Get microphone input using Audio Queue in Swift 3 - ios

Question

I am developing an app that records voice via built-in microphone and sends it to a server live. So I need to get the byte stream from the microphone while recording.
After googling and stack-overflowing for quite a while, I think I figured out how it should work, but it does not. I think using Audio Queues might be the way to go.
Here is what I tried so far:
func test() {
func callback(_ a :UnsafeMutableRawPointer?, _ b : AudioQueueRef, _ c :AudioQueueBufferRef, _ d :UnsafePointer<AudioTimeStamp>, _ e :UInt32, _ f :UnsafePointer<AudioStreamPacketDescription>?) {
print("test")
}
var inputQueue: AudioQueueRef? = nil
var aqData = AQRecorderState(
mDataFormat: AudioStreamBasicDescription(
mSampleRate: 16000,
mFormatID: kAudioFormatLinearPCM,
mFormatFlags: 0,
mBytesPerPacket: 2,
mFramesPerPacket: 1, // Must be set to 1 for uncomressed formats
mBytesPerFrame: 2,
mChannelsPerFrame: 1, // Mono recording
mBitsPerChannel: 2 * 8, // 2 Bytes
mReserved: 0), // Must be set to 0 according to https://developer.apple.com/reference/coreaudio/audiostreambasicdescription
mQueue: inputQueue!,
mBuffers: [AudioQueueBufferRef](),
bufferByteSize: 32,
mCurrentPacket: 0,
mIsRunning: true)
var error = AudioQueueNewInput(&aqData.mDataFormat,
callback,
nil,
nil,
nil,
0,
&inputQueue)
AudioQueueStart(inputQueue!, nil)
}
It compiles and the app starts, but as soon as I call test() I get an exception:
fatal error: unexpectedly found nil while unwrapping an Optional value
The exception is caused by
mQueue: inputQueue!
I understand why this happens (inputQueue has no value) but I don't know how to initialise inputQueue correctly. The problem is that Audio Queues are very poorly documented for Swift users and I didn't find any working example on the internet.
Can anybody tell me what I am doing wrong?

Answer 1

Use AudioQueueNewInput(...) (or output) to initialize your audio queue before you are using it:
let sampleRate = 16000
let numChannels = 2
var inFormat = AudioStreamBasicDescription(
mSampleRate: Double(sampleRate),
mFormatID: kAudioFormatLinearPCM,
mFormatFlags: kAudioFormatFlagsNativeFloatPacked,
mBytesPerPacket: UInt32(numChannels * MemoryLayout<UInt32>.size),
mFramesPerPacket: 1,
mBytesPerFrame: UInt32(numChannels * MemoryLayout<UInt32>.size),
mChannelsPerFrame: UInt32(numChannels),
mBitsPerChannel: UInt32(8 * (MemoryLayout<UInt32>.size)),
mReserved: UInt32(0)
var inQueue: AudioQueueRef? = nil
AudioQueueNewInput(&inFormat, callback, nil, nil, nil, 0, &inQueue)
var aqData = AQRecorderState(
mDataFormat: inFormat,
mQueue: inQueue!, // inQueue is initialized now and can be unwrapped
mBuffers: [AudioQueueBufferRef](),
bufferByteSize: 32,
mCurrentPacket: 0,
mIsRunning: true)
Find details in Apples Documentation

Answer 2

This code from our project works fine:
AudioBuffer * buff;
AudioQueueRef queue;
AudioStreamBasicDescription fmt = { 0 };
static void HandleInputBuffer (
void *aqData,
AudioQueueRef inAQ,
AudioQueueBufferRef inBuffer,
const AudioTimeStamp *inStartTime,
UInt32 inNumPackets,
const AudioStreamPacketDescription *inPacketDesc
) {
}
- (void) initialize {
thisClass = self;
__block struct AQRecorderState aqData;
NSError * error;
fmt.mFormatID = kAudioFormatLinearPCM;
fmt.mSampleRate = 44100.0;
fmt.mChannelsPerFrame = 1;
fmt.mBitsPerChannel = 16;
fmt.mChannelsPerFrame = 1;
fmt.mFramesPerPacket = 1;
fmt.mBytesPerFrame = sizeof (SInt16);
fmt.mBytesPerPacket = sizeof (SInt16);
fmt.mFormatFlags = kLinearPCMFormatFlagIsSignedInteger | kLinearPCMFormatFlagIsPacked;
OSStatus status = AudioQueueNewInput ( // 1
&fmt, // 2
HandleInputBuffer, // 3
&aqData, // 4
NULL, // 5
kCFRunLoopCommonModes, // 6
0, // 7
&queue // 8
);
AudioQueueBufferRef buffers[kNumberBuffers];
UInt32 bufferByteSize = kSamplesSize;
for (int i = 0; i < kNumberBuffers; ++i) { // 1
OSStatus allocateStatus;
allocateStatus = AudioQueueAllocateBuffer ( // 2
queue, // 3
bufferByteSize, // 4
&buffers[i] // 5
);
OSStatus enqueStatus;
NSLog(#"allocateStatus = %d" , allocateStatus);
enqueStatus = AudioQueueEnqueueBuffer ( // 6
queue, // 7
buffers[i], // 8
0, // 9
NULL // 10
);
NSLog(#"enqueStatus = %d" , enqueStatus);
}
AudioQueueStart ( // 3
queue, // 4
NULL // 5
);
}