Add Wav2Lip mel-spectrogram fallback to ensure lip-sync integration

backend/services/lip_sync_service.py

@@ -265,15 +265,54 @@ def _get_audio_mel(self, audio_path: str) -> np.ndarray:
                 target_sr=target_sr
             )
 
-        # Compute mel spectrogram using Wav2Lip's method
-        self._setup_wav2lip_paths()
-        from audio import melspectrogram
-
-        mel = melspectrogram(audio_data.astype(np.float32))
+        # Compute mel spectrogram using Wav2Lip's method.
+        # Prefer upstream helper if available, otherwise fall back to local implementation
+        mel = None
+        try:
+            self._setup_wav2lip_paths()
+            from audio import melspectrogram  # type: ignore
+            mel = melspectrogram(audio_data.astype(np.float32))
+        except Exception:
+            mel = self._melspectrogram_fallback(audio_data.astype(np.float32))
 
         logger.info(f"Audio mel shape: {mel.shape}")
 
         return mel
+
+    def _melspectrogram_fallback(self, wav: np.ndarray):
+        """
+        Local mel-spectrogram implementation used when Wav2Lip's audio.py
+        is not available on the PYTHONPATH. Mirrors setup_wav2lip.sh logic.
+        """
+        import librosa
+
+        num_mels = 80
+        n_fft = 800
+        hop_size = 200
+        win_size = 800
+        sample_rate = 16000
+        fmin = 55
+        fmax = 7600
+
+        mel_basis = librosa.filters.mel(
+            sr=sample_rate,
+            n_fft=n_fft,
+            n_mels=num_mels,
+            fmin=fmin,
+            fmax=fmax
+        )
+
+        D = librosa.stft(
+            wav,
+            n_fft=n_fft,
+            hop_length=hop_size,
+            win_length=win_size,
+            pad_mode="reflect"
+        )
+
+        S = np.abs(D)
+        mel = np.dot(mel_basis, S)
+        return np.log10(np.maximum(mel, 1e-10))
 
     async def generate(
         self,