diff --git a/.flake8 b/.flake8
index 229cf1d6c..523ac9296 100644
--- a/.flake8
+++ b/.flake8
@@ -14,3 +14,7 @@ exclude =
   .git,
   **/data/**,
   icefall/shared/make_kn_lm.py
+
+ignore =
+  # E203 whitespace before ':'
+  E203,
diff --git a/egs/librispeech/ASR/transducer_emformer/emformer.py b/egs/librispeech/ASR/transducer_emformer/emformer.py
index b3693d660..631ff43fb 100644
--- a/egs/librispeech/ASR/transducer_emformer/emformer.py
+++ b/egs/librispeech/ASR/transducer_emformer/emformer.py
@@ -63,11 +63,11 @@ class Emformer(EncoderInterface):
           num_encoder_layers:
             Number of encoder layers.
           segment_length:
-            Number of frames per segment.
+            Number of frames per segment before subsampling.
           left_context_length:
-            Number of frames in the left context.
+            Number of frames in the left context before subsampling.
           right_context_length:
-            Number of frames in the right context.
+            Number of frames in the right context before subsampling.
           max_memory_size:
             TODO.
           dropout:
@@ -94,6 +94,7 @@ class Emformer(EncoderInterface):
         else:
             self.encoder_embed = Conv2dSubsampling(num_features, d_model)
 
+        self.segment_length = segment_length
         self.right_context_length = right_context_length
 
         assert right_context_length % subsampling_factor == 0
diff --git a/egs/librispeech/ASR/transducer_emformer/export.py b/egs/librispeech/ASR/transducer_emformer/export.py
new file mode 100755
index 000000000..9c665ea1a
--- /dev/null
+++ b/egs/librispeech/ASR/transducer_emformer/export.py
@@ -0,0 +1,184 @@
+#!/usr/bin/env python3
+#
+# Copyright 2021 Xiaomi Corporation (Author: Fangjun Kuang)
+#
+# 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 converts several saved checkpoints
+# to a single one using model averaging.
+"""
+Usage:
+./transducer_emformer/export.py \
+  --exp-dir ./transducer_emformer/exp \
+  --bpe-model data/lang_bpe_500/bpe.model \
+  --epoch 20 \
+  --avg 10
+
+It will generate a file exp_dir/pretrained.pt
+
+To use the generated file with `transducer_emformer/decode.py`,
+you can do:
+
+    cd /path/to/exp_dir
+    ln -s pretrained.pt epoch-9999.pt
+
+    cd /path/to/egs/librispeech/ASR
+    ./transducer_emformer/decode.py \
+        --exp-dir ./transducer_emformer/exp \
+        --epoch 9999 \
+        --avg 1 \
+        --max-duration 1000 \
+        --bpe-model data/lang_bpe_500/bpe.model
+"""
+
+import argparse
+import logging
+from pathlib import Path
+
+import sentencepiece as spm
+import torch
+from train import add_model_arguments, get_params, get_transducer_model
+
+from icefall.checkpoint import average_checkpoints, load_checkpoint
+from icefall.utils import str2bool
+
+
+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 decoding."
+        "Note: Epoch counts from 0.",
+    )
+
+    parser.add_argument(
+        "--avg",
+        type=int,
+        default=15,
+        help="Number of checkpoints to average. Automatically select "
+        "consecutive checkpoints before the checkpoint specified by "
+        "'--epoch'. ",
+    )
+
+    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(
+        "--jit",
+        type=str2bool,
+        default=False,
+        help="""True to save a model after applying torch.jit.script.
+        """,
+    )
+
+    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 main():
+    args = get_parser().parse_args()
+    args.exp_dir = Path(args.exp_dir)
+
+    assert args.jit is False, "Support torchscript will be added later"
+
+    params = get_params()
+    params.update(vars(args))
+
+    device = torch.device("cpu")
+    if torch.cuda.is_available():
+        device = torch.device("cuda", 0)
+
+    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.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.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))
+
+    model.eval()
+
+    model.to("cpu")
+    model.eval()
+
+    if params.jit:
+        logging.info("Using torch.jit.script")
+        model = torch.jit.script(model)
+        filename = params.exp_dir / "cpu_jit.pt"
+        model.save(str(filename))
+        logging.info(f"Saved to {filename}")
+    else:
+        logging.info("Not using torch.jit.script")
+        # Save it using a format so that it can be loaded
+        # by :func:`load_checkpoint`
+        filename = params.exp_dir / "pretrained.pt"
+        torch.save({"model": model.state_dict()}, str(filename))
+        logging.info(f"Saved to {filename}")
+
+
+if __name__ == "__main__":
+    formatter = (
+        "%(asctime)s %(levelname)s [%(filename)s:%(lineno)d] %(message)s"
+    )
+
+    logging.basicConfig(format=formatter, level=logging.INFO)
+    main()
diff --git a/egs/librispeech/ASR/transducer_emformer/streaming_decode.py b/egs/librispeech/ASR/transducer_emformer/streaming_decode.py
index 0b21b3f59..aca6e444d 100755
--- a/egs/librispeech/ASR/transducer_emformer/streaming_decode.py
+++ b/egs/librispeech/ASR/transducer_emformer/streaming_decode.py
@@ -20,14 +20,14 @@ import argparse
 import logging
 import time
 from pathlib import Path
-from typing import List, Optional
 
