Refactor online recognizer (#250)

* Refactor online recognizer.

Make it easier to support other streaming models.

Note that it is a breaking change for the Python API.
`sherpa_onnx.OnlineRecognizer()` used before should be
replaced by `sherpa_onnx.OnlineRecognizer.from_transducer()`.

@@ -205,7 +205,7 @@ def main():
     assert_file_exists(args.joiner)
     assert_file_exists(args.tokens)
 
-    recognizer = sherpa_onnx.OnlineRecognizer(
+    recognizer = sherpa_onnx.OnlineRecognizer.from_transducer(
         tokens=args.tokens,
         encoder=args.encoder,
         decoder=args.decoder,

@@ -91,7 +91,7 @@ def create_recognizer():
     # Please replace the model files if needed.
     # See https://k2-fsa.github.io/sherpa/onnx/pretrained_models/index.html
     # for download links.
-    recognizer = sherpa_onnx.OnlineRecognizer(
+    recognizer = sherpa_onnx.OnlineRecognizer.from_transducer(
         tokens=args.tokens,
         encoder=args.encoder,
         decoder=args.decoder,

@@ -145,7 +145,7 @@ def create_recognizer():
     # Please replace the model files if needed.
     # See https://k2-fsa.github.io/sherpa/onnx/pretrained_models/index.html
     # for download links.
-    recognizer = sherpa_onnx.OnlineRecognizer(
+    recognizer = sherpa_onnx.OnlineRecognizer.from_transducer(
         tokens=args.tokens,
         encoder=args.encoder,
         decoder=args.decoder,

@@ -94,7 +94,7 @@ def create_recognizer(args):
     # Please replace the model files if needed.
     # See https://k2-fsa.github.io/sherpa/onnx/pretrained_models/index.html
     # for download links.
-    recognizer = sherpa_onnx.OnlineRecognizer(
+    recognizer = sherpa_onnx.OnlineRecognizer.from_transducer(
         tokens=args.tokens,
         encoder=args.encoder,
         decoder=args.decoder,

@@ -294,7 +294,7 @@ def get_args():
 
 
 def create_recognizer(args) -> sherpa_onnx.OnlineRecognizer:
-    recognizer = sherpa_onnx.OnlineRecognizer(
+    recognizer = sherpa_onnx.OnlineRecognizer.from_transducer(
         tokens=args.tokens,
         encoder=args.encoder_model,
         decoder=args.decoder_model,

@@ -38,11 +38,11 @@ SherpaOnnxOnlineRecognizer *CreateOnlineRecognizer(
   recognizer_config.feat_config.feature_dim =
       SHERPA_ONNX_OR(config->feat_config.feature_dim, 80);
 
-  recognizer_config.model_config.encoder_filename =
+  recognizer_config.model_config.transducer.encoder =
       SHERPA_ONNX_OR(config->model_config.encoder, "");
-  recognizer_config.model_config.decoder_filename =
+  recognizer_config.model_config.transducer.decoder =
       SHERPA_ONNX_OR(config->model_config.decoder, "");
-  recognizer_config.model_config.joiner_filename =
+  recognizer_config.model_config.transducer.joiner =
       SHERPA_ONNX_OR(config->model_config.joiner, "");
   recognizer_config.model_config.tokens =
       SHERPA_ONNX_OR(config->model_config.tokens, "");
@@ -143,7 +143,7 @@ SherpaOnnxOnlineRecognizerResult *GetOnlineStreamResult(
   auto count = result.tokens.size();
   if (count > 0) {
     size_t total_length = 0;
-    for (const auto& token : result.tokens) {
+    for (const auto &token : result.tokens) {
       // +1 for the null character at the end of each token
       total_length += token.size() + 1;
     }
@@ -154,10 +154,10 @@ SherpaOnnxOnlineRecognizerResult *GetOnlineStreamResult(
     memset(reinterpret_cast<void *>(const_cast<char *>(r->tokens)), 0,
            total_length);
     r->timestamps = new float[r->count];
-    char **tokens_temp = new char*[r->count];
+    char **tokens_temp = new char *[r->count];
     int32_t pos = 0;
     for (int32_t i = 0; i < r->count; ++i) {
-      tokens_temp[i] = const_cast<char*>(r->tokens) + pos;
+      tokens_temp[i] = const_cast<char *>(r->tokens) + pos;
       memcpy(reinterpret_cast<void *>(const_cast<char *>(r->tokens + pos)),
              result.tokens[i].c_str(), result.tokens[i].size());
       // +1 to move past the null character

