fix(backend): count the S3TokenizerV2 repo in the Chatterbox MLX cache check; register the backend with PyInstaller

Review follow-ups: mlx-audio's Model.from_pretrained fetches the S3
speech tokenizer from mlx-community/S3TokenizerV2 (~470 MB) separately
from the chatterbox checkout, so _is_model_cached now requires both
repos (same shape as the Hume backend's codec check) and the config's
size_mb reflects the real footprint. backend.backends.chatterbox_mlx_backend
is a function-level import that PyInstaller's graph will not see, so it
is added to the Apple Silicon hidden-import list in build_binary.py and
voicebox-server.spec next to mlx_backend.

backend/backends/__init__.py

@@ -297,7 +297,8 @@ def _get_non_qwen_tts_configs() -> list[ModelConfig]:
     on_mlx = get_backend_type() == "mlx"
     if on_mlx:
         chatterbox_repo = "mlx-community/chatterbox-multilingual-v3"
-        chatterbox_size_mb = 2600
+        # 2.5 GB of weights plus the separately fetched S3TokenizerV2 (~470 MB)
+        chatterbox_size_mb = 3000
     else:
         chatterbox_repo = "ResembleAI/chatterbox"
         chatterbox_size_mb = 3200

backend/backends/chatterbox_mlx_backend.py

@@ -30,9 +30,13 @@ from .mlx_backend import _run_on_mlx_thread
 logger = logging.getLogger(__name__)
 
 CHATTERBOX_MLX_HF_REPO = "mlx-community/chatterbox-multilingual-v3"
+# mlx-audio's Model.from_pretrained fetches the S3 speech tokenizer from this
+# second repo (~470 MB), so the engine is only "downloaded" once both are cached.
+S3_TOKENIZER_HF_REPO = "mlx-community/S3TokenizerV2"
 
 # Files that must be present for the MLX multilingual model
 _MLX_WEIGHT_FILES = ["model.safetensors", "config.json", "tokenizer.json"]
+_S3_TOKENIZER_FILES = ["model.safetensors", "config.json"]
 
 
 class ChatterboxMLXTTSBackend:
@@ -51,7 +55,9 @@ class ChatterboxMLXTTSBackend:
         return CHATTERBOX_MLX_HF_REPO
 
     def _is_model_cached(self, model_size: str = "default") -> bool:
-        return is_model_cached(CHATTERBOX_MLX_HF_REPO, required_files=_MLX_WEIGHT_FILES)
+        model_cached = is_model_cached(CHATTERBOX_MLX_HF_REPO, required_files=_MLX_WEIGHT_FILES)
+        tokenizer_cached = is_model_cached(S3_TOKENIZER_HF_REPO, required_files=_S3_TOKENIZER_FILES)
+        return model_cached and tokenizer_cached
 
     async def load_model(self, model_size: str = "default") -> None:
         """Load the Chatterbox multilingual MLX model."""
@@ -75,7 +81,7 @@ class ChatterboxMLXTTSBackend:
 
             logger.info("Loading Chatterbox Multilingual TTS on MLX (Metal)...")
             ckpt_dir = snapshot_download(CHATTERBOX_MLX_HF_REPO)
-            self.model = Model.from_pretrained(ckpt_dir)
+            self.model = Model.from_pretrained(ckpt_dir, s3_tokenizer_repo=S3_TOKENIZER_HF_REPO)
 
         logger.info("Chatterbox Multilingual TTS (MLX) loaded successfully")
 

backend/build_binary.py

@@ -442,6 +442,8 @@ def build_server(cuda=False, rocm=False):
                 "mlx_lm",
                 "--hidden-import",
                 "backend.backends.qwen_llm_backend",
+                "--hidden-import",
+                "backend.backends.chatterbox_mlx_backend",
                 "--collect-submodules",
                 "mlx",
                 "--collect-submodules",

