[Bugfix][Model] Fix CohereASR streaming audio-token estimate (unit + subsampling)

tests/models/multimodal/test_cohere_asr.py

@@ -0,0 +1,34 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from types import SimpleNamespace
+
+import pytest
+
+from vllm.config import SpeechToTextConfig
+from vllm.model_executor.models.cohere_asr import CohereAsrForConditionalGeneration
+
+
+@pytest.mark.parametrize(
+    ("audio_duration_s", "expected_tokens"),
+    # window_stride=0.01s @ 16kHz -> 160-sample hop; subsampling_factor=8.
+    # frames = floor(duration * 16000 / 160); tokens = ceil(frames / 8).
+    [(1.0, 13), (10.0, 125), (30.0, 375)],
+)
+def test_get_num_audio_tokens_streaming_estimate(audio_duration_s, expected_tokens):
+    """The duration-based estimate must convert ``window_stride`` (seconds) to a
+    sample hop and divide by the encoder subsampling factor. Values are pinned to
+    concrete numbers so a rounding regression is actually caught."""
+    model_config = SimpleNamespace(
+        hf_config=SimpleNamespace(
+            preprocessor={"window_stride": 0.01, "sample_rate": 16000},
+            encoder={"subsampling_factor": 8},
+        )
+    )
+    stt_config = SpeechToTextConfig(sample_rate=16000)
+
+    got = CohereAsrForConditionalGeneration.get_num_audio_tokens(
+        audio_duration_s, stt_config, model_config
+    )
+
+    assert got == expected_tokens

vllm/model_executor/models/cohere_asr.py

@@ -2177,9 +2177,15 @@ def get_num_audio_tokens(
         stt_config: SpeechToTextConfig,
         model_config: ModelConfig,
     ) -> int | None:
-        hop_length = model_config.hf_config.preprocessor.get("window_stride")
-        assert hop_length is not None
-        return math.ceil(audio_duration_s * stt_config.sample_rate / hop_length)
+        hf_config = model_config.hf_config
+        preprocessor = hf_config.preprocessor
+        sample_rate = preprocessor["sample_rate"]
+        window_stride = preprocessor["window_stride"]
+        hop_length = int(window_stride * sample_rate)
+        # Floor-divide to match get_seq_len.
+        num_frames = int(audio_duration_s * sample_rate) // hop_length
+        subsampling_factor = hf_config.encoder["subsampling_factor"]
+        return math.ceil(num_frames / subsampling_factor)
 
     def get_num_encoder_cross_attn_tokens(self, num_encoder_input_tokens: int) -> int:
         return self.model.encoder.get_num_encoder_cross_attn_tokens(