diff --git a/speechx/examples/decoder/offline_decoder_main.cc b/speechx/examples/decoder/offline_decoder_main.cc
index cffca39a..44127c73 100644
--- a/speechx/examples/decoder/offline_decoder_main.cc
+++ b/speechx/examples/decoder/offline_decoder_main.cc
@@ -63,6 +63,7 @@ int main(int argc, char* argv[]) {
 
     int32 chunk_size = 35;
     decoder.InitDecoder();
+
     for (; !feature_reader.Done(); feature_reader.Next()) {
         string utt = feature_reader.Key();
         const kaldi::Matrix<BaseFloat> feature = feature_reader.Value();
@@ -90,6 +91,7 @@ int main(int argc, char* argv[]) {
         result = decoder.GetFinalBestPath();
         KALDI_LOG << " the result of " << utt << " is " << result;
         decodable->Reset();
+        decoder.Reset();
         ++num_done;
     }
 
diff --git a/speechx/speechx/decoder/ctc_beam_search_decoder.cc b/speechx/speechx/decoder/ctc_beam_search_decoder.cc
index 8106b710..7bbb9506 100644
--- a/speechx/speechx/decoder/ctc_beam_search_decoder.cc
+++ b/speechx/speechx/decoder/ctc_beam_search_decoder.cc
@@ -26,10 +26,10 @@ using FSTMATCH = fst::SortedMatcher<fst::StdVectorFst>;
 CTCBeamSearch::CTCBeamSearch(const CTCBeamSearchOptions& opts)
     : opts_(opts),
       init_ext_scorer_(nullptr),
-      blank_id(-1),
-      space_id(-1),
+      blank_id_(-1),
+      space_id_(-1),
       num_frame_decoded_(0),
-      root(nullptr) {
+      root_(nullptr) {
     LOG(INFO) << "dict path: " << opts_.dict_file;
     if (!ReadFileToVector(opts_.dict_file, &vocabulary_)) {
         LOG(INFO) << "load the dict failed";
@@ -40,37 +40,40 @@ CTCBeamSearch::CTCBeamSearch(const CTCBeamSearchOptions& opts)
     LOG(INFO) << "language model path: " << opts_.lm_path;
     init_ext_scorer_ = std::make_shared<Scorer>(
         opts_.alpha, opts_.beta, opts_.lm_path, vocabulary_);
-}
-
-void CTCBeamSearch::Reset() {
-    num_frame_decoded_ = 0;
-    ResetPrefixes();
-}
 
-void CTCBeamSearch::InitDecoder() {
-    blank_id = 0;
+    blank_id_ = 0;
     auto it = std::find(vocabulary_.begin(), vocabulary_.end(), " ");
 
-    space_id = it - vocabulary_.begin();
+    space_id_ = it - vocabulary_.begin();
     // if no space in vocabulary
-    if ((size_t)space_id >= vocabulary_.size()) {
-        space_id = -2;
+    if ((size_t)space_id_ >= vocabulary_.size()) {
+        space_id_ = -2;
     }
+}
+
+void CTCBeamSearch::Reset() {
+    //num_frame_decoded_ = 0;
+    //ResetPrefixes();
+    InitDecoder();
+}
 
-    ResetPrefixes();
+void CTCBeamSearch::InitDecoder() {
+    num_frame_decoded_ = 0;
+    //ResetPrefixes();
+    prefixes_.clear();
 
-    root = std::make_shared<PathTrie>();
-    root->score = root->log_prob_b_prev = 0.0;
-    prefixes.push_back(root.get());
+    root_ = std::make_shared<PathTrie>();
+    root_->score = root_->log_prob_b_prev = 0.0;
+    prefixes_.push_back(root_.get());
     if (init_ext_scorer_ != nullptr &&
         !init_ext_scorer_->is_character_based()) {
         auto fst_dict =
             static_cast<fst::StdVectorFst*>(init_ext_scorer_->dictionary);
         fst::StdVectorFst* dict_ptr = fst_dict->Copy(true);
-        root->set_dictionary(dict_ptr);
+        root_->set_dictionary(dict_ptr);
 
         auto matcher = std::make_shared<FSTMATCH>(*dict_ptr, fst::MATCH_INPUT);
-        root->set_matcher(matcher);
+        root_->set_matcher(matcher);
     }
 }
 
