Unlink video and audio tracks
Ordinarily, objects that contain both audio and video are linked so they remain in sync. This link is represented by an icon in the Timeline layers list.
Note: To display the Audio Timeline, click the Show/Hide Audio Timeline button, located in the lower-right corner of the Motion project window.
Objects that are linked are always edited together in the Timeline. Operations such as cut, copy, paste, and split affect both audio and video. However, if you ever want to break that relationship so you can move or edit the audio or video without the other tagging along, you can disable that link and move either object freely. Beware that this might result in your audio and video playing out of sync.
Manipulate audio and video elements separately
In the Timeline layers list, click the link icon to the right of the object name for the video or audio element.
A red slash appears over the link icon in all previously linked layers.
Move, trim, or slip the audio bar or video bar.
The link icon also appears in the Layers list and the Audio list of the Project pane.