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A video codec is
software Software is a collection of instructions Instruction or instructions may refer to: Computing * Instruction, one operation of a processor within a computer architecture instruction set * Computer program, a collection of instructions Music * I ...

software
or
hardware Hardware may refer to: Technology Computing and electronics * Computer hardware, physical parts of a computer * Digital electronics, electronics that operate on digital signals * Electronic component, device in an electronic system used to affect e ...

hardware
that compresses and decompresses
digital video Digital video is an electronic representation of moving visual images (video) in the form of encoded digital data. This is in contrast to analog video, which represents moving visual images in the form of analog signals. Digital video comprises ...
. In the context of video compression, ''
codec 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 ...
'' 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'' and ''decoder'', while a device that only compresses is typically called an ''encoder'', and one that only decompresses is a ''decoder''. The compressed data format usually conforms to a standard
video coding format A video coding format (or sometimes video compression format) is a content representation format for storage or transmission of digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Ha ...
. The compression is typically
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 ...
, meaning that the compressed video lacks some information present in the original video. A consequence of this is that decompressed video has lower quality than the original, uncompressed video because there is insufficient information to accurately reconstruct the original video. There are complex relationships between the
video quality Video quality is a characteristic of a 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 el ...
, the amount of data used to represent the video (determined by the
bit rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit Data rate units, bit per second unit (symbol: ''bit/s' ...
), the complexity of the encoding and decoding algorithms, sensitivity to data losses and errors, ease of editing, random access, and end-to-end delay (
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 ...
).


History

Historically, video was stored as an analog signal on
magnetic tape Magnetic tape is a medium for , made of a thin, magnetizable coating on a long, narrow strip of . It was developed in Germany in 1928, based on . Devices that record and playback audio and video using magnetic tape are s and s respectively. A ...

magnetic tape
. Around the time when the
compact disc The compact disc (CD) 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 electronics Electronics compri ...

compact disc
entered the market as a digital-format replacement for analog audio, it became feasible to also store and convey video in digital form. Because of the large amount of storage and bandwidth needed to record and convey raw video, a method was needed to reduce the amount of data used to represent the raw video. Since then,
engineers Engineers, as practitioners of engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of enginee ...

engineers
and
mathematicians A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry) ...
have developed a number of solutions for achieving this goal that involve compressing the digital video data. In 1974,
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 Data (; ) are ...
(DCT) compression was introduced by Nasir Ahmed, T. Natarajan and
K. R. Rao Kamisetty Ramamohan Rao was an Indian-American electrical engineer. He was a professor of Electrical Engineering at the University of Texas at Arlington (UT Arlington). Academically known as K. R. Rao, he is credited with the co-invention of ...
. During the late 1980s, a number of companies began experimenting with DCT
lossy compression 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 ...
for video coding, leading to the development of the
H.261 H.261 is an ITU-T The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications and Information Communication Technology such as X.509 for cybersecurity, Y.3172 and Y.3173 for machine learning, and H.264/MP ...
standard. H.261 was the first practical video coding standard,http://www.real.com/resources/digital-video-file-formats/ and was developed by a number of companies, including
Hitachi () is a Japanese multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, a sovereign ...

Hitachi
,
PictureTel PictureTel Corporation, often shortened to PictureTel Corp., was one of the first commercial videoconferencing product companies. It achieved peak revenues of over $490 million in 1996 and 1997 and was eventually acquired by Polycom in October ...
, NTT, BT, and
Toshiba is a Japanese multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Multinational state, a sovereign st ...
, among others. Since H.261, DCT compression has been adopted by all the major video coding standards that followed. The most popular
video coding standard A video coding format (or sometimes video compression format) is a content representation format for storage or transmission of digital video content (such as in a data file or bitstream). It typically uses a standardized video compression ...
s used for codecs have been the
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
standards.
MPEG-1 MPEG-1 is a standard for 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 ...
was developed by the
Motion Picture Experts Group The Moving Picture Experts Group (MPEG) is an alliance of working groupWorking Group may refer to: * Working group, an interdisciplinary group of researchers; or * Working Group (dogs), kennel club designation for certain purebred dog breeds; ...
(MPEG) in 1991, and it was designed to compress
VHS VHS (Video Home System) is a for consumer-level on tape . From the 1950s, video recording became a major contributor to the television industry, via the first commercialized s (VTRs). At that time, the expensive devices were used only i ...

