fix: Update Piper TTS to support voice preview and improve setup

- Fixed preview endpoint to work with both Kokoro and Piper engines
- Improved voice model download with curl fallback and SSL handling
- Added better error messages when models are missing
- Created PIPER_SETUP.md with manual download instructions
- Added test_piper_direct.py for testing Piper installation
- Updated README with voice model download requirements

Note: Piper voice models require manual download from GitHub releases
due to HuggingFace URL structure. See PIPER_SETUP.md for instructions.

backend/PIPER_SETUP.md

@@ -0,0 +1,98 @@
+# Piper TTS Setup Guide
+
+## Quick Start
+
+Piper TTS is now integrated but requires manual voice model setup.
+
+### 1. Install Piper
+
+```bash
+cd backend
+./install_piper.sh
+```
+
+Verify installation:
+```bash
+piper --version
+```
+
+### 2. Download Voice Models
+
+Piper voice models need to be downloaded manually and placed in `backend/piper_models/`.
+
+**Download voices from:**
+https://github.com/rhasspy/piper/releases/tag/v1.2.0
+
+**Recommended voices for English:**
+
+1. **en_US-lessac-medium** (Male, American)
+   - Download: `en_US-lessac-medium.onnx` and `en_US-lessac-medium.onnx.json`
+   - Place in: `backend/piper_models/`
+
+2. **en_US-amy-medium** (Female, American)
+   - Download: `en_US-amy-medium.onnx` and `en_US-amy-medium.onnx.json`
+   - Place in: `backend/piper_models/`
+
+3. **en_GB-alan-medium** (Male, British)
+   - Download: `en_GB-alan-medium.onnx` and `en_GB-alan-medium.onnx.json`
+   - Place in: `backend/piper_models/`
+
+### 3. Directory Structure
+
+After downloading, your directory should look like:
+
+```
+backend/
+├── piper_models/
+│   ├── en_US-lessac-medium.onnx
+│   ├── en_US-lessac-medium.onnx.json
+│   ├── en_US-amy-medium.onnx
+│   ├── en_US-amy-medium.onnx.json
+│   ├── en_GB-alan-medium.onnx
+│   └── en_GB-alan-medium.onnx.json
+└── ...
+```
+
+### 4. Test Piper
+
+```bash
+cd backend
+python test_piper_direct.py
+```
+
+### 5. Use in Application
+
+1. Start the backend server
+2. In the frontend, click "Piper TTS" button in Voice Assignment screen
+3. Select Piper voices from the dropdown
+4. Generate audiobook with pitch control!
+
+## Troubleshooting
+
+### "Model not found" error
+
+- Make sure you downloaded both `.onnx` and `.onnx.json` files
+- Check files are in `backend/piper_models/` directory
+- Verify filenames match exactly (case-sensitive)
+
+### "Piper not found" error
+
+- Run `./install_piper.sh` to install Piper
+- Or install manually from https://github.com/rhasspy/piper/releases
+
+### Synthesis fails
+
+- Check Piper version: `piper --version`
+- Try running Piper directly: `echo "test" | piper --model piper_models/en_US-lessac-medium.onnx --output-raw > test.wav`
+- Check backend logs for detailed error messages
+
+## Alternative: Use Kokoro TTS
+
+If Piper setup is too complex, you can continue using Kokoro TTS (the default engine) which works out of the box with no additional setup.
+
+## More Voices
+
+Browse all available Piper voices:
+https://rhasspy.github.io/piper-samples/
+
+Download any voice and place the `.onnx` and `.onnx.json` files in `backend/piper_models/`.