@@ -43,6 +43,8 @@ set(sources
   online-lm-config.cc
   online-lm.cc
   online-lstm-transducer-model.cc
+  online-model-config.cc
+  online-recognizer-impl.cc
   online-recognizer.cc
   online-rnn-lm.cc
   online-stream.cc

@@ -30,46 +30,46 @@
 namespace sherpa_onnx {
 
 OnlineConformerTransducerModel::OnlineConformerTransducerModel(
-    const OnlineTransducerModelConfig &config)
+    const OnlineModelConfig &config)
     : env_(ORT_LOGGING_LEVEL_WARNING),
       config_(config),
       sess_opts_(GetSessionOptions(config)),
       allocator_{} {
   {
-    auto buf = ReadFile(config.encoder_filename);
+    auto buf = ReadFile(config.transducer.encoder);
     InitEncoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(config.decoder_filename);
+    auto buf = ReadFile(config.transducer.decoder);
     InitDecoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(config.joiner_filename);
+    auto buf = ReadFile(config.transducer.joiner);
     InitJoiner(buf.data(), buf.size());
   }
 }
 
 #if __ANDROID_API__ >= 9
 OnlineConformerTransducerModel::OnlineConformerTransducerModel(
-    AAssetManager *mgr, const OnlineTransducerModelConfig &config)
+    AAssetManager *mgr, const OnlineModelConfig &config)
     : env_(ORT_LOGGING_LEVEL_WARNING),
       config_(config),
       sess_opts_(GetSessionOptions(config)),
       allocator_{} {
   {
-    auto buf = ReadFile(mgr, config.encoder_filename);
+    auto buf = ReadFile(mgr, config.transducer.encoder);
     InitEncoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(mgr, config.decoder_filename);
+    auto buf = ReadFile(mgr, config.transducer.decoder);
     InitDecoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(mgr, config.joiner_filename);
+    auto buf = ReadFile(mgr, config.transducer.joiner);
     InitJoiner(buf.data(), buf.size());
   }
 }

@@ -16,19 +16,18 @@
 #endif
 
 #include "onnxruntime_cxx_api.h"  // NOLINT
-#include "sherpa-onnx/csrc/online-transducer-model-config.h"
+#include "sherpa-onnx/csrc/online-model-config.h"
 #include "sherpa-onnx/csrc/online-transducer-model.h"
 
 namespace sherpa_onnx {
 
 class OnlineConformerTransducerModel : public OnlineTransducerModel {
  public:
-  explicit OnlineConformerTransducerModel(
-      const OnlineTransducerModelConfig &config);
+  explicit OnlineConformerTransducerModel(const OnlineModelConfig &config);
 
 #if __ANDROID_API__ >= 9
   OnlineConformerTransducerModel(AAssetManager *mgr,
-                                 const OnlineTransducerModelConfig &config);
+                                 const OnlineModelConfig &config);
 #endif
 
   std::vector<Ort::Value> StackStates(
@@ -88,7 +87,7 @@ class OnlineConformerTransducerModel : public OnlineTransducerModel {
   std::vector<std::string> joiner_output_names_;
   std::vector<const char *> joiner_output_names_ptr_;
 
-  OnlineTransducerModelConfig config_;
+  OnlineModelConfig config_;
 
   int32_t num_encoder_layers_ = 0;
   int32_t T_ = 0;

