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A video codec is a device or software that enables video compression and/or decompression for digital video. A codec is a device or program capable of encoding and/or decoding a Digital Data stream or signal. Video compression refers to reducing the quantity of Data used to represent video images and is a straightforward combination of Image compression and Motion The compression usually employs lossy data compression. A lossy compression method is one where compressing data and then decompressing it retrieves data that may well be different from the original but is close enough to be useful Historically, video was stored as an analog signal on magnetic tape. Magnetic tape is a medium for Magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of Plastic. Around the time when the compact disc entered the market as a digital-format replacement for analog audio, it became feasible to also begin storing and using video in digital form, and a variety of such technologies began to emerge. A Compact Disc (also known as a CD) is an Optical disc used to store digital data, originally developed for storing digital audio

Audio and video call for customized methods of compression. Engineers and mathematicians have tried a number of solutions for tackling this problem. An engineer is a person professionally engaged in a field of Engineering. A mathematician is a person whose primary area of study and research is the field of Mathematics.

There is a complex balance between the video quality, the quantity of the data needed to represent it, also known as the bit rate, the complexity of the encoding and decoding algorithms, robustness to data losses and errors, ease of editing, random access, the state of the art of compression algorithm design, end-to-end delay, and a number of other factors. Video quality is a characteristic of a Video passed through a video transmission/processing system a formal or informal measure of perceived video degradation (typically compared In Telecommunications and Computing, bitrate (sometimes written bit rate, data rate or as a Variable R or f b

Contents

Applications

Digital video codecs are found in DVD (MPEG-2), VCD (MPEG-1), in emerging satellite and terrestrial broadcast systems, and on the Internet. Online video material is encoded in 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.

Encoding media by the public has seen an upsurge with the availability of DVD-writers. Since commercially available DVDs are usually dual-layer, and hence bigger than the more common single layer writable DVDs, it is often the case that the material has to be compressed again, sacrificing quality so that the media will fit onto a single layer disc.

Video codec design

Video codecs seek to represent a fundamentally analog data set in a digital way. Because of the design of analog video signals, which represent luma and color information separately, a common first step in image compression in codec design is to represent and store the image in a YCbCr color space. As applied to video signals luma represents the brightness in an image (the "black and white" or achromatic portion of the image YCbCr or Y'CbCr is a family of Color spaces used as a part of the Color image pipeline in Video and Digital photography systems 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 to achieve more efficient data compression. YCbCr or Y'CbCr is a family of Color spaces used as a part of the Color image pipeline in Video and Digital photography systems As applied to video signals luma represents the brightness in an image (the "black and white" or achromatic portion of the image Chrominance ( chroma for short is the signal used in many Video systems to carry the color information of the picture separately from the accompanying luma It is common to represent the ratios of information stored in these different channels in the following way Y:Cb:Cr. Refer to the following article for more information about Chroma subsampling. Chroma subsampling is the practice of encoding images by implementing less resolution for chroma Information than for luma information

Different codecs will use different chroma subsampling ratios as appropriate to their compression needs. Chroma subsampling is the practice of encoding images by implementing less resolution for chroma Information than for luma information Video compression schemes for Web and DVD use make use of a 4:2:0 color sampling pattern, and the DV standard uses 4:1:1 sampling ratios. Digital Video (DV is a Digital video format created by Sony JVC Panasonic and other video camera procuers and launched in 1995 and in its smaller tape Form factor 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 3:1:1 (uncommon), 4:2:2 and 4:4:4 ratios. Examples of these codecs include Panasonic's DVCPRO50 and DVCPROHD codecs (4:2:2), and then Sony's HDCAM-SR (4:4:4) or Panasonic's HDD5 (4:2:2). Apple's new Prores HQ 422 codec also samples in 4:2:2 color space. More codecs that sample in 4:4:4 patterns exist as well, but are less common, and tend to be used internally in post-production houses. 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 no perceptual motivation for doing so.

