[Frontend] Speaker embedding support for speech and voices APIs (#1227)

Signed-off-by: marksverdhei <marksverdhei@hotmail.com>
Signed-off-by: Yueqian Lin <70319226+linyueqian@users.noreply.github.com>
Signed-off-by: linyueqian <linyueqian@outlook.com>
Co-authored-by: Yueqian Lin <70319226+linyueqian@users.noreply.github.com>
Co-authored-by: linyueqian <linyueqian@outlook.com>

tests/examples/test_slerp_interpolation.py

@@ -0,0 +1,55 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Unit tests for the SLERP interpolation math in speaker_embedding_interpolation.py."""
+
+import sys
+from pathlib import Path
+
+import numpy as np
+import pytest
+
+# Import the slerp function from the example script.
+_examples_dir = str(Path(__file__).parent.parent.parent / "examples" / "online_serving" / "qwen3_tts")
+sys.path.insert(0, _examples_dir)
+from speaker_embedding_interpolation import slerp  # noqa: E402
+
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
+
+class TestSlerp:
+    def test_endpoints(self):
+        """t=0 returns v0, t=1 returns v1."""
+        v0 = np.random.randn(1024).astype(np.float64)
+        v1 = np.random.randn(1024).astype(np.float64)
+        np.testing.assert_allclose(slerp(v0, v1, 0.0), v0, atol=1e-6)
+        np.testing.assert_allclose(slerp(v0, v1, 1.0), v1, atol=1e-6)
+
+    def test_midpoint_unit_norm(self):
+        """Midpoint of two unit vectors should also be approximately unit norm."""
+        v0 = np.random.randn(1024)
+        v0 /= np.linalg.norm(v0)
+        v1 = np.random.randn(1024)
+        v1 /= np.linalg.norm(v1)
+        mid = slerp(v0, v1, 0.5)
+        assert abs(np.linalg.norm(mid) - 1.0) < 0.05
+
+    def test_parallel_vectors_fallback(self):
+        """Parallel vectors (omega~0) fall back to lerp without error."""
+        v0 = np.ones(1024)
+        v1 = np.ones(1024) * 1.001  # nearly parallel
+        result = slerp(v0, v1, 0.5)
+        expected = 0.5 * v0 + 0.5 * v1
+        np.testing.assert_allclose(result, expected, atol=1e-4)
+
+    def test_antiparallel_vectors(self):
+        """Antiparallel vectors (omega~pi) should not produce NaN."""
+        v0 = np.ones(1024)
+        v1 = -np.ones(1024)
+        result = slerp(v0, v1, 0.5)
+        assert not np.any(np.isnan(result))
+
+    def test_output_shape_matches_input(self):
+        """Output shape must match input shape."""
+        v0 = np.random.randn(2048)
+        v1 = np.random.randn(2048)
+        assert slerp(v0, v1, 0.3).shape == (2048,)