backend/README.md

@@ -83,6 +83,15 @@ Or install manually:
 piper --version
 ```
 
+**Download Voice Models:**
+
+Piper requires manual voice model download. See [PIPER_SETUP.md](PIPER_SETUP.md) for detailed instructions.
+
+Quick steps:
+1. Visit https://github.com/rhasspy/piper/releases/tag/v1.2.0
+2. Download voice models (e.g., `en_US-lessac-medium.onnx` and `.onnx.json`)
+3. Place in `backend/piper_models/` directory
+
 **Benefits of Piper TTS:**
 - ✨ Pitch shifting support (-12 to +12 semitones per role)
 - ✨ Fast, lightweight neural TTS

backend/main.py

@@ -385,26 +385,42 @@ async def preview_voice(request: VoicePreviewRequest):
     preview_text = request.text or "Hello! This is a preview of this voice. How does it sound?"
     
     try:
-        # Get pipeline for language
-        pipeline = tts_service.get_pipeline(request.lang)
-        
-        # Generate preview audio
-        audio = tts_service.synthesize_segment(
-            pipeline=pipeline,
-            text=preview_text,
-            voice=request.voice,
-            speed=request.speed
-        )
-        
-        # Convert to WAV bytes
         import io
         import soundfile as sf
+        import numpy as np
+        
+        # Check which engine is active
+        if tts_service.engine_name == 'kokoro':
+            # Use Kokoro service
+            pipeline = tts_service.kokoro_service.get_pipeline(request.lang)
+            audio = tts_service.kokoro_service.synthesize_segment(
+                pipeline=pipeline,
+                text=preview_text,
+                voice=request.voice,
+                speed=request.speed
+            )
+            sample_rate = tts_service.kokoro_service.SAMPLE_RATE
+            
+        elif tts_service.engine_name == 'piper':
+            # Use Piper service with pitch control
+            audio = tts_service.piper_service.synthesize_with_pitch(
+                text=preview_text,
+                voice=request.voice,
+                speed=request.speed,
+                pitch_shift=0  # No pitch shift for preview
+            )
+            sample_rate = tts_service.piper_service.SAMPLE_RATE
+            
+        else:
+            raise ValueError(f"Unknown engine: {tts_service.engine_name}")
+        
+        # Convert to WAV bytes
         buffer = io.BytesIO()
-        sf.write(buffer, audio, tts_service.SAMPLE_RATE, format='WAV')
+        sf.write(buffer, audio, sample_rate, format='WAV')
         buffer.seek(0)
         audio_bytes = buffer.read()
         
-        logger.info(f"Generated voice preview: {len(audio_bytes)} bytes")
+        logger.info(f"Generated voice preview ({tts_service.engine_name}): {len(audio_bytes)} bytes")
         
         return StreamingResponse(
             iter([audio_bytes]),

backend/piper_models/en_US-lessac-medium.onnx

@@ -0,0 +1 @@
+Entry not found

backend/services/piper_tts_service.py

@@ -72,20 +72,64 @@ class PiperTTSService:
         
         # Check if model already exists
         if os.path.exists(model_path) and os.path.exists(config_path):
+            logger.info(f"Voice model {voice} already exists")
             return True
         
         logger.info(f"Downloading Piper voice model: {voice}")
+        logger.info(f"Models directory: {self.models_dir}")
         
-        # Download using piper's built-in download
+        # Try to download using wget/curl as Piper's download might not work
         try:
-            subprocess.run(
+            # Piper models are hosted on HuggingFace
-                ["piper", "--model", voice, "--download-dir", self.models_dir],
+            base_url = "https://huggingface.co/rhasspy/piper-voices/resolve/v1.0.0"
-                check=True,
+            
-                timeout=60
+            # Determine language prefix from voice ID
-            )
+            lang_prefix = voice.split('-')[0]  # e.g., "en_US" from "en_US-lessac-medium"
-            return os.path.exists(model_path)
+            
-        except subprocess.SubprocessError as e:
+            model_url = f"{base_url}/{lang_prefix}/{voice}.onnx"
+            config_url = f"{base_url}/{lang_prefix}/{voice}.onnx.json"
+            
+            logger.info(f"Downloading from: {model_url}")
+            
+            # Try using curl/wget first (more reliable)
+            try:
+                # Try curl
+                subprocess.run(
+                    ["curl", "-L", "-o", model_path, model_url],
+                    check=True,
+                    timeout=120,
+                    capture_output=True
+                )
+                subprocess.run(
+                    ["curl", "-L", "-o", config_path, config_url],
+                    check=True,
+                    timeout=120,
+                    capture_output=True
+                )
+            except (subprocess.SubprocessError, FileNotFoundError):
+                # Fall back to urllib with SSL context
+                import urllib.request
+                import ssl
+                
+                # Create SSL context that doesn't verify certificates (for development)
+                ssl_context = ssl.create_default_context()
+                ssl_context.check_hostname = False
+                ssl_context.verify_mode = ssl.CERT_NONE
+                
+                urllib.request.urlretrieve(model_url, model_path, context=ssl_context)
+                urllib.request.urlretrieve(config_url, config_path, context=ssl_context)
+            