@@ -96,12 +99,13 @@ void CTCBeamSearch::AdvanceDecode(
 }
 
 void CTCBeamSearch::ResetPrefixes() {
-    for (size_t i = 0; i < prefixes.size(); i++) {
-        if (prefixes[i] != nullptr) {
-            delete prefixes[i];
-            prefixes[i] = nullptr;
+    for (size_t i = 0; i < prefixes_.size(); i++) {
+        if (prefixes_[i] != nullptr) {
+            delete prefixes_[i];
+            prefixes_[i] = nullptr;
         }
     }
+    prefixes_.clear();
 }
 
 int CTCBeamSearch::DecodeLikelihoods(const vector<vector<float>>& probs,
@@ -115,12 +119,12 @@ int CTCBeamSearch::DecodeLikelihoods(const vector<vector<float>>& probs,
 }
 
 vector<std::pair<double, string>> CTCBeamSearch::GetNBestPath() {
-    return get_beam_search_result(prefixes, vocabulary_, opts_.beam_size);
+    return get_beam_search_result(prefixes_, vocabulary_, opts_.beam_size);
 }
 
 string CTCBeamSearch::GetBestPath() {
     std::vector<std::pair<double, std::string>> result;
-    result = get_beam_search_result(prefixes, vocabulary_, opts_.beam_size);
+    result = get_beam_search_result(prefixes_, vocabulary_, opts_.beam_size);
     return result[0].second;
 }
 
@@ -153,19 +157,19 @@ void CTCBeamSearch::AdvanceDecoding(const vector<vector<BaseFloat>>& probs) {
         float min_cutoff = -NUM_FLT_INF;
         bool full_beam = false;
         if (init_ext_scorer_ != nullptr) {
-            size_t num_prefixes = std::min(prefixes.size(), beam_size);
-            std::sort(prefixes.begin(),
-                      prefixes.begin() + num_prefixes,
+            size_t num_prefixes_ = std::min(prefixes_.size(), beam_size);
+            std::sort(prefixes_.begin(),
+                      prefixes_.begin() + num_prefixes_,
                       prefix_compare);
 
-            if (num_prefixes == 0) {
+            if (num_prefixes_ == 0) {
                 continue;
             }
-            min_cutoff = prefixes[num_prefixes - 1]->score +
-                         std::log(prob[blank_id]) -
+            min_cutoff = prefixes_[num_prefixes_ - 1]->score +
+                         std::log(prob[blank_id_]) -
                          std::max(0.0, init_ext_scorer_->beta);
 
-            full_beam = (num_prefixes == beam_size);
+            full_beam = (num_prefixes_ == beam_size);
         }
 
         vector<std::pair<size_t, float>> log_prob_idx =
@@ -177,18 +181,18 @@ void CTCBeamSearch::AdvanceDecoding(const vector<vector<BaseFloat>>& probs) {
             SearchOneChar(full_beam, log_prob_idx[index], min_cutoff);
         }
 
-        prefixes.clear();
+        prefixes_.clear();
 
         // update log probs
-        root->iterate_to_vec(prefixes);
-        // only preserve top beam_size prefixes
-        if (prefixes.size() >= beam_size) {
-            std::nth_element(prefixes.begin(),
-                             prefixes.begin() + beam_size,
-                             prefixes.end(),
+        root_->iterate_to_vec(prefixes_);
+        // only preserve top beam_size prefixes_
+        if (prefixes_.size() >= beam_size) {
+            std::nth_element(prefixes_.begin(),
+                             prefixes_.begin() + beam_size,
+                             prefixes_.end(),
                              prefix_compare);
-            for (size_t i = beam_size; i < prefixes.size(); ++i) {
-                prefixes[i]->remove();
+            for (size_t i = beam_size; i < prefixes_.size(); ++i) {
+                prefixes_[i]->remove();
             }
         }  // if
         num_frame_decoded_++;
@@ -202,15 +206,15 @@ int32 CTCBeamSearch::SearchOneChar(
     size_t beam_size = opts_.beam_size;
     const auto& c = log_prob_idx.first;
     const auto& log_prob_c = log_prob_idx.second;
-    size_t prefixes_len = std::min(prefixes.size(), beam_size);
+    size_t prefixes__len = std::min(prefixes_.size(), beam_size);
 
