Mask Tracking

The mask tracker transforms a mask so that it follows the motion of an object (or objects) in a movie. You usually create and use masks to hide clips from the final output, select a part of the image or video to apply effects, or combine clips from different sequences.

To use the mask tracker, select a mask and click the Mask Path setting under the mask. Right-click the selected mask and select Track Mask to begin tracking a mask.

When a mask is selected, the Tracker panel switches to mask tracking mode, and displays the following controls:

• Track forward either one frame at a time or until the end of the layer.
• Track backward either one frame at a time or until the end of the layer.
  
• Different methods with which you can choose to modify position, scale, rotation, skew, and perspective of the mask.

If the Tracker panel is not displayed, select a mask and go to Animation > Track Mask to display the panel. You can also context-click a mask and choose Track Mask from the context menu.

The result of using the mask tracker can be seen in the application of keyframes for the Mask Path property; the mask shape matches the transformations tracked in the layer, depending on the type of method that is chosen.

• For effective tracking, the tracked object must maintain the same shape throughout the movie, though the position, scale, and perspective of the tracked object can change.
• You can select multiple masks before beginning the tracking operation, and keyframes are then added to the Mask Path property for each selected mask.
• The layer being tracked must be a track matte, an adjustment layer, or a layer with a source that can contain motion. This includes layers based on video footage and precompositions, but not solid-color layers or still images.

The mask tracking analysis searches for content inside the mask. Use the Mask Expansion property to expand or contract the area of the mask.