From 5f066d3d538e093d72c94e48ad6be4c23da71f84 Mon Sep 17 00:00:00 2001
From: Zengwei Yao <yaozengwei@outlook.com>
Date: Wed, 12 Apr 2023 19:04:50 +0800
Subject: [PATCH] support decoding and computing RTF on test sets with onnx
 models (#995)

* support decode and compute RTF on test sets with onnx models

* support onnx export and decode in pruned_transducer_stateless
---
 .../export-onnx.py                            | 527 ++++++++++++++++++
 .../pruned_transducer_stateless/onnx_check.py |   1 +
 .../onnx_decode.py                            | 319 +++++++++++
 .../onnx_pretrained.py                        |   1 +
 .../onnx_decode.py                            | 321 +++++++++++
 .../onnx_pretrained.py                        |   3 +-
 .../export-onnx.py                            |  30 +
 .../onnx_decode.py                            | 326 +++++++++++
 .../onnx_decode.py                            | 319 +++++++++++
 .../ASR/transducer_stateless/conformer.py     |  83 ++-
 10 files changed, 1901 insertions(+), 29 deletions(-)
 create mode 100755 egs/librispeech/ASR/pruned_transducer_stateless/export-onnx.py
 create mode 120000 egs/librispeech/ASR/pruned_transducer_stateless/onnx_check.py
 create mode 100755 egs/librispeech/ASR/pruned_transducer_stateless/onnx_decode.py
 create mode 120000 egs/librispeech/ASR/pruned_transducer_stateless/onnx_pretrained.py
 create mode 100755 egs/librispeech/ASR/pruned_transducer_stateless3/onnx_decode.py
 create mode 100755 egs/librispeech/ASR/pruned_transducer_stateless5/onnx_decode.py
 create mode 100755 egs/librispeech/ASR/pruned_transducer_stateless7/onnx_decode.py