Some amount of spatial and temporal downsampling may also be used to reduce the raw data rate before the basic encoding process. In signal processing downsampling (or "subsampling" is the process of reducing the sampling rate of a signal. The most popular such transform is the 8x8 discrete cosine transform (DCT). A discrete cosine transform ( DCT) expresses a sequence of finitely many data points in terms of a sum of Cosine functions oscillating at different frequencies Codecs which make use of a wavelet transform are also entering the market, especially in camera workflows which involve dealing with RAW image formatting in motion sequences. A wavelet is a mathematical function used to divide a given function or continuous-time signal into different frequency components and study each component with a resolution A raw image file contains minimally processed data from the image sensor of a Digital camera or Image scanner. The output of the transform is first quantized, then entropy encoding is applied to the quantized values. In Information theory an entropy encoding is a lossless Data compression scheme that is independent of the specific characteristics of the medium 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. History In 1951 David A Huffman and his MIT information theory classmates were given Some encoders can compress the video in a multiple step process called n-pass encoding (e. g. 2-pass), which performs a slower but potentially better 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.

This process involves representing the video image as a set of macroblocks. Macroblock is a term used in Video compression, which represents a block of 16 by 16 Pixels. For more information about this critical facet of video codec design, see B pictures. I-frame redirects here For the HTML-element see IFrame. The three major picture types found in typical Video compression designs are

Video codec designs are often standardized or will be in the future- i. e. , specified precisely in a published document. However, only the decoding process needs to 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 standards and codecs

A variety of codecs can be implemented with relative ease on PCs and in consumer electronics equipment. It is therefore possible for multiple codecs to be available in the same product, avoiding the need to choose a single dominant codec for compatibility reasons. In the end it seems unlikely that one codec will replace them all. Some widely-used video codecs are listed below, starting with a chronological-order list of the ones specified in international standards. International standards are Standards developed by international Standards organisations International standards are available for consideration and use worldwide

H.261: Used primarily in older videoconferencing and videotelephony products. H261 is a 1990 ITU-T video coding standard originally designed for transmission over ISDN lines on which data rates are multiples of 64 kbit/s H. 261, developed by the ITU-T, was the first practical digital video compression standard. The ITU Telecommunication Standardization Sector ( ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Essentially all subsequent standard video codec designs are based on it. It included such well-established concepts as YCbCr color representation, the 4:2:0 sampling format, 8-bit sample precision, 16x16 macroblocks, block-wise motion compensation, 8x8 block-wise discrete cosine transformation, zig-zag coefficient scanning, scalar quantization, run+value symbol mapping, and variable-length coding. One method used by various video formats to reduce file size is motion compensation. A discrete cosine transform ( DCT) expresses a sequence of finitely many data points in terms of a sum of Cosine functions oscillating at different frequencies History In 1951 David A Huffman and his MIT information theory classmates were given H. 261 supported only progressive scan video. Progressive or noninterlaced scanning is a method for displaying storing or transmitting Moving images in which all the lines of each frame are drawn in

MPEG-1 Part 2: Used for Video CDs, and also sometimes for online video. MPEG-1 was an early Standard for Lossy compression of Video and audio. If the source video quality is good and the bitrate is high enough, VCD can look slightly better than VHS. To exceed VHS quality, a higher resolution would be necessary. However, to get a fully compliant VCD file, bitrates higher than 1150 kbit/s and resolutions higher than 352 x 288 should not be used. In telecommunications Bit rate or Data transfer rate is the average number of Bits characters or blocks per unit time passing between equipment in a data transmission When it comes to compatibility, VCD has the highest compatibility of any digital video/audio system. Very few DVD players do not support VCD, but they all inherently support the MPEG-1 codec. Almost every computer in the world can also play videos using this codec. In terms of technical design, the most significant enhancements in MPEG-1 relative to H. 261 were half-pel and bi-predictive motion compensation support. One method used by various video formats to reduce file size is motion compensation. MPEG-1 supports only progressive scan video. Progressive or noninterlaced scanning is a method for displaying storing or transmitting Moving images in which all the lines of each frame are drawn in

