diff --git a/speechx/speechx/codelab/decoder_test/offline_decoder_main.cc b/speechx/speechx/codelab/decoder_test/offline_decoder_main.cc
new file mode 100644
index 0000000000000000000000000000000000000000..1d7b09df8d26db6d28f2252812f1333fd286fc6c
--- /dev/null
+++ b/speechx/speechx/codelab/decoder_test/offline_decoder_main.cc
@@ -0,0 +1,58 @@
+// todo refactor, repalce with gtest
+
+#include "decoder/ctc_beam_search_decoder.h"
+#include "kaldi/util/table-types.h"
+#include "base/log.h"
+#include "base/flags.h"
+
+DEFINE_string(feature_respecifier, "", "test nnet prob");
+
+using kaldi::BaseFloat;
+
+void SplitFeature(kaldi::Matrix<BaseFloat> feature, 
+                  int32 chunk_size,
+                  std::vector<kaldi::Matrix<BaseFloat>> feature_chunks) {
+
+}
+
+int main(int argc, char* argv[]) {
+  gflags::ParseCommandLineFlags(&argc, &argv, false);
+  google::InitGoogleLogging(argv[0]);
+  
+  kaldi::SequentialBaseFloatMatrixReader feature_reader(FLAGS_feature_respecifier);
+
+  // test nnet_output --> decoder result
+  int32 num_done = 0, num_err = 0;
+  
+  CTCBeamSearchOptions opts;
+  CTCBeamSearch decoder(opts);
+  
+  ModelOptions model_opts;
+  std::shared_ptr<PaddleNnet> nnet(new PaddleNnet(model_opts));
+
+  Decodable decodable();
+  decodable.SetNnet(nnet);
+
+  int32 chunk_size = 0;
+  for (; !feature_reader.Done(); feature_reader.Next()) {
+    string utt = feature_reader.Key();
+    const kaldi::Matrix<BaseFloat> feature = feature_reader.Value();
+    vector<Matrix<BaseFloat>> feature_chunks;
+    SplitFeature(feature, chunk_size, &feature_chunks);  
+    for (auto feature_chunk : feature_chunks) {
+      decodable.FeedFeatures(feature_chunk);
+      decoder.InitDecoder();
+      decoder.AdvanceDecode(decodable, chunk_size);
+    }
+    decodable.InputFinished();
+    std::string result;
+    result = decoder.GetFinalBestPath();
+    KALDI_LOG << " the result of " << utt << " is " << result;
+    decodable.Reset();
+    ++num_done;
+  }
+
+  KALDI_LOG << "Done " << num_done << " utterances, " << num_err
+            << " with errors.";
+  return (num_done != 0 ? 0 : 1);
+}
\ No newline at end of file
diff --git a/speechx/speechx/decoder/ctc_beam_search_decoder.cc b/speechx/speechx/decoder/ctc_beam_search_decoder.cc
index dc21dcb47951f77502c711deec4701bf84d4d8ab..d4407b535c45b41b107c2d3efd7bbcc14745eee1 100644
--- a/speechx/speechx/decoder/ctc_beam_search_decoder.cc
+++ b/speechx/speechx/decoder/ctc_beam_search_decoder.cc
@@ -14,22 +14,28 @@ CTCBeamSearch::CTCBeamSearch(std::shared_ptr<CTCBeamSearchOptions> opts) :
     init_ext_scorer_(nullptr), 
     blank_id(-1),
     space_id(-1),
+    num_frame_decoded(0),
     root(nullptr) {
 
-    LOG(INFO) << "dict path: " << _opts.dict_file;
+    LOG(INFO) << "dict path: " << opts_.dict_file;
     vocabulary_ = std::make_shared<vector<string>>();
-    if (!basr::ReadDictToVector(_opts.dict_file, *vocabulary_)) {
+    if (!basr::ReadDictToVector(opts_.dict_file, *vocabulary_)) {
         LOG(INFO) << "load the dict failed";
     }
     LOG(INFO) << "read the vocabulary success, dict size: " << vocabulary_->size();
 
-    LOG(INFO) << "language model path: " << _opts.lm_path;
-    init_ext_scorer_ = std::make_shared<Scorer>(_opts.alpha, 
-                                                _opts.beta, 
-                                                _opts.lm_path, 
+    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;
@@ -41,7 +47,7 @@ void CTCBeamSearch::InitDecoder() {
         space_id = -2;
     }  
 
