mjpeg-howto: Trading Quality/Speed
10 Trading Quality/Speed
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If absolute quality is your objective a modest improvement can be
achieved using the -4 and -2 flags. These control how ruthlessly
mpeg2enc discards bad looking matches between sections of adjacent
frames during the early stages of the search when it is working with
4*4 and 2*2 clusters of pixels rather than individual pixels. Setting
-4 1 -2 1 maximizes quality. -4 4 -2 4 maximizes speed. Note that
because the statistical criteria mpeg2enc uses for discarding bad
looking matches are usually fairly reliable the increase/decrease in
quality is modest (but noticeable).
Reducing the radius of the search for matching sections of images
also increases speed. However due to the way the search algorithm works
the search radius is in effect rounded to the nearest multiple of 8.
Furthermore, on modern CPU's the speed gained by reducing the radius
below 16 is not large enough to make the marked quality reduction
worthwhile for most applications.
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