Swift -Recording in Stereo using the Built-In Microphones - ios

Question

I want to use stereo instead of mono. I downloaded Apple's sample app. It says
Because a user can hold an iOS device in a variety of ways, you need to specify the orientation of the right and left channels in the stereo field. Set the built-in microphone’s directionality by configuring:
Polar pattern. The system represents the individual device >microphones, and beamformers that use multiple microphones, as >data sources. Select the front or back data source and set its >polar pattern to stereo.
Input orientation. When recording video, set the input >orientation to match the video orientation. When recording audio >only, set the input orientation to match the user interface >orientation. In both cases, don’t change the orientation during >recording.
I found this YCombinator thread that says there are issues when recording using the stereo speakers and holding the phone in different orientations. In Apple's sample code there is a Orientation enum, but this isn't clearly explained on what the differences are for.
With their app there is a segmented control that lets you choose between which speaker to use but it's not very clear on how to roll this into your own app.
I want to make it seamless so that the user doesn't have to choose, they can simply press record and the AVAudioRecorder takes it from there.
Start/Stop Recording
var micRecorder: AVAudioRecorder?
let audioSettings: [String:Any] = [AVFormatIDKey: kAudioFormatMPEG4AAC,
AVNumberOfChannelsKey: 2,
AVSampleRateKey: 44100.0,
AVEncoderBitRateKey: 64000,
AVEncoderAudioQualityKey: AVAudioQuality.min.rawValue]
func viewDidLoad() {
super.viewDidLoad()
do {
try AVAudioSession.sharedInstance().setCategory(.playAndRecord, mode: .default, options: [ .allowBluetoothA2DP, .defaultToSpeaker]
try AVAudioSession.sharedInstance().setActive(true)
} catch {
}
enableBuiltInMic()
}
#IBAction func startRecording(_ sender: UIButton) {
do {
// How to use the AVAudioRecorder to start recording using the Stereo speaker here?
let fileURL = NSTemporaryDirectory()...
micRecorder = try AVAudioRecorder(url: fileURL, settings: audioSettings)
micRecorder?.delegate = self
micRecorder?.isMeteringEnabled = true
micRecorder?.record()
} catch {
}
}
This is the code that I pulled from Apple's sample app. I stuffed into the same file that the micRecorder is in above.
enum Orientation: Int {
case unknown = 0
case portrait = 1
case portraitUpsideDown = 2
case landscapeLeft = 4
case landscapeRight = 3
}
fileprivate extension Orientation {
// Convenience property to retrieve the AVAudioSession.StereoOrientation.
var inputOrientation: AVAudioSession.StereoOrientation {
return AVAudioSession.StereoOrientation(rawValue: rawValue)!
}
}
var isStereoSupported = false
private var windowOrientation: UIInterfaceOrientation { view.window?.windowScene?.interfaceOrientation ?? .unknown }
struct RecordingOption: Comparable {
let name: String
fileprivate let dataSourceName: String
static func < (lhs: RecordingOption, rhs: RecordingOption) -> Bool {
lhs.name < rhs.name
}
}
var recordingOptions: [RecordingOption] = {
let front = AVAudioSession.Orientation.front
let back = AVAudioSession.Orientation.back
let bottom = AVAudioSession.Orientation.bottom
let session = AVAudioSession.sharedInstance()
guard let dataSources = session.preferredInput?.dataSources else { return [] }
var options = [RecordingOption]()
dataSources.forEach { dataSource in
switch dataSource.orientation {
case front:
options.append(RecordingOption(name: "Front Stereo", dataSourceName: front.rawValue))
case back:
options.append(RecordingOption(name: "Back Stereo", dataSourceName: back.rawValue))
case bottom:
options.append(RecordingOption(name: "Mono", dataSourceName: bottom.rawValue))
default: ()
}
}
// Sort alphabetically
options.sort()
return options
}()
func enableBuiltInMic() {
// Get the shared audio session.
let session = AVAudioSession.sharedInstance()
// Find the built-in microphone input.
guard let availableInputs = session.availableInputs,
let builtInMicInput = availableInputs.first(where: { $0.portType == .builtInMic }) else {
print("The device must have a built-in microphone.")
return
}
// Make the built-in microphone input the preferred input.
do {
try session.setPreferredInput(builtInMicInput)
} catch {
print("Unable to set the built-in mic as the preferred input.")
}
}
func selectRecordingOption(_ option: RecordingOption, orientation: Orientation, completion: (StereoLayout) -> Void) {
// Get the shared audio session.
let session = AVAudioSession.sharedInstance()
// Find the built-in microphone input's data sources,
// and select the one that matches the specified name.
guard let preferredInput = session.preferredInput,
let dataSources = preferredInput.dataSources,
let newDataSource = dataSources.first(where: { $0.dataSourceName == option.dataSourceName }),
let supportedPolarPatterns = newDataSource.supportedPolarPatterns else {
completion(.none)
return
}
do {
isStereoSupported = supportedPolarPatterns.contains(.stereo)
// If the data source supports stereo, set it as the preferred polar pattern.
if isStereoSupported {
// Set the preferred polar pattern to stereo.
try newDataSource.setPreferredPolarPattern(.stereo)
}
// Set the preferred data source and polar pattern.
try preferredInput.setPreferredDataSource(newDataSource)
// Update the input orientation to match the current user interface orientation.
try session.setPreferredInputOrientation(orientation.inputOrientation)
} catch {
print("Unable to select the \(option.dataSourceName) data source.")
}
// Call the completion handler with the updated stereo layout.
completion(StereoLayout(orientation: newDataSource.orientation!,
stereoOrientation: session.inputOrientation))
}
Stero File:
import AVFoundation
enum StereoLayout: String {
case none = "none"
case mono = "Mono"
case frontLandscapeLeft = "Front LandscapeLeft"
case frontLandscapeRight = "Front LandscapeRight"
case frontPortrait = "Front Portrait"
case frontPortraitUpsideDown = "Front PortraitUpsideDown"
case backLandscapeLeft = "Back LandscapeLeft"
case backLandscapeRight = "Back LandscapeRight"
case backPortrait = "Back Portrait"
case backPortraitUpsideDown = "Back PortraitUpsideDown"
init(orientation: AVAudioSession.Orientation, stereoOrientation: AVAudioSession.StereoOrientation) {
let front: AVAudioSession.Orientation = .front
let back: AVAudioSession.Orientation = .back
switch (orientation, stereoOrientation) {
// Front
case (front, .none):
self.init(rawValue: StereoLayout.mono.rawValue)!
case (front, .landscapeLeft):
self.init(rawValue: StereoLayout.frontLandscapeLeft.rawValue)!
case (front, .landscapeRight):
self.init(rawValue: StereoLayout.frontLandscapeRight.rawValue)!
case (front, .portrait):
self.init(rawValue: StereoLayout.frontPortrait.rawValue)!
case (front, .portraitUpsideDown):
self.init(rawValue: StereoLayout.frontPortraitUpsideDown.rawValue)!
// Back
case (back, .none):
self.init(rawValue: StereoLayout.mono.rawValue)!
case (back, .landscapeLeft):
self.init(rawValue: StereoLayout.backLandscapeLeft.rawValue)!
case (back, .landscapeRight):
self.init(rawValue: StereoLayout.backLandscapeRight.rawValue)!
case (back, .portrait):
self.init(rawValue: StereoLayout.backPortrait.rawValue)!
case (back, .portraitUpsideDown):
self.init(rawValue: StereoLayout.backPortraitUpsideDown.rawValue)!
default:
self.init(rawValue: StereoLayout.none.rawValue)!
}
}
}