Skip to main content

Platform-Specific Considerations

This document covers platform-specific configurations, optimizations, and considerations for expo-edge-speech across iOS and Android platforms.

Minimum Platform Requirements​

Expo SDK 52 Requirements:

  • iOS: iOS 15.1+ (minimum deployment target raised from iOS 13.4)
  • Android: API level 24+ / Android 7.0+ (minSdkVersion raised from 23)

These requirements are enforced by Expo SDK 52 and React Native 0.76.9. Applications targeting older platform versions will need to use an earlier version of expo-edge-speech compatible with previous Expo SDK versions.

Required Dependencies:

  • expo: ~52.0.47
  • expo-av: ~15.0.2 (for audio playback)
  • react-native: 0.76.9

Platform Support Matrix​

FeatureiOSAndroidNotes
Speech Synthesis✅✅Full compatibility with Microsoft Edge TTS
Background Playback⚠️*✅*iOS restrictions in Expo Go environment
Word Boundaries✅✅Real-time word boundary events
Audio Queue Management✅✅Intelligent queue handling
Offline Playback✅✅Cached audio playback without network
Voice Caching✅✅Automatic voice list caching
Network Recovery✅✅Automatic retry with circuit breaker
Pause/Resume✅✅Enhanced Android support vs expo-speech

expo-speech API Compatibility​

expo-edge-speech provides full compatibility with the expo-speech API while offering enhanced functionality and improved cross-platform behavior.

Usage Pattern​

import * as Speech from 'expo-edge-speech';

// Works consistently across all platforms (iOS, Android)
await Speech.speak("Hello world", {
  onStart: () => console.log("Speech started"),
  onDone: () => console.log("Speech completed"),
  onError: (error) => console.error("Speech error:", error),
});

// Enhanced pause/resume operations
await Speech.pause();   // ✅ Works on Android (unlike expo-speech)
await Speech.resume();  // ✅ Works on Android (unlike expo-speech)

// State checking
const isSpeaking = await Speech.isSpeakingAsync();
console.log(`Currently speaking: ${isSpeaking}`);

Architecture and State Management​

Two-Phase Synthesis Architecture: expo-edge-speech uses a sophisticated two-phase workflow that ensures reliable audio delivery:

Phase 1: Network Synthesis​

  • Text is processed and complete audio is generated on Microsoft's servers
  • Audio data is fully downloaded and cached locally
  • No audio playback occurs during this phase
  • isSpeakingAsync() returns false
  • Pause/resume operations are not available

Phase 2: Local Playback​

  • Complete audio file is played locally using expo-av
  • High-quality playback with full control capabilities
  • isSpeakingAsync() returns true during active playback
  • Pause/resume operations are fully available
  • Word boundary events are fired in real-time

API Behavior:

  • isSpeakingAsync() returns true even when speech is paused (matches expo-speech behavior)
  • Pause/resume operations only function during the local playback phase
  • State transitions are consistent across iOS and Android platforms
  • Always check isSpeakingAsync() before calling pause/resume operations

Architectural Advantages:

  • Better Audio Quality: Complete synthesis before playback ensures optimal audio fidelity
  • Reliable Cross-Platform Behavior: Consistent experience across iOS and Android
  • Enhanced Android Support: Full pause/resume functionality that expo-speech cannot provide
  • Network Resilience: Complete download before playback prevents interruptions

Background Playback Considerations​

iOS Background Playback:

  • Supported in standalone apps with proper configuration
  • Not supported in Expo Go due to platform restrictions
  • Requires background audio capability in app.json configuration
  • See expo-av AudioMode documentation for implementation details

Android Background Playback:

  • Fully supported in both Expo Go and standalone apps
  • No additional configuration required for basic background playback
  • Enhanced control capabilities compared to expo-speech

Platform-Specific Optimizations​

iOS Optimizations:

  • Intelligent memory management for audio caching
  • Optimized for iOS audio session management
  • Efficient handling of audio interruptions

Android Optimizations:

  • Enhanced audio focus management
  • Optimized for Android audio routing
  • Better integration with system audio controls

Cross-Platform Features:

  • Consistent voice caching behavior
  • Unified error handling and recovery
  • Standardized word boundary event timing