@@ -28,46 +28,46 @@
 namespace sherpa_onnx {
 
 OnlineLstmTransducerModel::OnlineLstmTransducerModel(
-    const OnlineTransducerModelConfig &config)
+    const OnlineModelConfig &config)
     : env_(ORT_LOGGING_LEVEL_WARNING),
       config_(config),
       sess_opts_(GetSessionOptions(config)),
       allocator_{} {
   {
-    auto buf = ReadFile(config.encoder_filename);
+    auto buf = ReadFile(config.transducer.encoder);
     InitEncoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(config.decoder_filename);
+    auto buf = ReadFile(config.transducer.decoder);
     InitDecoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(config.joiner_filename);
+    auto buf = ReadFile(config.transducer.joiner);
     InitJoiner(buf.data(), buf.size());
   }
 }
 
 #if __ANDROID_API__ >= 9
 OnlineLstmTransducerModel::OnlineLstmTransducerModel(
-    AAssetManager *mgr, const OnlineTransducerModelConfig &config)
+    AAssetManager *mgr, const OnlineModelConfig &config)
     : env_(ORT_LOGGING_LEVEL_WARNING),
       config_(config),
       sess_opts_(GetSessionOptions(config)),
       allocator_{} {
   {
-    auto buf = ReadFile(mgr, config.encoder_filename);
+    auto buf = ReadFile(mgr, config.transducer.encoder);
     InitEncoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(mgr, config.decoder_filename);
+    auto buf = ReadFile(mgr, config.transducer.decoder);
     InitDecoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(mgr, config.joiner_filename);
+    auto buf = ReadFile(mgr, config.transducer.joiner);
     InitJoiner(buf.data(), buf.size());
   }
 }

@@ -15,18 +15,18 @@
 #endif
 
 #include "onnxruntime_cxx_api.h"  // NOLINT
-#include "sherpa-onnx/csrc/online-transducer-model-config.h"
+#include "sherpa-onnx/csrc/online-model-config.h"
 #include "sherpa-onnx/csrc/online-transducer-model.h"
 
 namespace sherpa_onnx {
 
 class OnlineLstmTransducerModel : public OnlineTransducerModel {
  public:
-  explicit OnlineLstmTransducerModel(const OnlineTransducerModelConfig &config);
+  explicit OnlineLstmTransducerModel(const OnlineModelConfig &config);
 
 #if __ANDROID_API__ >= 9
   OnlineLstmTransducerModel(AAssetManager *mgr,
-                            const OnlineTransducerModelConfig &config);
+                            const OnlineModelConfig &config);
 #endif
 
   std::vector<Ort::Value> StackStates(
@@ -86,7 +86,7 @@ class OnlineLstmTransducerModel : public OnlineTransducerModel {
   std::vector<std::string> joiner_output_names_;
   std::vector<const char *> joiner_output_names_ptr_;
 
-  OnlineTransducerModelConfig config_;
+  OnlineModelConfig config_;
 
   int32_t num_encoder_layers_ = 0;
   int32_t T_ = 0;

