a user with a low bitrate codec talks to a user with another codec, additional distortion is introduced by each
transcoding Transcoding is the direct digital-to-digital conversion of one encoding In communication Communication (from Latin ''communicare'', meaning "to share") is the act of developing Semantics, meaning among Subject (philosophy), entities or Org ...
.
Audio Video Interleave Audio Video Interleave (also Audio Video Interleaved), known by its initials AVI and the .avi filename extension A filename extension, file extension or file type is an identifier specified as a suffix to the name A name is a term used for i ...
(AVI) is sometimes erroneously described as a codec, but AVI is actually a container format, while a codec is a software or hardware tool that encodes or decodes audio or video into or from some audio or video format. Audio and video encoded with many codecs might be put into an AVI container, although AVI is not an
ISO standard The International Organization for Standardization (ISO ) is an international standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization develops and publish ...
. There are also other well-known container formats, such as
Ogg Ogg is a free, open Open or OPEN may refer to: citizen * Open (band), Australian pop/rock band * The Open (band), English indie rock band * ''Open'' (Blues Image album), 1969 * ''Open'' (Gotthard album), 1999 * ''Open'' (Cowboy Junkies ...
, ASF,
QuickTime QuickTime is an extensible multimedia framework A multimedia Multimedia is a form of communication that combines different content forms such as text, audio, images, animations, or video into a single presentation, in contrast to traditi ...

QuickTime
,
RealMedia RealMedia is a proprietary multimedia container format (digital), container format created by RealNetworks. Its extension is ".rm". It is typically used in conjunction with RealVideo and RealAudio and is used for Streaming media, streaming content ...
,
Matroska The Matroska Multimedia Container is a free, open-standard container format, a file format ogg-file: 154 kilobytes. A file format is a standard way that information is encoded for storage in a computer file. It specifies how bits are use ...

Matroska
, and DivX Media Format.
MPEG transport stream MPEG transport stream (MPEG-TS, MTS) or simply transport stream (TS) is a standard digital container format A container format (informally, sometimes called a wrapper) is a file format that allows multiple data streams to be embedded int ...
,
MPEG program stream Program stream (PS or MPEG-PS) is a container format for multiplexing digital audio, video and more. The PS format is specified in MPEG-1 Part 1 (ISO/IEC 11172-1) and MPEG-2 Part 1, Systems (ISO/IEC standard 13818-1/ITU-T H.222.0). The MPEG-2 Pro ...
, MP4, and
ISO base media file format ISO/IEC base media file format ( ISO/ IEC 14496-12 – MPEG-4 Part 12) defines a general structure for time-based multimedia Multimedia is a form of communication that combines different content forms such as text, audio, images, animations, ...
are examples of container formats that are ISO standardized.


Malware

are used when an online user takes a type of codec and installs viruses and other
malware Malware (a portmanteau for malicious software) is any software intentionally designed to cause disruption to a computer, server (computing), server, Client (computing), client, or computer network, leak private information, gain unauthorized acc ...

malware
into whatever data is being compressed and uses it as a disguise. This disguise appears as a codec download through a pop up alert or ad. When a user goes to click or download that codec the malware is then installed on the computer. Once a fake codec is installed it is often used to access private data, corrupt an entire computer system or to keep spreading the malware. One of the previous most used ways to spread malware was fake AV pages and with the rise of codec technology both have been used in combination to take advantage of online users. This combination allows fake codecs to be automatically downloaded to a device through a website linked in a pop up ad, virus/codec alerts or articles as well.


See also

*
Audio signal processing Audio signal processing is a subfield of signal processing that is concerned with the electronic manipulation of audio signals. Audio signals are electronic representations of sound waves—longitudinal waves which travel through air, consisting ...
*
Comparison of audio coding formats The following tables compare general and technical information for a variety of audio coding format An audio coding format (or sometimes audio compression format) is a content representation format for storage or transmission of digital audio ...
*
Comparison of video codecsΑ video codec is software Software is a collection of Instruction (computer science), instructions and data (computing), data that tell a computer how to work. This is in contrast to Computer hardware, physical hardware, from which the system ...
* Comparison of video container formats *
Digital signal processing Digital signal processing (DSP) is the use of digital processing Digital data, in information theory and information systems, is information represented as a string of discrete symbols each of which can take on one of only a finite number of ...
*
List of codecs The following is a list of compression formats and related codec A codec is a device or which encodes or a or . ''Codec'' is a of coder/decoder. In electronic communications, an endec is a device which acts as both an encoder and a decoder ...
*
List of open-source codecs This is a listing of open-source codecs—that is, open-source software Implementation#Computer_science, implementations of audio coding format, audio or video coding format, video coding formats. Many of the codecs listed implement media formats t ...


References

{{Compression Methods
Digital signal processingDigital signal processing (DSP) is the study of signal processing, signals in a Digital data, digital representation and the processing methods of these signals. DSP and analog signal processing are subsets of signal processing. It has three major su ...