Media Center is a free app with in-app purchases. You can watch additional (paid) video formats without advertising and watermark, for this you need to buy the corresponding codec for video that you want to watch. For example: you want to watch video in .flv – you need to buy FLV codec. All information about expanding features in the app you can find at Store description.
Here is also the link to app for you: https://www.microsoft.com/store/p/9nblggh10xs8
