AVAudioRecorder in Swift 3: Get Byte stream instead of saving to file - ios

Question

I am new to iOS programming and I want to port an Android app to iOS using Swift 3. The core functionality of the app is to read the byte stream from the microphone and to process this stream live. So it is not sufficient to store the audio stream to a file and process it after recording has stopped.
I already found the AVAudioRecorder class which works, but I don't know how to process the data stream live (filtering, sending it to a server, etc). The init-function of the AVAudioRecorder looks like that:
AVAudioRecorder(url: filename, settings: settings)
What I would need is a class where I can register an event handler or something like that which is called every time x bytes have been read so I can process it.
Is this possible with AVAudioRecorder? If not, is there another class in the Swift library that allows me to process audio streams live? In Android I use android.media.AudioRecord so It would be great if there's an equivalent class in Swift.
Regards

Answer 1

Use Audio Queue service in Core Audio framework.
https://developer.apple.com/library/content/documentation/MusicAudio/Conceptual/AudioQueueProgrammingGuide/AQRecord/RecordingAudio.html#//apple_ref/doc/uid/TP40005343-CH4-SW1
static const int kNumberBuffers = 3; // 1
struct AQRecorderState {
AudioStreamBasicDescription mDataFormat; // 2
AudioQueueRef mQueue; // 3
AudioQueueBufferRef mBuffers[kNumberBuffers]; // 4
AudioFileID mAudioFile; // 5
UInt32 bufferByteSize; // 6
SInt64 mCurrentPacket; // 7
bool mIsRunning; // 8
};
Here’s a description of the fields in this structure:
1 Sets the number of audio queue buffers to use.
2 An AudioStreamBasicDescription structure (from CoreAudioTypes.h)
representing the audio data format to write to disk. This format gets
used by the audio queue specified in the mQueue field. The mDataFormat
field gets filled initially by code in your program, as described in
Set Up an Audio Format for Recording. It is good practice to then
update the value of this field by querying the audio queue's
kAudioQueueProperty_StreamDescription property, as described in
Getting the Full Audio Format from an Audio Queue. On Mac OS X v10.5,
use the kAudioConverterCurrentInputStreamDescription property instead.
For details on the AudioStreamBasicDescription structure, see Core
Audio Data Types Reference.
3 The recording audio queue created by your application.
4 An array holding pointers to the audio queue buffers managed by the
audio queue.
5 An audio file object representing the file into which your program
records audio data.
6 The size, in bytes, for each audio queue buffer. This value is
calculated in these examples in the DeriveBufferSize function, after
the audio queue is created and before it is started. See Write a
Function to Derive Recording Audio Queue Buffer Size.
7 The packet index for the first packet to be written from the current
audio queue buffer.
8 A Boolean value indicating whether or not the audio queue is
running.