About using masks in templates
You can use shapes and masks in any Final Cut Pro template type. For the best template results, use the following guidelines:
Limit the use of shapes to generator templates. Shapes are ideal generator template elements because they can be scaled in Final Cut Pro X without degradation. (However, too many shapes in a template can adversely impact performance in Final Cut Pro.)
A shape added to a placeholder layer is converted to a mask. When a template with a masked placeholder is applied to a clip in Final Cut Pro, the mask is applied to the clip. Objects in the template outside the placeholder are not affected.
Mask parameters (Roundness, Feather, and Mask Blend Mode, and so on) can be published so they are editable in Final Cut Pro. However, the onscreen mask controls in Motion are not available in Final Cut Pro. To reposition a template mask in Final Cut Pro, publish the mask’s transform parameters (located in the mask’s Properties Inspector). For more information on publishing, see Add parameter controls overview.
For more information on working with shapes and masks, see Shapes, masks, and paint strokes overview.