Extrapolation is used to determine the behavior of a channel before the first, or after the last, keyframe. Extrapolation is useful when you want to create a cyclical effect, such as shutter flicker (as you would find in an old-time movie). You create one period in the flicker cycle, then use extrapolation to repeat the period over and over again. You will see the effects of extrapolation only if the film image has frames before the first keyframe or after the last keyframe.

The following extrapolation types are supported:

• Constant Applies the value at the first or last keyframe to all the frames that come before or after the last or first keyframe.
• Linear Continues the curve in a linear fashion before the first keyframe or after the last keyframe using the tangent.
• Loop Cycles the animation as it appears between the first and last keyframe.
• Ping Pong Cycles the animation as it appears between the first and last keyframes forward then backward.
• Relative Cycles the animation as it appears between the first and last keyframe. This is similar to “Loop”, but the relative offset is based on the channel value derived from either the first or last keyframe.
• Key Linear Continues the curve in a linear fashion before the first keyframe or after the last keyframe, disregarding all tangents.