-    for (size_t i = 0; i < prefixes_len; ++i) {
-        auto prefix = prefixes[i];
+    for (size_t i = 0; i < prefixes__len; ++i) {
+        auto prefix = prefixes_[i];
         if (full_beam && log_prob_c + prefix->score < min_cutoff) {
             break;
         }
 
-        if (c == blank_id) {
+        if (c == blank_id_) {
             prefix->log_prob_b_cur =
                 log_sum_exp(prefix->log_prob_b_cur, log_prob_c + prefix->score);
             continue;
@@ -238,7 +242,7 @@ int32 CTCBeamSearch::SearchOneChar(
 
             // language model scoring
             if (init_ext_scorer_ != nullptr &&
-                (c == space_id || init_ext_scorer_->is_character_based())) {
+                (c == space_id_ || init_ext_scorer_->is_character_based())) {
                 PathTrie* prefix_to_score = nullptr;
                 // skip scoring the space
                 if (init_ext_scorer_->is_character_based()) {
@@ -266,17 +270,17 @@ int32 CTCBeamSearch::SearchOneChar(
 
 void CTCBeamSearch::CalculateApproxScore() {
     size_t beam_size = opts_.beam_size;
-    size_t num_prefixes = std::min(prefixes.size(), beam_size);
+    size_t num_prefixes_ = std::min(prefixes_.size(), beam_size);
     std::sort(
-        prefixes.begin(), prefixes.begin() + num_prefixes, prefix_compare);
+        prefixes_.begin(), prefixes_.begin() + num_prefixes_, prefix_compare);
 
     // compute aproximate ctc score as the return score, without affecting the
     // return order of decoding result. To delete when decoder gets stable.
-    for (size_t i = 0; i < beam_size && i < prefixes.size(); ++i) {
-        double approx_ctc = prefixes[i]->score;
+    for (size_t i = 0; i < beam_size && i < prefixes_.size(); ++i) {
+        double approx_ctc = prefixes_[i]->score;
         if (init_ext_scorer_ != nullptr) {
             vector<int> output;
-            prefixes[i]->get_path_vec(output);
+            prefixes_[i]->get_path_vec(output);
             auto prefix_length = output.size();
             auto words = init_ext_scorer_->split_labels(output);
             // remove word insert
@@ -285,7 +289,7 @@ void CTCBeamSearch::CalculateApproxScore() {
             approx_ctc -= (init_ext_scorer_->get_sent_log_prob(words)) *
                           init_ext_scorer_->alpha;
         }
-        prefixes[i]->approx_ctc = approx_ctc;
+        prefixes_[i]->approx_ctc = approx_ctc;
     }
 }
 