+// sherpa-onnx/csrc/online-model-config.cc
+//
+// Copyright (c)  2023  Xiaomi Corporation
+#include "sherpa-onnx/csrc/online-model-config.h"
+
+#include <string>
+
+#include "sherpa-onnx/csrc/file-utils.h"
+#include "sherpa-onnx/csrc/macros.h"
+
+namespace sherpa_onnx {
+
+void OnlineModelConfig::Register(ParseOptions *po) {
+  transducer.Register(po);
+
+  po->Register("tokens", &tokens, "Path to tokens.txt");
+
+  po->Register("num-threads", &num_threads,
+               "Number of threads to run the neural network");
+
+  po->Register("debug", &debug,
+               "true to print model information while loading it.");
+
+  po->Register("provider", &provider,
+               "Specify a provider to use: cpu, cuda, coreml");
+
+  po->Register("model-type", &model_type,
+               "Specify it to reduce model initialization time. "
+               "Valid values are: conformer, lstm, zipformer, zipformer2."
+               "All other values lead to loading the model twice.");
+}
+
+bool OnlineModelConfig::Validate() const {
+  if (num_threads < 1) {
+    SHERPA_ONNX_LOGE("num_threads should be > 0. Given %d", num_threads);
+    return false;
+  }
+
+  if (!FileExists(tokens)) {
+    SHERPA_ONNX_LOGE("tokens: %s does not exist", tokens.c_str());
+    return false;
+  }
+
+  return transducer.Validate();
+}
+
+std::string OnlineModelConfig::ToString() const {
+  std::ostringstream os;
+
+  os << "OnlineModelConfig(";
+  os << "transducer=" << transducer.ToString() << ", ";
+  os << "tokens=\"" << tokens << "\", ";
+  os << "num_threads=" << num_threads << ", ";
+  os << "debug=" << (debug ? "True" : "False") << ", ";
+  os << "provider=\"" << provider << "\", ";
+  os << "model_type=\"" << model_type << "\")";
+
+  return os.str();
+}
+
+}  // namespace sherpa_onnx

+// sherpa-onnx/csrc/online-model-config.h
+//
+// Copyright (c)  2023  Xiaomi Corporation
+#ifndef SHERPA_ONNX_CSRC_ONLINE_MODEL_CONFIG_H_
+#define SHERPA_ONNX_CSRC_ONLINE_MODEL_CONFIG_H_
+
+#include <string>
+
+#include "sherpa-onnx/csrc/online-transducer-model-config.h"
+
+namespace sherpa_onnx {
+
+struct OnlineModelConfig {
+  OnlineTransducerModelConfig transducer;
+  std::string tokens;
+  int32_t num_threads = 1;
+  bool debug = false;
+  std::string provider = "cpu";
+
+  // Valid values:
+  //  - conformer, conformer transducer from icefall
+  //  - lstm, lstm transducer from icefall
+  //  - zipformer, zipformer transducer from icefall
+  //  - zipformer2, zipformer2 transducer from icefall
+  //
+  // All other values are invalid and lead to loading the model twice.
+  std::string model_type;
+
+  OnlineModelConfig() = default;
+  OnlineModelConfig(const OnlineTransducerModelConfig &transducer,
+                    const std::string &tokens, int32_t num_threads, bool debug,
+                    const std::string &provider, const std::string &model_type)
+      : transducer(transducer),
+        tokens(tokens),
+        num_threads(num_threads),
+        debug(debug),
+        provider(provider),
+        model_type(model_type) {}
+
+  void Register(ParseOptions *po);
+  bool Validate() const;
+
+  std::string ToString() const;
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_ONLINE_MODEL_CONFIG_H_

+// sherpa-onnx/csrc/online-recognizer-impl.cc
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#include "sherpa-onnx/csrc/online-recognizer-impl.h"
+
+#include "sherpa-onnx/csrc/online-recognizer-transducer-impl.h"
+
+namespace sherpa_onnx {
+
+std::unique_ptr<OnlineRecognizerImpl> OnlineRecognizerImpl::Create(
+    const OnlineRecognizerConfig &config) {
+  if (!config.model_config.transducer.encoder.empty()) {
+    return std::make_unique<OnlineRecognizerTransducerImpl>(config);
+  }
+
+  SHERPA_ONNX_LOGE("Please specify a model");
+  exit(-1);
+}
+
+#if __ANDROID_API__ >= 9
+std::unique_ptr<OnlineRecognizerImpl> OnlineRecognizerImpl::Create(
+    AAssetManager *mgr, const OnlineRecognizerConfig &config) {
+  if (!config.model_config.transducer.encoder.empty()) {
+    return std::make_unique<OnlineRecognizerTransducerImpl>(mgr, config);
+  }
+
+  SHERPA_ONNX_LOGE("Please specify a model");
+  exit(-1);
+}
+#endif
+
+}  // namespace sherpa_onnx

