How to convert PCM to G711 µlaw raw format - ios

Question

I am trying PCM (microphone input)->G711 and am having trouble getting it to work.
With the current implementation, the conversion itself succeeds, but it is as if there is no data stored in the buffer.
I have been doing a lot of research, but I can't seem to find the cause of the problem, so I would appreciate your advice.
var audioEngine = AVAudioEngine()
var convertFormatBasicDescription = AudioStreamBasicDescription(
mSampleRate: 8000,
mFormatID: kAudioFormatULaw,
mFormatFlags: AudioFormatFlags(kAudioFormatULaw),
mBytesPerPacket: 1,
mFramesPerPacket: 1,
mBytesPerFrame: 1,
mChannelsPerFrame: 1,
mBitsPerChannel: 8,
mReserved: 0
)
func convert () {
let inputNode = audioEngine.inputNode
let micInputFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: 44100, channels: 1, interleaved: true)!
let convertFormat = AVAudioFormat(streamDescription: &convertFormatBasicDescription)!
let converter = AVAudioConverter(from: micInputFormat, to: convertFormat)!
inputNode.installTap(onBus: 0, bufferSize: 1024, format: micInputFormat) { [weak self] (buffer, time) in
var newBufferAvailable = true
let inputCallback: AVAudioConverterInputBlock = { inNumPackets, outStatus in
if newBufferAvailable {
outStatus.pointee = .haveData
newBufferAvailable = false
return buffer
} else {
outStatus.pointee = .noDataNow
return nil
}
}
let convertedBuffer = AVAudioPCMBuffer(pcmFormat: convertFormat, frameCapacity: AVAudioFrameCount(convertFormat.sampleRate) * buffer.frameLength / AVAudioFrameCount(buffer.format.sampleRate))!
convertedBuffer.frameLength = convertedBuffer.frameCapacity
var error: NSError?
let status = converter.convert(to: convertedBuffer, error: &error, withInputFrom: inputCallback)
print(convertedBuffer.floatChannelData) <- nil
}
audioEngine.prepare()
try audioEngine.start()
}
Thank you.

Answer 1

It was audioBufferList.pointee.mBuffers.mData, not floatChannelData, that was needed to get the data converted to G711.