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{{Refimprove|date=October 2015}}
'''Transcoding''' is the direct digital-to-digital conversion of one
"Advancements in Compression and Transcoding: 2008 and Beyond",
[[Society of Motion Picture and Television Engineers]] (SMPTE),
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</ref> 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]] and [[DPX]] files have been widely used as a common format for [[digital cinema]], but the data size of a two-hour movie is about 8 [[
Transcoding is commonly a [[lossy compression|lossy process]], introducing [[generation loss]]; however, transcoding can be lossless if the output is either losslessly compressed or uncompressed.<ref name=SMP/> The process of transcoding into a lossy format introduces varying degrees of
==Process==
Transcoding is a two-step process in which the original data is decoded to an intermediate uncompressed format (e.g., [[
==Re-encoding/recoding ==
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: If one wishes to edit data in a compressed format (for instance, perform image editing on a [[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;<ref name="Ryan">{{cite web|
; [[Image scaling]]
: 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 [[
One can also use formats with [[bitrate peeling]], that allow one to easily lower the bitrate without re-encoding, but quality is often lower than a re-encode. For example, in [[Vorbis]] bitrate peeling as of 2008, the quality is inferior to re-encoding.
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The key drawback of transcoding in lossy formats is decreased quality. [[Compression artifact]]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 [[data compression#Audio|lossless format]] (such as [[FLAC]], [[Apple Lossless|ALAC]],
For [[image editing]] users are advised to capture or save images in a [[raw image format|raw]] 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.
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==History==
Before the advent of semiconductors and integrated circuits, realtime resolution and frame rate transcoding between different [[Composite video|analog video]] standards was achieved by a [[Cathode
==See also==
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* [[Data transformation]]
* [[Lossy data conversion]]
* [[Video coding]]
* [[Adaptive bitrate streaming]]
; Comparison
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