An encoder is hardware or a software program that compresses audio and/or video signals for the purposes of streaming.

It is the process of changing data from one form to another, according to a set of rules specified by a codec.

The data is usually a file containing audio, video and/or still images. Often the encoding is done to make a file compatible with specific hardware (such as a DVD Player), or to minimize the amount of space required by the data.

Common video encoding methods include: DivX, MPEG-1, MPEG-2 and MPEG-4.

Common audio encoding methods include: MP3, DTS, and Dolby Digital.