[Freeswitch-users] How to mix audio in FreeSWITCH

Hi all, I want create a js scripts to execute a simple karaoke application. When user make call to my system, js scripts will play a audio file and user can sing. The js scripts will record the song and mix it with audio that is playing. Now, I can create a js to play audio, record call but I don't know how I can mix audio. Please help me. Thanks & Best regards, Khue.