How to use safe areas
Safe areas in Subtitle can be used to display an overlay image on top of the video, which can be helpful for ensuring that content is placed correctly on the screen.
Configuration
Safe areas are configured with the safe areas setting in the launch template.
Usage
Selecting a safe area
The safe area select is available in the toolbar, and it will show the safe areas that were provided in the launch template as options
The safe area select in the toolbar will only display safe areas matching the aspect ratio of the video currently playing.

Viewing the safe area
Selecting a safe area will display the safe area on top of the video.

Toggling safe area select visibility
Once the safe area feature is enabled, you can toggle the visibility of the safe area select in the toolbar through the safe area setting in the User Preferences menu.

Reference
See reference for details: Launch template settings › Safe Areas.