Transcoding

Transcoding is the direct analog-to-analog or digital-to-digital conversion of one encoding to another, such as for movie data files (e.g., PAL, SECAM, NTSC), audio files (e.g., MP3, WAV), or character encoding (e.g., UTF-8, ISO/IEC 8859). This is usually done in cases where a target device (or workflow) does not support the format or has limited storage capacity that mandates a reduced file size, 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 terabytes (TB). That large size can increase the cost and difficulty of handling movie files. However, transcoding into a JPEG2000 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; 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, 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.

The terms encoding and transcoding are occasionaly used interchangeably. The primary difference between the two is that encoding refers to the compression of raw data to a digital format, whereas transcoding comprises of video decoding from one format to an uncompressed format, and then re-encoding the uncompressed data to the desired digital format. Video transcoding is mostly used when a video file is transferred from a source to a different destination, wherein both the source and destination support different file formats.

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