Save audio file with changed time pitch using AVAudioEngine in Swift

问题

Currently, I am trying to change the time pitch of an existing audio file from the Document folder, then override the old file with the modified one using AVAudioEngine. I have got the first part working using AVAudioPlayerNode and AVAudioUnitTimePitch. I have no idea about the second part though. Can someone point me to the right direction?

Thanks.

来源：https://stackoverflow.com/questions/29012139/save-audio-file-with-changed-time-pitch-using-avaudioengine-in-swift