diff --git a/egs/librispeech/ASR/pruned_transducer_stateless/export-onnx.py b/egs/librispeech/ASR/pruned_transducer_stateless/export-onnx.py
new file mode 100755
index 000000000..a3ebe9d8c
--- /dev/null
+++ b/egs/librispeech/ASR/pruned_transducer_stateless/export-onnx.py
@@ -0,0 +1,527 @@
+#!/usr/bin/env python3
+#
+# Copyright 2023 Xiaomi Corporation (Author: Fangjun Kuang)
+
+"""
+This script exports a transducer model from PyTorch to ONNX.
+
+We use the pre-trained model from
+https://huggingface.co/csukuangfj/icefall-asr-librispeech-pruned-transducer-stateless-2022-03-12
+as an example to show how to use this file.
+
+1. Download the pre-trained model
+
+cd egs/librispeech/ASR
+
+repo_url=https://huggingface.co/csukuangfj/icefall-asr-librispeech-pruned-transducer-stateless-2022-03-12
+GIT_LFS_SKIP_SMUDGE=1 git clone $repo_url
+repo=$(basename $repo_url)
+
+pushd $repo
+git lfs pull --include "data/lang_bpe_500/bpe.model"
+git lfs pull --include "exp/pretrained.pt"
+
+cd exp
+ln -s pretrained.pt epoch-9999.pt
+popd
+
+2. Export the model to ONNX
+
+./pruned_transducer_stateless/export-onnx.py \
+  --bpe-model $repo/data/lang_bpe_500/bpe.model \
+  --epoch 9999 \
+  --avg 1 \
+  --exp-dir $repo/exp/
+
+It will generate the following 3 files inside $repo/exp:
+
+  - encoder-epoch-9999-avg-1.onnx
+  - decoder-epoch-9999-avg-1.onnx
+  - joiner-epoch-9999-avg-1.onnx
+
+See ./onnx_pretrained.py and ./onnx_check.py for how to
+use the exported ONNX models.
+"""
+
+import argparse
+import logging
+from pathlib import Path
+from typing import Dict, Tuple
+
+import onnx
+import sentencepiece as spm
+import torch
+import torch.nn as nn
+from conformer import Conformer
+from decoder import Decoder
+from onnxruntime.quantization import QuantType, quantize_dynamic
+from train import add_model_arguments, get_params, get_transducer_model
+
+from icefall.checkpoint import average_checkpoints, find_checkpoints, load_checkpoint
+from icefall.utils import setup_logger
+
+
+def get_parser():
+    parser = argparse.ArgumentParser(
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter
+    )
+
+    parser.add_argument(
+        "--epoch",
+        type=int,
+        default=28,
+        help="""It specifies the checkpoint to use for averaging.
+        Note: Epoch counts from 0.
+        You can specify --avg to use more checkpoints for model averaging.""",
+    )
+
+    parser.add_argument(
+        "--iter",
+        type=int,
+        default=0,
+        help="""If positive, --epoch is ignored and it
+        will use the checkpoint exp_dir/checkpoint-iter.pt.
+        You can specify --avg to use more checkpoints for model averaging.
+        """,
+    )
+
+    parser.add_argument(
+        "--avg",
+        type=int,
+        default=15,
+        help="Number of checkpoints to average. Automatically select "
+        "consecutive checkpoints before the checkpoint specified by "
+        "'--epoch' and '--iter'",
+    )
+
+    parser.add_argument(
+        "--exp-dir",
+        type=str,
+        default="pruned_transducer_stateless/exp",
+        help="""It specifies the directory where all training related
+        files, e.g., checkpoints, log, etc, are saved
+        """,
+    )
+
+    parser.add_argument(
+        "--bpe-model",
+        type=str,
+        default="data/lang_bpe_500/bpe.model",
+        help="Path to the BPE model",
+    )
+
+    parser.add_argument(
+        "--context-size",
+        type=int,
+        default=2,
+        help="The context size in the decoder. 1 means bigram; 2 means tri-gram",
+    )
+
+    add_model_arguments(parser)
+
+    return parser
+
+
+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)
+    for key, value in meta_data.items():
+        meta = model.metadata_props.add()
+        meta.key = key
+        meta.value = value
+
+    onnx.save(model, filename)
+
+
+class OnnxEncoder(nn.Module):
+    """A wrapper for Conformer"""
+
+    def __init__(self, encoder: Conformer):
+        """
+        Args:
+          encoder:
+            A Conformer encoder.
+        """
+        super().__init__()
+        self.encoder = encoder
+
+    def forward(
+        self,
+        x: torch.Tensor,
+        x_lens: torch.Tensor,
+    ) -> Tuple[torch.Tensor, torch.Tensor]:
+        """Please see the help information of Conformer.forward
+
+        Args:
+          x:
+            A 3-D tensor of shape (N, T, C)
+          x_lens:
+            A 1-D tensor of shape (N,). Its dtype is torch.int64
+        Returns:
+          Return a tuple containing:
+            - encoder_out, A 3-D tensor of shape (N, T', joiner_dim)
+            - encoder_out_lens, A 1-D tensor of shape (N,)
+        """
+        encoder_out, encoder_out_lens = self.encoder(x, x_lens)
+        # Now encoder_out is of shape (N, T, joiner_dim)
+
+        return encoder_out, encoder_out_lens
+
+
+class OnnxDecoder(nn.Module):
+    """A wrapper for Decoder"""
+
+    def __init__(self, decoder: Decoder):
+        super().__init__()
+        self.decoder = decoder
+
+    def forward(self, y: torch.Tensor) -> torch.Tensor:
+        """
+        Args:
+          y:
+            A 2-D tensor of shape (N, context_size).
+        Returns
+          Return a 2-D tensor of shape (N, joiner_dim)
+        """
+        need_pad = False
+        decoder_output = self.decoder(y, need_pad=need_pad)
+        output = decoder_output.squeeze(1)
+
+        return output
+
+
+class OnnxJoiner(nn.Module):
+    """A wrapper for the joiner"""
+
+    def __init__(self, inner_linear: nn.Linear, output_linear: nn.Linear):
+        super().__init__()
+        self.inner_linear = inner_linear
+        self.output_linear = output_linear
+
+    def forward(
+        self,
+        encoder_out: torch.Tensor,
+        decoder_out: torch.Tensor,
+    ) -> torch.Tensor:
+        """
+        Args:
+          encoder_out:
+            A 2-D tensor of shape (N, joiner_dim)
+          decoder_out:
+            A 2-D tensor of shape (N, joiner_dim)
+        Returns:
+          Return a 2-D tensor of shape (N, vocab_size)
+        """
+        logit = encoder_out + decoder_out
+        logit = self.inner_linear(torch.tanh(logit))
+        output = self.output_linear(nn.functional.relu(logit))
+
+        return output
+
+
+def export_encoder_model_onnx(
+    encoder_model: OnnxEncoder,
+    encoder_filename: str,
+    opset_version: int = 11,
+) -> None:
+    """Export the given encoder model to ONNX format.
+    The exported model has two inputs:
+
+        - x, a tensor of shape (N, T, C); dtype is torch.float32
+        - x_lens, a tensor of shape (N,); dtype is torch.int64
+
+    and it has two outputs:
+
+        - encoder_out, a tensor of shape (N, T', joiner_dim)
+        - encoder_out_lens, a tensor of shape (N,)
+
+    Args:
+      encoder_model:
+        The input encoder model
+      encoder_filename:
+        The filename to save the exported ONNX model.
+      opset_version:
+        The opset version to use.
+    """
+    x = torch.zeros(1, 100, 80, dtype=torch.float32)
+    x_lens = torch.tensor([100], dtype=torch.int64)
+
+    torch.onnx.export(
+        encoder_model,
+        (x, x_lens),
+        encoder_filename,
+        verbose=False,
+        opset_version=opset_version,
+        input_names=["x", "x_lens"],
+        output_names=["encoder_out", "encoder_out_lens"],
+        dynamic_axes={
+            "x": {0: "N", 1: "T"},
+            "x_lens": {0: "N"},
+            "encoder_out": {0: "N", 1: "T"},
+            "encoder_out_lens": {0: "N"},
+        },
+    )
+
+    meta_data = {
+        "model_type": "conformer",
+        "version": "1",
+        "model_author": "k2-fsa",
+        "comment": "stateless3",
+    }
+    logging.info(f"meta_data: {meta_data}")
+
+    add_meta_data(filename=encoder_filename, meta_data=meta_data)
+
+
+def export_decoder_model_onnx(
+    decoder_model: OnnxDecoder,
+    decoder_filename: str,
+    opset_version: int = 11,
+) -> None:
+    """Export the decoder model to ONNX format.
+
+    The exported model has one input:
+
+        - y: a torch.int64 tensor of shape (N, decoder_model.context_size)
+
+    and has one output:
+
+        - decoder_out: a torch.float32 tensor of shape (N, joiner_dim)
+
+    Args:
+      decoder_model:
+        The decoder model to be exported.
+      decoder_filename:
+        Filename to save the exported ONNX model.
+      opset_version:
+        The opset version to use.
+    """
+    context_size = decoder_model.decoder.context_size
+    vocab_size = decoder_model.decoder.vocab_size
+
+    y = torch.zeros(10, context_size, dtype=torch.int64)
+    torch.onnx.export(
+        decoder_model,
+        y,
+        decoder_filename,
+        verbose=False,
+        opset_version=opset_version,
+        input_names=["y"],
+        output_names=["decoder_out"],
+        dynamic_axes={
+            "y": {0: "N"},
+            "decoder_out": {0: "N"},
+        },
+    )
+
+    meta_data = {
+        "context_size": str(context_size),
+        "vocab_size": str(vocab_size),
+    }
+    add_meta_data(filename=decoder_filename, meta_data=meta_data)
+
+
+def export_joiner_model_onnx(
+    joiner_model: nn.Module,
+    joiner_filename: str,
+    opset_version: int = 11,
+) -> None:
+    """Export the joiner model to ONNX format.
+    The exported joiner model has two inputs:
+
+        - encoder_out: a tensor of shape (N, joiner_dim)
+        - decoder_out: a tensor of shape (N, joiner_dim)
+
+    and produces one output:
+
+        - logit: a tensor of shape (N, vocab_size)
+    """
+    joiner_dim = joiner_model.inner_linear.weight.shape[1]
+    logging.info(f"joiner dim: {joiner_dim}")
+
+    projected_encoder_out = torch.rand(11, joiner_dim, dtype=torch.float32)
+    projected_decoder_out = torch.rand(11, joiner_dim, dtype=torch.float32)
+
+    torch.onnx.export(
+        joiner_model,
+        (projected_encoder_out, projected_decoder_out),
+        joiner_filename,
+        verbose=False,
+        opset_version=opset_version,
+        input_names=[
+            "encoder_out",
+            "decoder_out",
+        ],
+        output_names=["logit"],
+        dynamic_axes={
+            "encoder_out": {0: "N"},
+            "decoder_out": {0: "N"},
+            "logit": {0: "N"},
+        },
+    )
+    meta_data = {
+        "joiner_dim": str(joiner_dim),
+    }
+    add_meta_data(filename=joiner_filename, meta_data=meta_data)
+
+
+@torch.no_grad()
+def main():
+    args = get_parser().parse_args()
+    args.exp_dir = Path(args.exp_dir)
+
+    params = get_params()
+    params.update(vars(args))
+
+    device = torch.device("cpu")
+    if torch.cuda.is_available():
+        device = torch.device("cuda", 0)
+
+    setup_logger(f"{params.exp_dir}/log-export/log-export-onnx")
+
+    logging.info(f"device: {device}")
+
+    sp = spm.SentencePieceProcessor()
+    sp.load(params.bpe_model)
+
+    # <blk> is defined in local/train_bpe_model.py
+    params.blank_id = sp.piece_to_id("<blk>")
+    params.unk_id = sp.piece_to_id("<unk>")
+    params.vocab_size = sp.get_piece_size()
+
+    logging.info(params)
+
+    logging.info("About to create model")
+    model = get_transducer_model(params)
+
+    model.to(device)
+
+    if params.iter > 0:
+        filenames = find_checkpoints(params.exp_dir, iteration=-params.iter)[
+            : params.avg
+        ]
+        if len(filenames) == 0:
+            raise ValueError(
+                f"No checkpoints found for --iter {params.iter}, --avg {params.avg}"
+            )
+        elif len(filenames) < params.avg:
+            raise ValueError(
+                f"Not enough checkpoints ({len(filenames)}) found for"
+                f" --iter {params.iter}, --avg {params.avg}"
