speech_to_text

pub package build status

A library that exposes device specific speech recognition capability.

This plugin contains a set of classes that make it easy to use the speech recognition capabilities of the mobile device in Flutter. It supports both Android and iOS. The target use cases for this library are commands and short phrases, not continuous spoken conversion or always on listening.

Recent Updates

The 2.3.0 version adds SpeechToTextProvider as a simpler way to interact with the plugin. Checkout the new provider_example.dart for intended usage.

The 2.2.0 version improves audio session handling and start / stop sound playback on iOS.

Note: Feedback from any test devices is welcome.

Using

To recognize text from the microphone import the package and call the plugin, like so:

import 'package:speech_to_text/speech_to_text.dart' as stt;

    stt.SpeechToText speech = stt.SpeechToText();
    bool available = await speech.initialize( onStatus: statusListener, onError: errorListener );
    if ( available ) {
        speech.listen( onResult: resultListener );
    }
    else {
        print("The user has denied the use of speech recognition.");
    }
    // some time later...
    speech.stop()

Initialize once

The initialize method only needs to be called once per application session. After that listen, start, stop, and cancel can be used to interact with the plugin. Subsequent calls to initialize are ignored which is safe but does mean that the onStatus and onError callbacks cannot be reset after the first call to initialize. For that reason there should be only one instance of the plugin per application. The SpeechToTextProvider is one way to create a single instance and easily reuse it in multiple widgets.

Permissions

Applications using this plugin require user permissions.

iOS

Add the following keys to your Info.plist file, located in <project root>/ios/Runner/Info.plist:

  • NSSpeechRecognitionUsageDescription - describe why your app uses speech recognition. This is called Privacy - Speech Recognition Usage Description in the visual editor.
  • NSMicrophoneUsageDescription - describe why your app needs access to the microphone. This is called Privacy - Microphone Usage Description in the visual editor.

Android

Add the record audio permission to your AndroidManifest.xml file, located in <project root>/android/app/src/main/AndroidManifest.xml.

  • android.permission.RECORD_AUDIO - this permission is required for microphone access.
  • android.permission.INTERNET - this permission is required because speech recognition may use remote services.

Adding Sounds for iOS (optional)

Android automatically plays system sounds when speech listening starts or stops but iOS does not. This plugin supports playing sounds to indicate listening status on iOS if sound files are available as assets in the application. To enable sounds in an application using this plugin add the sound files to the project and reference them in the assets section of the application pubspec.yaml. The location and filenames of the sound files must exactly match what is shown below or they will not be found. The example application for the plugin shows the usage. Note These files should be very short as they delay the start / end of the speech recognizer until the sound playback is complete.

  assets:
  - assets/sounds/speech_to_text_listening.m4r
  - assets/sounds/speech_to_text_cancel.m4r
  - assets/sounds/speech_to_text_stop.m4r
  • speech_to_text_listening.m4r - played when the listen method is called.
  • speech_to_text_cancel.m4r - played when the cancel method is called.
  • speech_to_text_stop.m4r - played when the stop method is called.

Troubleshooting

SDK version error trying to compile for Android

Manifest merger failed : uses-sdk:minSdkVersion 16 cannot be smaller than version 21 declared in library [:speech_to_text] 

The speech_to_text plugin requires at least Android SDK 21 because some of the speech functions in Android were only introduced in that version. To fix this error you need to change the build.gradle entry to reflect this version. Here's what the relevant part of that file looked like as of this writing:

   defaultConfig {
        applicationId "com.example.app"
        minSdkVersion 21
        targetSdkVersion 28
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

Incorrect Swift version trying to compile for iOS

/Users/markvandergon/flutter/.pub-cache/hosted/pub.dartlang.org/speech_to_text-1.1.0/ios/Classes/SwiftSpeechToTextPlugin.swift:224:44: error: value of type 'SwiftSpeechToTextPlugin' has no member 'AVAudioSession'
                rememberedAudioCategory = self.AVAudioSession.Category
                                          ~~~~ ^~~~~~~~~~~~~~
    /Users/markvandergon/flutter/.pub-cache/hosted/pub.dartlang.org/speech_to_text-1.1.0/ios/Classes/SwiftSpeechToTextPlugin.swift:227:63: error: type 'Int' has no member 'notifyOthersOnDeactivation'
                try self.audioSession.setActive(true, withFlags: .notifyOthersOnDeactivation)

This happens when the Swift language version is not set correctly. See this thread for help https://github.com/csdcorp/speech_to_text/issues/45.

Swift not supported trying to compile for iOS

`speech_to_text` does not specify a Swift version and none of the targets (`Runner`) integrating it have the `SWIFT_VERSION` attribute set.

This usually happens for older projects that only support Objective-C. See this thread for help https://github.com/csdcorp/speech_to_text/issues/88.

Not working on a particular Android device

The symptom for this issue is that the initialize method will always fail. If you turn on debug logging using the debugLogging: true flag on the initialize method you'll see 'Speech recognition unavailable' in the Android log. There's a lengthy issue discussion here https://github.com/csdcorp/speech_to_text/issues/36 about this. The issue seems to be that the recognizer is not always automatically enabled on the device. Two key things helped resolve the issue in this case at least.

First

  1. Go to Google Play
  2. Search for 'Google'
  3. You should find this app: https://play.google.com/store/apps/details?id=com.google.android.googlequicksearchbox If 'Disabled' enable it

This is the SO post that helped: https://stackoverflow.com/questions/28769320/how-to-check-wether-speech-recognition-is-available-or-not

Second

Ensure the app has the required permissions. The symptom for this that you get a permanent error notification 'error_audio_error` when starting a listen session. Here's a Stack Overflow post that addresses that https://stackoverflow.com/questions/46376193/android-speechrecognizer-audio-recording-error Here's the important excerpt:

You should go to system setting, Apps, Google app, then enable its permission of microphone.

iOS recognition guidelines

Apple has quite a good guide on the user experience for using speech, the original is here https://developer.apple.com/documentation/speech/sfspeechrecognizer This is the section that I think is particularly relevant:

Create a Great User Experience for Speech Recognition

Here are some tips to consider when adding speech recognition support to your app.

Be prepared to handle failures caused by speech recognition limits. Because speech recognition is a network-based service, limits are enforced so that the service can remain freely available to all apps. Individual devices may be limited in the number of recognitions that can be performed per day, and each app may be throttled globally based on the number of requests it makes per day. If a recognition request fails quickly (within a second or two of starting), check to see if the recognition service became unavailable. If it is, you may want to ask users to try again later.

Plan for a one-minute limit on audio duration. Speech recognition places a relatively high burden on battery life and network usage. To minimize this burden, the framework stops speech recognition tasks that last longer than one minute. This limit is similar to the one for keyboard-related dictation. Remind the user when your app is recording. For example, display a visual indicator and play sounds at the beginning and end of speech recognition to help users understand that they're being actively recorded. You can also display speech as it is being recognized so that users understand what your app is doing and see any mistakes made during the recognition process.

Do not perform speech recognition on private or sensitive information. Some speech is not appropriate for recognition. Don't send passwords, health or financial data, and other sensitive speech for recognition.

Libraries

speech_recognition_error
speech_recognition_event
speech_recognition_result
speech_to_text
speech_to_text_provider