Sync and Video : Working with Video in Pro Tools : General Video Editing : Selecting within Video Frame Boundaries

Selecting within Video Frame Boundaries
Pro Tools does not let you select, play back, or edit a partial video frame. The following rules apply when selecting or editing video:
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When you make a selection in a video track, the selection boundaries follow the current Grid setting but round to the nearest video frame boundary, as follows:
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If the selection includes more than half of a video frame, the full video frame is included within the selection.
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If the selection includes less than half of a video frame, that video frame is not included in a video selection.
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When you paste a selection containing video to a video track, the insertion point automatically aligns with the closest video frame boundary.
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When you paste audio and video simultaneously, this video frame re-alignment may result in the audio not being positioned exactly where you placed it. A warning dialog displays when this occurs.