+            )
+        logging.info(f"averaging {filenames}")
+        model.to(device)
+        model.load_state_dict(
+            average_checkpoints(filenames, device=device), strict=False
+        )
+    elif params.avg == 1:
+        load_checkpoint(f"{params.exp_dir}/epoch-{params.epoch}.pt", model)
+    else:
+        start = params.epoch - params.avg + 1
+        filenames = []
+        for i in range(start, params.epoch + 1):
+            if start >= 0:
+                filenames.append(f"{params.exp_dir}/epoch-{i}.pt")
+        logging.info(f"averaging {filenames}")
+        model.to(device)
+        model.load_state_dict(
+            average_checkpoints(filenames, device=device), strict=False
+        )
+
+    model.to("cpu")
+    model.eval()
+
+    encoder = OnnxEncoder(encoder=model.encoder)
+
+    decoder = OnnxDecoder(decoder=model.decoder)
+
+    joiner = OnnxJoiner(
+        inner_linear=model.joiner.inner_linear, output_linear=model.joiner.output_linear
+    )
+
+    encoder_num_param = sum([p.numel() for p in encoder.parameters()])
+    decoder_num_param = sum([p.numel() for p in decoder.parameters()])
+    joiner_num_param = sum([p.numel() for p in joiner.parameters()])
+    total_num_param = encoder_num_param + decoder_num_param + joiner_num_param
+    logging.info(f"encoder parameters: {encoder_num_param}")
+    logging.info(f"decoder parameters: {decoder_num_param}")
+    logging.info(f"joiner parameters: {joiner_num_param}")
+    logging.info(f"total parameters: {total_num_param}")
+
+    if params.iter > 0:
+        suffix = f"iter-{params.iter}"
+    else:
+        suffix = f"epoch-{params.epoch}"
+
+    suffix += f"-avg-{params.avg}"
+
+    opset_version = 13
+
+    logging.info("Exporting encoder")
+    encoder_filename = params.exp_dir / f"encoder-{suffix}.onnx"
+    export_encoder_model_onnx(
+        encoder,
+        encoder_filename,
+        opset_version=opset_version,
+    )
+    logging.info(f"Exported encoder to {encoder_filename}")
+
+    logging.info("Exporting decoder")
+    decoder_filename = params.exp_dir / f"decoder-{suffix}.onnx"
+    export_decoder_model_onnx(
+        decoder,
+        decoder_filename,
+        opset_version=opset_version,
+    )
+    logging.info(f"Exported decoder to {decoder_filename}")
+
+    logging.info("Exporting joiner")
+    joiner_filename = params.exp_dir / f"joiner-{suffix}.onnx"
+    export_joiner_model_onnx(
+        joiner,
+        joiner_filename,
+        opset_version=opset_version,
+    )
+    logging.info(f"Exported joiner to {joiner_filename}")
+
+    # Generate int8 quantization models
+    # See https://onnxruntime.ai/docs/performance/model-optimizations/quantization.html#data-type-selection
+
+    logging.info("Generate int8 quantization models")
+
+    encoder_filename_int8 = params.exp_dir / f"encoder-{suffix}.int8.onnx"
+    quantize_dynamic(
+        model_input=encoder_filename,
+        model_output=encoder_filename_int8,
+        op_types_to_quantize=["MatMul"],
+        weight_type=QuantType.QInt8,
+    )
+
+    decoder_filename_int8 = params.exp_dir / f"decoder-{suffix}.int8.onnx"
+    quantize_dynamic(
+        model_input=decoder_filename,
+        model_output=decoder_filename_int8,
+        op_types_to_quantize=["MatMul"],
+        weight_type=QuantType.QInt8,
+    )
+
+    joiner_filename_int8 = params.exp_dir / f"joiner-{suffix}.int8.onnx"
+    quantize_dynamic(
+        model_input=joiner_filename,
+        model_output=joiner_filename_int8,
+        op_types_to_quantize=["MatMul"],
+        weight_type=QuantType.QInt8,
+    )
+
+
+if __name__ == "__main__":
+    formatter = "%(asctime)s %(levelname)s [%(filename)s:%(lineno)d] %(message)s"
+
+    main()
diff --git a/egs/librispeech/ASR/pruned_transducer_stateless/onnx_check.py b/egs/librispeech/ASR/pruned_transducer_stateless/onnx_check.py
new file mode 120000
index 000000000..66d63b807
--- /dev/null
+++ b/egs/librispeech/ASR/pruned_transducer_stateless/onnx_check.py
@@ -0,0 +1 @@
+../pruned_transducer_stateless3/onnx_check.py
\ No newline at end of file
diff --git a/egs/librispeech/ASR/pruned_transducer_stateless/onnx_decode.py b/egs/librispeech/ASR/pruned_transducer_stateless/onnx_decode.py
new file mode 100755
index 000000000..8134d43f8
--- /dev/null
+++ b/egs/librispeech/ASR/pruned_transducer_stateless/onnx_decode.py
@@ -0,0 +1,319 @@
+#!/usr/bin/env python3
+#
+# Copyright 2021-2022 Xiaomi Corporation (Author: Fangjun Kuang,
+#                                                 Zengwei Yao,
+#                                                 Xiaoyu Yang)
+#
+# See ../../../../LICENSE for clarification regarding multiple authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+This script loads ONNX exported models and uses them to decode the test sets.
+
+We use the pre-trained model from
+https://huggingface.co/csukuangfj/icefall-asr-librispeech-pruned-transducer-stateless-2022-03-12
+as an example to show how to use this file.
+
+1. Download the pre-trained model
+
+cd egs/librispeech/ASR
+
+repo_url=https://huggingface.co/csukuangfj/icefall-asr-librispeech-pruned-transducer-stateless-2022-03-12
+GIT_LFS_SKIP_SMUDGE=1 git clone $repo_url
+repo=$(basename $repo_url)
+
+pushd $repo
+git lfs pull --include "data/lang_bpe_500/bpe.model"
+git lfs pull --include "exp/pretrained.pt"
+
+cd exp
+ln -s pretrained.pt epoch-9999.pt
+popd
+
+2. Export the model to ONNX
+
+./pruned_transducer_stateless/export-onnx.py \
+  --bpe-model $repo/data/lang_bpe_500/bpe.model \
+  --epoch 9999 \
+  --avg 1 \
+  --exp-dir $repo/exp/
+
+It will generate the following 3 files inside $repo/exp:
+
+  - encoder-epoch-9999-avg-1.onnx
+  - decoder-epoch-9999-avg-1.onnx
+  - joiner-epoch-9999-avg-1.onnx
+
+3. Run this file
+
+./pruned_transducer_stateless/onnx_decode.py \
+  --exp-dir ./pruned_transducer_stateless/exp \
+  --max-duration 600 \
+  --encoder-model-filename $repo/exp/encoder-epoch-9999-avg-1.onnx \
+  --decoder-model-filename $repo/exp/decoder-epoch-9999-avg-1.onnx \
+  --joiner-model-filename $repo/exp/joiner-epoch-9999-avg-1.onnx \
+"""
+
+
+import argparse
+import logging
+import time
+from pathlib import Path
+from typing import List, Tuple
+
+import sentencepiece as spm
+import torch
+import torch.nn as nn
+from asr_datamodule import LibriSpeechAsrDataModule
+
+from onnx_pretrained import greedy_search, OnnxModel
+
+from icefall.utils import setup_logger, store_transcripts, write_error_stats
+
+
+def get_parser():
+    parser = argparse.ArgumentParser(
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter
+    )
+
+    parser.add_argument(
+        "--encoder-model-filename",
+        type=str,
+        required=True,
+        help="Path to the encoder onnx model. ",
+    )
+
+    parser.add_argument(
+        "--decoder-model-filename",
+        type=str,
+        required=True,
+        help="Path to the decoder onnx model. ",
+    )
+
+    parser.add_argument(
+        "--joiner-model-filename",
+        type=str,
+        required=True,
+        help="Path to the joiner onnx model. ",
+    )
+
+    parser.add_argument(
+        "--exp-dir",
+        type=str,
+        default="pruned_transducer_stateless7/exp",
+        help="The experiment dir",
+    )
+
+    parser.add_argument(
+        "--bpe-model",
+        type=str,
+        default="data/lang_bpe_500/bpe.model",
+        help="Path to the BPE model",
+    )
+
+    parser.add_argument(
+        "--decoding-method",
+        type=str,
+        default="greedy_search",
+        help="Valid values are greedy_search and modified_beam_search",
+    )
+
+    return parser
+
+
+def decode_one_batch(
+    model: OnnxModel, sp: spm.SentencePieceProcessor, batch: dict
+) -> List[List[str]]:
+    """Decode one batch and return the result.
+    Currently it only greedy_search is supported.
+
+    Args:
+      model:
+        The neural model.
+      sp:
+        The BPE model.
+      batch:
+        It is the return value from iterating
+        `lhotse.dataset.K2SpeechRecognitionDataset`. See its documentation
+        for the format of the `batch`.
+
+    Returns:
+      Return the decoded results for each utterance.
+    """
+    feature = batch["inputs"]
+    assert feature.ndim == 3
+    # at entry, feature is (N, T, C)
+
+    supervisions = batch["supervisions"]
+    feature_lens = supervisions["num_frames"].to(dtype=torch.int64)
+
+    encoder_out, encoder_out_lens = model.run_encoder(x=feature, x_lens=feature_lens)
+
+    hyps = greedy_search(
+        model=model, encoder_out=encoder_out, encoder_out_lens=encoder_out_lens
+    )
+
+    hyps = [sp.decode(h).split() for h in hyps]
+    return hyps
+
+
+def decode_dataset(
+    dl: torch.utils.data.DataLoader,
+    model: nn.Module,
+    sp: spm.SentencePieceProcessor,
+) -> Tuple[List[Tuple[str, List[str], List[str]]], float]:
+    """Decode dataset.
+
+    Args:
+      dl:
+        PyTorch's dataloader containing the dataset to decode.
+      model:
+        The neural model.
+      sp:
+        The BPE model.
+
+    Returns:
+      - A list of tuples. Each tuple contains three elements:
+         - cut_id,
+         - reference transcript,
+         - predicted result.
+      - The total duration (in seconds) of the dataset.
+    """
+    num_cuts = 0
+
+    try:
+        num_batches = len(dl)
+    except TypeError:
+        num_batches = "?"
+
+    log_interval = 10
+    total_duration = 0
+
+    results = []
+    for batch_idx, batch in enumerate(dl):
+        texts = batch["supervisions"]["text"]
+        cut_ids = [cut.id for cut in batch["supervisions"]["cut"]]
+        total_duration += sum([cut.duration for cut in batch["supervisions"]["cut"]])
+
+        hyps = decode_one_batch(model=model, sp=sp, batch=batch)
+
+        this_batch = []
+        assert len(hyps) == len(texts)
+        for cut_id, hyp_words, ref_text in zip(cut_ids, hyps, texts):
+            ref_words = ref_text.split()
+            this_batch.append((cut_id, ref_words, hyp_words))
+
+        results.extend(this_batch)
+
+        num_cuts += len(texts)
+
+        if batch_idx % log_interval == 0:
+            batch_str = f"{batch_idx}/{num_batches}"
+
+            logging.info(f"batch {batch_str}, cuts processed until now is {num_cuts}")
+
+    return results, total_duration
+
+
+def save_results(
+    res_dir: Path,
+    test_set_name: str,
+    results: List[Tuple[str, List[str], List[str]]],
+):
+    recog_path = res_dir / f"recogs-{test_set_name}.txt"
+    results = sorted(results)
+    store_transcripts(filename=recog_path, texts=results)
+    logging.info(f"The transcripts are stored in {recog_path}")
+
+    # The following prints out WERs, per-word error statistics and aligned
+    # ref/hyp pairs.
+    errs_filename = res_dir / f"errs-{test_set_name}.txt"
+    with open(errs_filename, "w") as f:
+        wer = write_error_stats(f, f"{test_set_name}", results, enable_log=True)
+
+    logging.info("Wrote detailed error stats to {}".format(errs_filename))
+
+    errs_info = res_dir / f"wer-summary-{test_set_name}.txt"
+    with open(errs_info, "w") as f:
+        print("WER", file=f)
+        print(wer, file=f)
+
+    s = "\nFor {}, WER is {}:\n".format(test_set_name, wer)
+    logging.info(s)
+
+
+@torch.no_grad()
+def main():
+    parser = get_parser()
+    LibriSpeechAsrDataModule.add_arguments(parser)
+    args = parser.parse_args()
+
+    assert (
+        args.decoding_method == "greedy_search"
+    ), "Only supports greedy_search currently."
+    res_dir = Path(args.exp_dir) / f"onnx-{args.decoding_method}"
+
+    setup_logger(f"{res_dir}/log-decode")
+    logging.info("Decoding started")
+
+    device = torch.device("cpu")
+    logging.info(f"Device: {device}")
+