-import kaldifeat
 import numpy as np
 import sentencepiece as spm
 import torch
 import torch.nn as nn
 from asr_datamodule import LibriSpeechAsrDataModule
+from emformer import LOG_EPSILON
+from streaming_feature_extractor import Stream
 from train import add_model_arguments, get_params, get_transducer_model
 
 from icefall.checkpoint import (
@@ -147,10 +147,10 @@ def get_parser():
     )
 
     parser.add_argument(
-        "--sample-rate",
-        type=int,
+        "--sampling-rate",
+        type=float,
         default=16000,
-        help="The sample rate of the input sound file",
+        help="Sample rate of the audio",
     )
 
     add_model_arguments(parser)
@@ -158,32 +158,159 @@ def get_parser():
     return parser
 
 
-def get_feature_extractor(
-    params: AttributeDict,
-) -> kaldifeat.Fbank:
-    logging.info("Constructing Fbank computer")
-    opts = kaldifeat.FbankOptions()
-    opts.device = params.device
-    opts.frame_opts.dither = 0
-    opts.frame_opts.snip_edges = True
-    opts.frame_opts.samp_freq = params.sample_rate
-    opts.mel_opts.num_bins = params.feature_dim
+def greedy_search(
+    model: nn.Module,
+    stream: Stream,
+    encoder_out: torch.Tensor,
+    sp: spm.SentencePieceProcessor,
+):
+    """
+    Args:
+      model:
+        The RNN-T model.
+      stream:
+        A stream object.
+      encoder_out:
+        A 2-D tensor of shape (T, encoder_out_dim) containing the output of
+        the encoder model.
+      sp:
+        The BPE model.
+    """
+    blank_id = model.decoder.blank_id
+    context_size = model.decoder.context_size
+    device = model.device
 
