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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 Organization, groups through the use of sufficiently mutually understood sign ...
to another, such as for
movie A film, also called a movie, motion picture or moving picture, is a work of visual art used to simulate experiences that communicate ideas, stories, perceptions, feelings, beauty, or atmosphere through the use of moving images. These imag ...

movie
data files, audio files (e.g.,
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
,
WAV Waveform Audio File Format (WAVE, or WAV due to its 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 identification by an external observer. T ...

WAV
), or
character encoding Character encoding is the process of assigning numbers to graphical Graphics (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country ...
(e.g.,
UTF-8 UTF-8 is a variable-width character encoding Character encoding is the process of assigning numbers to Graphics, graphical character (computing), characters, especially the written characters of Language, human language, allowing them to be ...
,
ISO/IEC 8859 ISO/IEC 8859 is a joint ISO The International Organization for Standardization (ISO; ) is an international standard are technical standards developed by international organizations (intergovernmental organizations), such as Codex Alimentarius ...
). This is usually done in cases where a target device (or
workflow A workflow consists of an orchestrated and repeatable of activity, enabled by the atic organization of s into es that transform materials, provide services, or process information. It can be depicted as a sequence of operations, the work of a p ...

workflow
) does not support the format or has limited storage capacity that mandates a reduced file size, "Advancements in Compression and Transcoding: 2008 and Beyond",
Society of Motion Picture and Television Engineers The Society of Motion Picture and Television Engineers (SMPTE) (, rarely ), founded in 1916 as the Society of Motion Picture Engineers or SMPE, is a global professional association of engineers, technologists, and executives working in the m ...
(SMPTE), 2008, webpage
SMPTE-spm
or to convert incompatible or obsolete data to a better-supported or modern format. In the analog video world, transcoding can be performed just while files are being searched, as well as for presentation. For example,
Cineon The Cineon System was one of the first computer based Digital intermediate, digital film systems, created by Eastman Kodak, Kodak in the early 1990s. It was an integrated suite of components consisting a Motion picture film scanner, a film recorde ...
and
DPX Digital Picture Exchange (DPX) is a common file format A file format is a way that information is encoded for storage in a . It specifies how s are used to encode information in a digital storage medium. File formats may be either or a ...
files have been widely used as a common format for
digital cinema Digital cinema refers to adoption of 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 c ...
, but the data size of a two-hour movie is about 8
terabytes The byte is a units of information, unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character (computing), character of text in a computer and for this ...
(TB). That large size can increase the cost and difficulty of handling movie files. However, transcoding into a
JPEG2000 JPEG 2000 (JP2) is an image compression standard and coding system. It was developed from 1997 to 2000 by a Joint Photographic Experts Group committee chaired by Touradj Ebrahimi (later the JPEG president), with the intention of superseding their ...
lossless format has better compression performance than other lossless coding technologies, and in many cases, JPEG2000 can compress images to half-size. Transcoding is commonly a lossy process, introducing
generation loss Generation loss is the loss of quality between subsequent copies or transcodes of data. Anything that reduces the quality of the representation when copying, and would cause further reduction in quality on making a copy of the copy, can be consi ...
; however, transcoding can be lossless if the output is either losslessly compressed or uncompressed. The process of transcoding into a lossy format introduces varying degrees of
generation loss Generation loss is the loss of quality between subsequent copies or transcodes of data. Anything that reduces the quality of the representation when copying, and would cause further reduction in quality on making a copy of the copy, can be consi ...
, while the transcoding from lossy to lossless or uncompressed is technically a lossless conversion because no information is lost; however, the process is irreversible and is more correctly known as ''destructive''.


Process

Transcoding is a two-step process in which the original data is decoded to an intermediate uncompressed format (e.g.,
PCM 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 ...
for audio;
YUV YUV is a color encoding system typically used as part of a color image pipelineAn image pipeline or video pipeline is the set of components commonly used between an image source (such as a camera, a scanner, or the rendering engine in a compute ...
for video), which is then encoded into the target format.