+    sp = spm.SentencePieceProcessor()
+    sp.load(args.bpe_model)
+
+    blank_id = sp.piece_to_id("<blk>")
+    assert blank_id == 0, blank_id
+
+    logging.info(vars(args))
+
+    logging.info("About to create model")
+    model = OnnxModel(
+        encoder_model_filename=args.encoder_model_filename,
+        decoder_model_filename=args.decoder_model_filename,
+        joiner_model_filename=args.joiner_model_filename,
+    )
+
+    # we need cut ids to display recognition results.
+    args.return_cuts = True
+    librispeech = LibriSpeechAsrDataModule(args)
+
+    test_clean_cuts = librispeech.test_clean_cuts()
+    test_other_cuts = librispeech.test_other_cuts()
+
+    test_clean_dl = librispeech.test_dataloaders(test_clean_cuts)
+    test_other_dl = librispeech.test_dataloaders(test_other_cuts)
+
+    test_sets = ["test-clean", "test-other"]
+    test_dl = [test_clean_dl, test_other_dl]
+
+    for test_set, test_dl in zip(test_sets, test_dl):
+        start_time = time.time()
+        results, total_duration = decode_dataset(dl=test_dl, model=model, sp=sp)
+        end_time = time.time()
+        elapsed_seconds = end_time - start_time
+        rtf = elapsed_seconds / total_duration
+
+        logging.info(f"Elapsed time: {elapsed_seconds:.3f} s")
+        logging.info(f"Wave duration: {total_duration:.3f} s")
+        logging.info(
+            f"Real time factor (RTF): {elapsed_seconds:.3f}/{total_duration:.3f} = {rtf:.3f}"
+        )
+
+        save_results(res_dir=res_dir, test_set_name=test_set, results=results)
+
+    logging.info("Done!")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/egs/librispeech/ASR/pruned_transducer_stateless/onnx_pretrained.py b/egs/librispeech/ASR/pruned_transducer_stateless/onnx_pretrained.py
new file mode 120000
index 000000000..7607623c8
--- /dev/null
+++ b/egs/librispeech/ASR/pruned_transducer_stateless/onnx_pretrained.py
@@ -0,0 +1 @@
+../pruned_transducer_stateless3/onnx_pretrained.py
\ No newline at end of file
diff --git a/egs/librispeech/ASR/pruned_transducer_stateless3/onnx_decode.py b/egs/librispeech/ASR/pruned_transducer_stateless3/onnx_decode.py
new file mode 100755
index 000000000..3b1c72cf1
--- /dev/null
+++ b/egs/librispeech/ASR/pruned_transducer_stateless3/onnx_decode.py
@@ -0,0 +1,321 @@
+#!/usr/bin/env python3
+#
+# Copyright 2021-2022 Xiaomi Corporation (Author: Fangjun Kuang,
+#                                                 Zengwei Yao,
+#                                                 Xiaoyu Yang)
+#
+# See ../../../../LICENSE for clarification regarding multiple authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+This script loads ONNX exported models and uses them to decode the test sets.
+
+We use the pre-trained model from
+https://huggingface.co/csukuangfj/icefall-asr-librispeech-pruned-transducer-stateless3-2022-05-13
+as an example to show how to use this file.
+
+1. Download the pre-trained model
+
+cd egs/librispeech/ASR
+
+repo_url=https://huggingface.co/csukuangfj/icefall-asr-librispeech-pruned-transducer-stateless3-2022-05-13
+GIT_LFS_SKIP_SMUDGE=1 git clone $repo_url
+repo=$(basename $repo_url)
+
+pushd $repo
+git lfs pull --include "data/lang_bpe_500/bpe.model"
+git lfs pull --include "exp/pretrained-iter-1224000-avg-14.pt"
+
+cd exp
+ln -s pretrained-iter-1224000-avg-14.pt epoch-9999.pt
+popd
+
+2. Export the model to ONNX
+
+./pruned_transducer_stateless3/export-onnx.py \
+  --bpe-model $repo/data/lang_bpe_500/bpe.model \
+  --epoch 9999 \
+  --avg 1 \
+  --exp-dir $repo/exp/
+
+It will generate the following 3 files inside $repo/exp:
+
+  - encoder-epoch-9999-avg-1.onnx
+  - decoder-epoch-9999-avg-1.onnx
+  - joiner-epoch-9999-avg-1.onnx
+
+2. Run this file
+
+./pruned_transducer_stateless3/onnx_decode.py \
+  --exp-dir ./pruned_transducer_stateless3/exp \
+  --max-duration 600 \
+  --encoder-model-filename $repo/exp/encoder-epoch-9999-avg-1.onnx \
+  --decoder-model-filename $repo/exp/decoder-epoch-9999-avg-1.onnx \
+  --joiner-model-filename $repo/exp/joiner-epoch-9999-avg-1.onnx \
+"""
+
+
+import argparse
+import logging
+import time
+from pathlib import Path
+from typing import List, Tuple
+
+import sentencepiece as spm
+import torch
+import torch.nn as nn
+from asr_datamodule import AsrDataModule
+from librispeech import LibriSpeech
+
+from onnx_pretrained import greedy_search, OnnxModel
+
+from icefall.utils import setup_logger, store_transcripts, write_error_stats
+
+
+def get_parser():
+    parser = argparse.ArgumentParser(
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter
+    )
+
+    parser.add_argument(
+        "--encoder-model-filename",
+        type=str,
+        required=True,
+        help="Path to the encoder onnx model. ",
+    )
+
+    parser.add_argument(
+        "--decoder-model-filename",
+        type=str,
+        required=True,
+        help="Path to the decoder onnx model. ",
+    )
+
+    parser.add_argument(
+        "--joiner-model-filename",
+        type=str,
+        required=True,
+        help="Path to the joiner onnx model. ",
+    )
+
+    parser.add_argument(
+        "--exp-dir",
+        type=str,
+        default="pruned_transducer_stateless3/exp",
+        help="The experiment dir",
+    )
+
+    parser.add_argument(
+        "--bpe-model",
+        type=str,
+        default="data/lang_bpe_500/bpe.model",
+        help="Path to the BPE model",
+    )
+
+    parser.add_argument(
+        "--decoding-method",
+        type=str,
+        default="greedy_search",
+        help="Valid values are greedy_search and modified_beam_search",
+    )
+
+    return parser
+
+
+def decode_one_batch(
+    model: OnnxModel, sp: spm.SentencePieceProcessor, batch: dict
+) -> List[List[str]]:
+    """Decode one batch and return the result.
+    Currently it only greedy_search is supported.
+
+    Args:
+      model:
+        The neural model.
+      sp:
+        The BPE model.
+      batch:
+        It is the return value from iterating
+        `lhotse.dataset.K2SpeechRecognitionDataset`. See its documentation
+        for the format of the `batch`.
+
+    Returns:
+      Return the decoded results for each utterance.
+    """
+    feature = batch["inputs"]
+    assert feature.ndim == 3
+    # at entry, feature is (N, T, C)
+
+    supervisions = batch["supervisions"]
+    feature_lens = supervisions["num_frames"].to(dtype=torch.int64)
+
+    encoder_out, encoder_out_lens = model.run_encoder(x=feature, x_lens=feature_lens)
+
+    hyps = greedy_search(
+        model=model, encoder_out=encoder_out, encoder_out_lens=encoder_out_lens
+    )
+
+    hyps = [sp.decode(h).split() for h in hyps]
+    return hyps
+
+
+def decode_dataset(
+    dl: torch.utils.data.DataLoader,
+    model: nn.Module,
+    sp: spm.SentencePieceProcessor,
+) -> Tuple[List[Tuple[str, List[str], List[str]]], float]:
+    """Decode dataset.
+
+    Args:
+      dl:
+        PyTorch's dataloader containing the dataset to decode.
+      model:
+        The neural model.
+      sp:
+        The BPE model.
+
+    Returns:
+      - A list of tuples. Each tuple contains three elements:
+         - cut_id,
+         - reference transcript,
+         - predicted result.
+      - The total duration (in seconds) of the dataset.
+    """
+    num_cuts = 0
+
+    try:
+        num_batches = len(dl)
+    except TypeError:
+        num_batches = "?"
+
+    log_interval = 10
+    total_duration = 0
+
+    results = []
+    for batch_idx, batch in enumerate(dl):
+        texts = batch["supervisions"]["text"]
+        cut_ids = [cut.id for cut in batch["supervisions"]["cut"]]
+        total_duration += sum([cut.duration for cut in batch["supervisions"]["cut"]])
+
+        hyps = decode_one_batch(model=model, sp=sp, batch=batch)
+
+        this_batch = []
+        assert len(hyps) == len(texts)
+        for cut_id, hyp_words, ref_text in zip(cut_ids, hyps, texts):
+            ref_words = ref_text.split()
+            this_batch.append((cut_id, ref_words, hyp_words))
+
+        results.extend(this_batch)
+
+        num_cuts += len(texts)
+
+        if batch_idx % log_interval == 0:
+            batch_str = f"{batch_idx}/{num_batches}"
+
+            logging.info(f"batch {batch_str}, cuts processed until now is {num_cuts}")
+
+    return results, total_duration
+
+
+def save_results(
+    res_dir: Path,
+    test_set_name: str,
+    results: List[Tuple[str, List[str], List[str]]],
+):
+    recog_path = res_dir / f"recogs-{test_set_name}.txt"
+    results = sorted(results)
+    store_transcripts(filename=recog_path, texts=results)
+    logging.info(f"The transcripts are stored in {recog_path}")
+
+    # The following prints out WERs, per-word error statistics and aligned
+    # ref/hyp pairs.
+    errs_filename = res_dir / f"errs-{test_set_name}.txt"
+    with open(errs_filename, "w") as f:
+        wer = write_error_stats(f, f"{test_set_name}", results, enable_log=True)
+
+    logging.info("Wrote detailed error stats to {}".format(errs_filename))
+
+    errs_info = res_dir / f"wer-summary-{test_set_name}.txt"
+    with open(errs_info, "w") as f:
+        print("WER", file=f)
+        print(wer, file=f)
+
+    s = "\nFor {}, WER is {}:\n".format(test_set_name, wer)
+    logging.info(s)
+
+
+@torch.no_grad()
+def main():
+    parser = get_parser()
+    AsrDataModule.add_arguments(parser)
+    args = parser.parse_args()
+
+    assert (
+        args.decoding_method == "greedy_search"
+    ), "Only supports greedy_search currently."
+    res_dir = Path(args.exp_dir) / f"onnx-{args.decoding_method}"
+
+    setup_logger(f"{res_dir}/log-decode")
+    logging.info("Decoding started")
+
+    device = torch.device("cpu")
+    logging.info(f"Device: {device}")
+
+    sp = spm.SentencePieceProcessor()
+    sp.load(args.bpe_model)
+
+    blank_id = sp.piece_to_id("<blk>")
+    assert blank_id == 0, blank_id
+
+    logging.info(vars(args))
+
+    logging.info("About to create model")
+    model = OnnxModel(
+        encoder_model_filename=args.encoder_model_filename,
+        decoder_model_filename=args.decoder_model_filename,
+        joiner_model_filename=args.joiner_model_filename,
+    )
+
+    # we need cut ids to display recognition results.
+    args.return_cuts = True
+    asr_datamodule = AsrDataModule(args)
+    librispeech = LibriSpeech(manifest_dir=args.manifest_dir)
+
+    test_clean_cuts = librispeech.test_clean_cuts()
+    test_other_cuts = librispeech.test_other_cuts()
+
+    test_clean_dl = asr_datamodule.test_dataloaders(test_clean_cuts)
+    test_other_dl = asr_datamodule.test_dataloaders(test_other_cuts)
+
+    test_sets = ["test-clean", "test-other"]
+    test_dl = [test_clean_dl, test_other_dl]
+
+    for test_set, test_dl in zip(test_sets, test_dl):
+        start_time = time.time()
+        results, total_duration = decode_dataset(dl=test_dl, model=model, sp=sp)
+        end_time = time.time()
+        elapsed_seconds = end_time - start_time
+        rtf = elapsed_seconds / total_duration
+
+        logging.info(f"Elapsed time: {elapsed_seconds:.3f} s")
+        logging.info(f"Wave duration: {total_duration:.3f} s")
+        logging.info(
+            f"Real time factor (RTF): {elapsed_seconds:.3f}/{total_duration:.3f} = {rtf:.3f}"
+        )
+
+        save_results(res_dir=res_dir, test_set_name=test_set, results=results)
+
+    logging.info("Done!")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/egs/librispeech/ASR/pruned_transducer_stateless3/onnx_pretrained.py b/egs/librispeech/ASR/pruned_transducer_stateless3/onnx_pretrained.py
index 3947aa102..e10915086 100755
--- a/egs/librispeech/ASR/pruned_transducer_stateless3/onnx_pretrained.py
+++ b/egs/librispeech/ASR/pruned_transducer_stateless3/onnx_pretrained.py
@@ -71,7 +71,6 @@ from typing import List, Tuple
 
