Fix beam search with batch processing in Whisper decoding

* It ensures that audio features are correctly duplicated across beams for each batch item.
* Added a test for `decode()` that includes a regression test for this.
* Update *.github/workflows/test.yml* to run the new test for `decode()` in tiny.
* This issue was introduced in PR openai#1483.

.github/workflows/test.yml

@@ -53,4 +53,4 @@ jobs:
       - uses: actions/checkout@v3
       - run: echo "$CONDA/envs/test/bin" >> $GITHUB_PATH
       - run: pip install .["dev"]
-      - run: pytest --durations=0 -vv -k 'not test_transcribe or test_transcribe[tiny] or test_transcribe[tiny.en]' -m 'not requires_cuda'
+      - run: pytest --durations=0 -vv -k 'not (test_transcribe or test_decode) or test_transcribe[tiny] or test_transcribe[tiny.en] or test_decode[tiny] or test_decode[tiny.en]' -m 'not requires_cuda'

tests/test_decode.py

@@ -0,0 +1,52 @@
+import os
+
+import pytest
+import torch
+
+import whisper
+
+
+@pytest.mark.parametrize("model_name", whisper.available_models())
+def test_decode(model_name: str):
+    # Regression test: batch_size and beam_size should work together
+    beam_size = 2
+    batch_size = 2
+
+    device = "cuda" if torch.cuda.is_available() else "cpu"
+    model = whisper.load_model(model_name).to(device)
+    audio_path = os.path.join(os.path.dirname(__file__), "jfk.flac")
+
+    language = "en" if model_name.endswith(".en") else None
+
+    options = whisper.DecodingOptions(language=language, beam_size=beam_size)
+
+    audio = whisper.load_audio(audio_path)
+    audio = whisper.pad_or_trim(audio)
+    mel = whisper.log_mel_spectrogram(audio).to(device)
+
+    # Create a small batch
+    batch_mel = mel.unsqueeze(0).repeat(batch_size, 1, 1)
+
+    results = model.decode(batch_mel, options)
+
+    # Since both examples are the same, results should be identical
+    assert len(results) == batch_size
+    assert results[0].text == results[1].text
+
+    decoded_text = results[0].text.lower()
+    assert "my fellow americans" in decoded_text
+    assert "your country" in decoded_text
+    assert "do for you" in decoded_text
+
+    timing_checked = False
+    if hasattr(results[0], "segments"):
+        for segment in results[0].segments:
+            for timing in segment["words"]:
+                assert timing["start"] < timing["end"]
+                if timing["word"].strip(" ,") == "Americans":
+                    assert timing["start"] <= 1.8
+                    assert timing["end"] >= 1.8
+                    timing_checked = True
+
+    if hasattr(results[0], "segments"):
+        assert timing_checked

whisper/decoding.py

@@ -731,6 +731,9 @@ def run(self, mel: Tensor) -> List[DecodingResult]:
             ]
 
         # repeat text tensors by the group size, for beam search or best-of-n sampling
+        audio_features = audio_features.repeat_interleave(self.n_group, dim=0).to(
+            audio_features.device
+        )
         tokens = tokens.repeat_interleave(self.n_group, dim=0).to(audio_features.device)
 
         # call the main sampling loop