Region of interest

The region of interest is the area of the composition, layer, or footage item that is rendered for previews. Create a smaller region of interest to use less processing power and memory when previewing, thereby improving interaction speed and increasing RAM preview duration. Changing the region of interest does not affect file output, though you can change the size of your composition and select what portion is rendered by cropping to the region of interest.

Note: When the region of interest is selected, the Info panel displays the horizontal and vertical distances of the top (T), left (L), bottom (B), and right (R) edges of the region from the top-left corner of the composition.

To draw a region of interest, click the Region Of Interest button at the bottom of the Composition, Layer, or Footage panel, and then drag to select a viewable area of the panel.
To start over with the marquee tool, hold down Alt (Windows) or Option (Mac OS) and click the Region Of Interest button.
To switch between using the region of interest and using the full composition, layer, or footage frame, click the Region Of Interest button.
To move or resize the region of interest, drag its edges or handles. Shift-drag a corner handle to resize while preserving aspect ratio.
To crop to the region of interest, choose Composition > Crop Comp To Region Of Interest.