 import k2
 import kaldifeat
-import numpy as np
 import onnxruntime as ort
 import torch
 import torchaudio
@@ -139,7 +138,7 @@ class OnnxModel:
     ):
         session_opts = ort.SessionOptions()
         session_opts.inter_op_num_threads = 1
-        session_opts.intra_op_num_threads = 1
+        session_opts.intra_op_num_threads = 4
 
         self.session_opts = session_opts
 
diff --git a/egs/librispeech/ASR/pruned_transducer_stateless5/export-onnx.py b/egs/librispeech/ASR/pruned_transducer_stateless5/export-onnx.py
index 3d94760dc..e89d94d82 100755
--- a/egs/librispeech/ASR/pruned_transducer_stateless5/export-onnx.py
+++ b/egs/librispeech/ASR/pruned_transducer_stateless5/export-onnx.py
@@ -60,6 +60,7 @@ import sentencepiece as spm
 import torch
 import torch.nn as nn
 from conformer import Conformer
+from onnxruntime.quantization import QuantType, quantize_dynamic
 from decoder import Decoder
 from scaling_converter import convert_scaled_to_non_scaled
 from train import add_model_arguments, get_params, get_transducer_model
@@ -568,6 +569,35 @@ def main():
     )
     logging.info(f"Exported joiner to {joiner_filename}")
 
+    # Generate int8 quantization models
+    # See https://onnxruntime.ai/docs/performance/model-optimizations/quantization.html#data-type-selection
+
+    logging.info("Generate int8 quantization models")
+
+    encoder_filename_int8 = params.exp_dir / f"encoder-{suffix}.int8.onnx"
+    quantize_dynamic(
+        model_input=encoder_filename,
+        model_output=encoder_filename_int8,
+        op_types_to_quantize=["MatMul"],
+        weight_type=QuantType.QInt8,
+    )
+
+    decoder_filename_int8 = params.exp_dir / f"decoder-{suffix}.int8.onnx"
+    quantize_dynamic(
+        model_input=decoder_filename,
+        model_output=decoder_filename_int8,
+        op_types_to_quantize=["MatMul"],
+        weight_type=QuantType.QInt8,
+    )
+
+    joiner_filename_int8 = params.exp_dir / f"joiner-{suffix}.int8.onnx"
+    quantize_dynamic(
+        model_input=joiner_filename,
+        model_output=joiner_filename_int8,
+        op_types_to_quantize=["MatMul"],
+        weight_type=QuantType.QInt8,
+    )
+
 
