Speech Recognition in Uno

Tip

This article covers Uno-specific information for Windows.Media.SpeechRecognition. For a full description of the feature and instructions on using it, see SpeechRecognition Namespace.

• The Windows.Media.SpeechRecognition class allows an application to recognize voice input.

Uno's implementation currently supports basic native speech recognition.

Supported Features

The following features of Windows.Media.SpeechRecognition.SpeechRecognizer are currently supported:

Feature	iOS	Android	macOS (Skia)	WebAssembly	Remarks
SpeechRecognizer()	X	X	X	X
SpeechRecognizer(Language)	X	X	X	X
Constraints	-	-	-	-
ContinuousRecognitionSession	-	-	-	-
CurrentLanguage	X	X	X	X
State	X	X	X	X
SupportedGrammarLanguages	-	-	-	-
SupportedTopicLanguages	-	-	-	-
SystemSpeechLanguage	-	-	-	-
Timeouts	X	X	X	X
UIOptions	X	X	X	X	Not used
CompileConstraintsAsync()	X	X	X	X	Always return Success (implemented to meet WinUI constraint that requires CompileConstraintsAsync() to be called before RecognizeAsync())
Dispose()	X	X	X	X
RecognizeAsync()	X	X	X	X
RecognizeWithUIAsync()	-	-	-	-
StopRecognitionAsync()	X	X	X	X
TrySetSystemSpeechLanguageAsync(Language)	-	-	-	-
HypothesisGenerated	X	X	X	X
RecognitionQualityDegrading	-	-	-	-
StateChanged	X	X	X	X

Requirement

iOS

• iOS 10 or later is required.

• The following lines need to be added to your info.plist:

  <key>NSSpeechRecognitionUsageDescription</key>  
  <string>[SpeechRecognition usage description]</string>  
  <key>NSMicrophoneUsageDescription</key>  
  <string>[SpeechRecognition usage description]</string> 
  

Android

The following lines need to be added to your AndroidManifest.xml:

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.RECORD_AUDIO" />

macOS (Skia)

• macOS 10.15 or later is required.

• The following lines need to be added to your app bundle's Info.plist:

  <key>NSSpeechRecognitionUsageDescription</key>
  <string>[SpeechRecognition usage description]</string>
  <key>NSMicrophoneUsageDescription</key>
  <string>[SpeechRecognition usage description]</string>
  

• The app must be packaged as an .app bundle when running speech recognition — macOS only displays the TCC authorization prompt for bundled apps. Launching the executable directly from a terminal (dotnet run) will result in SFSpeechRecognizer returning Denied without prompting.

Note

For contributors: The Uno samples app (SamplesApp.Skia.Generic) ships a build target that automatically produces a minimal .app bundle next to the regular output on macOS. After dotnet build, launch it with:

open src/SamplesApp/SamplesApp.Skia.Generic/bin/Debug/net10.0/SamplesApp.Skia.Generic.app

WebAssembly

Speech recognition on WebAssembly relies on the browser's Web Speech API implementation:

• window.SpeechRecognition, or
• window.webkitSpeechRecognition (vendor-prefixed fallback).

Requirements and behavior notes:

• The app must run in a browser that exposes one of the APIs above.
• The user must grant microphone permission in the browser.
• Browsers typically require a secure context (https://), with http://localhost commonly allowed for local development.
• Starting recognition may require user interaction (for example, a button click) depending on browser policies.

Limitation

In Windows.Media.SpeechRecognition.SpeechRecognitionResult, only Text, Alternates, and GetAlternates(uint maxAlternates) are implemented. In particular, RawConfidence and Confidence fields are not currently supported.

On WebAssembly specifically, availability is browser-dependent. If speech recognition is not available in the current browser, RecognizeAsync() fails with an InvalidOperationException.