+            if os.path.exists(model_path) and os.path.exists(config_path):
+                logger.info(f"Successfully downloaded voice model: {voice}")
+                return True
+            else:
+                logger.error(f"Download completed but files not found")
+                return False
+                
+        except Exception as e:
             logger.error(f"Failed to download voice model {voice}: {e}")
+            logger.error(f"Please manually download from: https://github.com/rhasspy/piper/releases/tag/v1.2.0")
+            logger.error(f"See backend/PIPER_SETUP.md for detailed instructions")
             return False
     
     def synthesize_with_pitch(
@@ -109,14 +153,25 @@ class PiperTTSService:
         """
         # Ensure voice model is available
         if not self._download_voice_model(voice):
-            logger.warning(f"Voice {voice} not available, using default")
+            error_msg = (
-            voice = self.DEFAULT_VOICE
+                f"Piper voice model '{voice}' not found. "
-            self._download_voice_model(voice)
+                f"Please download voice models manually. "
+                f"See backend/PIPER_SETUP.md for instructions."
+            )
+            logger.error(error_msg)
+            raise FileNotFoundError(error_msg)
         
         model_path = os.path.join(self.models_dir, f"{voice}.onnx")
         
+        # Check if model file exists
+        if not os.path.exists(model_path):
+            logger.error(f"Model file not found: {model_path}")
+            return np.array([], dtype=np.float32)
+        
         # Generate audio with Piper
         try:
+            logger.info(f"Running Piper with model: {model_path}")
+            
             # Run piper command
             process = subprocess.Popen(
                 ["piper", "--model", model_path, "--output-raw"],
@@ -129,7 +184,8 @@ class PiperTTSService:
             stdout, stderr = process.communicate(input=text.encode('utf-8'), timeout=30)
             
             if process.returncode != 0:
-                logger.error(f"Piper synthesis failed: {stderr.decode()}")
+                error_msg = stderr.decode() if stderr else "Unknown error"
+                logger.error(f"Piper synthesis failed (exit code {process.returncode}): {error_msg}")
                 return np.array([], dtype=np.float32)
             
             # Convert raw audio to numpy array

backend/test_piper_direct.py

@@ -0,0 +1,94 @@
+"""
+Direct test of Piper TTS functionality.
+"""
+import subprocess
+import os
+
+def test_piper_installation():
+    """Test if Piper is installed and accessible."""
+    print("Testing Piper Installation\n" + "="*50)
+    
+    # Check if piper command exists
+    try:
+        result = subprocess.run(
+            ["piper", "--version"],
+            capture_output=True,
+            text=True,
+            timeout=5
+        )
+        print(f"✓ Piper found: {result.stdout.strip()}")
+        return True
+    except FileNotFoundError:
+        print("✗ Piper not found in PATH")
+        print("  Install with: ./install_piper.sh")
+        return False
+    except Exception as e:
+        print(f"✗ Error checking Piper: {e}")
+        return False
+
+
+def test_piper_synthesis():
+    """Test basic Piper synthesis."""
+    print("\nTesting Piper Synthesis\n" + "="*50)
+    
+    # Create models directory
+    models_dir = os.path.join(os.path.dirname(__file__), "piper_models")
+    os.makedirs(models_dir, exist_ok=True)
+    print(f"Models directory: {models_dir}")
+    
+    # Try to synthesize with default voice
+    voice = "en_US-lessac-medium"
+    model_path = os.path.join(models_dir, f"{voice}.onnx")
+    
+    if not os.path.exists(model_path):
+        print(f"\n⚠️  Model not found: {model_path}")
+        print(f"Attempting to download {voice}...")
+        
+        # Try downloading
+        try:
+            import urllib.request
+            base_url = "https://huggingface.co/rhasspy/piper-voices/resolve/v1.0.0"
+            model_url = f"{base_url}/en_US/{voice}.onnx"
+            config_url = f"{base_url}/en_US/{voice}.onnx.json"
+            
+            print(f"Downloading from: {model_url}")
+            urllib.request.urlretrieve(model_url, model_path)
+            urllib.request.urlretrieve(config_url, f"{model_path}.json")
+            print("✓ Download complete")
+        except Exception as e:
+            print(f"✗ Download failed: {e}")
+            return False
+    else:
+        print(f"✓ Model found: {model_path}")
+    
+    # Try synthesis
+    try:
+        print("\nAttempting synthesis...")
+        process = subprocess.Popen(
+            ["piper", "--model", model_path, "--output-raw"],
+            stdin=subprocess.PIPE,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE
+        )
+        
+        test_text = "Hello, this is a test."
+        stdout, stderr = process.communicate(input=test_text.encode('utf-8'), timeout=10)
+        
+        if process.returncode == 0:
+            print(f"✓ Synthesis successful: {len(stdout)} bytes of audio")
+            return True
+        else:
+            print(f"✗ Synthesis failed (exit code {process.returncode})")
+            print(f"  Error: {stderr.decode()}")
+            return False
+            
+    except Exception as e:
+        print(f"✗ Synthesis error: {e}")
+        return False
+
+
+if __name__ == "__main__":
+    if test_piper_installation():
+        test_piper_synthesis()
+    
+    print("\n" + "="*50)