 if __name__ == "__main__":
     formatter = "%(asctime)s %(levelname)s [%(filename)s:%(lineno)d] %(message)s"
diff --git a/egs/librispeech/ASR/pruned_transducer_stateless5/onnx_decode.py b/egs/librispeech/ASR/pruned_transducer_stateless5/onnx_decode.py
new file mode 100755
index 000000000..6f26e34b5
--- /dev/null
+++ b/egs/librispeech/ASR/pruned_transducer_stateless5/onnx_decode.py
@@ -0,0 +1,326 @@
+#!/usr/bin/env python3
+#
+# Copyright 2021-2022 Xiaomi Corporation (Author: Fangjun Kuang,
+#                                                 Zengwei Yao,
+#                                                 Xiaoyu Yang)
+#
+# See ../../../../LICENSE for clarification regarding multiple authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+This script loads ONNX exported models and uses them to decode the test sets.
+
+We use the pre-trained model from
+https://huggingface.co/Zengwei/icefall-asr-librispeech-pruned-transducer-stateless5-2022-07-07
+as an example to show how to use this file.
+
+1. Download the pre-trained model
+
+cd egs/librispeech/ASR
+
+repo_url=https://huggingface.co/Zengwei/icefall-asr-librispeech-pruned-transducer-stateless5-2022-07-07
+GIT_LFS_SKIP_SMUDGE=1 git clone $repo_url
+repo=$(basename $repo_url)
+
+pushd $repo
+git lfs pull --include "data/lang_bpe_500/bpe.model"
+git lfs pull --include "exp/pretrained-epoch-30-avg-10.pt"
+
+cd exp
+ln -s pretrained-epoch-30-avg-10.pt epoch-9999.pt
+popd
+
+2. Export the model to ONNX
+
+./pruned_transducer_stateless5/export-onnx.py \
+  --bpe-model $repo/data/lang_bpe_500/bpe.model \
+  --epoch 9999 \
+  --avg 1 \
+  --use-averaged-model 0 \
+  --exp-dir $repo/exp/ \
+  --num-encoder-layers 18 \
+  --dim-feedforward 2048 \
+  --nhead 8 \
+  --encoder-dim 512 \
+  --decoder-dim 512 \
+  --joiner-dim 512
+
+It will generate the following 3 files inside $repo/exp:
+
+  - encoder-epoch-9999-avg-1.onnx
+  - decoder-epoch-9999-avg-1.onnx
+  - joiner-epoch-9999-avg-1.onnx
+
+2. Run this file
+
+./pruned_transducer_stateless5/onnx_decode.py \
+  --exp-dir ./pruned_transducer_stateless5/exp \
+  --max-duration 600 \
+  --encoder-model-filename $repo/exp/encoder-epoch-9999-avg-1.onnx \
+  --decoder-model-filename $repo/exp/decoder-epoch-9999-avg-1.onnx \
+  --joiner-model-filename $repo/exp/joiner-epoch-9999-avg-1.onnx \
+"""
+
+
+import argparse
+import logging
+import time
+from pathlib import Path
+from typing import List, Tuple
+
+import sentencepiece as spm
+import torch
+import torch.nn as nn
+from asr_datamodule import LibriSpeechAsrDataModule
+
+from onnx_pretrained import greedy_search, OnnxModel
+
+from icefall.utils import setup_logger, store_transcripts, write_error_stats
+
+
+def get_parser():
+    parser = argparse.ArgumentParser(
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter
+    )
+
+    parser.add_argument(
+        "--encoder-model-filename",
+        type=str,
+        required=True,
+        help="Path to the encoder onnx model. ",
+    )
+
+    parser.add_argument(
+        "--decoder-model-filename",
+        type=str,
+        required=True,
+        help="Path to the decoder onnx model. ",
+    )
+
+    parser.add_argument(
+        "--joiner-model-filename",
+        type=str,
+        required=True,
+        help="Path to the joiner onnx model. ",
+    )
+
+    parser.add_argument(
+        "--exp-dir",
+        type=str,
+        default="pruned_transducer_stateless5/exp",
+        help="The experiment dir",
+    )
+
+    parser.add_argument(
+        "--bpe-model",
+        type=str,
+        default="data/lang_bpe_500/bpe.model",
+        help="Path to the BPE model",
+    )
+
+    parser.add_argument(
+        "--decoding-method",
+        type=str,
+        default="greedy_search",
+        help="Valid values are greedy_search and modified_beam_search",
+    )
+
+    return parser
+
+
+def decode_one_batch(
+    model: OnnxModel, sp: spm.SentencePieceProcessor, batch: dict
+) -> List[List[str]]:
+    """Decode one batch and return the result.
+    Currently it only greedy_search is supported.
+
+    Args:
+      model:
+        The neural model.
+      sp:
+        The BPE model.
+      batch:
+        It is the return value from iterating
+        `lhotse.dataset.K2SpeechRecognitionDataset`. See its documentation
+        for the format of the `batch`.
+
+    Returns:
+      Return the decoded results for each utterance.
+    """
+    feature = batch["inputs"]
+    assert feature.ndim == 3
+    # at entry, feature is (N, T, C)
+
+    supervisions = batch["supervisions"]
+    feature_lens = supervisions["num_frames"].to(dtype=torch.int64)
+
+    encoder_out, encoder_out_lens = model.run_encoder(x=feature, x_lens=feature_lens)
+
+    hyps = greedy_search(
+        model=model, encoder_out=encoder_out, encoder_out_lens=encoder_out_lens
+    )
+
+    hyps = [sp.decode(h).split() for h in hyps]
+    return hyps
+
+
+def decode_dataset(
+    dl: torch.utils.data.DataLoader,
+    model: nn.Module,
+    sp: spm.SentencePieceProcessor,
+) -> Tuple[List[Tuple[str, List[str], List[str]]], float]:
+    """Decode dataset.
+
+    Args:
+      dl:
+        PyTorch's dataloader containing the dataset to decode.
+      model:
+        The neural model.
+      sp:
+        The BPE model.
+
+    Returns:
+      - A list of tuples. Each tuple contains three elements:
+         - cut_id,
+         - reference transcript,
+         - predicted result.
+      - The total duration (in seconds) of the dataset.
+    """
+    num_cuts = 0
+
+    try:
+        num_batches = len(dl)
+    except TypeError:
+        num_batches = "?"
+
+    log_interval = 10
+    total_duration = 0
+
+    results = []
+    for batch_idx, batch in enumerate(dl):
+        texts = batch["supervisions"]["text"]
+        cut_ids = [cut.id for cut in batch["supervisions"]["cut"]]
+        total_duration += sum([cut.duration for cut in batch["supervisions"]["cut"]])
+
+        hyps = decode_one_batch(model=model, sp=sp, batch=batch)
+
+        this_batch = []
+        assert len(hyps) == len(texts)
+        for cut_id, hyp_words, ref_text in zip(cut_ids, hyps, texts):
+            ref_words = ref_text.split()
+            this_batch.append((cut_id, ref_words, hyp_words))
+
+        results.extend(this_batch)
+
+        num_cuts += len(texts)
+
+        if batch_idx % log_interval == 0:
+            batch_str = f"{batch_idx}/{num_batches}"
+
+            logging.info(f"batch {batch_str}, cuts processed until now is {num_cuts}")
+
+    return results, total_duration
+
+
+def save_results(
+    res_dir: Path,
+    test_set_name: str,
+    results: List[Tuple[str, List[str], List[str]]],
+):
+    recog_path = res_dir / f"recogs-{test_set_name}.txt"
+    results = sorted(results)
+    store_transcripts(filename=recog_path, texts=results)
+    logging.info(f"The transcripts are stored in {recog_path}")
+
+    # The following prints out WERs, per-word error statistics and aligned
+    # ref/hyp pairs.
+    errs_filename = res_dir / f"errs-{test_set_name}.txt"
+    with open(errs_filename, "w") as f:
+        wer = write_error_stats(f, f"{test_set_name}", results, enable_log=True)
+
+    logging.info("Wrote detailed error stats to {}".format(errs_filename))
+
+    errs_info = res_dir / f"wer-summary-{test_set_name}.txt"
+    with open(errs_info, "w") as f:
+        print("WER", file=f)
+        print(wer, file=f)
+
+    s = "\nFor {}, WER is {}:\n".format(test_set_name, wer)
+    logging.info(s)
+
+
+@torch.no_grad()
+def main():
+    parser = get_parser()
+    LibriSpeechAsrDataModule.add_arguments(parser)
+    args = parser.parse_args()
+
+    assert (
+        args.decoding_method == "greedy_search"
+    ), "Only supports greedy_search currently."
+    res_dir = Path(args.exp_dir) / f"onnx-{args.decoding_method}"
+
+    setup_logger(f"{res_dir}/log-decode")
+    logging.info("Decoding started")
+
+    device = torch.device("cpu")
+    logging.info(f"Device: {device}")
+
+    sp = spm.SentencePieceProcessor()
+    sp.load(args.bpe_model)
+
+    blank_id = sp.piece_to_id("<blk>")
+    assert blank_id == 0, blank_id
+
+    logging.info(vars(args))
+
+    logging.info("About to create model")
+    model = OnnxModel(
+        encoder_model_filename=args.encoder_model_filename,
+        decoder_model_filename=args.decoder_model_filename,
+        joiner_model_filename=args.joiner_model_filename,
+    )
+
+    # we need cut ids to display recognition results.
+    args.return_cuts = True
+    librispeech = LibriSpeechAsrDataModule(args)
+
+    test_clean_cuts = librispeech.test_clean_cuts()
+    test_other_cuts = librispeech.test_other_cuts()
+
+    test_clean_dl = librispeech.test_dataloaders(test_clean_cuts)
+    test_other_dl = librispeech.test_dataloaders(test_other_cuts)
+
+    test_sets = ["test-clean", "test-other"]
+    test_dl = [test_clean_dl, test_other_dl]
+
+    for test_set, test_dl in zip(test_sets, test_dl):
+        start_time = time.time()
+        results, total_duration = decode_dataset(dl=test_dl, model=model, sp=sp)
+        end_time = time.time()
+        elapsed_seconds = end_time - start_time
+        rtf = elapsed_seconds / total_duration
+
+        logging.info(f"Elapsed time: {elapsed_seconds:.3f} s")
+        logging.info(f"Wave duration: {total_duration:.3f} s")
+        logging.info(
+            f"Real time factor (RTF): {elapsed_seconds:.3f}/{total_duration:.3f} = {rtf:.3f}"
+        )
+
+        save_results(res_dir=res_dir, test_set_name=test_set, results=results)
+
+    logging.info("Done!")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/egs/librispeech/ASR/pruned_transducer_stateless7/onnx_decode.py b/egs/librispeech/ASR/pruned_transducer_stateless7/onnx_decode.py
