Word timings

const result = await tts.generate('Highlight these words during playback.');

console.table(result.wordTimings);

Each timing contains wordIndex, word, startTime, and endTime.

Browser highlighting

await tts.play(result, {
  onPlaybackStart: () => {
    const startedAt = Date.now();
    const timer = setInterval(() => {
      const seconds = (Date.now() - startedAt) / 1000;
      const active = result.wordTimings.find(
        word => seconds >= word.startTime && seconds < word.endTime,
      );
      renderActiveWord(active?.wordIndex ?? null);
    }, 50);
  },
});

Start from the player's callback, not generation completion, so loading time does not shift highlights.

Limits

• Timings are model-predicted and are not forced alignment.
• Generate a sentence or short paragraph for best mapping.
• Indexes are local to one result.
• Duration data can be unavailable for some outputs.
• Use stream() and switch timing arrays for long documents.

The repository includes a complete Vite React word-timings example.