Apple has released a new app under the radar called Apple Partner Media Review. The tool is aimed at studios and production companies, who can use it to view their content on Apple TV before it is released. This allows you to determine early on whether the content is being displayed correctly, whether iTunes Extras are working correctly, etc.
Apple Partner Media Review allows studios and encoding companies to review their video content before publishing it on an Apple TV. A provider can simply browse through their media library and play the content directly in the app. The provider can either approve or deny HDR and iTunes Extras content in the app. An iTunes Connect ID with the appropriate access rights is required to use the app.