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del in the decoder which reproduces the sound lossy formats are often used for the distribution of streaming audio or interactive communication such as in cell phone networks in such applications the data must be decompressed as the data flows rather than after the entire data stream has been transmitted not all audio codecs can be used for streaming applications 50 latency is introduced by the methods used to encode and decode the data some codecs will analyze a longer segment called a frame of the data to optimize efficiency and then code it in a manner that requires a larger segment of data at one time to decode the inherent latency of the coding algorithm can be critical for example when there is a two way transmission of data such as with a telephone conversation significant delays may seriously degrade the perceived quality in contrast to the speed of compression which is proportional to the number of operations required by the algorithm here latency refers to the number of samples that must be analyzed before a block of audio is processed in the minimum case latency is zero samples e g if the coder decoder simply reduces the number of bits used to quantize the signal time domain algorithms such as lpc also often have low latencies hence their popularity in speech coding for telephony in algorithms such as mp3 however a large number of samples have to be analyzed to implement a psychoacoustic model in the frequency domain and latency is on the order of 23 ms speech encoding edit speech encoding is an important category of audio data compression the perceptual models used to estimate what aspects of speech a human ear can hear are generally somewhat different from those used for music the range of frequencies needed to convey the sounds of a human voice is normally far narrower than that needed for music and the sound is normally less complex as a result speech can be encoded at high quality using a relatively low bit rate this is accomplished in general by some combination of two approaches only encoding sounds that could be made by a single human voice throwing away more of the data in the signal keeping just enough to reconstruct an intelligible voice rather than the full frequency range of human hearing the earliest algorithms used in speech encoding and audio data compression in general were the a law algorithm and the μ law algorithm history edit solidyne 922 the world s first commercial audio bit compression sound card for pc 1990 early audio research was conducted at bell labs there in 1950 c chapin cutler filed the patent on differential pulse code modulation dpcm 52 in 1973 adaptive dpcm adpcm was introduced by p cummiskey nikil s jayant and james l flanagan 53 54 perceptual coding was first used for speech coding compression with linear predictive coding lpc 55 initial concepts for lpc date back to the work of fumitada itakura nagoya university and shuzo saito nippon telegraph and telephone in 1966 56 during the 1970s bishnu s atal and manfred r schroeder at bell labs developed a form of lpc called adaptive predictive coding apc a perceptual coding algorithm that exploited the masking properties of the human ear followed in the early 1980s with the code excited linear prediction celp algorithm which achieved a significant compression ratio for its time 55 perceptual coding is used by modern audio compression formats such as mp3 55 and aac discrete cosine transform dct developed by nasir ahmed t natarajan and k r rao in 1974 16 provided the basis for the modified discrete cosine transform mdct used by modern audio compression formats such as mp3 57 dolby digital 58 59 and aac 60 mdct was proposed by j p princen a w johnson and a b bradley in 1987 61 following earlier work by princen and bradley in 1986 62 the world s first commercial broadcast automation audio compression system was developed by oscar bonello an engineering professor at the university of buenos aires 63 this broadcast automation system was launched in 1987 under the name audicom 64 65 a literature compendium for a large variety of audio coding systems was published in the ieee s journal on selected areas in communications jsac in february 1988 while there were some papers from before that time this collection documented an entire variety of finished working audio coders nearly all of them using perceptual techniques and some kind of frequency analysis and back end noiseless coding 66 video edit see also video coding format and video codec uncompressed video requires a very high data rate although lossless video compression codecs perform at a compression factor of 5 to 12 a typical h 264 lossy compression video has a compression factor between 20 and 200 67 the two key video compression techniques used in video coding standards are the dct and motion compensation mc most video coding standards such as the h 26x and mpeg formats typically use motion compensated dct video coding block motion compensation 68 69 most video codecs are used alongside audio compression techniques to store the separate but complementary data streams as one combined package using so called container formats 70 encoding theory edit video data may be represented as a series of still image frames such data usually contains abundant amounts of spatial and temporal redundancy video compression algorithms attempt to reduce redundancy and store information more compactly most video compression formats and codecs exploit both spatial and temporal redundancy e g through difference coding with motion compensation similarities can be encoded by only storing differences between e g temporally adjacent frames inter frame coding or spatially adjacent pixels intra frame coding inter frame compression a temporal delta encoding re uses data from one or more earlier or later frames in a sequence to describe the current frame intra frame coding on the other hand uses only data from within the current frame effectively being still image compression 51 the intra frame video coding formats used in camcorders and video editing employ simpler compression that uses only intra frame prediction this simplifies video editing software as it prevents a situation in which a compressed frame refers to data that the editor has deleted usually video compression additionally employs lossy compression techniques like quantization that reduce aspects of the source data that are more or less irrelevant to the human visual perception by exploiting perceptual features of human vision for example small differences in color are more difficult to perceive than are changes in brightness compression algorithms can average a color across these similar areas in a manner similar to those used in jpeg image compression 9 as in all lossy compression there is a trade off between video quality and bit rate cost of processing the compression and decompression and system requirements highly compressed video may present visible or distracting artifacts other methods other than the prevalent dct based transform formats such as fractal compression matching pursuit and the use of a discrete wavelet transform dwt have been the subject of some research but are typically not used in practical products wavelet compression is used in still image coders and video coders without motion compensation interest in fractal compression seems to be waning due to recent theoretical analysis showing a comparative lack of effectiveness of such methods 51 inter