-    return kaldifeat.Fbank(opts)
+    if stream.decoder_out is None:
+        decoder_input = torch.tensor(
+            [stream.hyp.ys[-context_size:]],
+            device=device,
+            dtype=torch.int64,
+        )
+        stream.decoder_out = model.decoder(
+            decoder_input,
+            need_pad=False,
+        ).unsqueeze(1)
+        # stream.decoder_out is of shape (1, 1, decoder_out_dim)
+
+    assert encoder_out.ndim == 2
+
+    T = encoder_out.size(0)
+    for t in range(T):
+        current_encoder_out = encoder_out[t].reshape(
+            1, 1, 1, encoder_out.size(-1)
+        )
+        logits = model.joiner(current_encoder_out, stream.decoder_out)
+        # logits is of shape (1, 1, 1, vocab_size)
+        y = logits.argmax().item()
+        if y == blank_id:
+            continue
+        stream.hyp.ys.append(y)
+
+        decoder_input = torch.tensor(
+            [stream.hyp.ys[-context_size:]],
+            device=device,
+            dtype=torch.int64,
+        )
+
+        stream.decoder_out = model.decoder(
+            decoder_input,
+            need_pad=False,
+        ).unsqueeze(1)
+
+        logging.info(
+            f"Partial result:\n{sp.decode(stream.hyp.ys[context_size:])}"
+        )
+
+
+def process_feature_frames(
+    model: nn.Module,
+    stream: Stream,
+    sp: spm.SentencePieceProcessor,
+):
+    """Process the feature frames contained in ``stream.feature_frames``.
+    Args:
+      model:
+        The RNN-T model.
+      stream:
+        The stream corresponding to the input audio samples.
+      sp:
+        The BPE model.
+    """
+    # number of frames before subsampling
+    segment_length = model.encoder.segment_length
+
+    right_context_length = model.encoder.right_context_length
+
+    chunk_length = (segment_length + 3) + right_context_length
+
+    device = model.device
+    while len(stream.feature_frames) >= chunk_length:
+        # a list of tensor, each with a shape (1, feature_dim)
+        this_chunk = stream.feature_frames[:chunk_length]
+
+        stream.feature_frames = stream.feature_frames[segment_length:]
+        features = torch.cat(this_chunk, dim=0).to(device)  # (T, feature_dim)
+        features = features.unsqueeze(0)  # (1, T, feature_dim)
+        feature_lens = torch.tensor([features.size(1)], device=device)
+        (
+            encoder_out,
+            encoder_out_lens,
+            stream.states,
+        ) = model.encoder.streaming_forward(
+            features,
+            feature_lens,
+            stream.states,
+        )
+        greedy_search(
+            model=model,
+            stream=stream,
+            encoder_out=encoder_out[0],
+            sp=sp,
+        )
+
+    if stream.feature_extractor.is_last_frame(stream.num_fetched_frames - 1):
+        assert len(stream.feature_frames) < chunk_length
+
+        if len(stream.feature_frames) > 0:
+            this_chunk = stream.feature_frames[:chunk_length]
+            stream.feature_frames = []
+            features = torch.cat(this_chunk, dim=0)  # (T, feature_dim)
+            features = features.to(device).unsqueeze(0)  # (1, T, feature_dim)
+            features = torch.nn.functional.pad(
+                features,
+                (0, 0, 0, chunk_length - features.size(1)),
+                value=LOG_EPSILON,
+            )
+            feature_lens = torch.tensor([features.size(1)], device=device)
+            (
+                encoder_out,
+                encoder_out_lens,
+                stream.states,
+            ) = model.encoder.streaming_forward(
+                features,
+                feature_lens,
+                stream.states,
+            )
+            greedy_search(
+                model=model,
+                stream=stream,
+                encoder_out=encoder_out[0],
+                sp=sp,
+            )
 
 
 def decode_one_utterance(
     audio_samples: torch.Tensor,
     model: nn.Module,
-    fbank: kaldifeat.Fbank,
+    stream: Stream,
     params: AttributeDict,
     sp: spm.SentencePieceProcessor,
 ):
     """Decode one utterance.
     Args:
       audio_samples:
-        A 1-D float32 tensor of shape (num_samples,) containing the normalized
-        audio samples. Normalized means the samples is in the range [-1, 1].
+        A 1-D float32 tensor of shape (num_samples,) containing the
+        audio samples.
       model:
         The RNN-T model.
       feature_extractor:
@@ -193,80 +320,23 @@ def decode_one_utterance(
       sp:
         The BPE model.
     """
-    sample_rate = params.sample_rate
-    frame_shift = sample_rate * fbank.opts.frame_opts.frame_shift_ms / 1000
-
-    frame_shift = int(frame_shift)  # number of samples
-
-    # Note: We add 3 here because the subsampling method ((n-1)//2-1))//2
-    # is not equal to n//4. We will switch to a subsampling method that
-    # satisfies n//4, where n is the number of input frames.
-    segment_length = (params.segment_length + 3) * frame_shift
-
-    right_context_length = params.right_context_length * frame_shift
-    chunk_size = segment_length + right_context_length
-
-    opts = fbank.opts.frame_opts
-    chunk_size += (
-        (opts.frame_length_ms - opts.frame_shift_ms) / 1000 * sample_rate
-    )
-
-    chunk_size = int(chunk_size)
-
-    states: Optional[List[List[torch.Tensor]]] = None
-
-    blank_id = model.decoder.blank_id
-    context_size = model.decoder.context_size
-
-    device = model.device
-
-    hyp = [blank_id] * context_size
-
-    decoder_input = torch.tensor(hyp, device=device, dtype=torch.int64).reshape(
-        1, context_size
-    )
-
-    decoder_out = model.decoder(decoder_input, need_pad=False)
-
     i = 0
     num_samples = audio_samples.size(0)
     while i < num_samples:
-        # Note: The current approach of computing the features is not ideal
-        # since it re-computes the features for the right context.
-        chunk = audio_samples[i : i + chunk_size]  # noqa
-        i += segment_length
-        if chunk.size(0) < chunk_size:
-            chunk = torch.nn.functional.pad(
-                chunk, pad=(0, chunk_size - chunk.size(0))
-            )
-        features = fbank(chunk)
-        feature_lens = torch.tensor([features.size(0)], device=params.device)
+        # Simulate streaming.
+        this_chunk_num_samples = torch.randint(2000, 5000, (1,)).item()
 
