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Overview

AudioManager handles all audio-related functionality within a user session. It processes incoming audio data from smart glasses, manages buffering, handles LC3 codec decoding (when enabled), and distributes audio to transcription services and subscribed apps. File: packages/cloud/src/services/session/AudioManager.ts

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Key Responsibilities

  1. Audio Processing: Receives and processes raw audio data
  2. Codec Handling: LC3 audio decoding (optional)
  3. Buffer Management: Maintains recent audio buffer and ordered processing
  4. Service Integration: Feeds audio to transcription and translation services
  5. App Distribution: Relays audio to subscribed apps
  6. Debug Support: Optional audio file writing for debugging

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Architecture

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Audio Processing Pipeline

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Main Processing Method

async processAudioData(
  audioData: ArrayBuffer | any,
  isLC3 = this.IS_LC3
): Promise<ArrayBuffer | void> {
  // Update timestamp
  this.userSession.lastAudioTimestamp = Date.now();
  
  // Notify microphone manager
  this.userSession.microphoneManager.onAudioReceived();
  
  // Process the audio
  const processedAudioData = audioData; // Or LC3 decode if needed
  
  if (processedAudioData) {
    // Feed to services
    this.userSession.transcriptionManager.feedAudio(processedAudioData);
    this.userSession.translationManager.feedAudio(processedAudioData);
    
    // Relay to apps
    this.relayAudioToApps(processedAudioData);
  }
  
  return processedAudioData;
}

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LC3 Codec Support

When LC3 is enabled: 
private async processAudioInternal(
  audioData: ArrayBuffer,
  isLC3: boolean
): Promise<ArrayBuffer | void> {
  if (isLC3 && this.lc3Service) {
    try {
      // Decode LC3 to PCM
      const decodedData = await this.lc3Service.decodeAudioChunk(audioData);
      
      if (!decodedData) {
        this.logger.warn(`⚠️ LC3 decode returned null`);
        return undefined;
      }
      
      return decodedData;
    } catch (error) {
      this.logger.error(`❌ Error decoding LC3 audio:`, error);
      await this.reinitializeLc3Service();
      return undefined;
    }
  }
  
  return audioData; // Return as-is for PCM
}

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Buffer Management

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Recent Audio Buffer

Maintains last 10 seconds of audio: 
private addToRecentBuffer(audioData: ArrayBufferLike): void {
  const now = Date.now();
  
  // Add to buffer
  this.recentAudioBuffer.push({
    data: audioData,
    timestamp: now
  });
  
  // Prune old data (keep only last 10 seconds)
  const tenSecondsAgo = now - 10_000;
  this.recentAudioBuffer = this.recentAudioBuffer.filter(
    chunk => chunk.timestamp >= tenSecondsAgo
  );
}

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Ordered Audio Buffer

For handling out-of-order audio chunks: 
interface OrderedAudioBuffer {
  chunks: SequencedAudioChunk[];
  lastProcessedSequence: number;
  processingInProgress: boolean;
  expectedNextSequence: number;
  bufferSizeLimit: number;         // Max 100 chunks
  bufferTimeWindowMs: number;      // 500ms window
  bufferProcessingInterval: NodeJS.Timeout | null;
}

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Adding to Ordered Buffer

addToOrderedBuffer(chunk: SequencedAudioChunk): void {
  // Add to buffer
  this.orderedBuffer.chunks.push(chunk);
  
  // Sort by sequence number
  this.orderedBuffer.chunks.sort(
    (a, b) => a.sequenceNumber - b.sequenceNumber
  );
  
  // Enforce size limit
  if (this.orderedBuffer.chunks.length > this.orderedBuffer.bufferSizeLimit) {
    this.orderedBuffer.chunks = this.orderedBuffer.chunks.slice(
      this.orderedBuffer.chunks.length - this.orderedBuffer.bufferSizeLimit
    );
  }
}

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Processing Ordered Buffer

async processOrderedBuffer(): Promise<void> {
  if (this.orderedBuffer.processingInProgress) return;
  
  try {
    this.orderedBuffer.processingInProgress = true;
    
    for (const chunk of this.orderedBuffer.chunks) {
      // Skip already processed
      if (chunk.sequenceNumber <= this.orderedBuffer.lastProcessedSequence) {
        continue;
      }
      
      // Process the chunk
      await this.processAudioData(chunk.data, chunk.isLC3);
      
      // Update tracking
      this.orderedBuffer.lastProcessedSequence = chunk.sequenceNumber;
      this.orderedBuffer.expectedNextSequence = chunk.sequenceNumber + 1;
    }
    
