Number of characters synthesized (for character-based billing).
Total synthesis duration in milliseconds.
Optional inputInput text tokens (for token-based billing, e.g., OpenAI TTS).
Optional metadata?: MetricsMetadataMetadata for model provider and name tracking.
Optional outputOutput audio tokens (for token-based billing, e.g., OpenAI TTS).
Optional segmentOptional speechTime to first byte in milliseconds.
Generated audio duration in milliseconds.