MPEG-2 Part 2 (a common-text standard with H.262): Used on DVD, SVCD, and in most digital video broadcasting and cable distribution systems. MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information" H262 is an ITU-T Digital video coding standard It falls under the purview of the ITU-T Video Coding Experts Group (VCEG and is maintained jointly with DVD (also known as " Digital Versatile Disc " or " Digital Video Disc " - see Etymology)is Super Video CD ( Super Video Compact Disc or SVCD) is a Digital format for storing Video on standard Compact discs SVCD was intended When used on a standard DVD, it offers good picture quality and supports widescreen. When used on SVCD, it is not as good as DVD but is certainly better than VCD due to higher resolution and allowed bitrate. Though uncommon, MPEG-1 can also be used on SVCDs, and anywhere else MPEG-2 is allowed, as MPEG-2 decoders are inherently backwards compatible. In terms of technical design, the most significant enhancement in MPEG-2 relative to MPEG-1 was the addition of support for interlaced video. For the method of incrementally displaying Raster graphics, see Interlace (bitmaps. MPEG-2 is now considered an aged codec, but has tremendous market acceptance and a very large installed base.

H.263: Used primarily for videoconferencing, videotelephony, and internet video. H263 is a Video codec standard originally designed as a low-bitrate compressed format for Videoconferencing. H. 263 represented a significant step forward in standardized compression capability for progressive scan video. Progressive or noninterlaced scanning is a method for displaying storing or transmitting Moving images in which all the lines of each frame are drawn in Especially at low bit rates, it could provide a substantial improvement in the bitrate needed to reach a given level of fidelity.

Sorenson Spark: A codec that was licensed to Macromedia for use in its Flash Player 6. The Sorenson codec (also known as Sorenson Video Codec, Sorenson Video Quantizer or SVQ) is a Digital video Codec devised by the company In the same family as H.263. H263 is a Video codec standard originally designed as a low-bitrate compressed format for Videoconferencing.

MPEG-4 Part 2: An MPEG standard that can be used for internet, broadcast, and on storage media. MPEG-4 is a collection of methods defining compression of audio and visual (AV digital data The Moving Picture Experts Group, commonly referred to as simply MPEG, is a Working group of ISO / IEC charged with the development of video and It offers improved quality relative to MPEG-2 and the first version of H. 263. Its major technical features beyond prior codec standards consisted of object-oriented coding features and a variety of other such features not necessarily intended for improvement of ordinary video coding compression capability. It also included some enhancements of compression capability, both by embracing capabilities developed in H. 263 and by adding new ones such as quarter-pel motion compensation. One method used by various video formats to reduce file size is motion compensation. Like MPEG-2, it supports both progressive scan and interlaced video. Progressive or noninterlaced scanning is a method for displaying storing or transmitting Moving images in which all the lines of each frame are drawn in For the method of incrementally displaying Raster graphics, see Interlace (bitmaps.

DivX, Xvid, FFmpeg MPEG-4 and 3ivx: Different implementations of MPEG-4 Part 2. DivX is a brand name of products created by DivX Inc (formerly DivXNetworks Inc Xvid (formerly " XviD " is a Video codec library following the MPEG-4 standard FFmpeg is a computer program that can record convert and stream digital audio and Video in numerous formats 3ivx is a Video codec created by 3ivx Technologies based in Sydney Australia

