Slip video layers in the Timeline track area
Slip a video layer when you want to use a different section of your source clip without changing the layer’s duration or where it appears in the Timeline.
Important: Slipping is only possible after you’ve trimmed a video layer’s timebar.
For example, if you have a shot of a door opening that is three seconds long and you want to trim it by one second, you can use the Slip function to select which one-second section to use: the first second as the door leaves the jamb, the next second where the door swings open, or the last second where it bangs against the wall.
As with trimming, when you slip a video layer in the track area, Motion provides a visual representation of how much additional footage is available in the object’s source clip: a dimmed extension on either end of the bar indicates that unused frames exist in the source video clip. You can only slip a bar as far as the existing unused frames in the source media.
Slip a video layer in the Timeline
With the pointer over the video layer’s timebar, press and hold down the Option key.
The pointer turns into the slip pointer.
Still holding down the Option key, drag the middle part of the bar left or right.
Dragging to the left replaces the frames with a section from later in the source material; dragging to the right uses frames from earlier in the clip.