-        features = features.unsqueeze(0)  # (1, T, C)
+        thiks_chunk_samples = audio_samples[i : (i + this_chunk_num_samples)]
+        i += this_chunk_num_samples
 
-        encoder_out, encoder_out_lens, states = model.encoder.streaming_forward(
-            features,
-            feature_lens,
-            states,
+        stream.accept_waveform(
+            sampling_rate=params.sampling_rate,
+            waveform=thiks_chunk_samples,
         )
-        for t in range(encoder_out_lens.item()):
-            # fmt: off
-            current_encoder_out = encoder_out[0:1, t:t+1, :].unsqueeze(2)
-            # fmt: on
-            logits = model.joiner(current_encoder_out, decoder_out.unsqueeze(1))
-            # logits is (1, 1, 1, vocab_size)
-            y = logits.argmax().item()
-            if y == blank_id:
-                continue
+        process_feature_frames(model=model, stream=stream, sp=sp)
 
-            hyp.append(y)
-
-            decoder_input = torch.tensor(
-                [hyp[-context_size:]], device=device, dtype=torch.int64
-            ).reshape(1, context_size)
-
-            decoder_out = model.decoder(decoder_input, need_pad=False)
-        logging.info(f"Partial result:\n{sp.decode(hyp[context_size:])}")
+    stream.input_finished()
+    process_feature_frames(model=model, stream=stream, sp=sp)
 
 
 @torch.no_grad()
@@ -333,10 +403,12 @@ def main():
 
     test_clean_cuts = librispeech.test_clean_cuts()
 
-    fbank = get_feature_extractor(params)
-
     for num, cut in enumerate(test_clean_cuts):
-        logging.info("Processing {num}")
+        logging.info(f"Processing {num}")
+        stream = Stream(
+            context_size=model.decoder.context_size,
+            blank_id=model.decoder.blank_id,
+        )
 
         audio: np.ndarray = cut.load_audio()
         # audio.shape: (1, num_samples)
@@ -347,16 +419,17 @@ def main():
         decode_one_utterance(
             audio_samples=torch.from_numpy(audio).squeeze(0).to(device),
             model=model,
-            fbank=fbank,
+            stream=stream,
             params=params,
             sp=sp,
         )
 
         logging.info(f"The ground truth is:\n{cut.supervisions[0].text}")
-        if num >= 0:
+        if num >= 2:
             break
         time.sleep(2)  # So that you can see the decoded results
 
