fix background playback

MusicPlayer Watch App/ContentView.swift

@@ -188,7 +188,7 @@ struct ContentView: View {
             print(self.player.error!)
         }
         else {
-            //self.player.play()
+            self.player.play()
         }
     }
     init() {
@@ -202,7 +202,7 @@ struct ContentView: View {
         
         do {
             let session = AVAudioSession.sharedInstance()
-            try session.setCategory(AVAudioSession.Category.playback)
+            try session.setCategory(AVAudioSession.Category.playback, mode: .default, policy: .longFormAudio, options: .duckOthers)
         } catch {
             print(error)
         }

MusicPlayer Watch App/PlaybackView.swift

@@ -69,6 +69,7 @@ struct PlaybackView: View {
                                         parent!.player.pause()
                                         self.playing = false
                                     } else {
+                                        parent!.player.audiovisualBackgroundPlaybackPolicy = .continuesIfPossible
                                         parent!.player.play()
                                         self.playing = true
                                     }