bed4670f_Background_Execution__3_1_Background_modes_for_apps_Xcode_background_mode
[UIBackgroundModes value] audio [Description] The app plays audible content to the user or records audio while in the background. (This content includes streaming audio or video content using AirPlay.) The user must grant permission for apps to use the microphone prior to the first use; for more information, see Supporting User Privacy. [Xcode background mode] 
Audio and AirPlay
Background Execution