Many video effects let you customize its properties, such as the intensity or other random settings, using keyframes and various sliders. Video effects only affect the clips in the Master Video Track that appear within the effect’s duration.
To modify a video effect, double click on it or select it and then click Modify (To modify a video effect that is applied to the entire clip, select the clip and then click Effect). The type of modifications that are available in Effect Settings depend on the effect you selected.
Some effects use keyframes to customize the effect properties. Keyframes are frames of your video that define the start and end points of an effect, for example the intensity of an effect between two keyframes.