Set curve extrapolation
When you begin adding keyframes, you instruct Motion to modify the in-between frames to interpolate the effect. But what values are used for the frames before the first keyframe and after the last one?
By default, when you add your first keyframe, that same value is extended forward and backward to the beginning and end of the clip (as if you hadn’t added a keyframe). In other words, the frames before that first keyframe remain at the value of that first keyframe. Similarly, the frames after the last keyframe hold at that last defined value.
You can override this default behavior to create loops and other patterns. This is known as extrapolation. When you apply an extrapolation method to a parameter, animation is added beyond your first or last keyframes. Extrapolation is useful when you need to extend the duration of an effect such as a moving background. Several extrapolation algorithms are available in the Before First Keyframe and After First Keyframe submenus of the Animation menu. For descriptions of the preset algorithms, see Curve extrapolation methods.
Apply an extrapolation method to a parameter before the first keyframe
In the Keyframe Editor, click in the fifth column of the parameter list to open the Animation menu for the parameter to change, then choose an item from the Before First Keyframe submenu.
Apply an extrapolation method to a parameter after the last keyframe
In the Keyframe Editor, click in the fifth column of the parameter list to open the Animation shortcut menu for the parameter to change, then choose an item from After Last Keyframe submenu.