Smoothing Keyframes with Bezier Handles

The keyframes of some motion settings and filter controls (but not audio levels) can be smoothed. When you smooth a keyframe, one or more Bezier handles are “attached” to the keyframe. These handles define the Bezier curve applied to a parameter’s interpolation from one keyframe to the next. This allows you to modify the acceleration and deceleration of the change from one keyframe’s value to the next. The velocity doesn’t cause the effect to happen faster or slower; the overall speed of an effect is determined solely by the distance from one keyframe to the next.

For example, if you space keyframes 2 seconds apart in the Rotation parameter, the resulting rotation lasts 2 seconds. If you apply smoothing to one of the keyframes, the total duration of the rotation remains 2 seconds, but the rate at which the clip rotates to full speed and then slows down to a stop is different over the course of those 2 seconds. If you move the two keyframes closer together, the rotation happens faster; if you move the two keyframes farther apart, the rotation happens slower.

Figure. Video track showing two keyframes with no smoothing.
Figure. Video track showing a curve between two keyframes created by a smoothed keyframe with a Bezier handle on one side.

Understanding Bezier Handles and Curves

When adjusting the Bezier handles that are attached to a smoothed clip, there are several kinds of curves you can create, which result in different velocity rates.

  • The steeper the curve of the Bezier handles in the parameter’s keyframe graph line (or overlay), the faster the rate of change.

  • The shallower the curve of the parameter’s keyframe graph line (or overlay), the slower the rate of change.

    Figure. Keyframe graph line showing a constant rate of change.
    Figure. Keyframe graph line showing a shallow rate of change.
    Figure. Keyframe graph line showing a steep rate of change.

The kinds of curves you can apply to a keyframe depend on that keyframe’s location relative to other keyframes on the parameter’s keyframe graph line.

One-Sided Bezier Handles

The first and last keyframes of a group have one-sided Bezier handles. These keyframes begin and end any dynamic changes in a clip’s parameters, and therefore they accelerate into a change and decelerate out of it.

Figure. Keyframe graph line showing a change made with keyframes that have one Bezier handle.

Two-Sided Bezier Handles

Keyframes that are in between other keyframes have two-sided Bezier handles. These handles are normally locked together, so that the curve of a parameter’s keyframe graph line has a smooth transition into and out of the keyframe, with no sudden changes.

Figure. Keyframe graph line showing a keyframe with two-sided Bezier handles between beginning and end keyframes.

By default, if you change one of these handles, there’s an equal change to both sides of the handle.

Figure. Keyframe graph line showing both sides of a Bezier handle lengthened by the same amount.
Figure. Keyframe graph line showing that raising the height of a curve using a two-sided Bezier handle lowers the curve on the other side by the same amount.

The link between these two handles can be suspended, however, to create different kinds of sudden changes in the curve. You do this by holding down the Command key while adjusting one of the handles.

Figure. Keyframe graph line showing one side of a Bezier handle being changed independently of the other.

Smoothing Keyframes

Smoothing a keyframe, or adding Bezier handles to it, makes the change from one keyframe’s value to the next more gradual by applying a curve instead of a straight line. The ability to apply smoothing to a parameter in Final Cut Pro depends on the kind of keyframes a parameter uses.

  • One-dimensional keyframes: Parameters that contain multiple values can’t be represented by curved graph lines in the keyframe graph area. Instead, all values of the parameter are represented by a single point on the graph. Examples of multidimensional parameters are the Center and Anchor Point parameters (which have two values: x and y) and the Color parameter for the Drop Shadow attribute (which has three values: hue, saturation, and brightness).

    You cannot use Bezier handles to smooth these types of keyframes, because the keyframe graph line cannot display multiple parameter values (such as x and y) simultaneously. In the case of the Center or Anchor Point parameter, you can adjust these values on curves directly in the Canvas.

  • Two-dimensional keyframes: Parameters that contain a single value can be animated with two-dimensional keyframes in the keyframe graph area. Keyframes in these parameters’ keyframe graph lines can be smoothed, using Bezier handles to modify their rate of change. Examples of parameters with only a single value are Scale, Rotation, Aspect Ratio, and Opacity.
To smooth a keyframe
  • Control-click the keyframe, then choose Smooth from the shortcut menu.

    Figure. Shortcut menu showing the Smooth command.

    You can manipulate the velocity of change that takes place from one keyframe to the next by adjusting the Bezier handles on the curve.

To change the shape of a Bezier curve
  • Drag the Bezier handle on the side of a keyframe.

To resize one side of a Bezier handle independently of the other
  • Hold down the Shift key as you drag a Bezier handle.

    When you release the Shift key, the relative length of the two handles is locked to the new unequal lengths you set.

To change the angle between one side of a Bezier handle and the other
  • Hold down the Command key as you drag a Bezier handle.

    When you release the Command key, the new relative angle of the two handles is locked to the angle you set.

    Figure. Keyframe graph line showing the angle of one side of a Bezier handle being changed independently of the other.
To change the length and the angle of one Bezier handle independently of the other
  • Hold down the Command and Shift keys as you drag a Bezier handle.

    When you release both keys, the new relative length and angle of the two handles are locked.

    Figure. Keyframe graph line showing the length and angle of one side of a Bezier handle being changed independently of the other.