Apple Final Cut Express HD - Manual (Page 721)

Chapter 50 Adjusting Parameters for Keyframed Effects 721
IX
Determining the Number of Keyframes to Use
The complexity of the changes in your effects depends on the number of keyframes
that you add to a clip. You need at least two keyframes in a clip to make a dynamic
change from one value in an effects parameter to another. A more sophisticated
change requires three keyframes. To isolate a keyframe change to a certain section of
the entire overlay for an effect, you need at least four keyframes.
Creating Simple Effects With Two Keyframes
The simplest thing you can do to make a change is to add two keyframes. For example,
you can change the size, or scale, of a clip by adjusting its scale from 25 percent in the
first keyframe to 75 percent in the second keyframe.
Using Three Keyframes
With three keyframes, you can create more complex effects, such as a curved motion
path. In the example below, the position of the clip starts at the location specified by
the first keyframe, moves to the position specified by the second keyframe, and then
continues on its journey until it reaches the position specified by the third keyframe.
(For more information about creating motion paths in the Canvas, see “
Creating
Keyframed Motion Paths in the Canvas ” on page 735.)
Using Four (or More) Keyframes for Complex Effects
You can make isolated changes to sections of an overlay for an effect if you have at
least four keyframes. For example, if you have a superimposed clip that’s set at 50
percent opacity for the duration of the clip, but you need it to go to 100 percent for 3
seconds right in the middle, you’d create four keyframes on that clip’s opacity overlay.
Now you can have the opacity level of the clip start at 50 percent, jump to 100 percent
for the duration the keyframes specify, and then drop back to 50 percent for the
remaining duration of the clip.
Keyframe 2
Keyframe 1
Keyframe 3