Refactor exporting NeMo models (#2362)

Refactors and extends model export support to include new NeMo Parakeet TDT int8 variants for English and Japanese, updating the Kotlin API, export scripts, test runners, and CI workflows.

- Added support for two new int8 model types in OfflineRecognizer.kt.
- Enhanced Python export scripts to perform dynamic quantization and metadata injection.
- Updated shell scripts and GitHub workflows to package, test, and publish int8 model artifacts.

scripts/nemo/parakeet-tdt_ctc-0.6b-ja/export-onnx-ctc.py

@@ -0,0 +1,91 @@
+#!/usr/bin/env python3
+# Copyright      2025  Xiaomi Corp.        (authors: Fangjun Kuang)
+import os
+from typing import Dict
+
+import nemo.collections.asr as nemo_asr
+import onnx
+import torch
+from onnxruntime.quantization import QuantType, quantize_dynamic
+
+
+def add_meta_data(filename: str, meta_data: Dict[str, str]):
+    """Add meta data to an ONNX model. It is changed in-place.
+
+    Args:
+      filename:
+        Filename of the ONNX model to be changed.
+      meta_data:
+        Key-value pairs.
+    """
+    model = onnx.load(filename)
+    while len(model.metadata_props):
+        model.metadata_props.pop()
+
+    for key, value in meta_data.items():
+        meta = model.metadata_props.add()
+        meta.key = key
+        meta.value = str(value)
+
+    onnx.save(model, filename)
+
+
+@torch.no_grad()
+def main():
+    asr_model = nemo_asr.models.ASRModel.from_pretrained(
+        model_name="nvidia/parakeet-tdt_ctc-0.6b-ja"
+    )
+
+    print(asr_model.cfg)
+    print(asr_model)
+
+    with open("./tokens.txt", "w", encoding="utf-8") as f:
+        for i, s in enumerate(asr_model.joint.vocabulary):
+            f.write(f"{s} {i}\n")
+        f.write(f"<blk> {i+1}\n")
+        print("Saved to tokens.txt")
+
+    decoder_type = "ctc"
+    asr_model.change_decoding_strategy(decoder_type=decoder_type)
+    asr_model.eval()
+
+    asr_model.set_export_config({"decoder_type": "ctc"})
+
+    filename = "model.onnx"
+
+    asr_model.export(filename, onnx_opset_version=18)
+
+    normalize_type = asr_model.cfg.preprocessor.normalize
+    if normalize_type == "NA":
+        normalize_type = ""
+
+    meta_data = {
+        "vocab_size": asr_model.decoder.vocab_size,
+        "normalize_type": normalize_type,
+        "subsampling_factor": 8,
+        "model_type": "EncDecHybridRNNTCTCBPEModel",
+        "version": "1",
+        "model_author": "NeMo",
+        "url": "https://huggingface.co/nvidia/parakeet-tdt_ctc-0.6b-ja",
+        "comment": "Only the CTC branch is exported",
+        "doc": "See https://huggingface.co/nvidia/parakeet-tdt_ctc-0.6b-ja",
+    }
+
+    os.system("ls -lh *.onnx")
+
+    quantize_dynamic(
+        model_input="./model.onnx",
+        model_output="./model.int8.onnx",
+        weight_type=QuantType.QUInt8,
+    )
+
+    add_meta_data("model.int8.onnx", meta_data)
+
+    os.system("ls -lh *.onnx")
+
+    print("preprocessor", asr_model.cfg.preprocessor)
+    print(meta_data)
+
+
+if __name__ == "__main__":
+    main()

scripts/nemo/parakeet-tdt_ctc-0.6b-ja/run-ctc.sh

@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+
+set -ex
+
+python3 ./export-onnx-ctc.py
+
+ls -lh *.onnx
+
+mkdir -p test_wavs
+pushd test_wavs
+curl -SL -O https://huggingface.co/csukuangfj/reazonspeech-k2-v2-ja-en/resolve/main/test_wavs/transcripts.txt
+curl -SL -O https://hf-mirror.com/csukuangfj/reazonspeech-k2-v2-ja-en/resolve/main/test_wavs/test_ja_1.wav
+curl -SL -O https://hf-mirror.com/csukuangfj/reazonspeech-k2-v2-ja-en/resolve/main/test_wavs/test_ja_2.wav
+popd
+
+d=sherpa-onnx-nemo-parakeet-tdt_ctc-0.6b-ja-35000-int8
+
+mkdir -p $d
+mv -v model.int8.onnx $d/
+cp -v tokens.txt $d/
+cp -av test_wavs $d
+ls -lh $d
+
+
+d=sherpa-onnx-nemo-parakeet-tdt_ctc-0.6b-ja-35000-int8
+python3 ./test-onnx-ctc-non-streaming.py \
+  --model $d/model.int8.onnx \
+  --tokens $d/tokens.txt \
+  --wav $d/test_wavs/test_ja_1.wav
+
+python3 ./test-onnx-ctc-non-streaming.py \
+  --model $d/model.int8.onnx \
+  --tokens $d/tokens.txt \
+  --wav $d/test_wavs/test_ja_2.wav

scripts/nemo/parakeet-tdt_ctc-0.6b-ja/test-onnx-ctc-non-streaming.py

@@ -0,0 +1 @@
+../fast-conformer-hybrid-transducer-ctc/test-onnx-ctc-non-streaming.py