-    clear_prefixes();
+    ResetPrefixes();
     
     root = std::make_shared<PathTrie>();
     root->score = root->log_prob_b_prev = 0.0;
@@ -57,6 +63,23 @@ void CTCBeamSearch::InitDecoder() {
     }
 }
 
+int32 CTCBeamSearch::NumFrameDecoded() {
+  return num_frame_decoded_;
+}
+
+// todo rename, refactor
+void CTCBeamSearch::AdvanceDecode(const std::shared_ptr<kaldi::DecodableInterface>& decodable, int max_frames) {
+    while (max_frames > 0) {
+      vector<vector<BaseFloat>> likelihood;
+      if (decodable->IsLastFrame(NumFrameDecoded() + 1)) {
+        break;
+      }
+      likelihood.push_back(decodable->FrameLogLikelihood(NumFrameDecoded() + 1));
+      AdvanceDecoding(result);
+      max_frames--;
+    }
+}
+
 void CTCBeamSearch::ResetPrefixes() {
   for (size_t i = 0; i < prefixes.size(); i++) {
     if (prefixes[i] != nullptr) {
@@ -81,19 +104,32 @@ int CTCBeamSearch::DecodeLikelihoods(const vector<vector<float>>&probs,
   }
 
   timer.Reset();
-  vector<std::pair<double, string>> results = AdvanceDecoding(double_probs);
+  AdvanceDecoding(double_probs);
   LOG(INFO) <<"ctc decoding elapsed time(s) " << static_cast<float>(timer.Elapsed()) / 1000.0f;
-  for (const auto& item : results) {
-    nbest_words.push_back(item.second);
-  }
   return 0;
 } 
 
-vector<std::pair<double, string>> CTCBeamSearch::AdvanceDecoding(const vector<vector<double>>& probs_seq) {
+vector<std::pair<double, string>> CTCBeamSearch::GetNBestPath() {
+  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);
+  return result[0]->second;
+}
+
+string CTCBeamSearch::GetFinalBestPath() {
+  CalculateApproxScore();
+  LMRescore();
+  return GetBestPath();
+}
+
+void CTCBeamSearch::AdvanceDecoding(const vector<vector<double>>& probs_seq) {
   size_t num_time_steps = probs_seq.size();
-  size_t beam_size = _opts.beam_size;
-  double cutoff_prob = _opts.cutoff_prob;
-  size_t cutoff_top_n = _opts.cutoff_top_n;
+  size_t beam_size = opts_.beam_size;
+  double cutoff_prob = opts_.cutoff_prob;
+  size_t cutoff_top_n = opts_.cutoff_top_n;
     
   for (size_t time_step = 0; time_step < num_time_steps; time_step++) {
     const auto& prob = probs_seq[time_step];
@@ -137,18 +173,14 @@ vector<std::pair<double, string>> CTCBeamSearch::AdvanceDecoding(const vector<ve
         prefixes[i]->remove();
       }
     } // if 
+    num_frame_decoded_++;
   } // for probs_seq
-
-  // score the last word of each prefix that doesn't end with space
-  LMRescore();
-  CalculateApproxScore();
-  return get_beam_search_result(prefixes, *vocabulary_, beam_size);
 }
 
 int CTCBeamSearch::SearchOneChar(const bool& full_beam,
                                  const std::pair<size_t, float>& log_prob_idx,
                                  const float& min_cutoff) {
-  size_t beam_size = _opts.beam_size;
+  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);
@@ -219,7 +251,7 @@ int CTCBeamSearch::SearchOneChar(const bool& full_beam,
 }
 
 void CTCBeamSearch::CalculateApproxScore() {
-  size_t beam_size = _opts.beam_size;
+  size_t beam_size = opts_.beam_size;
   size_t num_prefixes = std::min(prefixes.size(), beam_size);
   std::sort(
       prefixes.begin(), 
@@ -246,7 +278,7 @@ void CTCBeamSearch::CalculateApproxScore() {
 }
 
 void CTCBeamSearch::LMRescore() {
-  size_t beam_size = _opts.beam_size;
+  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];
diff --git a/speechx/speechx/decoder/ctc_beam_search_decoder.h b/speechx/speechx/decoder/ctc_beam_search_decoder.h
index 5bf388d3a8a19210d22e8301e3aa3d0582447efa..b461db8888bf4722a0287ab7682f7d43b87d2412 100644
--- a/speechx/speechx/decoder/ctc_beam_search_decoder.h
+++ b/speechx/speechx/decoder/ctc_beam_search_decoder.h
@@ -1,4 +1,5 @@
 #include "base/basic_types.h"
+#include "nnet/decodable-itf.h"
 
