The settings you use for editing to and on the timeline can be found to the right and above the timeline. Most of these settings also have a keyboard shortcut associated with them.
Insert Edit button
Click to insert the selected source into the timeline at the positioner. The overall length of the timeline may change.
Overwrite Edit button
Click to overwrite material in the timeline (at the positioner) with the selected source. The overall length of the timeline does not change.
Replace Edit button
Click to replace the selected timeline clip or clips with the selected source clip. The overall length of the timeline sequence does not change. The replacement clip must be of equal length or longer than each clip it is replacing. If longer, extra frames are added as tail frames.
Secondary Edit box
Select an editing operation to apply to the selected source clip.
An edit aligning a point on the timeline with a point on the source clip.
An insert edit that adds your source clip to the end of the edit sequence on the timeline.
An insert edit that adds your source clip to the beginning of the edit sequence on the timeline.
A combination of an insert and replace edit; where the source clip replaces the selected clip on the timeline, and the all of the clips to the right ripple to accommodate the length of the new clip.
A replace edit that retains any effects applied to the replaced clip or clips on the timeline.
Fit To Fill
A replace edit; but instead of adding tail frames to a longer source clip, a timewarp is added to the replacement clip so that it fits the same duration occupied by the clip it is replacing.
Editorial Mode box
Choose an editorial mode for working with clips on the timeline.
Select a timeline element, or perform general trim (or roll) operations on a clip.
Set Slip mode, a trimming mode that offsets the frames in a clip without trimming the clips before or after it.
Set Slide mode, a trimming mode that trims the clips before and after the clip without changing the frames used in it. The state of the Ripple button has an effect on this mode.
Set Slide Cuts mode, a trimming mode that trims the clips before and after it, while also changing the frames used in a clip. The state of the Ripple button has an effect on this mode.
Set Slide Keyframes mode, a trimming mode that slides only animation keyframes on a clip.
When gesturally adding material into an edit sequence, enable to perform an insert edit, disable to perform an overwrite edit. When moving (or trimming) clips on the timeline, enable to fill the gap left by the removed clip or frames, disable to leave the gap.
Enable to snap to the closest transition, positioner, or mark to help gesturally align edits on the timeline. Press Shift to invert the snap mode during manipulation.
Keyframe Move Modes box
Select how the animation channel is affected when you trim elements with animated effects.
Resize the channel as you trim. The animation channel is scaled to fit into the timeline element. This option has no effect when you slip or slide.
Shift With Media
Link the keyframes to their original frame numbers. The animation channel moves to follow the original frames as you trim.
Pin To Timeline
Unlink the keyframes from their original frame number. The animation channel remains with the timeline element as you trim.