The MPEG-4 Encoder

Now we need to consider the MPEG-4 encoder. MPEG-4 encoders and decoders can be
realized in hardware or software. The argument for realizing the encoder/decoder in
hardware is to reduce the amount of memory needed, minimize processor delay,
and reduce the overall processor power budget. Companies like Emblaze (www
.emblaze.com) and Amphion (www.amphion.com) develop specialist ASICs for video
processing. The ASICs are optimized to minimize power drain in the handset.
The MPEG-4 encoders use a discrete cosine transform to capture the frequency content
of an image that is subdivided into (typically) 16 × 16 pixel macroblocks. It is the
differences from block to block that then get encoded. If two blocks adjacent to each
other are both blue—for example, they both show a cloudless blue sky—the description
of the second block is effectively the same again. MPEG-4 then adds a frame-toframe
comparison—a process known as differencing or differential coding.