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Compressed video has bursty characteristics, which makes it uneconomical for
transmission over traditional videoconferencing or broadcast network platforms,
such as ISDN or digital TV. The main reason for this is the disparity between
the required bitrate of intra-coded and of motion predicted images. In other
words, the former have poor compression efficiency compared to the latter, which
require much less bits to be encoded with the same quality.
In order to overcome this problem, data is buffered before transmission,
smoothing out the short-term variations in bitrate. However, longer-term
variations, due to changes in the spatial and temporal content of the sequence,
cannot be smoothed out in this way, unless arbitrarily large buffers are
used [RR96]. What is usually applied in these cases is rate control,
which has the drawback that for high-motion sequences the quality is degrading
significantly, as described in the previous chapter.
Isaac Kokkinidis
1998-08-27