To fill gaps with interpolation:

1. Select the marker with the gap that you want to fill using interpolation.
2. Move the Timeline indicator to the gap that you want to interpolate. The Gap options display above the Optical editor.
3. Select one of the gap interpolation methods (Auto-Linear, Auto-Constant, and so on) from the Gap Interpolation field. By default, it is set to Auto-Rigid Body.
4. Change the gap interpolation to Control Curve. The interpolation keeps the shape of the previously selected Gap interpolation.
5. For more control over the shape of the data in the gap, add Gap keys.