Apple Final Cut Pro 7 - Manual (Page 1152)

Frame Blending, Optical Flow, and Motion Blur
Duplicating frames to create slow motion can result in a strobing, jittery effect. To minimize
this, you can turn on frame blending in the Change Speed dialogs. When slow motion is
created, frame blending uses the two frames that appear to either side of duplicate frames
and creates new in-between frames that are a composite of both. When blended frames
are inserted in place of frames that have simply been duplicated, slow-motion clips appear
to play back more smoothly. Speed changes can still play back in real time with the Frame
Blending option turned on.
Original Blended frame Original
While clips using frame blending can play in real time at preview quality, frame blending
on a field-per-field basis is much more processor-intensive and is only performed when
the clip is either rendered or played via a third-party video interface with real-time
hardware processing that’s capable of field blending.
For the most sophisticated slow-motion effects, consider using the optical flow technology
available in the Timing controls feature in Motion and the Frame Controls feature in
Compressor. For more information, see the Motion User Manual, available in Motion Help,
and the Compressor User Manual, available in Compressor Help.
Smoothing Slow Motion Using Motion Blur
Although using frame blending is an excellent way to smooth out the apparent motion
of a slow-motion clip, extremely slow speeds such as those below 20 percent can still
result in strobing. To further minimize this effect, you can use the Motion Blur attribute
in the Motion tab.
Drag the Samples slider to the right until you achieve the amount of blur you need to
cover the strobing of your clip (the higher the Samples setting, the longer rendering
takes) and then adjust the % Blur setting until you strike a good compromise between
the sharpness of the clip and the smoothness of the motion.
Using the Speed Tool
The Speed tool provides a quick method for adjusting the speed of two adjacent clips in
the Timeline by “rolling” their shared edit point. You can also adjust the speed of a single
clip by dragging its In or Out point with the Speed tool.
1152 Chapter 69 Changing Clip Speed