new file mode 100755
index 000000000..67585ee47
--- /dev/null
+++ b/egs/librispeech/ASR/pruned_transducer_stateless7/onnx_decode.py
@@ -0,0 +1,319 @@
+#!/usr/bin/env python3
+#
+# Copyright 2021-2022 Xiaomi Corporation (Author: Fangjun Kuang,
+#                                                 Zengwei Yao,
+#                                                 Xiaoyu Yang)
+#
+# See ../../../../LICENSE for clarification regarding multiple authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+This script loads ONNX exported models and uses them to decode the test sets.
+
+We use the pre-trained model from
+https://huggingface.co/csukuangfj/icefall-asr-librispeech-pruned-transducer-stateless7-2022-11-11
+as an example to show how to use this file.
+
+1. Download the pre-trained model
+
+cd egs/librispeech/ASR
+
+repo_url=https://huggingface.co/csukuangfj/icefall-asr-librispeech-pruned-transducer-stateless7-2022-11-11
+GIT_LFS_SKIP_SMUDGE=1 git clone $repo_url
+repo=$(basename $repo_url)
+
+pushd $repo
+git lfs pull --include "data/lang_bpe_500/bpe.model"
+git lfs pull --include "exp/pretrained-epoch-30-avg-9.pt"
+
+cd exp
+ln -s pretrained-epoch-30-avg-9.pt epoch-9999.pt
+popd
+
+2. Export the model to ONNX
+
+./pruned_transducer_stateless7/export-onnx.py \
+  --bpe-model $repo/data/lang_bpe_500/bpe.model \
+  --epoch 9999 \
+  --avg 1 \
+  --exp-dir $repo/exp/
+
+It will generate the following 3 files inside $repo/exp:
+
+  - encoder-epoch-9999-avg-1.onnx
+  - decoder-epoch-9999-avg-1.onnx
+  - joiner-epoch-9999-avg-1.onnx
+
+2. Run this file
+
+./pruned_transducer_stateless7/onnx_decode.py \
+  --exp-dir ./pruned_transducer_stateless7/exp \
+  --max-duration 600 \
+  --encoder-model-filename $repo/exp/encoder-epoch-9999-avg-1.onnx \
+  --decoder-model-filename $repo/exp/decoder-epoch-9999-avg-1.onnx \
+  --joiner-model-filename $repo/exp/joiner-epoch-9999-avg-1.onnx \
+"""
+
+
+import argparse
+import logging
+import time
+from pathlib import Path
+from typing import List, Tuple
+
+import sentencepiece as spm
+import torch
+import torch.nn as nn
+from asr_datamodule import LibriSpeechAsrDataModule
+
+from onnx_pretrained import greedy_search, OnnxModel
+
+from icefall.utils import setup_logger, store_transcripts, write_error_stats
+
+
+def get_parser():
+    parser = argparse.ArgumentParser(
+        formatter_class=argparse.ArgumentDefaultsHelpFormatter
+    )
+
+    parser.add_argument(
+        "--encoder-model-filename",
+        type=str,
+        required=True,
+        help="Path to the encoder onnx model. ",
+    )
+
+    parser.add_argument(
+        "--decoder-model-filename",
+        type=str,
+        required=True,
+        help="Path to the decoder onnx model. ",
+    )
+
+    parser.add_argument(
+        "--joiner-model-filename",
+        type=str,
+        required=True,
+        help="Path to the joiner onnx model. ",
+    )
+
+    parser.add_argument(
+        "--exp-dir",
+        type=str,
+        default="pruned_transducer_stateless7/exp",
+        help="The experiment dir",
+    )
+
+    parser.add_argument(
+        "--bpe-model",
+        type=str,
+        default="data/lang_bpe_500/bpe.model",
+        help="Path to the BPE model",
+    )
+
+    parser.add_argument(
+        "--decoding-method",
+        type=str,
+        default="greedy_search",
+        help="Valid values are greedy_search and modified_beam_search",
+    )
+
+    return parser
+
+
+def decode_one_batch(
+    model: OnnxModel, sp: spm.SentencePieceProcessor, batch: dict
+) -> List[List[str]]:
+    """Decode one batch and return the result.
+    Currently it only greedy_search is supported.
+
+    Args:
+      model:
+        The neural model.
+      sp:
+        The BPE model.
+      batch:
+        It is the return value from iterating
+        `lhotse.dataset.K2SpeechRecognitionDataset`. See its documentation
+        for the format of the `batch`.
+
+    Returns:
+      Return the decoded results for each utterance.
+    """
+    feature = batch["inputs"]
+    assert feature.ndim == 3
+    # at entry, feature is (N, T, C)
+
+    supervisions = batch["supervisions"]
+    feature_lens = supervisions["num_frames"].to(dtype=torch.int64)
+
+    encoder_out, encoder_out_lens = model.run_encoder(x=feature, x_lens=feature_lens)
+
+    hyps = greedy_search(
+        model=model, encoder_out=encoder_out, encoder_out_lens=encoder_out_lens
+    )
+
+    hyps = [sp.decode(h).split() for h in hyps]
+    return hyps
+
+
+def decode_dataset(
+    dl: torch.utils.data.DataLoader,
+    model: nn.Module,
+    sp: spm.SentencePieceProcessor,
+) -> Tuple[List[Tuple[str, List[str], List[str]]], float]:
+    """Decode dataset.
+
+    Args:
+      dl:
+        PyTorch's dataloader containing the dataset to decode.
+      model:
+        The neural model.
+      sp:
+        The BPE model.
+
+    Returns:
+      - A list of tuples. Each tuple contains three elements:
+         - cut_id,
+         - reference transcript,
+         - predicted result.
+      - The total duration (in seconds) of the dataset.
+    """
+    num_cuts = 0
+
+    try:
+        num_batches = len(dl)
+    except TypeError:
+        num_batches = "?"
+
+    log_interval = 10
+    total_duration = 0
+
+    results = []
+    for batch_idx, batch in enumerate(dl):
+        texts = batch["supervisions"]["text"]
+        cut_ids = [cut.id for cut in batch["supervisions"]["cut"]]
+        total_duration += sum([cut.duration for cut in batch["supervisions"]["cut"]])
+
+        hyps = decode_one_batch(model=model, sp=sp, batch=batch)
+
+        this_batch = []
+        assert len(hyps) == len(texts)
+        for cut_id, hyp_words, ref_text in zip(cut_ids, hyps, texts):
+            ref_words = ref_text.split()
+            this_batch.append((cut_id, ref_words, hyp_words))
+
+        results.extend(this_batch)
+
+        num_cuts += len(texts)
+
+        if batch_idx % log_interval == 0:
+            batch_str = f"{batch_idx}/{num_batches}"
+
+            logging.info(f"batch {batch_str}, cuts processed until now is {num_cuts}")
+
+    return results, total_duration
+
+
+def save_results(
+    res_dir: Path,
+    test_set_name: str,
+    results: List[Tuple[str, List[str], List[str]]],
+):
+    recog_path = res_dir / f"recogs-{test_set_name}.txt"
+    results = sorted(results)
+    store_transcripts(filename=recog_path, texts=results)
+    logging.info(f"The transcripts are stored in {recog_path}")
+
+    # The following prints out WERs, per-word error statistics and aligned
+    # ref/hyp pairs.
+    errs_filename = res_dir / f"errs-{test_set_name}.txt"
+    with open(errs_filename, "w") as f:
+        wer = write_error_stats(f, f"{test_set_name}", results, enable_log=True)
+
+    logging.info("Wrote detailed error stats to {}".format(errs_filename))
+
+    errs_info = res_dir / f"wer-summary-{test_set_name}.txt"
+    with open(errs_info, "w") as f:
+        print("WER", file=f)
+        print(wer, file=f)
+
+    s = "\nFor {}, WER is {}:\n".format(test_set_name, wer)
+    logging.info(s)
+
+
+@torch.no_grad()
+def main():
+    parser = get_parser()
+    LibriSpeechAsrDataModule.add_arguments(parser)
+    args = parser.parse_args()
+
+    assert (
+        args.decoding_method == "greedy_search"
+    ), "Only supports greedy_search currently."
+    res_dir = Path(args.exp_dir) / f"onnx-{args.decoding_method}"
+
+    setup_logger(f"{res_dir}/log-decode")
+    logging.info("Decoding started")
+
+    device = torch.device("cpu")
+    logging.info(f"Device: {device}")
+
+    sp = spm.SentencePieceProcessor()
+    sp.load(args.bpe_model)
+
+    blank_id = sp.piece_to_id("<blk>")
+    assert blank_id == 0, blank_id
+
+    logging.info(vars(args))
+
+    logging.info("About to create model")
+    model = OnnxModel(
+        encoder_model_filename=args.encoder_model_filename,
+        decoder_model_filename=args.decoder_model_filename,
+        joiner_model_filename=args.joiner_model_filename,
+    )
+
+    # we need cut ids to display recognition results.
+    args.return_cuts = True
+    librispeech = LibriSpeechAsrDataModule(args)
+
+    test_clean_cuts = librispeech.test_clean_cuts()
+    test_other_cuts = librispeech.test_other_cuts()
+
+    test_clean_dl = librispeech.test_dataloaders(test_clean_cuts)
+    test_other_dl = librispeech.test_dataloaders(test_other_cuts)
+
+    test_sets = ["test-clean", "test-other"]
+    test_dl = [test_clean_dl, test_other_dl]
+
+    for test_set, test_dl in zip(test_sets, test_dl):
+        start_time = time.time()
+        results, total_duration = decode_dataset(dl=test_dl, model=model, sp=sp)
+        end_time = time.time()
+        elapsed_seconds = end_time - start_time
+        rtf = elapsed_seconds / total_duration
+
+        logging.info(f"Elapsed time: {elapsed_seconds:.3f} s")
+        logging.info(f"Wave duration: {total_duration:.3f} s")
+        logging.info(
+            f"Real time factor (RTF): {elapsed_seconds:.3f}/{total_duration:.3f} = {rtf:.3f}"
+        )
+
+        save_results(res_dir=res_dir, test_set_name=test_set, results=results)
+
+    logging.info("Done!")
+
+
+if __name__ == "__main__":
+    main()
diff --git a/egs/librispeech/ASR/transducer_stateless/conformer.py b/egs/librispeech/ASR/transducer_stateless/conformer.py
index 94d0393c2..90b722bde 100644
--- a/egs/librispeech/ASR/transducer_stateless/conformer.py
+++ b/egs/librispeech/ASR/transducer_stateless/conformer.py
@@ -24,7 +24,7 @@ import torch
 from torch import Tensor, nn
 from transformer import Transformer
 
