# Streaming TTS Module

A dedicated Text-to-Speech (TTS) service that processes synthesis requests from NATS using Coqui XTTS.

## Overview

This module enables real-time text-to-speech synthesis by accepting text via NATS and streaming audio chunks back as they're generated. This reduces latency for voice assistant applications by allowing playback to begin before synthesis completes.

## Features

- **NATS Integration**: Accepts TTS requests via NATS messaging
- **Streaming Audio**: Streams audio chunks back for immediate playback
- **Voice Cloning**: Support for custom speaker voices via reference audio
- **Multi-language**: Support for multiple languages via XTTS
- **OpenTelemetry**: Full observability with tracing and metrics
- **HyperDX Support**: Optional cloud observability integration

## Architecture

```
┌─────────────────┐
│   Voice App     │ (voice-assistant, chat-handler)
│                 │
└────────┬────────┘
         │ Text
         ▼
┌─────────────────┐
│  NATS Subject   │ ai.voice.tts.request.{session_id}
│  TTS Request    │
└────────┬────────┘
         │
         ▼
┌─────────────────┐
│  TTS Streaming  │ (This Service)
│     Service     │ - Calls XTTS API
│                 │ - Streams audio chunks
└────────┬────────┘
         │
         ▼
┌─────────────────┐
│  NATS Subject   │ ai.voice.tts.audio.{session_id}
│  Audio Chunks   │
└─────────────────┘
```

## NATS Message Protocol

### TTS Request (ai.voice.tts.request.{session_id})

All messages use **msgpack** binary encoding.

**Request:**
```python
{
    "text": "Hello, how can I help you today?",
    "speaker": "default",  # Optional: speaker ID
    "language": "en",  # Optional: language code
    "speaker_wav_b64": "...",  # Optional: base64 reference audio for voice cloning
    "stream": True  # Optional: stream chunks (default) or send complete audio
}
```

### Audio Output (ai.voice.tts.audio.{session_id})

**Streamed Chunk:**
```python
{
    "session_id": "unique-session-id",
    "chunk_index": 0,
    "total_chunks": 5,
    "audio_b64": "base64-encoded-audio-chunk",
    "is_last": False,
    "timestamp": 1234567890.123,
    "sample_rate": 24000
}
```

**Complete Audio (when stream=False):**
```python
{
    "session_id": "unique-session-id",
    "audio_b64": "base64-encoded-complete-audio",
    "timestamp": 1234567890.123,
    "sample_rate": 24000
}
```

### Status Updates (ai.voice.tts.status.{session_id})

```python
{
    "session_id": "unique-session-id",
    "status": "processing",  # processing, completed, error
    "message": "Synthesizing 50 characters",
    "timestamp": 1234567890.123
}
```

## Environment Variables

| Variable | Default | Description |
|----------|---------|-------------|
| `NATS_URL` | `nats://nats.ai-ml.svc.cluster.local:4222` | NATS server URL |
| `XTTS_URL` | `http://xtts-predictor.ai-ml.svc.cluster.local` | Coqui XTTS service URL |
| `TTS_DEFAULT_SPEAKER` | `default` | Default speaker ID |
| `TTS_DEFAULT_LANGUAGE` | `en` | Default language code |
| `TTS_AUDIO_CHUNK_SIZE` | `32768` | Audio chunk size in bytes |
| `TTS_SAMPLE_RATE` | `24000` | Audio sample rate (Hz) |
| `OTEL_ENABLED` | `true` | Enable OpenTelemetry |
| `HYPERDX_ENABLED` | `false` | Enable HyperDX observability |

## Building

```bash
docker build -t tts-module:latest .
```

## Testing

```bash
# Port-forward NATS
kubectl port-forward -n ai-ml svc/nats 4222:4222

# Send TTS request
python -c "
import nats
import msgpack
import asyncio

async def test():
    nc = await nats.connect('nats://localhost:4222')
    
    request = {
        'text': 'Hello, this is a test of text to speech.',
        'stream': True
    }
    
    await nc.publish(
        'ai.voice.tts.request.test-session',
        msgpack.packb(request)
    )
    await nc.close()

asyncio.run(test())
"

# Subscribe to audio output
nats sub "ai.voice.tts.audio.>"
```

## Voice Cloning

To use a custom voice, provide reference audio in the request:

```python
import base64

with open("reference_voice.wav", "rb") as f:
    speaker_wav_b64 = base64.b64encode(f.read()).decode()

request = {
    "text": "This will sound like the reference voice.",
    "speaker_wav_b64": speaker_wav_b64
}
```

## License

MIT