Re-encoding/recoding

One may also re-encode data in the same format, for a number of reasons: ;Editing: If one wishes to edit data in a compressed format (for instance, perform image editing on a
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
image), one will generally decode it, edit it, then re-encode it. This re-encoding causes digital generation loss; thus if one wishes to edit a file repeatedly, one should only decode it ''once,'' and make all edits on that copy, rather than repeatedly re-encoding it. Similarly, if encoding to a lossy format is required, it should be deferred until the data is finalised, e.g. after mastering. ;Lower bitrate: Transrating is a process similar to transcoding in which files are coded to a lower bitrate without changing video formats; this can include
sample rate conversion Sample-rate conversion is the process of changing the sampling rate of a discrete signal to obtain a new discrete representation of the underlying continuous signal. Application areas include image scaling and audio/visual systems, where differe ...
, but may use an identical sampling rate with higher compression. This allows one to fit given media into smaller storage space (for instance, fitting a
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
onto a
Video CD Video CD (abbreviated as VCD, and also known as Compact Disc Digital Video) is a home video Home video is prerecorded media sold or rented for home viewing. The term originates from the VHS VHS (Video Home System) is a standard Sta ...
), or over a lower bandwidth channel. ;
Image scaling In computer graphics and digital imaging, image scaling refers to the resizing of a digital image. In video technology, the magnification of digital material is known as upscaling or resolution enhancement. When scaling a vector graphic imag ...
: Changing the picture size of video is known as transsizing, and is used if the output resolution differs from the resolution of the media. On a powerful enough device, image scaling can be done on playback, but it can also be done by re-encoding, particularly as part of transrating (such as a downsampled image requiring a lower bitrate). One can also use formats with
bitrate peeling Bitrate Peeling is a technique used in 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'' (Gotthar ...
, that allow one to easily lower the bitrate without re-encoding, but quality is often lower than a re-encode. For example, in
Vorbis Vorbis is a free and open-source software Free and open-source software (FOSS) is software Software is a collection of instructions that tell a computer A computer is a machine that can be programmed to carry out sequences of ari ...
bitrate peeling as of 2008, the quality is inferior to re-encoding.


Drawbacks

The key drawback of transcoding in lossy formats is decreased quality.
Compression artifact A compression artifact (or artefact) is a noticeable distortion of media (including Image, images, Sound recording, audio, and video) caused by the application of lossy compression. Lossy data compression involves discarding some of the medi ...
s are cumulative, so transcoding causes a progressive loss of quality with each successive generation, known as digital generation loss. For this reason, transcoding (in lossy formats) is generally discouraged unless unavoidable. For users wanting to be able to re-encode audio into any format, and for digital audio editing, it is best to retain a master copy in a (such as
FLAC FLAC (; Free Lossless Audio Codec) is an audio coding format for lossless compression of digital audio, developed by the Xiph.Org Foundation, and is also the name of the free software project producing the FLAC tools, the reference software p ...
, ALAC, TTA,
WavPack WavPack is a free and open-source Audio compression (data)#Lossless, lossless audio compression file format, format and application implementing the format. It is unique in the way that it supports hybrid audio compression alongside normal compres ...
, and others) that take around half the storage space needed when compared to original uncompressed
PCM 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 ...
formats (such as
WAV Waveform Audio File Format (WAVE, or WAV due to its 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 identification by an external observer. T ...

WAV
, and
AIFF Audio Interchange File Format (AIFF) is an audio file format An audio file format is a file format for storing digital audio data on a computer system. The bit layout of the audio data (excluding metadata) is called the audio coding format and can ...
), as lossless formats usually have the added benefit of having
meta data Metadata is "data Data are units of information Information can be thought of as the resolution of uncertainty; it answers the question of "What an entity is" and thus defines both its essence and the nature of its characteristics. T ...
options, which are either completely missing or very limited in PCM formats. These lossless formats can be transcoded to PCM formats or transcoded directly from one lossless format to another lossless format, without any loss in quality. They can be transcoded into a lossy format, but these copies will then not be able to be transcoded into another format of any kind (PCM, lossless, or lossy) without a subsequent loss of quality. For
image editing Image editing encompasses the processes of altering images, whether they are Digital photography, digital photographs, traditional Photographic processing, photo-chemical photographs, or illustrations. Traditional analog image editing is kno ...
users are advised to capture or save images in a
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 ...
or uncompressed format, and then edit a copy of that master version, only converting to lossy formats if smaller file sized images are needed for final distribution. As with audio, transcoding from lossy format to another format of any type will result in a loss of quality. For
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 ...
, (for video converting), images are normally compressed directly during the recording process due to the huge
file size File size is a measure of how much data Data (; ) are individual facts, statistics, or items of information, often numeric. In a more technical sense, data are a set of values of qualitative property, qualitative or quantity, quantitative varia ...
s that would be created if they were not, and because the huge storage demands being too cumbersome for the user otherwise. However, the amount of compression used at the recording stage can be highly variable, and is dependent on a number of factors, including the quality of images being recorded (e.g. analog or digital, standard def. or high def., etc.), and type of equipment available to the user, which is often related to budget constraints – as highest quality digital video equipment, and storage space, may be expensive. Effectively this means that any transcoding will involve some cumulative image loss, and hence the most practical solution insofar as minimizing loss of quality is for the original recording to be deemed the master copy, and for desired subsequent transcoded versions, which will often be in a different format and smaller file size, to be transcoded only from that master copy.


