The editing mode selector at the right-hand end of the timeline toolbar determines the behavior of other clips when editing changes are made. Material to the left of the edit point is never affected in timeline editing, so this applies only to clips that extend rightward from the edit point.
Three choices of editing mode are available: smart, insert and overwrite. The default is smart, in which Studio selects from insert, overwrite and sometimes more complex strategies in the context of each editing operation.
Smart mode is designed to maintain synchronization between timeline tracks as far as possible. In a multi-track editing situation, clips typically have vertical as well as horizontal relationships. When you have carefully placed your cuts to coincide with the beats of a music track, for example, you don’t want to disrupt everything when you make additional edits.
Insert mode is always non-destructive: it moves other clips on the track out of the way before inserting new material. It will also automatically close gaps created by removing material. Only the target track is affected. Any prior synchronization with other tracks from the edit point rightwards is lost.
Insert is most useful in the early stages of a project, when you are collecting and arranging clips on the timeline. It ensures that no material will be lost, and makes it very easy to reorder clips and sequences of clips.
In the later stages, when the structure of your project is approaching its final state and you have started carefully synchronizing material on different tracks, insert mode is less helpful. The very properties that favor its use for the early stages (the ‘ripple’ behavior) count against it when finalizing. This is whereoverwrite comes into play.
Overwrite Mode directly affects only the clips you select. Changing the length or position of a clip inoverwrite mode will overwrite neighboring clips (if you lengthen) or leave gaps (if you shorten). It will never affect the synchronization between tracks.