A set of important topics regarding media support in Windows Phone 8 applications, as well as regarding speech recognition, and synthesis can be found at the following links:
http://www.developer.nokia.com/Community/Wiki/Windows_Phone_8_Games_-_Migrating_from_XNA_to_DirectX
http://henry-chong.com/2012/02/pro-tip-including-background-music-for-your-windows-phone-app/
http://msdn.microsoft.com/library/hh191443
UserIdleDetectionMode
property used to disable the lock screen is described at:3.146.221.149