You still have not fixed your bug and I know you are simply not interested in fixing it.

Hi, Thanks for your help but as I know exactly how the file is structured (it becomes a read only data file) I managed to read it with no problem using similar functions from my Objective-C code. Regards, Paul

Apple did slightly fix their bug but not 100% fixed. It's now been 2 years and the ticket is still open. Doesn't matter anymore as the schools which were using my app have moved to ChromeBooks and we have an online site especially for them.

Found it, fixed it. recorderDefaults = [AVFormatIDKey: Int(kAudioFormatMPEG4AAC), AVEncoderAudioQualityKey: AVAudioQuality.min.rawValue] Don't use kAudioFormatMPEG4AAC.