Introduction to compression
MPEG is actually an acronym for the Moving Pictures Experts Group
which was formed by the ISO (International Standards Organization) to
set standards for audio and video compression and transmission.
Compression is summarized in Figure 1.1. It will be seen in (a) that the
data rate is reduced at source by the compressor. The compressed data are
then passed through a communication channel and returned to the
original rate by the expander. The ratio between the source data rate and
the channel data rate is called the compression factor. The term coding gain
is also used. Sometimes a compressor and expander in series are referred
to as a compander. The compressor may equally well be referred to as a
coder and the expander a decoder in which case the tandem pair may be
called a codec.