Added subtitles to video however audio is removed?

Question

I have followed the instructions in the link below for adding subtitles (under the section 'Just Like Those Foreign Films — Adding Subtitles to Videos'):

http://www.raywenderlich.com/30200/avfoundation-tutorial-adding-overlays-and-animations-to-videos#comments

However, for some reason, the sound is removed when I play the video created.

What should I do to maintain that audio in the final video too?

ANY help would be greatly appreciated.