Apple Final Cut Express 4 - Manual (Page 433)

Chapter 30 Linking and Editing Video and Audio in Sync 433
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In the following example, three stereo pairs of audio items are linked to a single
video item.
Moving a single pair of items out of sync results in a single out-of-sync duration, with
out-of-sync indicators with positive and negative durations in both the video and
audio items.
If you then move a second pair of audio items out of sync by a different amount, each
audio item that is out of sync from the anchor item has an out-of-sync indicator noting
its individual offset from the anchor item—in this example, the video item. The anchor
item displays a mixed-sync indicator with no duration. This tells you that multiple linked
items are out of sync by varying amounts.
A mixed-sync indicator
Out-of-sync indicators