Static AVAudioSessionMicrophoneInjectionCapabilitiesChangeNotification 

pub unsafe static AVAudioSessionMicrophoneInjectionCapabilitiesChangeNotification: Option<&'static NSNotificationName>

Available on crate feature AVAudioSessionTypes only.

Notification sent to registered listeners when the system’s capability to inject audio into input stream is changed

Check the notification’s userInfo dictionary for AVAudioSessionMicrophoneInjectionIsAvailableKey to check if microphone injection is available. Use AVAudioSession’s isMicrophoneInjectionAvailable property to check if microphone injection is available

See also Apple’s documentation