    // Remove processed chunks
    this.orderedBuffer.chunks = this.orderedBuffer.chunks.filter(
      chunk => chunk.sequenceNumber > this.orderedBuffer.lastProcessedSequence
    );
  } finally {
    this.orderedBuffer.processingInProgress = false;
  }
}

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App Distribution

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Relay to Subscribed Apps

private relayAudioToApps(audioData: ArrayBuffer): void {
  // Get subscribers
  const subscribedPackageNames = subscriptionService.getSubscribedApps(
    this.userSession,
    StreamType.AUDIO_CHUNK
  );
  
  if (subscribedPackageNames.length === 0) return;
  
  // Send to each subscriber
  for (const packageName of subscribedPackageNames) {
    const connection = this.userSession.appWebsockets.get(packageName);
    
    if (connection?.readyState === WebSocket.OPEN) {
      try {
        connection.send(audioData);
      } catch (sendError) {
        this.logger.error(
          `Error sending audio to ${packageName}:`, 
          sendError
        );
      }
    }
  }
}

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Debug Features

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Audio Writer

For debugging audio issues: 
private initializeAudioWriterIfNeeded(): void {
  if (this.DEBUG_AUDIO && !this.audioWriter) {
    this.audioWriter = new AudioWriter(this.userSession.userId);
  }
}

// Write audio data
if (this.DEBUG_AUDIO) {
  await this.audioWriter?.writePCM(processedAudioData);
  await this.audioWriter?.writeLC3(rawLC3Data);
}

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Service Recovery

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LC3 Service Reinitialization

Handles LC3 decoder failures: 
private async reinitializeLc3Service(): Promise<void> {
  try {
    if (this.lc3Service) {
      this.logger.warn(`⚠️ Attempting to reinitialize LC3 service`);
      
      // Clean up existing
      this.lc3Service.cleanup();
      this.lc3Service = undefined;
      
      // Create new service
      const newLc3Service = createLC3Service(this.userSession.sessionId);
      await newLc3Service.initialize();
      this.lc3Service = newLc3Service;
      
      this.logger.info(`✅ Successfully reinitialized LC3 service`);
    }
  } catch (reinitError) {
    this.logger.error(`❌ Failed to reinitialize LC3 service:`, reinitError);
  }
}

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Configuration

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Debug Flags

private readonly LOG_AUDIO = false;     // Enable audio logging
private readonly DEBUG_AUDIO = false;   // Enable audio file writing
private readonly IS_LC3 = false;        // Enable LC3 processing

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Buffer Configuration

  • Recent Buffer: Last 10 seconds of audio
  • Ordered Buffer Size: Maximum 100 chunks
  • Buffer Time Window: 500ms for ordering
  • Processing Interval: 100ms default

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Public Methods

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Get Recent Audio Buffer

getRecentAudioBuffer(): { data: ArrayBufferLike; timestamp: number }[] {
  return [...this.recentAudioBuffer];
}

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Lifecycle Management

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Initialization

constructor(userSession: UserSession) {
  this.userSession = userSession;
  this.logger = userSession.logger.child({ service: "AudioManager" });
  
  // Initialize ordered buffer
  this.orderedBuffer = {
    chunks: [],
    lastProcessedSequence: -1,
    processingInProgress: false,
    expectedNextSequence: 0,
    bufferSizeLimit: 100,
    bufferTimeWindowMs: 500,
    bufferProcessingInterval: null
  };
  
  // Initialize LC3 if needed
  this.initializeLc3Service();
}

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Disposal

dispose(): void {
  // Stop buffer processing
  this.stopOrderedBufferProcessing();
  
  // Clean up LC3 service
  if (this.lc3Service) {
    this.lc3Service.cleanup();
    this.lc3Service = undefined;
  }
  
  // Clean up audio writer
  if (this.audioWriter) {
    this.audioWriter = undefined;
  }
  
  // Clear buffers
  this.recentAudioBuffer = [];
  this.orderedBuffer.chunks = [];
  
  this.logger.info("AudioManager disposed");
}

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Integration Points

  • MicrophoneManager: Notified when audio is received
  • TranscriptionManager: Receives processed audio for speech-to-text
  • TranslationManager: Receives audio for translation services
  • SubscriptionService: Determines which apps receive audio
  • LC3Service: Handles audio codec operations

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Performance Considerations

  1. Buffer Pruning: Automatically removes old audio data
  2. Ordered Processing: Handles out-of-order packets gracefully
  3. Error Recovery: Reinitializes services on failure
  4. Selective Distribution: Only sends to subscribed apps

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Best Practices

  1. Monitor Buffer Sizes to prevent memory issues
  2. Handle LC3 Failures with automatic recovery
  3. Use Debug Flags sparingly in production
  4. Process Audio Efficiently to maintain real-time performance
  5. Clean Up Resources properly on disposal