@@ -293,9 +297,9 @@ void CTCBeamSearch::LMRescore() {
     size_t beam_size = opts_.beam_size;
     if (init_ext_scorer_ != nullptr &&
         !init_ext_scorer_->is_character_based()) {
-        for (size_t i = 0; i < beam_size && i < prefixes.size(); ++i) {
-            auto prefix = prefixes[i];
-            if (!prefix->is_empty() && prefix->character != space_id) {
+        for (size_t i = 0; i < beam_size && i < prefixes_.size(); ++i) {
+            auto prefix = prefixes_[i];
+            if (!prefix->is_empty() && prefix->character != space_id_) {
                 float score = 0.0;
                 vector<string> ngram = init_ext_scorer_->make_ngram(prefix);
                 score = init_ext_scorer_->get_log_cond_prob(ngram) *
diff --git a/speechx/speechx/decoder/ctc_beam_search_decoder.h b/speechx/speechx/decoder/ctc_beam_search_decoder.h
index 53700e27..451f33c0 100644
--- a/speechx/speechx/decoder/ctc_beam_search_decoder.h
+++ b/speechx/speechx/decoder/ctc_beam_search_decoder.h
@@ -83,10 +83,10 @@ class CTCBeamSearch {
     CTCBeamSearchOptions opts_;
     std::shared_ptr<Scorer> init_ext_scorer_;  // todo separate later
     std::vector<std::string> vocabulary_;      // todo remove later
-    size_t blank_id;
-    int space_id;
-    std::shared_ptr<PathTrie> root;
-    std::vector<PathTrie*> prefixes;
+    size_t blank_id_;
+    int space_id_;
+    std::shared_ptr<PathTrie> root_;
+    std::vector<PathTrie*> prefixes_;
     int num_frame_decoded_;
     DISALLOW_COPY_AND_ASSIGN(CTCBeamSearch);
 };
diff --git a/speechx/speechx/frontend/feature_cache.h b/speechx/speechx/frontend/feature_cache.h
index 03b11f57..459134ee 100644
--- a/speechx/speechx/frontend/feature_cache.h
+++ b/speechx/speechx/frontend/feature_cache.h
@@ -36,18 +36,23 @@ class FeatureCache : public FeatureExtractorInterface {
         Compute();
     }
     virtual bool IsFinished() const { return base_extractor_->IsFinished(); }
+    virtual void Reset() {
+        base_extractor_->Reset();
+        while (!cache_.empty()) {
+            cache_.pop();
+        }
+    }
 
   private:
     bool Compute();
 
-    bool finished_;
     std::mutex mutex_;
     size_t max_size_;
     std::queue<kaldi::Vector<BaseFloat>> cache_;
     std::unique_ptr<FeatureExtractorInterface> base_extractor_;
     std::condition_variable ready_feed_condition_;
     std::condition_variable ready_read_condition_;
-    //DISALLOW_COPY_AND_ASSGIN(FeatureCache);
+    // DISALLOW_COPY_AND_ASSGIN(FeatureCache);
 };
 
 }  // namespace ppspeech
diff --git a/speechx/speechx/frontend/feature_extractor_interface.h b/speechx/speechx/frontend/feature_extractor_interface.h
index 64cc67f3..cb6fec1b 100644
--- a/speechx/speechx/frontend/feature_extractor_interface.h
+++ b/speechx/speechx/frontend/feature_extractor_interface.h
@@ -33,7 +33,7 @@ class FeatureExtractorInterface {
     virtual size_t Dim() const = 0;
     virtual void SetFinished() = 0;
     virtual bool IsFinished() const = 0;
-    // virtual void Reset();
+    virtual void Reset() = 0;
 };
 
 }  // namespace ppspeech
diff --git a/speechx/speechx/frontend/linear_spectrogram.cc b/speechx/speechx/frontend/linear_spectrogram.cc
index 7491716c..b8a18e02 100644
--- a/speechx/speechx/frontend/linear_spectrogram.cc
+++ b/speechx/speechx/frontend/linear_spectrogram.cc
@@ -25,25 +25,6 @@ using kaldi::VectorBase;
 using kaldi::Matrix;
 using std::vector;
 
-// todo remove later
-void CopyVector2StdVector_(const VectorBase<BaseFloat>& input,
-                           vector<BaseFloat>* output) {
-    if (input.Dim() == 0) return;
-    output->resize(input.Dim());
-    for (size_t idx = 0; idx < input.Dim(); ++idx) {
-        (*output)[idx] = input(idx);
-    }
-}
-
-void CopyStdVector2Vector_(const vector<BaseFloat>& input,
-                           Vector<BaseFloat>* output) {
-    if (input.empty()) return;
-    output->Resize(input.size());
-    for (size_t idx = 0; idx < input.size(); ++idx) {
-        (*output)(idx) = input[idx];
-    }
-}
-
 LinearSpectrogram::LinearSpectrogram(
     const LinearSpectrogramOptions& opts,
     std::unique_ptr<FeatureExtractorInterface> base_extractor) {
@@ -76,7 +57,8 @@ bool LinearSpectrogram::Read(Vector<BaseFloat>* feats) {
     if (flag == false || input_feats.Dim() == 0) return false;
 
