A codec is a device or computer program capable of encoding and/or decoding a digital data stream or signal. The word codec is a portmanteau of 'compressor-decompressor' or, more commonly, 'coder-decoder'. A codec (the program) should not be confused with a coding or compression format or standard – a format is a document (the standard), a way of storing data, while a codec is a program (an implementation) which can read or write such files. In practice "codec" is sometimes used loosely to refer to formats, however.
A codec encodes a data stream or signal for transmission, storage or encryption, or decodes it for playback or editing. Codecs are used in videoconferencing, streaming media and video editing applications. A video camera's analog-to-digital converter (ADC) converts its analog signals into digital signals, which are then passed through a video compressor for digital transmission or storage. A receiving device then runs the signal through a video decompressor, then a digital-to-analog converter (DAC) for analog display. The term codec is also used as a generic name for a video conferencing unit.
An endec (encoder/decoder) is a similar yet different concept mainly used for hardware. In the mid 20th century, a "codec" was hardware that coded analog signals into Pulse-code modulation (PCM) and decoded them back. Late in the century the name came to be applied to a class of software for converting among digital signal formats, and including compander functions.
A modem is a contraction of modulator/demodulator (modem was called dataset by telcos) and converted digital data from computers to analog for phone line transmission. On the receiving end the analog was converted back to digital. Codecs do the opposite (convert audio analog to digital and then computer digital sound back to audio).
An audio codec converts analog audio signals into digital signals for transmission or storage. A receiving device then converts the digital signals back to analog using an audio decompressor, for playback. An example of this are the codecs used in the sound cards of personal computers.
Full article ▸