how to record internal or system voice on iPhone?

Hello, everyone:

I would like to ask one problem, I want to implement an internal recording function, for example, when the third party software on my mobile phone plays a piece of music, I click on the recording, he can record the music being played (just record the audio); or I want to recording the sound of the system sound; but I don't have any idea, I hope I can get help. Is there any sdk or framework that can help me to do the internal recording?and i need the audio only。