Transcoding is a process that is often used of many types of digital data. Literally, it means taking one code and translating it to another code.

Usually transcoding means that you take a high bitrate / high quality data, decode it, downsample / shrink / otherwise mess with it to reduce its size, and then re-encode it. (The result is, as you may imagine, often uglier than original - but if the receiver makes the thing sound or look worse anyway, it's often practical.)

It can also be used to mean the generic process of "tailoring" digital information to specific type of receiver. (For example, there can be a transcoding proxy that converts HTML pages optimized for desktop use to PDA-friendly format.)

In certain contexts, transcoding is evil. Sometimes people wish to convert one lossy file format to another, say MP3 to OGG Vorbis for the sake of consistancy. All too often folks don't realize that this results in decreased quality, no matter what bitrate the resulting file is encoding at. If you share transcoded music files with people, they will be very angry at you. Sometimes transcoding is necessary, for example when the source is compressed in a lossy format. This holds true for operations like compressing a DVD down to one or two CD's. For most forms of lossy compression, results will always be best if the highest quality input is used.

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