AVAudioRecorder settings empty after constructor call - ios

Question

I'm trying to record audio using the microphone and AVAudioRecorder.
It works on iOS 8 but my code does not work anymore on iOS 9.
The recordSettings dictionary is set properly, then I give it to the
AVAudioRecorder:URL:settings constructor.
But, just after, recorder.settings is empty, an assertion failure is thrown
let recordSettings: [String: AnyObject] = [
AVNumberOfChannelsKey: NSNumber(integer: 2),
AVFormatIDKey: NSNumber(integer: Int(kAudioFormatMPEG4AAC)),
AVEncoderBitRateKey: NSNumber(integer: 64)]
var recorder: AVAudioRecorder!
do {
recorder = try AVAudioRecorder(URL: tempURL, settings:recordSettings) // recordSettings.count = 3
assert(recorder.settings.count != 0, "Audio Recorder does not provide settings") // assertion failure threw
} catch let error as NSError {
print("error when intitializing recorder: \(error)")
return
}
Anyone can help me ? Is it a bug ?
EDIT : In my entire code I did not test recorder.settings just after. I did instantiate recorder like my code above, then I did that :
recorder.delegate = self
recorder.prepareToRecord()
recorder.meteringEnabled = true
And it crashes in this line :
for i in 1...(recorder.settings[AVNumberOfChannelsKey] as! Int) {
...
}
It crashes because recorder.settings[AVNumberOfChannelsKey] is nil

Answer 1

I'm not sure why you're checking the settings property, but
from the AVAudioRecorder header file, on the settings property:
these settings are fully valid only when prepareToRecord has been called
so you must call prepareToRecord() first BUT it will fail/return false, because your bitrate is way too low! Its unit is bits per second, not kilobits per second:
AVEncoderBitRateKey: NSNumber(integer: 64000)
This worked on iOS 8 because your too-low bitrate was simply discarded. Looks like it became an error in iOS 9.