Codec

From Free net encyclopedia

For other uses of codec, see Codec (disambiguation).

A Codec is a device or program capable of performing Encoding and Decoding on a data stream or signal. The word "codec" is a portmanteau of any of the following: 'Compressor-Decompressor', 'Coder-Decoder', or 'Compression/Decompression algorithm'.

Codecs encode a stream or signal for transmission, storage or encryption and decode it for viewing or editing. Codecs are often used in videoconferencing and streaming media solutions. A video camera's ADC converts its analog signals into digital signals, which are then passed through a video compressor for digital transmission. A receiving device then runs the signal through a video decompressor, then a DAC for analog display. An audio compressor converts analog audio signals into digital signals for transmission. A receiving device then converts the digital signals back to analog using an audio decompressor, for playback.

The raw encoded form of audio and video data is often called essence, to distinguish it from the metadata information that together make up the information content of the stream and any "wrapper" data that is then added to aid access to or improve the robustness of the stream.

Most codecs are lossy, in order to get a reasonably small file size. There are lossless codecs as well, but for most purposes the almost imperceptible increase in quality is not worth the considerable increase in data size. The main exception is if the data will undergo more processing in the future, in which case the repeated lossy encoding could damage the eventual quality too much.

Many multimedia data streams need to contain both audio and video data, and often some form of metadata that permits synchronization of the audio and video. Each of these three streams may be handled by different programs, processes, or hardware; but for the multimedia data stream to be useful in stored or transmitted form, they must be encapsulated together in a container format.

An endec is a similar (but not identical) concept for hardware.

It must be noted that while many people explain that AVI is a codec, they are incorrect - AVI (nowadays) is a container format, that many codecs might use (although not to ISO). There are other well known alternative containers such as ASF, MOV, RM, MP4, and MPG.

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