Add RoPE tests and warning for bfloat16 precision loss in RoPE calculations

mlx_video/models/ltx/rope.py

@@ -430,7 +430,19 @@ def _precompute_freqs_cis_double_precision(
     rope_type: LTXRopeType,
 ) -> Tuple[mx.array, mx.array]:
 
+    # Warn if positions are bfloat16 - this causes quality degradation
+    if indices_grid.dtype == mx.bfloat16:
+        import warnings
+        warnings.warn(
+            "Position grid has dtype bfloat16, which causes precision loss in RoPE that causes quality degradation in generated videos/audio. "
+            "Use float32 for position grids to avoid quality degradation. "
+            "See tests/test_rope.py::test_bfloat16_positions_cause_precision_loss",
+            UserWarning,
+            stacklevel=2
+        )
+
     # Convert to numpy float64 (first to float32 for numpy compatibility)
+    # Note: If input is bfloat16, precision is already lost at this step
     indices_grid_np = np.array(indices_grid.astype(mx.float32)).astype(np.float64)
 
     # Generate frequency indices in float64