 #pragma once
 
@@ -44,12 +45,14 @@ public:
     ~CTCBeamSearch() {
     }
     bool InitDecoder();
+    void Decode(std::shared_ptr<kaldi::DecodableInterface> decodable);
+    std::string GetBestPath(); 
+    std::vector<std::pair<double, std::string>> GetNBestPath(); 
+    std::string GetFinalBestPath(); 
+    int NumFrameDecoded();
     int DecodeLikelihoods(const std::vector<std::vector<BaseFloat>>&probs, 
                           std::vector<std::string>& nbest_words);
-
-    std::vector<DecodeResult>& GetDecodeResult() {
-        return decoder_results_;
-    }
+    void Reset();
 
 private:
   void ResetPrefixes();
@@ -58,17 +61,18 @@ private:
                       const BaseFloat& min_cutoff);
   void CalculateApproxScore();
   void LMRescore();
-  std::vector<std::pair<double, std::string>> 
-    AdvanceDecoding(const std::vector<std::vector<double>>& probs_seq);
+  void AdvanceDecoding(const std::vector<std::vector<double>>& probs_seq);
+  
   CTCBeamSearchOptions opts_;
   std::shared_ptr<Scorer> init_ext_scorer_; // todo separate later
-  std::vector<DecodeResult> decoder_results_;
+  //std::vector<DecodeResult> decoder_results_;
   std::vector<std::vector<std::string>> vocabulary_; // todo remove later
 
   size_t blank_id;        
   int space_id;
   std::shared_ptr<PathTrie> root;
   std::vector<PathTrie*> prefixes;
+  int num_frame_decoded_;
 };
 
 } // namespace basr
\ No newline at end of file
diff --git a/speechx/speechx/nnet/ctc_decodable.h b/speechx/speechx/nnet/ctc_decodable.h
deleted file mode 100644
index e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..0000000000000000000000000000000000000000
diff --git a/speechx/speechx/nnet/decodable.cc b/speechx/speechx/nnet/decodable.cc
new file mode 100644
index 0000000000000000000000000000000000000000..6c03b4a4097a786b650ea71e62f1caf214fcb635
--- /dev/null
+++ b/speechx/speechx/nnet/decodable.cc
@@ -0,0 +1,38 @@
+#include "nnet/decodable.h"
+
+namespace ppspeech {
+
+Decodable::Acceptlikelihood(const kaldi::Matrix<BaseFloat>& likelihood) {
+  frames_ready_ += likelihood.NumRows();
+}
+
+Decodable::Init(DecodableConfig config) {
+
+}
+
+Decodable::IsLastFrame(int32 frame) const {
+  CHECK_LE(frame, frames_ready_);
+  return finished_ && (frame == frames_ready_ - 1);
+}
+
+int32 Decodable::NumIndices() const {
+  return 0;
+}
+
+void Decodable::LogLikelihood(int32 frame, int32 index) {
+  return ;
+}
+
+void Decodable::FeedFeatures(const kaldi::Matrix<kaldi::BaseFloat>& features) {
+  // skip frame ???
+  nnet_->FeedForward(features, &nnet_cache_); 
+  frames_ready_ += nnet_cache_.NumRows(); 
+  return ;
+}
+
+void Decodable::Reset() {
+  // frontend_.Reset();
+  nnet_->Reset();
+}
+
+} // namespace ppspeech
diff --git a/speechx/speechx/nnet/decodable.h b/speechx/speechx/nnet/decodable.h
index eb7ac20a205912ab133ad93eb3a30a3688bde4a6..0bf28d9427a49af6f37133fb3e0f7c97bbdfb196 100644
--- a/speechx/speechx/nnet/decodable.h
+++ b/speechx/speechx/nnet/decodable.h
@@ -2,17 +2,27 @@
 
 #include "base/common.h"
 
