Determines the type of motion
prediction used for direct macroblocks in B-frames.
none
Direct macroblocks are not used.
spatial
Motion vectors are extrapolated from neighboring blocks.(default)
temporal
Motion vectors are interpolated from
the following P-frame.
auto
The codec selects between spatial and temporal
for each frame.
Spatial and temporal are approximately the same speed and PSNR,the
choice
between them depends on the video content.
Auto is slightly better, but slower. Auto is most effective
when combined with
multipass.
direct_pred=none is both slower and lower quality.
