fix save tensors

mlx_video/convert.py

@@ -595,18 +595,15 @@ def convert(
 def save_weights(path: Path, weights: Dict[str, mx.array]) -> None:
     """Save weights in safetensors format.
 
+    Uses mx.save_safetensors to preserve exact dtype (especially bfloat16).
+    Converting through numpy loses bfloat16 fidelity since numpy lacks native
+    bfloat16 support.
+
     Args:
         path: Output directory
         weights: Dictionary of weights
     """
-    from safetensors.numpy import save_file
-    import numpy as np
-
-    # Convert to numpy for safetensors
-    np_weights = {k: np.array(v) for k, v in weights.items()}
-
-    # Save to file
-    save_file(np_weights, path / "model.safetensors")
+    mx.save_safetensors(str(path / "model.safetensors"), weights)
 
 
 def load_model(