VHS
-quality video. It was succeeded in 1994 by
MPEG-2 MPEG-2 (a.k.a. H.222/H.262 as was defined by the ITU 260px, ITU Monument, Bern The International Telecommunication Union is a specialized agency of the United Nations responsible for all matters related to information and communicati ...
/
H.262 H.262 or MPEG-2 Part 2 (formally known as ITU-T Recommendation H.262 and ISO/IEC 13818-2, also known as MPEG-2 Video) is a video coding format A video coding format (or sometimes video compression format) is a content representation format ...
, which was developed by a number of companies, primarily
Sony , commonly known as Sony and stylized as SONY, is a Japanese multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from mult ...

Sony
, Thomson and
Mitsubishi Electric , established on 15 January 1921, is a Japanese multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in multiple countries * Multinational force, a military body from multiple countries * Mul ...
. MPEG-2 became the standard video format for
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 elect ...

DVD
and SD
digital television Digital television (DTV) is the transmission of television audiovisual Audiovisual (AV) is electronic media 200px, Graphical representations of electrical audio data. Electronic media uses either analog (red) or digital (blue) signal pr ...
. In 1999, it was followed by
MPEG-4 MPEG-4 is a method of defining compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression ...
/
H.263 H.263 is a video compression standard originally designed as a low-bit-rate compressed format for videoconferencing Videotelephony comprises the technologies for the reception and transmission of audio- video signals by users in different loc ...
, which was a major leap forward for video compression technology. It was developed by a number of companies, primarily Mitsubishi Electric, Hitachi and
Panasonic formerly is a major Japanese multinational corporation, multinational Conglomerate (company), conglomerate company, headquartered in Kadoma, Osaka, Kadoma, Osaka Prefecture, Osaka. It was founded by Kōnosuke Matsushita in 1918 as a lightbulb ...

Panasonic
. The most widely used video coding format, as of 2016, is H.264/MPEG-4 AVC. It was developed in 2003 by a number of organizations, primarily Panasonic, Godo Kaisha IP Bridge and
LG Electronics LG Electronics Inc. () is a South Korean Multinational corporation, multinational electronics company headquartered in Yeouido-dong, Seoul, South Korea. LG Electronics is a part of the LG Corporation, the fourth-largest ''chaebol'' in South K ...

LG Electronics
. H.264 is the main video encoding standard for
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
s, and is widely used by streaming internet services such as
YouTube YouTube is an American online video sharing and social media platform Social media are interactive technologies that allow the Content creation, creation or information sharing, sharing/exchange of information, ideas, career interests, an ...

YouTube
,
Netflix Netflix, Inc. is an American subscription The subscription business model is a business model in which a customer In sales Sales are activities related to selling or the number of goods sold in a given targeted time period. Th ...

Netflix
,
Vimeo Vimeo, Inc. () is an American video hosting, sharing, and services platform provider headquartered in New York City. Vimeo focuses on the delivery of high-definition video across a range of devices. Vimeo's business model is through software as ...

Vimeo
, and
iTunes Store The iTunes Store is a software-based online 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, v ...

iTunes Store
, web software such as
Adobe Flash Player Adobe Flash Player (also called Shockwave Flash in Internet Explorer Internet Explorer (formerly Microsoft Internet Explorer and Windows Internet Explorer, (from August 16, 1995 to March 30, 2021) commonly abbreviated IE or MSIE) is a disc ...
and
Microsoft Silverlight Microsoft Silverlight is a discontinued application framework In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a s ...
, and various
HDTV High-definition television (HD or HDTV) describes a television system providing a substantially higher image resolution Image resolution is the detail an holds. The term applies to s, film images, and other types of images. Higher resolution m ...