     vector<BaseFloat> input_feats_vec(input_feats.Dim());
-    CopyVector2StdVector_(input_feats, &input_feats_vec);
+    std::memcpy(input_feats_vec.data(), input_feats.Data(), 
+        input_feats.Dim()*sizeof(BaseFloat));
     vector<vector<BaseFloat>> result;
     Compute(input_feats_vec, result);
     int32 feat_size = 0;
@@ -103,9 +85,12 @@ bool LinearSpectrogram::NumpyFft(vector<BaseFloat>* v,
                                  vector<BaseFloat>* real,
                                  vector<BaseFloat>* img) const {
     Vector<BaseFloat> v_tmp;
-    CopyStdVector2Vector_(*v, &v_tmp);
+    v_tmp.Resize(v->size());
+    std::memcpy(v_tmp.Data(), v->data(), sizeof(BaseFloat)*(v->size()));
     RealFft(&v_tmp, true);
-    CopyVector2StdVector_(v_tmp, v);
+    v->resize(v_tmp.Dim());
+    std::memcpy(v->data(), v_tmp.Data(), sizeof(BaseFloat)*(v->size()));
+
     real->push_back(v->at(0));
     img->push_back(0);
     for (int i = 1; i < v->size() / 2; i++) {
diff --git a/speechx/speechx/frontend/linear_spectrogram.h b/speechx/speechx/frontend/linear_spectrogram.h
index 790263d9..b2bb414d 100644
--- a/speechx/speechx/frontend/linear_spectrogram.h
+++ b/speechx/speechx/frontend/linear_spectrogram.h
@@ -45,6 +45,9 @@ class LinearSpectrogram : public FeatureExtractorInterface {
     virtual size_t Dim() const { return dim_; }
     virtual void SetFinished() { base_extractor_->SetFinished(); }
     virtual bool IsFinished() const { return base_extractor_->IsFinished(); }
+    virtual void Reset() {
+        base_extractor_->Reset();
+    }
 
   private:
     void Hanning(std::vector<kaldi::BaseFloat>* data) const;
diff --git a/speechx/speechx/frontend/normalizer.cc b/speechx/speechx/frontend/normalizer.cc
index fbb2b645..285c8e03 100644
--- a/speechx/speechx/frontend/normalizer.cc
+++ b/speechx/speechx/frontend/normalizer.cc
@@ -48,25 +48,6 @@ bool DecibelNormalizer::Read(kaldi::Vector<BaseFloat>* waves) {
     return true;
 }
 
-// todo remove later
-void CopyVector2StdVector(const kaldi::VectorBase<BaseFloat>& input,
-                          vector<BaseFloat>* output) {
-    if (input.Dim() == 0) return;
-    output->resize(input.Dim());
-    for (size_t idx = 0; idx < input.Dim(); ++idx) {
-        (*output)[idx] = input(idx);
-    }
-}
-
-void CopyStdVector2Vector(const vector<BaseFloat>& input,
-                          VectorBase<BaseFloat>* output) {
-    if (input.empty()) return;
-    assert(input.size() == output->Dim());
-    for (size_t idx = 0; idx < input.size(); ++idx) {
-        (*output)(idx) = input[idx];
-    }
-}
-
 bool DecibelNormalizer::Compute(VectorBase<BaseFloat>* waves) const {
     // calculate db rms
     BaseFloat rms_db = 0.0;
@@ -107,7 +88,7 @@ bool DecibelNormalizer::Compute(VectorBase<BaseFloat>* waves) const {
         item *= std::pow(10.0, gain / 20.0);
     }
 