 
 if __name__ == "__main__":
+    torch.manual_seed(20220410)
     main()
diff --git a/egs/librispeech/ASR/transducer_emformer/streaming_feature_extractor.py b/egs/librispeech/ASR/transducer_emformer/streaming_feature_extractor.py
new file mode 100644
index 000000000..90f333694
--- /dev/null
+++ b/egs/librispeech/ASR/transducer_emformer/streaming_feature_extractor.py
@@ -0,0 +1,106 @@
+# Copyright    2022  Xiaomi Corp.        (authors: Fangjun Kuang)
+#
+# 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.
+
+from typing import List, Optional
+
+import torch
+from beam_search import Hypothesis
+from kaldifeat import FbankOptions, OnlineFbank, OnlineFeature
+
+
+def _create_streaming_feature_extractr() -> OnlineFeature:
+    """Create a CPU streaming feature extractor.
+
+    At present, we assume it returns a fbank feature extractor with
+    fixed options. In the future, we will support passing in the options
+    from outside.
+
+    Returns:
+      Return a CPU streaming feature extractor.
+    """
+    opts = FbankOptions()
+    opts.device = "cpu"
+    opts.frame_opts.dither = 0
+    opts.frame_opts.snip_edges = False
+    opts.frame_opts.samp_freq = 16000
+    opts.mel_opts.num_bins = 80
+    return OnlineFbank(opts)
+
+
+class Stream(object):
+    def __init__(self, context_size: int, blank_id: int = 0) -> None:
+        """Context size of the RNN-T decoder model."""
+        self.feature_extractor = _create_streaming_feature_extractr()
+        self.hyp = Hypothesis(
+            ys=([blank_id] * context_size),
+            log_prob=torch.tensor([0.0]),
+        )  # for greedy search, will extend it to beam search
+
+        # It contains a list of 1-D tensors representing the feature frames.
+        self.feature_frames: List[torch.Tensor] = []
+
+        self.num_fetched_frames = 0
+
+        # For the emformer model, it contains the states of each
+        # encoder layer.
+        self.states: Optional[List[List[torch.Tensor]]] = None
+
+        # For the RNN-T decoder, it contains the decoder output
+        # corresponding to the decoder input self.hyp.ys[-context_size:]
+        self.decoder_out: Optional[torch.Tensor] = None
+
+    def accept_waveform(
+        self,
+        sampling_rate: float,
+        waveform: torch.Tensor,
+    ) -> None:
+        """Feed audio samples to the feature extractor and compute features
+        if there are enough samples available.
+
+        Caution:
+          The range of the audio samples should match the one used in the
+          training. That is, if you use the range [-1, 1] in the training, then
+          the input audio samples should also be normalized to [-1, 1].
+
+        Args
+          sampling_rate:
+            The sampling rate of the input audio samples. It is used for sanity
+            check to ensure that the input sampling rate equals to the one
+            used in the extractor. If they are not equal, then no resampling
+            will be performed; instead an error will be thrown.
+        waveform:
+          A 1-D torch tensor of dtype torch.float32 containing audio samples.
+          It should be on CPU.
+        """
+        self.feature_extractor.accept_waveform(
+            sampling_rate=sampling_rate,
+            waveform=waveform,
+        )
+        self._fetch_frames()
+
+    def input_finished(self) -> None:
+        """Signal that no more audio samples available and the feature
+        extractor should flush the buffered samples to compute frames.
+        """
+        self.feature_extractor.input_finished()
+        self._fetch_frames()
+
+    def _fetch_frames(self) -> None:
+        """Fetch frames from the feature extractor"""
+        while self.num_fetched_frames < self.feature_extractor.num_frames_ready:
+            frame = self.feature_extractor.get_frame(self.num_fetched_frames)
+            self.feature_frames.append(frame)
+            self.num_fetched_frames += 1
diff --git a/egs/librispeech/ASR/transducer_emformer/test_streaming_feature_extractor.py b/egs/librispeech/ASR/transducer_emformer/test_streaming_feature_extractor.py
new file mode 100755
index 000000000..502668e83
--- /dev/null
+++ b/egs/librispeech/ASR/transducer_emformer/test_streaming_feature_extractor.py
@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+# Copyright    2022  Xiaomi Corp.        (authors: Fangjun Kuang)
+#
+# 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.
+
+
+"""
+To run this file, do:
+
+    cd icefall/egs/librispeech/ASR
+    python ./transducer_emformer/test_streaming_feature_extractor.py
+"""
+
+import torch
+from streaming_feature_extractor import Stream
+
+
+def test_streaming_feature_extractor():
+    stream = Stream(context_size=2, blank_id=0)
+    samples = torch.rand(16000)
+    start = 0
+    while True:
+        n = torch.randint(50, 500, (1,)).item()
+        end = start + n
+        this_chunk = samples[start:end]
+        start = end
+
+        if len(this_chunk) == 0:
+            break
+        stream.accept_waveform(sampling_rate=16000, waveform=this_chunk)
+        print(len(stream.feature_frames))
+    stream.input_finished()
+    print(len(stream.feature_frames))
+
+
+def main():
+    test_streaming_feature_extractor()
+
+
+if __name__ == "__main__":
+    main()