-namespace ppsepeech {
-  struct DecodeableConfig;
+namespace ppspeech {
 
-  class Decodeable : public kaldi::DecodableInterface {
-    public: 
-      virtual Init(Decodeable config) = 0;
-      virtual Acceptlikeihood() = 0;
-    private:
-      std::share_ptr<FeatureExtractorInterface> frontend_;
-      std::share_ptr<NnetInterface> nnet_;
-      //Cache nnet_cache_;
-  }
+struct DecodableConfig;
+
+class Decodable : public kaldi::DecodableInterface {
+  public: 
+    virtual void Init(DecodableOpts config);
+    virtual kaldi::BaseFloat LogLikelihood(int32 frame, int32 index);
+    virtual bool IsLastFrame(int32 frame) const;
+    virtual int32 NumIndices() const;
+    void Acceptlikelihood(const kaldi::Matrix<kaldi::BaseFloat>& likelihood); // remove later
+    void FeedFeatures(const kaldi::Matrix<kaldi::BaseFloat>& feature); // only for test, todo remove later
+    std::vector<BaseFloat> FrameLogLikelihood(int32 frame);
+    void Reset();
+    void InputFinished() { finished_ = true; }
+  private:
+    std::shared_ptr<FeatureExtractorInterface> frontend_;
+    std::shared_ptr<NnetInterface> nnet_;
+    kaldi::Matrix<kaldi::BaseFloat> nnet_cache_;
+    bool finished_;
+    int32 frames_ready_;
+};
 
 }  // namespace ppspeech
\ No newline at end of file
diff --git a/speechx/speechx/nnet/dnn_decodable.h b/speechx/speechx/nnet/dnn_decodable.h
deleted file mode 100644
index e69de29bb2d1d6434b8b29ae775ad8c2e48c5391..0000000000000000000000000000000000000000
diff --git a/speechx/speechx/nnet/nnet_interface.h b/speechx/speechx/nnet/nnet_interface.h
index c47f38094dcf18e441e1a65a396d56a512305cdf..5965f7e8b4eed7df6bbc7a90f252dde971c8c719 100644
--- a/speechx/speechx/nnet/nnet_interface.h
+++ b/speechx/speechx/nnet/nnet_interface.h
@@ -9,8 +9,9 @@ namespace ppspeech {
 class NnetInterface {
   public:
     virtual ~NnetInterface() {}
-    virtual void FeedForward(const kaldi::Matrix<BaseFloat>& features, 
-                             kaldi::Matrix<kaldi::BaseFloat>* inferences) const = 0;
+    virtual void FeedForward(const kaldi::Matrix<BaseFloat>& features,
+                             kaldi::Matrix<kaldi::BaseFloat>* inferences); 
+    virtual void Reset();
 
 };
 
diff --git a/speechx/speechx/nnet/paddle_nnet.cc b/speechx/speechx/nnet/paddle_nnet.cc
index d6f826194061cc7553ad1833674b5f680b131be1..e64850cb0095e103628dbb7ff216b289ddf79d3f 100644
--- a/speechx/speechx/nnet/paddle_nnet.cc
+++ b/speechx/speechx/nnet/paddle_nnet.cc
@@ -3,7 +3,7 @@
 
 namespace ppspeech {
 
-void PaddleNnet::init_cache_encouts(const ModelOptions& opts) {
+void PaddleNnet::InitCacheEncouts(const ModelOptions& opts) {
   std::vector<std::string> cache_names;
   cache_names = absl::StrSplit(opts.cache_names, ", ");
   std::vector<std::string> cache_shapes;
@@ -66,7 +66,7 @@ PaddleNet::PaddleNnet(const ModelOptions& opts) {
     }
     release_predictor(predictor);
 
-    init_cache_encouts(opts);
+    InitCacheEncouts(opts);
 }
 
 paddle_infer::Predictor* PaddleNnet::get_predictor() {
diff --git a/speechx/speechx/nnet/paddle_nnet.h b/speechx/speechx/nnet/paddle_nnet.h
index 1b3cad978a2055be99c4496e71b035a0423276d9..7f34eeafb1b6ec087216450c8c98c102bb27de88 100644
--- a/speechx/speechx/nnet/paddle_nnet.h
+++ b/speechx/speechx/nnet/paddle_nnet.h
@@ -94,7 +94,7 @@ class PaddleNnet : public NnetInterface {
     virtual void FeedForward(const kaldi::Matrix<BaseFloat>& features, 
                              kaldi::Matrix<kaldi::BaseFloat>* inferences) const;
     std::shared_ptr<Tensor<kaldi::BaseFloat>> GetCacheEncoder(const std::string& name);
-    void init_cache_encouts(const ModelOptions& opts); 
+    void InitCacheEncouts(const ModelOptions& opts); 
     
   private:
     std::unique_ptr<paddle_infer::services::PredictorPool> pool;