-    CopyStdVector2Vector(samples, waves);
+    std::memcpy(waves->Data(), samples.data(), sizeof(BaseFloat)*samples.size());
     return true;
 }
 
diff --git a/speechx/speechx/frontend/normalizer.h b/speechx/speechx/frontend/normalizer.h
index b9daa853..24542eba 100644
--- a/speechx/speechx/frontend/normalizer.h
+++ b/speechx/speechx/frontend/normalizer.h
@@ -52,6 +52,9 @@ class DecibelNormalizer : public FeatureExtractorInterface {
     virtual size_t Dim() const { return dim_; }
     virtual void SetFinished() { base_extractor_->SetFinished(); }
     virtual bool IsFinished() const { return base_extractor_->IsFinished(); }
+    virtual void Reset() {
+        base_extractor_->Reset();
+    }
 
   private:
     bool Compute(kaldi::VectorBase<kaldi::BaseFloat>* waves) const;
@@ -76,6 +79,9 @@ class CMVN : public FeatureExtractorInterface {
     virtual size_t Dim() const { return dim_; }
     virtual void SetFinished() { base_extractor_->SetFinished(); }
     virtual bool IsFinished() const { return base_extractor_->IsFinished(); }
+    virtual void Reset() {
+        base_extractor_->Reset();
+    }
 
   private:
     void Compute(kaldi::VectorBase<kaldi::BaseFloat>* feats) const;
diff --git a/speechx/speechx/frontend/raw_audio.h b/speechx/speechx/frontend/raw_audio.h
index 1a326b3c..7726f825 100644
--- a/speechx/speechx/frontend/raw_audio.h
+++ b/speechx/speechx/frontend/raw_audio.h
@@ -34,6 +34,11 @@ class RawAudioCache : public FeatureExtractorInterface {
         finished_ = true;
     }
     virtual bool IsFinished() const { return finished_; }
+    virtual void Reset() {
+      start_ = 0;
+      data_length_ = 0;
+      finished_ = false;
+    }
 
   private:
     std::vector<kaldi::BaseFloat> ring_buffer_;
@@ -67,6 +72,9 @@ class RawDataCache : public FeatureExtractorInterface {
     virtual void SetFinished() { finished_ = true; }
     virtual bool IsFinished() const { return finished_; }
     void SetDim(int32 dim) { dim_ = dim; }
+    virtual void Reset() {
+      finished_ = true;
+    }
 
   private:
     kaldi::Vector<kaldi::BaseFloat> data_;
diff --git a/speechx/speechx/nnet/decodable.cc b/speechx/speechx/nnet/decodable.cc
index 79c896aa..3cc07f38 100644
--- a/speechx/speechx/nnet/decodable.cc
+++ b/speechx/speechx/nnet/decodable.cc
@@ -25,7 +25,6 @@ Decodable::Decodable(const std::shared_ptr<NnetInterface>& nnet,
                      const std::shared_ptr<FeatureExtractorInterface>& frontend)
     : frontend_(frontend),
       nnet_(nnet),
-      finished_(false),
       frame_offset_(0),
       frames_ready_(0) {}
 
@@ -81,8 +80,10 @@ bool Decodable::FrameLogLikelihood(int32 frame, vector<BaseFloat>* likelihood) {
 }
 
 void Decodable::Reset() {
-    // frontend_.Reset();
+    frontend_->Reset();
     nnet_->Reset();
+    frame_offset_ = 0;
+    frames_ready_ = 0; 
 }
 
 }  // namespace ppspeech
\ No newline at end of file
diff --git a/speechx/speechx/nnet/decodable.h b/speechx/speechx/nnet/decodable.h
index 72d194b9..7938b582 100644
--- a/speechx/speechx/nnet/decodable.h
+++ b/speechx/speechx/nnet/decodable.h
@@ -45,7 +45,6 @@ class Decodable : public kaldi::DecodableInterface {
     std::shared_ptr<NnetInterface> nnet_;
     kaldi::Matrix<kaldi::BaseFloat> nnet_cache_;
     // std::vector<std::vector<kaldi::BaseFloat>> nnet_cache_;
-    bool finished_;
     int32 frame_offset_;
     int32 frames_ready_;
     // todo: feature frame mismatch with nnet inference frame