I am playing audio from my server using AVPlayer in my application. Now I want that when it completely buffer the audio then I can save that data in the application to play
You can't access the buffer of the AVPlayer. Some hints: You can put previews (short versions of audios) of your audio files on your server, so that Your users could listen the previews before they download the full audio files, or you may search for custom open source audio stream players, maybe those will allow you to access the stream buffer. Good Luck!