Speech Recognition Flutter in 2018

This project intends to instruct Flutter developers to use Speech Recognition.

This project gives credit to rxlabz/sytody

• Android Setup

  1. The first thing you should do is add permission in AndroidManifest.xml in android/app/src/main

  2. Next thing to do is to add Platform Channel in dart. Refer to recognizer.dart.

  3. Add Platform Channel solution to MainActivity.java in android/app/src/main/java/com/example/speechrecognition/MainActivity.java.

  4. The folder under /main/java may be different, it depends on your java configuration.

  5. The only essential difference in MainActivity.java is requestRecordAudioPermission function, since android sdk increase the permission security level in sdk 27.

  6. Add custom layout and styling to your flutter frontend.

• IOS Setup

  1. flutter create speech -i swift
  2. add to /ios/Runner/Info.plist

  <key>NSMicrophoneUsageDescription</key>
  <string>This application needs to access your microphone</string>
  <key>NSSpeechRecognitionUsageDescription</key>
  <string>This application needs the speech recognition permission</string>

  3. add to /ios/Runner/AppDelegate.swift

  import UIKit
  import Flutter
  import Speech
  
  @UIApplicationMain
  class AppDelegate: FlutterAppDelegate, SFSpeechRecognizerDelegate {
  
  private let speechRecognizerEn = SFSpeechRecognizer(locale: Locale(identifier: "en_US"))!
  
  private var speechChannel: FlutterMethodChannel?
  
  private var recognitionRequest: SFSpeechAudioBufferRecognitionRequest?
  
  private var recognitionTask: SFSpeechRecognitionTask?
  
  private let audioEngine = AVAudioEngine()
  
  override func application(
      _ application: UIApplication,
      didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
  
      let controller: FlutterViewController = window?.rootViewController as! FlutterViewController
  
      speechChannel = FlutterMethodChannel.init(name: "speech_recognizer",
      binaryMessenger: controller)
      speechChannel!.setMethodCallHandler({
      (call: FlutterMethodCall, result: @escaping FlutterResult) -> Void in
      if ("start" == call.method) {
          self.startRecognition(lang: call.arguments as! String, result: result)
      } else if ("stop" == call.method) {
          self.stopRecognition(result: result)
      } else if ("cancel" == call.method) {
          self.cancelRecognition(result: result)
      } else if ("activate" == call.method) {
          self.activateRecognition(result: result)
      } else {
          result(FlutterMethodNotImplemented)
      }
      })
      return true
  }
  
  func activateRecognition(result: @escaping FlutterResult) {
      speechRecognizerEn.delegate = self
      speechRecognizerIt.delegate = self
  
      SFSpeechRecognizer.requestAuthorization { authStatus in
      OperationQueue.main.addOperation {
          switch authStatus {
          case .authorized:
          result(true)
  
          case .denied:
          result(false)
  
          case .restricted:
          result(false)
  
          case .notDetermined:
          result(false)
          }
      }
      }
  }
  
  private func startRecognition(lang: String, result: FlutterResult) {
      if audioEngine.isRunning {
      audioEngine.stop()
      recognitionRequest?.endAudio()
      result(false)
      } else {
      try! start(lang: lang)
      result(true)
      }
  }
  
  private func cancelRecognition(result: FlutterResult?) {
      if let recognitionTask = recognitionTask {
      recognitionTask.cancel()
      self.recognitionTask = nil
      if let r = result {
          r(false)
      }
      }
  }
  
  private func stopRecognition(result: FlutterResult) {
      if audioEngine.isRunning {
      audioEngine.stop()
      recognitionRequest?.endAudio()
      }
      result(false)
  }
  
  private func start(lang: String) throws {
  
      cancelRecognition(result: nil)
  
      let audioSession = AVAudioSession.sharedInstance()
      try audioSession.setCategory(AVAudioSessionCategoryRecord)
      try audioSession.setMode(AVAudioSessionModeMeasurement)
      try audioSession.setActive(true, with: .notifyOthersOnDeactivation)
  
      recognitionRequest = SFSpeechAudioBufferRecognitionRequest()
  
      guard let inputNode = audioEngine.inputNode else {
      fatalError("Audio engine has no input node")
      }
      guard let recognitionRequest = recognitionRequest else {
      fatalError("Unable to created a SFSpeechAudioBufferRecognitionRequest object")
      }
  
      recognitionRequest.shouldReportPartialResults = true
  
      let speechRecognizer = getRecognizer(lang: lang)
  
      recognitionTask = speechRecognizer.recognitionTask(with: recognitionRequest) { result, error in
      var isFinal = false
  
      if let result = result {
          print("Speech : \(result.bestTranscription.formattedString)")
          self.speechChannel?.invokeMethod("onSpeech", arguments: result.bestTranscription.formattedString)
          isFinal = result.isFinal
          if isFinal {
          self.speechChannel!.invokeMethod(
              "onRecognitionComplete",
              arguments: result.bestTranscription.formattedString
          )
          }
      }
  
      if error != nil || isFinal {
          self.audioEngine.stop()
          inputNode.removeTap(onBus: 0)
          self.recognitionRequest = nil
          self.recognitionTask = nil
      }
      }
  
      let RecognitionFormat = inputNode.outputFormat(forBus: 0)
      inputNode.installTap(onBus: 0, bufferSize: 1024, format: RecognitionFormat) {
      (buffer: AVAudioPCMBuffer, when: AVAudioTime) in
      self.recognitionRequest?.append(buffer)
      }
  
      audioEngine.prepare()
      try audioEngine.start()
  
      speechChannel!.invokeMethod("onRecognitionStarted", arguments: nil)
  }
  
  private func getRecognizer(lang: String) -> Speech.SFSpeechRecognizer {
      return speechRecognizerEn
  }
  
  public func speechRecognizer(_ speechRecognizer: SFSpeechRecognizer, availabilityDidChange available: Bool) {
      if available {
      speechChannel?.invokeMethod("onSpeechAvailability", arguments: true)
      } else {
      speechChannel?.invokeMethod("onSpeechAvailability", arguments: false)
      }
  }
  
  }

Because of iOS updated to 12.0.1 and swift updated to 4.0, iOS feature is not correctly implemented yet.

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For this feature to work correctly, you may need to have Google App run in the background.