MPEG-4 Part 10 (a technically aligned standard with the ITU-T's H.264 and often also referred to as AVC). MPEG-4 is a collection of methods defining compression of audio and visual (AV digital data The ITU Telecommunication Standardization Sector ( ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication H264 is a standard for Video compression. It is also known as MPEG-4 Part 10, or MPEG-4 AVC (for Advanced Video Coding) This emerging new standard is the current state of the art of ITU-T and MPEG standardized compression technology, and is rapidly gaining adoption into a wide variety of applications. The ITU Telecommunication Standardization Sector ( ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication The Moving Picture Experts Group, commonly referred to as simply MPEG, is a Working group of ISO / IEC charged with the development of video and It contains a number of significant advances in compression capability, and it has recently been adopted into a number of company products, including for example the XBOX 360, PlayStation Portable, iPod, iPhone, the Nero Digital product suite, Mac OS X v10.4, as well as HD DVD/Blu-ray Disc. The Xbox 360 is the second Video game console produced by Microsoft, and was developed in cooperation with IBM, ATI, and SiS. The PlayStation Portable (officially abbreviated PSP) is a Handheld game console manufactured and marketed by Sony Computer Entertainment. iPod is a popular brand of Portable media players designed and marketed by Apple Inc The iPhone is an internet-connected Multimedia Smartphone designed and marketed by Apple Inc Nero Digital is a brand name applied to a suite of MPEG-4 -compatible video and audio compression Codecs developed by Nero AG of Germany and Mac OS X version 104 “Tiger” was the fifth major release of Mac OS X, Apple’s desktop and server Operating system for Macintosh not insert the publicly disclosed HD DVD key into this article for the time being

x264: A GPL-licensed implementation of H. x264 is a Free software library for encoding H264/MPEG-4 AVC video streams 264 encoding standard, x264 is only an encoder.

VP6: A proprietary video codec developed by On2 Technologies and used in Adobe Flash Player 8 and above. TrueMotion VP6 is a Video codec developed by On2 Technologies as a successor to earlier efforts such as VP3 and VP5.

Sorenson 3: A codec that is popularly used by Apple's QuickTime, basically the ancestor of H.264. The Sorenson codec (also known as Sorenson Video Codec, Sorenson Video Quantizer or SVQ) is a Digital video Codec devised by the company QuickTime is a Multimedia framework developed by Apple Inc, capable of handling various formats of Digital video, Media clips sound text H264 is a standard for Video compression. It is also known as MPEG-4 Part 10, or MPEG-4 AVC (for Advanced Video Coding) Many of the QuickTime movie trailers found on the web use this codec.

Theora: Developed by the Xiph.org Foundation as part of their Ogg project, based upon On2 Technologies' VP3 codec, and christened by On2 as the successor in VP3's lineage, Theora is targeted at competing with MPEG-4 video and similar lower-bitrate video compression schemes. Theora is an open and royalty-free Lossy Video compression technology being developed by the Xiph The XiphOrg Foundation is a 501(c(3 Non-profit organization dedicated to producing free Multimedia formats and tools To learn how to create video or audio files for Wikipedia and its sister projects check WikipediaCreation and usage of media files. On2 Technologies ( formerly known as The Duck Corporation, is a small publicly-traded company (on the American Stock Exchange) headquartered in Tarrytown Theora is an open and royalty-free Lossy Video compression technology being developed by the Xiph MPEG-4 is a collection of methods defining compression of audio and visual (AV digital data

WMV (Windows Media Video): Microsoft's family of video codec designs including WMV 7, WMV 8, and WMV 9. Windows Media Video ( WMV) is a compressed Video file format for several proprietary Codecs developed by Microsoft. Microsoft Corporation is an American multinational Computer technology Corporation, which rose to dominate the Home computer It can do anything from low resolution video for dial up internet users to HDTV. High-definition television (HDTV is a Digital television Broadcasting system with higher resolution than traditional television systems (standard-definition The latest generation of WMV is standardized by SMPTE as the VC-1 standard. VC-1 is the informal name of the SMPTE 421M Video codec standard initially developed by Microsoft.

VC-1: SMPTE standardized video compression standard (SMPTE 421M). VC-1 is the informal name of the SMPTE 421M Video codec standard initially developed by Microsoft. Based on Microsoft's WMV9 video codec. Windows Media Video ( WMV) is a compressed Video file format for several proprietary Codecs developed by Microsoft. One of the 3 mandatory video codecs in both HD DVD and Blu-Ray high-definition optical disc standards. not insert the publicly disclosed HD DVD key into this article for the time being Commonly found in portable devices and on streaming video websites in its Windows Media Video implementation. Windows Media Video ( WMV) is a compressed Video file format for several proprietary Codecs developed by Microsoft.

