AVFoundation Session with Core Audio AudioQueue

Working on a audio video processing app. Followed RosyWriter example to get a working video processor using AV Foundation and OpenGL. Problem is no audio preview, that is real-time audio playback.... (yes, this causes feedback)!

In RosyWriterCapturePipeline.m under the captureOutput method send audio sample buffers to a Core Audio AudioQueue for playback. AudioQueue is working, but audio data stops coming into the captureOutput method.

What is going on? Could Core Audio be interfering with AV Foundation? Or is it more likely the dispatch queue handling the audio capture is getting plugged up? And what is a good way to test and correct for this?

AVCaptureSessionRuntimeErrorNotification isn't supplying any indication that audio capture has failed.