You can now use Transporter, Apple’s command-line delivery tool, to upload app previews to iTunes Connect. Transporter integrates with your content management system to deliver your app metadata in bulk using XML, which is especially useful for adding and managing multiple localizations.
App previews demonstrate the features, functionality, and user interface of apps using footage captured on device. You can have up to three app previews for each language your app supports, and each preview can be up to 30 seconds long.
Learn more about app previews at the link below! For details on using Transporter to upload app previews, see the App Metadata Specification.