is there anyway to limit AvAudioEngine's buffer size? - ios

Question

I cant find anywhere how can i limit avaudioengine or mixer nodes output buffer? i found this from raywenderlich tutorial site but they say buffer size is not guaranteed
"installTap(onBus: 0, bufferSize: 1024, format: format) gives you >access to the audio data on the mainMixerNode‘s output bus. You >request a buffer size of 1024 bytes, but the requested size isn’t >guaranteed, especially if you request a buffer that’s too small or >large. Apple’s documentation doesn’t specify what those limits are."
https://www.raywenderlich.com/5154-avaudioengine-tutorial-for-ios-getting-started
i already tried installTap and SetCurrentIOBufferFrameSize(OSstatus) methods but all of it not working on buffer limitation.
func SetCurrentIOBufferFrameSize(inAUHAL: AudioUnit,inIOBufferFrameSize: UInt32) -> OSStatus {
var inIOBufferFrameSize = inIOBufferFrameSize
var propSize = UInt32(MemoryLayout<UInt32>.size)
return AudioUnitSetProperty(inAUHAL, AudioUnitPropertyID(kAudioUnitProperty_ScheduledFileBufferSizeFrames), kAudioUnitScope_Global, 0, &inIOBufferFrameSize, propSize)
}
func initalizeEngine() {
sampleRateConversionRatio = Float(44100 / SampleRate)
engine = AVAudioEngine()
SetCurrentIOBufferFrameSize(inAUHAL: engine.outputNode.audioUnit!, inIOBufferFrameSize: 15)
do {
try AVAudioSession.sharedInstance().setCategory(.playAndRecord , mode: .default , options: .defaultToSpeaker)
try AVAudioSession.sharedInstance().setPreferredIOBufferDuration(ioBufferDuration)
try AVAudioSession.sharedInstance().setPreferredSampleRate(Double(SampleRate))
try AVAudioSession.sharedInstance().setPreferredInputNumberOfChannels(channelCount)
} catch {
assertionFailure("AVAudioSession setup error: \(error)")
}
}
func startRecording() {
downMixer.installTap(onBus: 0, bufferSize: bufferSize, format: format) { buffer, when in
self.serialQueue.async {
let pcmBuffer = AVAudioPCMBuffer(pcmFormat: self.format16KHzMono, frameCapacity: AVAudioFrameCount(Float(buffer.frameCapacity)/self.sampleRateConversionRatio))
var error: NSError? = nil
let inputBlock: AVAudioConverterInputBlock = {inNumPackets, outStatus in
outStatus.pointee = AVAudioConverterInputStatus.haveData
return buffer
}
self.formatConverter.convert(to: pcmBuffer!, error: &error, withInputFrom: inputBlock)
if error != nil {
print(error!.localizedDescription)
}
else if let channelData = pcmBuffer!.int16ChannelData {
let channelDataPointer = channelData.pointee
let channelData = stride(from: 0,
to: Int(pcmBuffer!.frameLength),
by: buffer.stride).map{ channelDataPointer[$0] }
//Return channelDataValueArray
let data = Data(fromArray: channelData)
var byteArray = data.toByteArray()
}
}
}
}