Apple Final Cut Pro X (10.1.2) - Manual (Page 106)

Chapter 7 Edit your project 106
When you rearrange, move, ripple, or remove clips in the primary storyline, any clips connected
to them will move (or be deleted) along with the primary storyline clips.
When you connect clips by dragging them, you have the option to put video clips below the
primary storyline or put audio clips above the primary storyline.
Connected
audio-only clip
Connected
audio/video clip
Title
Note: In Final Cut Pro, if you connect clips, the topmost video clips block out any video clips
below them. Exceptions to this rule are clips with some type of transparency, keying, or
compositing settings. For more information, see
Compositing overview on page 372. Audio clips
never affect video output, even when they are placed above video clips in the Timeline.
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