Usage

Although transcoding can be found in many areas of content adaptation, it is commonly used in the area of
mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone A telephone is a telecommunication Telecommunication is the tra ...

mobile phone
content adaptation. In this case, transcoding is a must, due to the diversity of
mobile device A mobile device (or handheld computer) is a computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets ...
s and their capabilities. This diversity requires an intermediate state of content adaptation in order to make sure that the source content will adequately function on the target device to which it is sent. Transcoding video from most consumer
digital cameras A digital camera is a camera A camera is an optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behav ...

digital cameras
can reduce the file size significantly while keeping the quality about the same. This is possible because most consumer cameras are real-time, power-constrained devices having neither the processing power nor the robust power supplies of desktop CPUs. One of the most popular technologies in which transcoding is used is the
Multimedia Messaging Service Multimedia Messaging Service (MMS) is a standard way to send messages that include multimedia Multimedia is a form of communication that combines different content forms such as text, audio, images, animations, or video into a single presenta ...
(MMS), which is the technology used to send or receive messages with media (image, sound, text and video) between mobile phones. For example, when a camera phone is used to take a digital picture, a high-quality image of usually at least 640x480
pixels In digital imaging Digital imaging or digital image acquisition is the creation of a representation of the visual characteristics of an object, such as a physical scene or the interior structure of an object. The term is often assumed to imp ...

pixels
is created. When sending the image to another phone, this high resolution image might be transcoded to a lower resolution image with fewer colors in order to better fit the target device's screen size and color limitations. This size and color reduction improves the user experience on the target device, and is sometimes the only way for content to be sent between different mobile devices. Transcoding is extensively used by home theatre PC software to reduce the usage of
disk space A spindle of DVD-RW's. Computer data storage is a technology consisting of computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perfor ...
by video files. The most common operation in this application is the transcoding of
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 ...
files to the
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 ...
or
H.264 Advanced Video Coding (AVC), also referred to as H.264 or MPEG-4 MPEG-4 is a method of defining compression of audio and visual (AV) digital data. It was introduced in late 1998 and designated a standard for a group of audio and video codin ...
format. Real-time transcoding in a many-to-many way (any input format to any output format) is becoming a necessity to provide true search capability for any multimedia content on any mobile device, with over 500 million videos on the web and a plethora of mobile devices.


History

Before the advent of semiconductors and integrated circuits, realtime resolution and frame rate transcoding between different
analog 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 ...

analog video
standards was achieved by a
CRT CRT may refer to: Science and technology Medicine * Calreticulin, a protein *Capillary refill time, the rate at which blood refills empty capillaries *Cardiac resynchronization therapy, a treatment for heart failure, and CRT defibrillator (CRT-D ...

CRT
/ camera tube combination. The CRT part does not write onto a
phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or ...

phosphor
, but onto a thin, dielectric target; the camera part reads the deposited charge pattern at a different scan rate from the back side of this target. The setup could also be used as a
genlock Genlock (generator locking) is a common technique where the video output of one source (or a specific reference signal from a signal generator A signal generator is one of a class of electronic devices that generates electronic signals with set ...
.


See also

;Concepts *
Data conversion Data conversion is the conversion of computer data from one file format, format to another. Throughout a computer environment, data is Character encoding, encoded in a variety of ways. For example, computer hardware is built on the basis of cert ...
* Lossy data conversion * Data transformation *
Type conversion In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of co ...
*
Video coding 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 ...
;Comparison *
Comparison of video converters Video converters are computer programs that can change the storage format of digital video. They may recompress the video to another format in a process called transcoding, or may simply change the Digital container format, container format without ...
*
Comparison of DVD ripper software This article lists DVD ripper Ripping is extracting all or parts of digital contents from a container. Originally, it meant to rip music out of Amiga The Amiga is a family of personal computer File:Crystal Project computer.png, upright=0.9 ...


Notes


References

*
Federal Standard 1037C Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms, is a United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country Contiguous United St ...
*
MIL-STD-188 200 px, Cover of CHQ’s commercial reprint of the MIL-STD-188 Military Standards series MIL-STD-188 is a series of U.S. military standards relating to telecommunications. Purpose Faced with "past technical deficiencies in telecommunications syst ...
* List of Portable Multimedia Software * P. A. A. Assuncao and M. Ghanbari,
A frequency-domain video transcoder for dynamic bit-rate reduction of MPEG-2 bit streams
" in IEEE Transactions on Circuits and Systems for Video Technology, vol. 8, no. 8, pp. 953-967, Dec. 1998. * Huifang Sun, Xuemin Chen, and Tihao Chiang,
Digital Video Transcoding for Transmission and Storage
', New York, CRC Press, 2005.


External links


IDC Report on Video Transcoding


* ttp://www.ateme.com/-White-papers- Transcoding White Papers {{Authority control Video conversion software Film and video technology