Prepare content for new App Store in iOS 11
From the Developer Center:
“Product pages now offer more opportunities to showcase your apps with additional app previews, localization, and new text fields. Show more of your user experience with up to three app previews that autoplay, so customers can quickly see how your app works or watch what it’s like to play your game. You can also localize all of your app previews and screenshots. The new subtitle field allows you to convey your app’s essence and unique qualities in a few words, and promotional text lets you share the latest news about your app, such as timely marketing messages, limited-time events, and announcements of new content.
To start preparing your apps, see Making the Most of Your Product Page.”