-from icefall.utils import make_pad_mask, subsequent_chunk_mask
+from icefall.utils import is_jit_tracing, make_pad_mask, subsequent_chunk_mask
 
 
 class Conformer(Transformer):
@@ -154,7 +154,8 @@ class Conformer(Transformer):
         # Note: rounding_mode in torch.div() is available only in torch >= 1.8.0
         lengths = (((x_lens - 1) >> 1) - 1) >> 1
 
-        assert x.size(0) == lengths.max().item()
+        if not is_jit_tracing():
+            assert x.size(0) == lengths.max().item()
 
         src_key_padding_mask = make_pad_mask(lengths)
 
@@ -768,6 +769,14 @@ class RelPositionalEncoding(torch.nn.Module):
     def __init__(self, d_model: int, dropout_rate: float, max_len: int = 5000) -> None:
         """Construct an PositionalEncoding object."""
         super(RelPositionalEncoding, self).__init__()
+        if is_jit_tracing():
+            # 10k frames correspond to ~100k ms, e.g., 100 seconds, i.e.,
+            # It assumes that the maximum input won't have more than
+            # 10k frames.
+            #
+            # TODO(fangjun): Use torch.jit.script() for this module
+            max_len = 10000
+
         self.d_model = d_model
         self.xscale = math.sqrt(self.d_model)
         self.dropout = torch.nn.Dropout(p=dropout_rate)
@@ -975,22 +984,34 @@ class RelPositionMultiheadAttention(nn.Module):
           the key, while time1 is for the query).
         """
         (batch_size, num_heads, time1, n) = x.shape
+
         time2 = time1 + left_context
+        if not is_jit_tracing():
+            assert (
+                n == left_context + 2 * time1 - 1
+            ), f"{n} == {left_context} + 2 * {time1} - 1"
 
-        assert (
-            n == left_context + 2 * time1 - 1
-        ), f"{n} == {left_context} + 2 * {time1} - 1"
+        if is_jit_tracing():
+            rows = torch.arange(start=time1 - 1, end=-1, step=-1)
+            cols = torch.arange(time2)
+            rows = rows.repeat(batch_size * num_heads).unsqueeze(-1)
+            indexes = rows + cols
 
-        # Note: TorchScript requires explicit arg for stride()
-        batch_stride = x.stride(0)
-        head_stride = x.stride(1)
-        time1_stride = x.stride(2)
-        n_stride = x.stride(3)
-        return x.as_strided(
-            (batch_size, num_heads, time1, time2),
-            (batch_stride, head_stride, time1_stride - n_stride, n_stride),
-            storage_offset=n_stride * (time1 - 1),
-        )
+            x = x.reshape(-1, n)
+            x = torch.gather(x, dim=1, index=indexes)
+            x = x.reshape(batch_size, num_heads, time1, time2)
+            return x
+        else:
+            # Note: TorchScript requires explicit arg for stride()
+            batch_stride = x.stride(0)
+            head_stride = x.stride(1)
+            time1_stride = x.stride(2)
+            n_stride = x.stride(3)
+            return x.as_strided(
+                (batch_size, num_heads, time1, time2),
+                (batch_stride, head_stride, time1_stride - n_stride, n_stride),
+                storage_offset=n_stride * (time1 - 1),
+            )
 
     def multi_head_attention_forward(
         self,
@@ -1061,13 +1082,16 @@ class RelPositionMultiheadAttention(nn.Module):
         """
 
         tgt_len, bsz, embed_dim = query.size()
-        assert embed_dim == embed_dim_to_check
-        assert key.size(0) == value.size(0) and key.size(1) == value.size(1)
+        if not is_jit_tracing():
+            assert embed_dim == embed_dim_to_check
+            assert key.size(0) == value.size(0) and key.size(1) == value.size(1)
 
         head_dim = embed_dim // num_heads
-        assert (
-            head_dim * num_heads == embed_dim
-        ), "embed_dim must be divisible by num_heads"
+        if not is_jit_tracing():
+            assert (
+                head_dim * num_heads == embed_dim
+            ), "embed_dim must be divisible by num_heads"
+
         scaling = float(head_dim) ** -0.5
 
         if torch.equal(query, key) and torch.equal(key, value):
@@ -1181,7 +1205,8 @@ class RelPositionMultiheadAttention(nn.Module):
         q = q.transpose(0, 1)  # (batch, time1, head, d_k)
 
         pos_emb_bsz = pos_emb.size(0)
-        assert pos_emb_bsz in (1, bsz)  # actually it is 1
+        if not is_jit_tracing():
+            assert pos_emb_bsz in (1, bsz)  # actually it is 1
         p = self.linear_pos(pos_emb).view(pos_emb_bsz, -1, num_heads, head_dim)
 
         # (batch, 2*time1, head, d_k) --> (batch, head, d_k, 2*time -1)
@@ -1212,11 +1237,12 @@ class RelPositionMultiheadAttention(nn.Module):
 
         attn_output_weights = attn_output_weights.view(bsz * num_heads, tgt_len, -1)
 
-        assert list(attn_output_weights.size()) == [
-            bsz * num_heads,
-            tgt_len,
-            src_len,
-        ]
+        if not is_jit_tracing():
+            assert list(attn_output_weights.size()) == [
+                bsz * num_heads,
+                tgt_len,
+                src_len,
+            ]
 
         if attn_mask is not None:
             if attn_mask.dtype == torch.bool:
@@ -1265,7 +1291,10 @@ class RelPositionMultiheadAttention(nn.Module):
         )
 
         attn_output = torch.bmm(attn_output_weights, v)
-        assert list(attn_output.size()) == [bsz * num_heads, tgt_len, head_dim]
+
+        if not is_jit_tracing():
+            assert list(attn_output.size()) == [bsz * num_heads, tgt_len, head_dim]
+
         attn_output = (
             attn_output.transpose(0, 1).contiguous().view(tgt_len, bsz, embed_dim)
         )