Add C++ support for streaming NeMo CTC models. (#857)

python-api-examples/online-nemo-ctc-decode-files.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python3
+
+"""
+This file shows how to use a streaming CTC model from NeMo
+to decode files.
+
+Please download model files from
+https://github.com/k2-fsa/sherpa-onnx/releases/tag/asr-models
+
+
+The example model is converted from
+https://catalog.ngc.nvidia.com/orgs/nvidia/teams/nemo/models/stt_en_fastconformer_hybrid_large_streaming_80ms
+"""
+
+from pathlib import Path
+
+import numpy as np
+import sherpa_onnx
+import soundfile as sf
+
+
+def create_recognizer():
+    model = "./sherpa-onnx-nemo-streaming-fast-conformer-ctc-en-80ms/model.onnx"
+    tokens = "./sherpa-onnx-nemo-streaming-fast-conformer-ctc-en-80ms/tokens.txt"
+
+    test_wav = "./sherpa-onnx-nemo-streaming-fast-conformer-ctc-en-80ms/test_wavs/0.wav"
+
+    if not Path(model).is_file() or not Path(test_wav).is_file():
+        raise ValueError(
+            """Please download model files from
+            https://github.com/k2-fsa/sherpa-onnx/releases/tag/asr-models
+            """
+        )
+    return (
+        sherpa_onnx.OnlineRecognizer.from_nemo_ctc(
+            model=model,
+            tokens=tokens,
+            debug=True,
+        ),
+        test_wav,
+    )
+
+
+def main():
+    recognizer, wave_filename = create_recognizer()
+
+    audio, sample_rate = sf.read(wave_filename, dtype="float32", always_2d=True)
+    audio = audio[:, 0]  # only use the first channel
+
+    # audio is a 1-D float32 numpy array normalized to the range [-1, 1]
+    # sample_rate does not need to be 16000 Hz
+
+    stream = recognizer.create_stream()
+    stream.accept_waveform(sample_rate, audio)
+
+    tail_paddings = np.zeros(int(0.66 * sample_rate), dtype=np.float32)
+    stream.accept_waveform(sample_rate, tail_paddings)
+    stream.input_finished()
+
+    while recognizer.is_ready(stream):
+        recognizer.decode_stream(stream)
+    print(wave_filename)
+    print(recognizer.get_result_all(stream))
+
+
+if __name__ == "__main__":
+    main()