[Refactor] Remove dependency on librosa (#2273)

Signed-off-by: Nick Cao <ncao@redhat.com>
Co-authored-by: Claude <noreply@anthropic.com>

tests/utils/test_audio.py

@@ -0,0 +1,61 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+"""Unit tests for vllm_omni.utils.audio.mel_filter_bank."""
+
+import pytest
+import torch
+
+from vllm_omni.utils.audio import mel_filter_bank
+
+# Parameter combinations used across the codebase.
+_PARAM_SETS = [
+    # Qwen3-TTS talker / speaker encoder (sr=24000)
+    dict(sr=24000, n_fft=1024, n_mels=128, fmin=0, fmax=12000),
+    # CosyVoice3 whisper encoder, Qwen3-TTS 25Hz tokenizer (sr=16000, 80 mels)
+    dict(sr=16000, n_fft=400, n_mels=80),
+    # CosyVoice3 whisper encoder (sr=16000, 128 mels)
+    dict(sr=16000, n_fft=400, n_mels=128),
+]
+
+_parametrize_params = pytest.mark.parametrize(
+    "params", _PARAM_SETS, ids=lambda p: f"{p['sr']}_{p['n_fft']}_{p['n_mels']}"
+)
+
+
+class TestMelFilterBank:
+    @_parametrize_params
+    def test_output_shape(self, params):
+        fb = mel_filter_bank(**params)
+        n_freqs = params["n_fft"] // 2 + 1
+        assert fb.shape == (params["n_mels"], n_freqs)
+
+    @_parametrize_params
+    def test_non_negative(self, params):
+        fb = mel_filter_bank(**params)
+        assert (fb >= 0).all()
+
+    def test_dtype_is_float(self):
+        fb = mel_filter_bank(sr=16000, n_fft=400, n_mels=80)
+        assert fb.dtype == torch.float32
+
+    def test_fmax_defaults_to_nyquist(self):
+        """When fmax is omitted it should equal sr / 2."""
+        fb_default = mel_filter_bank(sr=16000, n_fft=400, n_mels=80)
+        fb_explicit = mel_filter_bank(sr=16000, n_fft=400, n_mels=80, fmax=8000.0)
+        torch.testing.assert_close(fb_default, fb_explicit)
+
+    def test_each_mel_band_has_nonzero_energy(self):
+        """Every mel band should have at least one nonzero frequency bin."""
+        fb = mel_filter_bank(sr=24000, n_fft=1024, n_mels=128, fmin=0, fmax=12000)
+        for i in range(fb.shape[0]):
+            assert fb[i].sum() > 0, f"mel band {i} is all zeros"
+
+    def test_higher_fmax_extends_coverage(self):
+        """A higher fmax should produce nonzero weights at higher frequency bins."""
+        fb_low = mel_filter_bank(sr=24000, n_fft=1024, n_mels=128, fmin=0, fmax=6000)
+        fb_high = mel_filter_bank(sr=24000, n_fft=1024, n_mels=128, fmin=0, fmax=12000)
+        # The highest nonzero column should be larger for fb_high.
+        last_nonzero_low = (fb_low.sum(dim=0) > 0).nonzero()[-1].item()
+        last_nonzero_high = (fb_high.sum(dim=0) > 0).nonzero()[-1].item()
+        assert last_nonzero_high > last_nonzero_low