Fix kokoro batch issue (#128)

* Fix kokoro batch issue

* code

* fix batch size

---------

Co-authored-by: Freddy Boulton <freddyboulton@hf-freddy.local>

backend/fastrtc/text_to_speech/tts.py

@@ -39,6 +39,48 @@ def get_tts_model(model: Literal["kokoro"] = "kokoro") -> TTSModel:
     return m
 
 
+class KokoroFixedBatchSize:
+    # Source: https://github.com/thewh1teagle/kokoro-onnx/issues/115#issuecomment-2676625392
+    def _split_phonemes(self, phonemes: str) -> list[str]:
+        MAX_PHONEME_LENGTH = 510
+        max_length = MAX_PHONEME_LENGTH - 1
+        batched_phonemes = []
+        while len(phonemes) > max_length:
+            # Find best split point within limit
+            split_idx = max_length
+
+            # Try to find the last period before max_length
+            period_idx = phonemes.rfind(".", 0, max_length)
+            if period_idx != -1:
+                split_idx = period_idx + 1  # Include period
+
+            else:
+                # Try other punctuation
+                match = re.search(
+                    r"[!?;,]", phonemes[:max_length][::-1]
+                )  # Search backwards
+                if match:
+                    split_idx = max_length - match.start()
+
+                else:
+                    # Try last space
+                    space_idx = phonemes.rfind(" ", 0, max_length)
+                    if space_idx != -1:
+                        split_idx = space_idx
+
+            # If no good split point is found, force split at max_length
+            chunk = phonemes[:split_idx].strip()
+            batched_phonemes.append(chunk)
+
+            # Move to the next part
+            phonemes = phonemes[split_idx:].strip()
+
+        # Add remaining phonemes
+        if phonemes:
+            batched_phonemes.append(phonemes)
+        return batched_phonemes
+
+
 class KokoroTTSModel(TTSModel):
     def __init__(self):
         from kokoro_onnx import Kokoro
@@ -48,6 +90,8 @@ class KokoroTTSModel(TTSModel):
             voices_path=hf_hub_download("fastrtc/kokoro-onnx", "voices-v1.0.bin"),
         )
 
+        self.model._split_phonemes = KokoroFixedBatchSize()._split_phonemes
+
     def tts(
         self, text: str, options: KokoroTTSOptions | None = None
     ) -> tuple[int, NDArray[np.float32]]:
@@ -74,6 +118,7 @@ class KokoroTTSModel(TTSModel):
             ):
                 if s_idx != 0 and chunk_idx == 0:
                     yield chunk[1], np.zeros(chunk[1] // 7, dtype=np.float32)
+                chunk_idx += 1
                 yield chunk[1], chunk[0]
 
     def stream_tts_sync(