A codec is a computer
hardware or
software
Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications.
The history of software is closely tied to the development of digital comput ...
component that encodes or
decodes a
data stream or
signal
A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology.
In ...
. ''Codec'' is a
portmanteau
In linguistics, a blend—also known as a blend word, lexical blend, or portmanteau—is a word formed by combining the meanings, and parts of the sounds, of two or more words together. of coder/decoder.
In electronic communications, an endec is a device that 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
In linguistics, a blend—also known as a blend word, lexical blend, or portmanteau—is a word formed by combining the meanings, and parts of the sounds, of two or more words together. of encoder/decoder.
A coder or encoder encodes a data stream or a signal for transmission or storage, possibly in
encrypted form, and the decoder function reverses the encoding for playback or editing. Codecs are used in
videoconferencing,
streaming media
Streaming media refers to multimedia delivered through a Computer network, network for playback using a Media player (disambiguation), media player. Media is transferred in a ''stream'' of Network packet, packets from a Server (computing), ...
, and
video editing applications.
History
Originally, in the mid-20th century, a codec was a hardware device that coded analog signals into digital form using
pulse-code modulation (PCM). Later, the term was also applied to software for converting between digital signal formats, including
companding
In telecommunications and signal processing, companding (occasionally called compansion) is a method of mitigating the detrimental effects of a channel with limited dynamic range. The name is a portmanteau of the words compressing and expandi ...
functions.
Examples
An
audio codec 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 is the codecs used in the sound cards of personal computers. A
video codec accomplishes the same task for video signals.
When implementing the
Infrared Data Association
IrDA is a wireless standard designed for exchanging data using infrared (IR). Infrared ports for this purpose have been implemented in portable electronic devices such as mobile telephones, laptops, cameras, printers, and medical devices. The mai ...
(IrDA) protocol, an endec may be used between the
UART and the
optoelectronic systems.
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 codecs and
lossless codecs.
Lossless codecs are often used for archiving data in 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, Image editing, visual, Audio engineer, audible, or Film editing, cinematic material used by a person or an entity to convey a message or information. The editing p ...
) 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
In mass communication, digital media is any media (communication), communication media that operates in conjunction with various encoded machine-readable data formats. Digital content can be created, viewed, distributed, modified, listened to, an ...
is based on the
discrete cosine transform (DCT), used in compression standards such as
JPEG
JPEG ( , short for Joint Photographic Experts Group and sometimes retroactively referred to as JPEG 1) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degr ...
images,
H.26x 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 ...
video, and
MP3 and
AAC audio. Smaller data sets ease the strain on relatively expensive storage sub-systems such as
non-volatile memory and
hard disk
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, pla ...
, as well as
write-once-read-many formats such as
CD-ROM
A CD-ROM (, compact disc read-only memory) is a type of read-only memory consisting of a pre-pressed optical compact disc that contains computer data storage, data computers can read, but not write or erase. Some CDs, called enhanced CDs, hold b ...
,
DVD, and
Blu-ray Disc
Blu-ray (Blu-ray Disc or BD) is a Digital media, digital optical disc data storage format designed to supersede the DVD format. It was invented and developed in 2005 and released worldwide on June 20, 2006, capable of storing several hours of ...
. 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. Codecs are often designed to emphasize certain aspects of the media to be encoded. For example, a digital video (using a
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 between source encoding and playback. In contrast, audio codecs for recording or broadcasting 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 on small portable devices. For example, raw uncompressed
PCM audio (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 uses a combination of different content forms, such as Text (literary theory), writing, Sound, audio, images, animations, or video, into a single presentation. T ...
data streams contain both
audio and
video
Video is an Electronics, electronic medium for the recording, copying, playback, broadcasting, and display of moving picture, moving image, visual Media (communication), media. Video was first developed for mechanical television systems, whi ...
, 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 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.
Audio Video Interleave
Audio Video Interleave (also Audio Video Interleaved and known by its initials and filename extension AVI, usually pronounced ) is a proprietary multimedia container format and Windows standard introduced by Microsoft in November 1992 as p ...
(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 independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries.
Me ...
. There are also other well-known container formats, such as
Ogg,
ASF,
QuickTime,
RealMedia
RealMedia is a proprietary multimedia container format (digital), container format created by RealNetworks with the filename extension . RealMedia is used in conjunction with RealVideo and RealAudio, while also being used for Streaming media, st ...
,
Matroska, and
DivX Media Format.
MPEG transport stream,
MPEG program stream
Program stream (PS or MPEG-PS) is a container format (digital), 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 ...
,
MP4, and
ISO base media file format 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 of ''malicious software'')Tahir, R. (2018)A study on malware and malware detection techniques . ''International Journal of Education and Management Engineering'', ''8''(2), 20. is any software intentionally designed to caus ...
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
*
Comparison of audio coding formats
*
Comparison of video codecs
*
Comparison of video container formats
These tables compare features of multimedia container format (digital), container formats, most often used for storing or streaming digital video or digital audio content. To see which multimedia players support which container format, look at com ...
*
Digital signal processing
Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner are a ...
*
List of codecs
*
List of open-source codecs
References
{{Compression Methods
Digital signal processing
Data compression