RealVideo: Developed by RealNetworks. RealVideo is a proprietary video format developed by RealNetworks. RealNetworks ( is a provider of Internet media delivery software and services based in Seattle, United States. A popular codec technology a few years ago, now fading in importance for a variety of reasons.

Cinepak: A very early codec used by Apple's QuickTime. Cinepak is a Video codec developed by SuperMatch a division of SuperMac Technologies, and released in 1992 as part of Apple Computer's

Huffyuv: Huffyuv (or HuffYUV) is a very fast, lossless Win32 video codec written by Ben Rudiak-Gould and published under the terms of the GPL as free software, meant to replace uncompressed YCbCr as a video capture format. Huffyuv (or HuffYUV) is a Lossless Video codec created by Ben Rudiak-Gould which is meant to replace uncompressed YCbCr as a video See Lagarith as a more up-to-date codec.

Lagarith: A more up-to-date fork of Huffyuv is available as Lagarith. Lagarith is an Open source Lossless Video codec written by Ben Greenwood

SheerVideo: A family of ultrafast lossless QuickTime and AVI codecs, developed by BitJazz Inc. SheerVideo is a family of proprietary lossless video codecs developed by BitJazz Inc , for RGB[A], Y'CbCr[A] 4:4:4[:4], Y'CbCr[A] and 4:2:2[:4] formats; for both 10-bit and 8-bit channels; for both progressive and interlaced data; for both Mac and PC.

Mobiclip, a codec created by Actimagine, maximising mobile phone battery life when playing full length films on a smart-phone handset. Actimagine (pronounced /ˈɑk t̬ə mə ˌdʒin/ is a French company which develops video and Vector graphics display software as well as Mobiclip a Mobile

All of the codecs above have their qualities and drawbacks. Comparisons are frequently published. The tradeoff between compression power, speed, and fidelity (including artifacts) is usually considered the most important figure of technical merit. A compression artifact (or artefact) is the result of an aggressive Data compression scheme applied to an Image, audio, or Video

Missing codecs and video-file issues

A common problem when an end user wants to watch a video stream encoded with a specific codec is that if the exact codec is not present and properly installed on the user's machine, the video won't play (or won't play optimally).

Windows XP SP2 itself only has a very limited number of video and audio codecs installed; other than Microsoft formats, Intel Indeo is the only available . Indeo Video (commonly known now simply as "Indeo" is a Video codec developed by Intel in 1992 avi Codec that is installed per default. All other codecs, such as DivX, Xvid or Theora, must be installed manually.

List of the available/default codecs after a Windows XP Installation List of the available/default codecs after a Windows XP SP2 Installation

Some video files and codec analysis tools have been made available to provide a user-friendly way to solve this common problem:

VideoInspector : Analyzes most containers (AVI, Matroska, MPEG, etc. ) and gives direct download links for missing codecs.

GSpot : A pioneer in troubleshooting video applications, GSpot remains a useful tool despite missing some features present in other software.

MediaInfo : Open-source alternative to GSpot.

AVICodec : Another useful application.

AVI2Clipboard : An extension for the Explorer context menu to easily view and save information about videos with an AVI container.

MPlayer or VLC media player resolve many of these issues because they contain many popular codecs in a portable standalone library, available for many operating systems, including Windows, Linux, and Mac OS X. MPlayer is a free and Open source media player. The program is available for all major Operating systems including Linux An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination This also resolves many issues within Windows in conflicting and poorly installed codecs.

Video codec benchmarking

To benchmark video decoders, try the Haali TimeCodec. You have to install the latest version of the Haali Media Splitter before using it.

Another method is using the internal audio and video decoders built into TCPMP for both mobile devices and desktop PC's. The Core Pocket Media Player ( TCPMP) is a software media player See Shinos TCPMP benchmark page

See also

External links

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