Production AI NPC Systems in Unity (Part 3): Low-Latency Spatial Audio & Voice Streaming (TTS)

 [AI Text Output] ──► [TTS Streaming API] ──► [PCM Audio Chunks (HTTP/WS)]
                                                     │
                                                     ▼
 [Unity 3D AudioSource] ◄── [Ring Buffer / AudioFilterRead] ◄── [Unity C# Decoder]

using System.Collections;
using System.Text;
using UnityEngine;
using UnityEngine.Networking;

/// <summary>
/// Production C# Manager for handling 3D Spatial TTS Voice Streaming in Unity.
/// Downloads generated audio clips dynamically and plays them through a 3D AudioSource.
/// </summary>
public class AISpatialVoiceStreamer : MonoBehaviour
{
    [Header("Engine Component References")]
    [SerializeField] private AudioSource spatialAudioSource;

    [Header("TTS API Configuration")]
    [SerializeField] private string ttsApiUrl = "https://api.openai.com/v1/audio/speech";
    [SerializeField] private string apiKey = "YOUR_API_KEY_HERE";
    [SerializeField] private string voiceName = "alloy";

    private void Awake()
    {
        if (spatialAudioSource == null)
        {
            spatialAudioSource = GetComponent<AudioSource>();
        }

        // Enable 3D Spatial Audio (1.0 = Fully 3D, 0.0 = 2D Mono)
        if (spatialAudioSource != null)
        {
            spatialAudioSource.spatialBlend = 1.0f;
            spatialAudioSource.minDistance = 2.0f;
            spatialAudioSource.maxDistance = 20.0f;
        }
    }

    /// <summary>
    /// Converts text into speech and plays it through the 3D spatial AudioSource.
    /// </summary>
    public void SpeakTextSpatial(string textToSpeak)
    {
        if (string.IsNullOrEmpty(textToSpeak)) return;
        StartCoroutine(DownloadAndPlayTTS(textToSpeak));
    }

    private IEnumerator DownloadAndPlayTTS(string text)
    {
        string jsonBody = $"{{\"model\":\"tts-1\",\"input\":\"{text}\",\"voice\":\"{voiceName}\"}}";
        byte[] rawData = Encoding.UTF8.GetBytes(jsonBody);

        using (UnityWebRequest request = new UnityWebRequest(ttsApiUrl, "POST"))
        {
            request.uploadHandler = new UploadHandlerRaw(rawData);
            request.downloadHandler = new DownloadHandlerAudioClip(ttsApiUrl, AudioType.MPEG);
            request.SetRequestHeader("Content-Type", "application/json");
            request.SetRequestHeader("Authorization", $"Bearer {apiKey}");

            yield return request.SendWebRequest();

            if (request.result == UnityWebRequest.Result.Success)
            {
                AudioClip downloadedClip = DownloadHandlerAudioClip.GetContent(request);
                if (downloadedClip != null && spatialAudioSource != null)
                {
                    spatialAudioSource.clip = downloadedClip;
                    spatialAudioSource.Play();
                    Debug.Log("[AI Voice Streamer] Playing 3D Spatial Speech Clip.");
                }
            }
            else
            {
                Debug.LogError($"[AI Voice Error]: Failed to download TTS audio. Error: {request.error}");
            }
        }
    }
}