[excerpt from DivX (TM) site]

The center of DivX MPEG-4 Codec is the DivX codec core. It is the
engine of the codec. The codec core processes either the video
image or MPEG-4 bitstream, and it uses the compression and
decompression to convert information between the formats. The codec
core includes two parts - an encoder (that compresses the video
image into MPEG-4 bitstreams) and a decoder (that decompresses the
MPEG-4 bitstream back into video images). The encoder core is named
"encore", and the decoder core "decore".

WWW: http://www.divx.com/