An encoder is a device used to encode a bitstream or other signal or data into a form that is acceptable for transmission or storage. This is usually done by means of an algorithm, especially if any part is digital, while most analogue is done with circuitry.
A decoder is a device which is the reverse, undoing the encoding so that the original information can be retrieved. The same method used to encode is usually just reversed in order to decode.
An endec is a device which both encodes and decodes, either with the same or separate circuitry or algorithm.
The general difference between an endec and a codec is that hardware is usually considered to be an endec, while software is considered to be the codec. Similarly, the word "encoding" is usually used for hardware, while "coding" is usually used in regards to software.
Examples of encoders, decoders, and endecs:
- a modem is an endec, likewise a modulator is an encoder and a demodulator is a decoder
- an Emergency Alert System unit is usually an endec, but sometimes just a decoder
- a stereo generator used in broadcast is an encoder
- a program (or hardware) which uses a compression algorithm to create MPEG audio and/or video is an encoder, and one which plays back such files is a decoder
