How to get real-time microphone input in macOS? - swift

Question

I'm attempting to access real-time microphone data with the following code:
import AVFoundation // for AVAudioEngine
class Mic
{
public let audioEngine = AVAudioEngine()
func startRecording() throws
{
// https://forums.developer.apple.com/thread/44833
//audioEngine.mainMixerNode // causes DIFFERENT crash!
audioEngine.prepare() // CRASHES
let inputNode = audioEngine.inputNode
if inputNode.inputFormat(forBus: 0).sampleRate == 0 {
exit(0);
}
let recordingFormat = inputNode.outputFormat(forBus: 0)
inputNode.installTap(onBus: 0, bufferSize: 1024, format: recordingFormat) { (buffer: AVAudioPCMBuffer, when: AVAudioTime) in
print( "YES! Got some samples!")
}
audioEngine.prepare()
try audioEngine.start()
}
//public
func stopRecording()
{
audioEngine.stop()
}
}
However it crashes on:
audioEngine.prepare() // CRASHES
2019-07-16 17:51:34.448107+0300 realtime_mic[8992:386743] [avae]
AVAEInternal.h:76 required condition is false:
[AVAudioEngineGraph.mm:1318:Initialize: (inputNode != nullptr ||
outputNode != nullptr)]
realtime_mic[8992:386743] required condition is false: inputNode !=
nullptr || outputNode != nullptr2019-07-16 17:51:34.449214+0300
As can be seen, I've tried to apply a hack/patch:
// https://forums.developer.apple.com/thread/44833
audioEngine.mainMixerNode
but this causes a different crash:
2019-07-16 17:50:34.315005+0300 realtime_mic[8901:385699] [plugin]
AddInstanceForFactory:
No factory registered for id F8BB1C28-BAE8-11D6-9C31-00039315CD46 2019-07-16
17:50:34.349337+0300 realtime_mic[8901:385699]
HALC_ShellDriverPlugIn::Open: Can't get a pointer to the Open routine
2019-07-16 17:50:34.354277+0300 realtime_mic[8901:385699] [ddagg]
AggregateDevice.mm:776 couldn't get default input device, ID = 0,
err = 0!
I've sent entitlements just in case: macOS Entitlements audio-input vs. microphone -- but to no avail.
What is the correct way to do this?
Test case at: https://github.com/p-i-/macOS_rt_mic

Answer 1

Entered the following code into testRecord.swift :
import Foundation
import AVFoundation
print("starting")
public let audioEngine = AVAudioEngine()
var flag = 0
func startRecording() throws {
let inputNode = audioEngine.inputNode
let srate = inputNode.inputFormat(forBus: 0).sampleRate
print("sample rate = \(srate)")
if srate == 0 {
exit(0);
}
let recordingFormat = inputNode.outputFormat(forBus: 0)
inputNode.installTap(onBus: 0,
bufferSize: 1024,
format: recordingFormat) {
(buffer: AVAudioPCMBuffer, when: AVAudioTime) in
let n = buffer.frameLength
let c = buffer.stride
if flag == 0 {
print( "num samples = \(n)") ;
print( "num channels = \(c)") ;
flag = 1
}
}
try audioEngine.start()
}
func stopRecording() {
audioEngine.stop()
}
do {
try startRecording()
} catch {
print("error?")
}
usleep(UInt32(1000*1000)) // sleep 1 second before quitting
stopRecording()
print("done")
exit(0)
Compiled testRecord.swift using swiftc on macOS 10.14.5 / Xcode 10.2.1 ; then tried to run the result from Terminal. The first time it ran, macOS asked if Terminal could have microphone permissions. Replied yes, but no output.
But then on subsequent runs it output:
starting
sample rate = 44100.0
num samples = 4410
num channels = 1
done
So it might be you need to allow your app some permissions in System Preferences : Privacy : Microphone