HDTV
broadcasts over terrestrial and satellite television. AVC has been succeeded by
HEVC High Efficiency Video Coding (HEVC), also known as H.265 and MPEG-H Part 2, is a video compression standard A video coding format (or sometimes video compression format) is a content representation format for storage or transmission of digita ...
(H.265), developed in 2013. It is heavily patented, with the majority of patents belonging to
Samsung Electronics Samsung Electronics Co., Ltd. (; lit. "tristar electronics", sometimes shortened to SEC and stylized as SΛMSUNG) is a South Korean multinational Multinational may refer to: * Multinational corporation, a corporate organization operating in ...
, GE, NTT and
JVC Kenwood , stylized as JVCKENWOOD, is a Japanese Multinational corporation, multinational electronics company headquartered in Yokohama, Japan. It was formed from the merger of JVC, Victor Company of Japan, Ltd (JVC) and Kenwood Corporation on October 1, 2 ...

JVC Kenwood
. The adoption of HEVC has been hampered by its complex licensing structure. HEVC is in turn succeeded by
Versatile Video Coding Versatile Video Coding (VVC), also known as H.266, ISO/IEC 23090-3, MPEG-I Part 3 and Future Video Coding (FVC), is a video compression standard finalized on 6 July 2020, by the Joint Video Experts Team (JVET), a joint video expert team of the ...
(VVC). There are also the open and free
VP8 VP8 is an open format, open and royalty-free Video coding format, video compression format created by On2 Technologies as a successor to VP7 and owned by Google from 2010. In May 2010, after the purchase of On2 Technologies, Google provided an ir ...
,
VP9 VP9 is an open Open or OPEN may refer to: Music * Open (band) Open is a band. Background Drummer Pete Neville has been involved in the Sydney/Australian music scene for a number of years. He has recently completed a Masters in screen mus ...
and
AV1 AOMedia Video 1 (AV1) is an , initially designed for video transmissions over the Internet. It was developed as a successor to by the (AOMedia), a consortium founded in 2015 that includes semiconductor firms, providers, video content prod ...

AV1
video coding formats, used by YouTube, all of which were developed with involvement from Google.


Applications

Video codecs are used in DVD players,
Internet video Internet video (online video / cloud-based video) is the general field that deals with the transmission of digital video Digital video is an electronic representation of moving visual images (video Video is an Electronics, electronic m ...
,
video on demand Video on demand (VOD) is a media distribution system that allows users to access videos without a traditional video playback device and the constraints of a typical static broadcasting schedule. In the 20th century, broadcasting in the form of ...
,
digital cable Digital cable is the distributionDistribution may refer to: Mathematics *Distribution (mathematics) Distributions, also known as Schwartz distributions or generalized functions, are objects that generalize the classical notion of fun ...
,
digital terrestrial television Digital terrestrial television (DTTV or DTT, or DTTB with "broadcasting") is a technology for terrestrial television Terrestrial television is a type of television broadcasting Broadcasting is the distribution of sound, audio or video c ...
,
videotelephony Videotelephony, sometimes also referred to as video teleconference or videoconferencing, comprises the technologies for the reception and transmission of audio Audio most commonly refers to sound In physics Physics (from grc, φυ ...
and a variety of other applications. In particular, they are widely used in applications that record or transmit video, which may not be feasible with the high data volumes and bandwidths of uncompressed video. For example, they are used in
operating theater An operating theater (also known as an operating room (OR), operating suite, or operation suite) is a facility within a hospital where surgical operations are carried out in an asepsis, aseptic environment. Historically, the term "operating theat ...
s to record surgical operations, in
IP camera An Internet Protocol camera, or IP camera, is a type of digital video camera A video camera is a camera A camera is an optical instrument used to capture an image An SAR radar imaging, radar image acquired by the SIR-C/X-SAR ra ...
s in security systems, and in
remotely operated underwater vehicle A remotely operated underwater vehicle (technically ROUV or just ROV) is a tether A tether is a cord, fixture, or flexible attachment that characteristically anchors something movable to something fixed; it also maybe used to connect two movab ...
s and
unmanned aerial vehicle , a hunter-killer surveillance UAV , rotorcraft A rotorcraft or rotary-wing aircraft is a heavier-than-air aircraft An aircraft is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters th ...

unmanned aerial vehicle
s.


