Adding an Aspect Ratio Matte or Overlay in the player
Turning Guides on or off, and modifying the settings can be done via the icon in the toolbar below the timeline.
Mattes: Focuses attention on the selected aspect ratio, by blocking out pixels that fall outside of it
Overlays: Convenient option to view a standard Grid, Rule of Thirds grid, or Safe Areas on top of the media
Opacity: Select an opacity level that affects both Mattes and Overlays
Turn On and Off: Use the option at the bottom of the menu to turn Guides on or off, or alternatively use the "shift+g" keyboard shortcut. Your last setting will be remembered, so you can quickly turn Guides off and back on without having to set all options again.
Adjusting Project Settings for Guides
Settings for Guides can be found by navigating to the Media Settings tab within your Project Settings, and scrolling down to the "Custom Aspect Ratio Mattes" section.
Ratios: Limits list of available aspect ratio mattes in the Guides menu to those included in this comma separated list. Also allows setting any custom ratio by adding the desired value to the list. If no values are added to this setting, we will display the default list of standard aspect ratios in the Guides menu.
Default Ratio: This setting, available only if a comma separated list is added in the above Ratios setting, allows you to specify the default aspect ratio used when Guides are turned on.
Safe Area Percent: Set a custom percentage for the Safe Area Overlay by adjusting this value