I need to determine when my RemoteIO callback is changing the buffer size. Until iOS 7 we could add a session property listener using AudioSessionAddPropertyListener and then property kAudioSessionProperty_PreferredHardwareIOBufferDuration. This is now deprecated. Is there any replacement? AVAudioSession is meant to be KVO compliant, but not for the IOBufferDuration or preferredIOBufferDuration properties.
What is the replacement here?
The buffer duration is given to the RemoteIO callback in the form of the frameCount (proportional to the number of samples in the callback buffer) at a known sample rate. Any other notification would be asynchronous to this callback information, and thus possibly received at the wrong time compared to the actual change (which happens in the audio thread, not in the UI main run loop).
But your audio callback could change some visible state (global or in the parameter struct) which could be found by any other polling thread or consumer thread after the buffer duration update.