Video codec design

Video codecs seek to represent a fundamentally analog data set in a digital format. Because of the design of analog video signals, which represent
luminance Luminance is a photometricPhotometry can refer to: * Photometry (optics), the science of measurement of visible light in terms of its perceived brightness to human vision * Photometry (astronomy), the measurement of the flux or intensity of an ...
(luma) and color information (chrominance, chroma) separately, a common first step in image compression in codec design is to represent and store the image in a
YCbCr YCbCr, Y′CbCr, or Y Pb/Cb Pr/Cr, also written as YCBCR or Y′CBCR, is a family of color space A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports repr ...
color space. The conversion to YCbCr provides two benefits: first, it improves compressibility by providing decorrelation of the color signals; and second, it separates the luma signal, which is perceptually much more important, from the chroma signal, which is less perceptually important and which can be represented at lower resolution using
chroma subsampling Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information Information is processed, organised and structured data. It provides context for data and enables decision making process. For examp ...
to achieve more efficient data compression. It is common to represent the ratios of information stored in these different channels in the following way Y:Cb:Cr. Different codecs use different chroma subsampling ratios as appropriate to their compression needs. Video compression schemes for Web and DVD make use of a 4:2:1 color sampling pattern, and the standard uses 4:1:1 sampling ratios. Professional video codecs designed to function at much higher bitrates and to record a greater amount of color information for post-production manipulation sample in 4:2:2 and 4:4:4 ratios. Examples of these codecs include Panasonic's DVCPRO50 and DVCPROHD codecs (4:2:2), Sony's HDCAM-SR (4:4:4), Panasonic's HDD5 (4:2:2),
Apple An apple is an edible fruit In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this fie ...
's Prores HQ 422 (4:2:2). It is also worth noting that video codecs can operate in RGB space as well. These codecs tend not to sample the red, green, and blue channels in different ratios, since there is less perceptual motivation for doing so—just the blue channel could be undersampled. Some amount of spatial and temporal
downsamplingIn digital signal processing, downsampling, compression, and decimation are terms associated with the process of sample rate conversion, ''resampling'' in a multi-rate digital signal processing system. Both ''downsampling'' and ''decimation'' can be ...
may also be used to reduce the raw data rate before the basic encoding process. The most popular encoding transform is the 8x8 DCT. Codecs which make use of a
wavelet A wavelet is a wave In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion a ...

wavelet
transform are also entering the market, especially in camera workflows which involve dealing with
RAW Raw is an adjective usually describing: * Raw materials, basic materials from which products are manufactured or made * Raw food, uncooked food Raw or RAW may also refer to: Computing * .RAW, a proprietary mass spectrometry data format * Raw audi ...
image formatting in motion sequences. This process involves representing the video image as a set of
macroblocksThe macroblock is a processing unit in image File:TEIDE.JPG, An Synthetic aperture radar, SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide volcano. The city of Santa Cruz de T ...
. For more information about this critical facet of video codec design, see B-frames. The output of the transform is first quantized, then
entropy encoding In information theory, an entropy coding (or entropy encoding) is a lossless compression , lossless data compression scheme that is independent of the specific characteristics of the medium. One of the main types of entropy coding creates and assi ...
is applied to the quantized values. When a DCT has been used, the coefficients are typically scanned using a zig-zag scan order, and the entropy coding typically combines a number of consecutive zero-valued quantized coefficients with the value of the next non-zero quantized coefficient into a single symbol, and also has special ways of indicating when all of the remaining quantized coefficient values are equal to zero. The entropy coding method typically uses variable-length coding tables. Some encoders compress the video in a multiple step process called ''n-pass'' encoding (e.g. 2-pass), which performs a slower but potentially higher quality compression. The decoding process consists of performing, to the extent possible, an inversion of each stage of the encoding process. The one stage that cannot be exactly inverted is the quantization stage. There, a best-effort approximation of inversion is performed. This part of the process is often called ''inverse quantization'' or ''dequantization'', although quantization is an inherently non-invertible process. Video codec designs are usually standardized or eventually become standardized—i.e., specified precisely in a published document. However, only the decoding process need be standardized to enable interoperability. The encoding process is typically not specified at all in a standard, and implementers are free to design their encoder however they want, as long as the video can be decoded in the specified manner. For this reason, the quality of the video produced by decoding the results of different encoders that use the same video codec standard can vary dramatically from one encoder implementation to another.


