Apple Final Cut Pro 7 - Manual (Page 501)

To change Source and Destination control connections
Do one of the following:
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Control-click a Source control, then choose a track from the shortcut menu.
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Control-click a Destination control, then choose a Source control from the shortcut menu.
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Click a Destination control.
The first Source control above that track moves to that track.
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Option-click a Destination control.
The first Source control beneath that track moves to that track.
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Drag one Source control on top of another to switch their connections.
For example, if Source control a1 is connected to Destination control A1, and Source
control a2 is connected to Destination control A2, when you drag the a2 Source control
onto the a1 Source control, the connections are reversed (a1 is connected to A2, and a2
is connected to A1).
Disconnecting Source and Destination Controls
You can prevent specific video or audio source clip items from being edited into your
sequence by disconnecting Source and Destination controls. For example, if you disconnect
the video Source control prior to making an edit, only the audio source clip items are
edited into the Timeline.
501 Chapter 34 Working with Tracks in the Timeline