I want to know when my AVAudioRecorder is inaccessible (e.g when music starts playing).
AVAudioRecorder
As audioRecorderEndInterruption will be deprecated
audioRecorderEndInterruption
If you haven't already, try setting your AVCaptureSession's property usesApplicationAudioSession to NO.
AVCaptureSession
usesApplicationAudioSession
This question & answer may act as a good reference if you're looking for any more detail.