Custom voice controller

You can provide a custom text-to-speech implementation for the Navigation SDK to use.

To provide a custom text-to-speech implementation:

  1. Implement a type that conforms to the SpeechSynthesizing protocol. Checkout the CustomVoiceController implementation in the example below.
  2. Customize and present NavigationViewController. Learn how in the CustomVoiceControllerUI.presentNavigationWithCustomVoiceController(_:_:) method below.
This code example is part of the Mapbox Navigation SDK for iOS demo app,
which you can build and run:
To learn more about each example in this app, including descriptions and links
to documentation, see our docs:
import Foundation
import UIKit
import MapboxCoreNavigation
import MapboxNavigation
import MapboxDirections
import MapboxSpeech
import AVFoundation
class CustomVoiceControllerUI: UIViewController {
override func viewDidLoad() {
let origin = CLLocationCoordinate2DMake(37.77440680146262, -122.43539772352648)
let destination = CLLocationCoordinate2DMake(37.76556957793795, -122.42409811526268)
let routeOptions = NavigationRouteOptions(coordinates: [origin, destination])
Directions.shared.calculate(routeOptions) { [weak self] (_, result) in
switch result {
case .failure(let error):
case .success(let response):
self?.presentNavigationWithCustomVoiceController(routeOptions: routeOptions, response: response)
func presentNavigationWithCustomVoiceController(routeOptions: NavigationRouteOptions, response: RouteResponse) {
// For demonstration purposes, simulate locations if the Simulate Navigation option is on.
let navigationService = MapboxNavigationService(routeResponse: response,
routeIndex: 0,
routeOptions: routeOptions,
simulating: simulationIsEnabled ? .always : .onPoorGPS)
// `MultiplexedSpeechSynthesizer` will provide "a backup" functionality to cover cases, which
// our custom implementation cannot handle.
let speechSynthesizer = MultiplexedSpeechSynthesizer([CustomVoiceController(), SystemSpeechSynthesizer()])
// Create a `RouteVoiceController` type with a customized `SpeechSynthesizing` instance.
// A route voice controller monitors turn-by-turn navigation events and triggers playing spoken instructions
// as audio using the custom `speechSynthesizer` we created above.
let routeVoiceController = RouteVoiceController(navigationService: navigationService,
speechSynthesizer: speechSynthesizer)
// Remember to pass our RouteVoiceController` to `Navigation Options`!
let navigationOptions = NavigationOptions(navigationService: navigationService,
voiceController: routeVoiceController)
// Create `NavigationViewController` with the custom `NavigationOptions`.
let navigationViewController = NavigationViewController(for: response,
routeIndex: 0,
routeOptions: routeOptions,
navigationOptions: navigationOptions)
navigationViewController.modalPresentationStyle = .fullScreen
present(navigationViewController, animated: true, completion: nil)
class CustomVoiceController: MapboxSpeechSynthesizer {
// You will need audio files for as many or few cases as you'd like to handle
// This example just covers left and right. All other cases will fail the Custom Voice Controller and
// force a backup System Speech to kick in
let turnLeft = NSDataAsset(name: "turnleft")!.data
let turnRight = NSDataAsset(name: "turnright")!.data
override func speak(_ instruction: SpokenInstruction, during legProgress: RouteLegProgress, locale: Locale? = nil) {
guard let soundForInstruction = audio(for: legProgress.currentStep) else {
// When `MultiplexedSpeechSynthesizer` receives an error from one of it's Speech Synthesizers,
// it requests the next on the list
didSpeak: instruction,
with: SpeechError.noData(instruction: instruction,
options: SpeechOptions(text: instruction.text)))
speak(instruction, data: soundForInstruction)
func audio(for step: RouteStep) -> Data? {
switch step.maneuverDirection {
case .left:
return turnLeft
case .right:
return turnRight
return nil // this will force report that Custom View Controller is unable to handle this case