Visual QuickStart Guide [Electronic resources] : Final Cut Express HD for Mac OS X نسخه متنی

Editing a Motion Path

Once you have created it, you can adjust a motion path directly in the Canvas (or Viewer) by moving or deleting motion path keyframes. When you're working with a motion path in the Canvas, the playhead doesn't need to be over a keyframe for you to move or delete it, nor does the playhead location prohibit you from adding a motion path keyframe.

Remember that a keyframe is like an edit point: It signals a change in an effect. In a motion path, keyframes are placed automatically only when a motion path changes direction. A straight motion path requires only two keyframes: a start keyframe and an end keyframe.

The two motion path variables you are adjusting are your clip's speed of travel (determined by the ratio of duration to distance between keyframes) and the path's route (indicated by the shape of the white line that connects the start and end keyframes). The little dots that appear between the keyframes indicate the duration between path points.

Adjusting motion path curves and corners

Final Cut Express features two types of motion path keyframes: corners and curves. The default motion path keyframe is a corner, which creates an instant change in direction. If you want a smoother motion effect, the curve keyframes have Bézier handles, which you can use to fine-tune the shape of the path's curve, as well as ease handles, which you can use to fine-tune your clip's speed immediately before and after the keyframe location.

You switch a corner type motion path keyframe to a curve type as the first step in smoothing your motion path and finessing its timing.

Tip

You can use the Shift and Command keys while dragging a Bézier or ease handle to influence the connections between the angles of the curve.

To toggle a keyframe between corner and curve types in Wireframe mode:

With your clip displayed in Wireframe mode in the Canvas, Control-click a keyframe and

choose one of the following options:

Figure 15.54 ).



Figure 15.54. Control-click a keyframe on the Canvas; then choose Make Corner Point to toggle the keyframe from a curve type to a corner type.







• Ease In/Ease Out accesses the ease handles, which are discussed later in this section.

• Linear applies a constant rate of speed to the path immediately before and after the keyframe location.

• Delete Point deletes the keyframe.

Adjusting speed along a motion path

You can increase the speed of a clip's movement by shortening the timecode duration between two keyframes without changing their spatial coordinates. The clip's speed increases, since it takes less time to travel between the two locations on your motion path. Or keep the time interval the same and move the keyframes farther apart on the motion path, so the clip travels farther in the same amount of time. Other timing factors in your sequence composition will dictate your choice.

Ease handles, located in the Canvas between the Bézier handles and the keyframe's position point (Figure 15.55 ), fine-tune the rate of speed at which a clip approaches and leaves a curve keyframe. The default Ease In and Out setting slows the speed on the motion path by 33 percent before and after the keyframe, but you can customize that setting. Drag both handles to set the clip's ease in and ease out to the same rate, or drag the handles separately to set different ease-in and ease-out rates.

To make a clip ease in and out of a keyframe: