In the Project panel, clips that contain both video and audio appear as a single item, represented by . When you add the clip to the sequence, however, the video and audio appear as two objects, each in its appropriate track (provided you specified both the video and audio sources when adding the clip).
The video and audio portions of the clip are linked so that when you drag the video portion in a Timeline panel, the linked audio moves with it, and vice versa. For this reason, the audio/video pair is called a linked clip. In a Timeline panel, each part of the linked clip is labeled with the same clip name, which is underlined. The video is marked [V] and the audio is marked [A].
Ordinarily, all editing functions act on both parts of a linked clip. When you want to work with the audio and video individually, you can unlink them. When you do, you can use the video and audio as though they were not linked; even the clip names no longer appear underlined or bear the [V] and [A] labels. Even so, Premiere Pro keeps track of the link. If you relink the clips, they indicate whether they have been moved out of sync, and by how much. You can have Premiere Pro automatically resynchronize the clips.
You can also create a link between previously unlinked clips. This is particularly useful if you need to synchronize video and audio that were recorded separately.
Ordinarily, you set one In point and one Out point for a source clip. Even if it’s a linked clip (a clip containing video and audio tracks), In and Out points apply to both tracks of the clip. Set in a sequence, the audio and video of the standard clip appear at the same time. Sometimes you want to set the video and audio In or Out points independently, however, in order to create split edits (also known as L-cuts and J-cuts). When placed in a sequence, a clip trimmed for a split edit will have its audio appear before its video, or its video before its audio.