"App Previews" allow you to display your app in action. You first upload all your app previews to AppManager, where we automatically detect device sizes, languages, and order. Once all app previews got processed and correctly recognized, simply click on the "Upload App Preview" button and all app previews will get uploaded to the store portal.
For iOS, this includes the following screenshot and image categories, which you can directly upload to AppManager:
iPad Pro (12.9-inch)
iPad Pro (11-inch)
iPad Pro (10.5-inch)
iPhone XS Max and iPhone XR (6.5-inch)
iPhone X (5.8-inch)
iPhone 6 Plus (5.5-inch)
iPhone 6 (4.7-inch)
iPhone 5 (4-inch)
The poster frame is the still image that gets shown to users if the video is loading, if they are on a slow connection or autoplay is disabled. It basically acts like the "fallback" if the video cannot get loaded fast enough.
By default Apple uses the 05:00 second frame for the poster frame. If you want to change it, you can do this directly in AppManager, no matter what browser you are using. Simply click on the app preview and change the time stamp on the right. If you are unsure, which second to choose you can view the video on the left.
If you want to change the poster frame value for many videos at one, make sure to check the checkbox shown in the screenshot above. AppManager will then use the specified value for all app previews across languages and devices, but the same position of course. In the above example this would change the value for the first trailer across all languages and devices.