Commonly used video codecs

A variety of video compression formats can be implemented on PCs and in consumer electronics equipment. It is therefore possible for multiple codecs to be available in the same product, reducing the need to choose a single dominant video compression format to achieve
interoperability Interoperability is a characteristic of a product or system, whose interfaces are completely understood, to work with other products or systems, at present or in the future, in either implementation or access, without any restrictions. While the ...

interoperability
. Standard
video compression format A video coding format (or sometimes video compression format) is a content representation format for storage or transmission of digital video content (such as in a data file or bitstream). It typically uses a standardized video compression ...
s can be supported by multiple encoder and decoder implementations from multiple sources. For example, video encoded with a standard MPEG-4 Part 2 codec such as Xvid can be decoded using any other standard MPEG-4 Part 2 codec such as FFmpeg MPEG-4 or DivX Pro Codec, because they all use the same video format. Codecs have their qualities and drawbacks. Comparisons are frequently published. The trade-off between compression power, speed, and fidelity (including artifacts) is usually considered the most important figure of technical merit.


Codec packs

Online video material is encoded by a variety of codecs, and this has led to the availability of codec packs — a pre-assembled set of commonly used codecs combined with an installer available as a software package for PCs, such as
K-Lite Codec Pack The K-Lite Codec Pack is a collection of Audio codec, audio and video codecs for Microsoft Windows DirectShow that enables an operating system and its software to play various audio and video formats generally not supported by the operating syste ...
,
Perian Perian is a discontinued open-source QuickTime component that enabled Apple Inc. Apple Inc. is an American multinational technology company headquartered in Cupertino, California, that designs, develops, and sells consumer electronics, ...
and
Combined Community Codec Pack The Combined Community Codec Pack, more commonly referred to by its acronym CCCP, is a collected archive of codecs (video compression filters) packed for Microsoft Windows, designed originally for the playback of anime fansubs. The CCCP is develope ...
.


See also

*
Video coding format A video coding format (or sometimes video compression format) is a content representation format for storage or transmission of digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Ha ...
*
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 ...
*
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 ...
* *
Display resolution The display resolution or display modes of a digital television Digital television (DTV) is the transmission of television audiovisual Audiovisual (AV) is electronic media 200px, Graphical representations of electrical audio data. ...
*
Frame rate Frame rate (expressed in or FPS) is the frequency Frequency is the number of occurrences of a repeating event per unit of time A unit of time is any particular time Time is the indefinite continued sequence, progress of existence an ...
* *
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 ...
*
Multiplexing 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 ...
*
Sampling rate In , sampling is the reduction of a to a . A common example is the conversion of a (a continuous signal) to a sequence of samples (a discrete-time signal). A sample is a value or set of values at a point in time and/or space. A sampler is a su ...
*
Subjective video quality Subjective video quality is video quality as experienced by humans. It is concerned with how video is perceived by a viewer (also called "observer" or "subject") and designates their opinion on a particular video sequence. It is related to the fi ...
*
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 ...
*
Video quality Video quality is a characteristic of a 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 el ...


References


External links


Wyner-Ziv Coding of Video
describes another algorithm for video compression that performs close to the Slepian–Wolf bound (with links to source code).
AMD Media Codecs
optional download (formerly called
ATI Avivo ATI Avivo is a set of hardware and low level software features present on the ATI Radeon R520 family of GPUs A graphics processing unit (GPU) is a specialized designed to rapidly manipulate and alter to accelerate the creation of in a in ...
) {{DEFAULTSORT:Video Codec Videotelephony