frame coding edit main article inter frame further information motion compensation in inter frame coding individual frames of a video sequence are compared from one frame to the next and the video compression codec records the differences to the reference frame if the frame contains areas where nothing has moved the system can simply issue a short command that copies that part of the previous frame into the next one if sections of the frame move in a simple manner the compressor can emit a slightly longer command that tells the decompressor to shift rotate lighten or darken the copy this longer command still remains much shorter than data generated by intra frame compression usually the encoder will also transmit a residue signal which describes the remaining more subtle differences to the reference imagery using entropy coding these residue signals have a more compact representation than the full signal in areas of video with more motion the compression must encode more data to keep up with the larger number of pixels that are changing commonly the high frequency detail of explosions flames flocks of animals and some panning shots will lead to decreases in quality or increases in the variable bitrate hybrid block based transform formats edit processing stages of a typical video encoder many commonly used video compression methods e g those in standards approved by the itu t or iso share the same basic architecture that dates back to h 261 which was standardized in 1988 by the itu t they mostly rely on the dct applied to rectangular blocks of neighboring pixels and temporal prediction using motion vectors as well as nowadays also an in loop filtering step in the prediction stage various deduplication and difference coding techniques are applied that help decorrelate data and describe new data based on already transmitted data then rectangular blocks of remaining pixel data are transformed to the frequency domain in the main lossy processing stage frequency domain data gets quantized in order to reduce information that is irrelevant to human visual perception in the last stage statistical redundancy gets largely eliminated by an entropy coder which often applies some form of arithmetic coding in an additional in loop filtering stage various filters can be applied to the reconstructed image signal by computing these filters also inside the encoding loop they can help compression because they can be applied to reference material before it gets used in the prediction process and they can be guided using the original signal the most popular example are deblocking filters that blur out blocking artifacts from quantization discontinuities at transform block boundaries history edit main article video coding format history in 1967 a h robinson and c cherry proposed a run length encoding bandwidth compression scheme for the transmission of analog television signals 71 the dct which is fundamental to modern video compression 72 was introduced by nasir ahmed t natarajan and k r rao in 1974 16 73 h 261 which debuted in 1988 commercially introduced the prevalent basic architecture of video compression technology 74 it was the first video coding format based on dct compression 72 h 261 was developed by a number of companies including hitachi picturetel ntt bt and toshiba 75 the most popular video coding standards used for codecs have been the mpeg standards mpeg 1 was developed by the motion picture experts group mpeg in 1991 and it was designed to compress vhs quality video it was succeeded in 1994 by mpeg 2 h 262 74 which was developed by a number of companies primarily sony thomson and mitsubishi electric 76 mpeg 2 became the standard video format for dvd and sd digital television 74 in 1999 it was followed by mpeg 4 h 263 74 it was also developed by a number of companies primarily mitsubishi electric hitachi and panasonic 77 h 264 mpeg 4 avc was developed in 2003 by a number of organizations primarily panasonic godo kaisha ip bridge and lg electronics 78 avc commercially introduced the modern context adaptive binary arithmetic coding cabac and context adaptive variable length coding cavlc algorithms avc is the main video encoding standard for blu ray discs and is widely used by video sharing websites and streaming internet services such as youtube netflix vimeo and itunes store web software such as adobe flash player and microsoft silverlight and various hdtv broadcasts over terrestrial and satellite television 79 genetics edit genetics compression algorithms are the latest generation of lossless algorithms that compress data typically sequences of nucleotides using both conventional compression algorithms and genetic algorithms adapted to the specific datatype in 2012 a team of scientists from johns hopkins university published a genetic compression algorithm that does not use a reference genome for compression hapzipper was tailored for hapmap data and achieves over 20 fold compression 95 reduction in file size providing 2 to 4 fold better compression and is less computationally intensive than the leading general purpose compression utilities for this chanda elhaik and bader introduced maf based encoding mafe which reduces the heterogeneity of the dataset by sorting snps by their minor allele frequency thus homogenizing the dataset 80 other algorithms developed in 2009 and 2013 dnazip and genomezip have compression ratios of up to 1200 fold allowing 6 billion basepair diploid human genomes to be stored in 2 5 megabytes relative to a reference genome or averaged over many genomes 81 82 for a benchmark in genetics genomics data compressors see 83 outlook and currently unused potential edit it is estimated that the total amount of data that is stored on the world s storage devices could be further compressed with existing compression algorithms by a remaining average factor of 4 5 1 84 it is estimated that the combined technological capacity of the world to store information provides 1 300 exabytes of hardware digits in 2007 but when the corresponding content is optimally compressed this only represents 295 exabytes of shannon information 85 data compression algorithms edit lossless edit 842 adaptive coding adaptive huffman coding algorithm bstw arithmetic coding asymmetric numeral systems brotli burrows wheeler transform byte pair encoding bzip2 canonical huffman code chain code context mixing context tree weighting deflate delta encoding dictionary coder dynamic markov compression elias gamma coding exponential golomb coding felics fibonacci coding golomb coding grammar based code huffman coding incremental encoding lempel ziv oberhumer lzs lempel ziv storer szymanski lzss lempel ziv welch lzw levenshtein coding lz4 lz77 and lz78 lzfse lzma lzrw lzwl lzx modified huffman coding move to front transform negafibonacci coding packbits paq prediction by partial matching range coding re pair recursive indexing rice coding run length encoding sequitur algorithm shannon coding shannon fano coding shannon fano elias coding snappy truncated binary encoding tunstall coding unary coding universal code zopfli zstandard lossy edit 3dc a law algorithm adaptive differential pulse code modulation adaptive scalable texture compression algebraic code excited linear prediction block truncation coding code excited linear prediction color cell compression delta modulation differential pulse code modulation discrete cosine transform discrete sine transform discrete wavelet 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