backend/voicebox-server.spec

@@ -5,7 +5,7 @@ from PyInstaller.utils.hooks import copy_metadata
 
 datas = []
 binaries = []
-hiddenimports = ['backend', 'backend.main', 'backend.config', 'backend.database', 'backend.models', 'backend.services.profiles', 'backend.services.history', 'backend.services.tts', 'backend.services.transcribe', 'backend.utils.platform_detect', 'backend.backends', 'backend.backends.pytorch_backend', 'backend.backends.qwen_custom_voice_backend', 'backend.utils.audio', 'backend.utils.cache', 'backend.utils.progress', 'backend.utils.hf_progress', 'backend.services.cuda', 'backend.services.effects', 'backend.utils.effects', 'backend.services.versions', 'pedalboard', 'chatterbox', 'chatterbox.tts_turbo', 'chatterbox.mtl_tts', 'backend.backends.chatterbox_backend', 'backend.backends.chatterbox_turbo_backend', 'backend.backends.luxtts_backend', 'zipvoice', 'zipvoice.luxvoice', 'torch', 'transformers', 'fastapi', 'uvicorn', 'sqlalchemy', 'soundfile', 'qwen_tts', 'qwen_tts.inference', 'qwen_tts.inference.qwen3_tts_model', 'qwen_tts.inference.qwen3_tts_tokenizer', 'qwen_tts.core', 'qwen_tts.cli', 'requests', 'pkg_resources.extern', 'backend.backends.hume_backend', 'tada', 'tada.modules', 'tada.modules.tada', 'tada.modules.encoder', 'tada.modules.decoder', 'tada.modules.aligner', 'tada.modules.acoustic_spkr_verf', 'tada.nn', 'tada.nn.vibevoice', 'tada.utils', 'tada.utils.gray_code', 'tada.utils.text', 'backend.utils.dac_shim', 'torchaudio', 'backend.backends.kokoro_backend', 'en_core_web_sm', 'loguru', 'backend.mcp_server', 'backend.mcp_server.server', 'backend.mcp_server.tools', 'backend.mcp_server.context', 'backend.mcp_server.resolve', 'backend.mcp_server.events', 'sse_starlette', 'backend.backends.mlx_backend', 'mlx', 'mlx.core', 'mlx.nn', 'mlx_audio', 'mlx_audio.tts', 'mlx_audio.stt', 'mlx_lm', 'backend.backends.qwen_llm_backend']
+hiddenimports = ['backend', 'backend.main', 'backend.config', 'backend.database', 'backend.models', 'backend.services.profiles', 'backend.services.history', 'backend.services.tts', 'backend.services.transcribe', 'backend.utils.platform_detect', 'backend.backends', 'backend.backends.pytorch_backend', 'backend.backends.qwen_custom_voice_backend', 'backend.utils.audio', 'backend.utils.cache', 'backend.utils.progress', 'backend.utils.hf_progress', 'backend.services.cuda', 'backend.services.effects', 'backend.utils.effects', 'backend.services.versions', 'pedalboard', 'chatterbox', 'chatterbox.tts_turbo', 'chatterbox.mtl_tts', 'backend.backends.chatterbox_backend', 'backend.backends.chatterbox_turbo_backend', 'backend.backends.luxtts_backend', 'zipvoice', 'zipvoice.luxvoice', 'torch', 'transformers', 'fastapi', 'uvicorn', 'sqlalchemy', 'soundfile', 'qwen_tts', 'qwen_tts.inference', 'qwen_tts.inference.qwen3_tts_model', 'qwen_tts.inference.qwen3_tts_tokenizer', 'qwen_tts.core', 'qwen_tts.cli', 'requests', 'pkg_resources.extern', 'backend.backends.hume_backend', 'tada', 'tada.modules', 'tada.modules.tada', 'tada.modules.encoder', 'tada.modules.decoder', 'tada.modules.aligner', 'tada.modules.acoustic_spkr_verf', 'tada.nn', 'tada.nn.vibevoice', 'tada.utils', 'tada.utils.gray_code', 'tada.utils.text', 'backend.utils.dac_shim', 'torchaudio', 'backend.backends.kokoro_backend', 'en_core_web_sm', 'loguru', 'backend.mcp_server', 'backend.mcp_server.server', 'backend.mcp_server.tools', 'backend.mcp_server.context', 'backend.mcp_server.resolve', 'backend.mcp_server.events', 'sse_starlette', 'backend.backends.mlx_backend', 'mlx', 'mlx.core', 'mlx.nn', 'mlx_audio', 'mlx_audio.tts', 'mlx_audio.stt', 'mlx_lm', 'backend.backends.qwen_llm_backend', 'backend.backends.chatterbox_mlx_backend']
 datas += copy_metadata('qwen-tts')
 datas += copy_metadata('requests')
 datas += copy_metadata('transformers')