+// sherpa-onnx/csrc/online-recognizer-impl.h
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#ifndef SHERPA_ONNX_CSRC_ONLINE_RECOGNIZER_IMPL_H_
+#define SHERPA_ONNX_CSRC_ONLINE_RECOGNIZER_IMPL_H_
+
+#include <memory>
+#include <vector>
+
+#include "sherpa-onnx/csrc/macros.h"
+#include "sherpa-onnx/csrc/online-recognizer.h"
+#include "sherpa-onnx/csrc/online-stream.h"
+
+namespace sherpa_onnx {
+
+class OnlineRecognizerImpl {
+ public:
+  static std::unique_ptr<OnlineRecognizerImpl> Create(
+      const OnlineRecognizerConfig &config);
+
+#if __ANDROID_API__ >= 9
+  static std::unique_ptr<OnlineRecognizerImpl> Create(
+      AAssetManager *mgr, const OnlineRecognizerConfig &config);
+#endif
+
+  virtual ~OnlineRecognizerImpl() = default;
+
+  virtual void InitOnlineStream(OnlineStream *stream) const = 0;
+
+  virtual std::unique_ptr<OnlineStream> CreateStream() const = 0;
+
+  virtual std::unique_ptr<OnlineStream> CreateStream(
+      const std::vector<std::vector<int32_t>> &contexts) const {
+    SHERPA_ONNX_LOGE("Only transducer models support contextual biasing.");
+    exit(-1);
+  }
+
+  virtual bool IsReady(OnlineStream *s) const = 0;
+
+  virtual void DecodeStreams(OnlineStream **ss, int32_t n) const = 0;
+
+  virtual OnlineRecognizerResult GetResult(OnlineStream *s) const = 0;
+
+  virtual bool IsEndpoint(OnlineStream *s) const = 0;
+
+  virtual void Reset(OnlineStream *s) const = 0;
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_ONLINE_RECOGNIZER_IMPL_H_

+// sherpa-onnx/csrc/online-recognizer-transducer-impl.h
+//
+// Copyright (c)  2022-2023  Xiaomi Corporation
+
+#ifndef SHERPA_ONNX_CSRC_ONLINE_RECOGNIZER_TRANSDUCER_IMPL_H_
+#define SHERPA_ONNX_CSRC_ONLINE_RECOGNIZER_TRANSDUCER_IMPL_H_
+
+#include <algorithm>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "sherpa-onnx/csrc/file-utils.h"
+#include "sherpa-onnx/csrc/macros.h"
+#include "sherpa-onnx/csrc/online-lm.h"
+#include "sherpa-onnx/csrc/online-recognizer-impl.h"
+#include "sherpa-onnx/csrc/online-recognizer.h"
+#include "sherpa-onnx/csrc/online-transducer-decoder.h"
+#include "sherpa-onnx/csrc/online-transducer-greedy-search-decoder.h"
+#include "sherpa-onnx/csrc/online-transducer-model.h"
+#include "sherpa-onnx/csrc/online-transducer-modified-beam-search-decoder.h"
+#include "sherpa-onnx/csrc/symbol-table.h"
+
+namespace sherpa_onnx {
+
+static OnlineRecognizerResult Convert(const OnlineTransducerDecoderResult &src,
+                                      const SymbolTable &sym_table,
+                                      int32_t frame_shift_ms,
+                                      int32_t subsampling_factor) {
+  OnlineRecognizerResult r;
+  r.tokens.reserve(src.tokens.size());
+  r.timestamps.reserve(src.tokens.size());
+
+  for (auto i : src.tokens) {
+    auto sym = sym_table[i];
+
+    r.text.append(sym);
+    r.tokens.push_back(std::move(sym));
+  }
+
+  float frame_shift_s = frame_shift_ms / 1000. * subsampling_factor;
+  for (auto t : src.timestamps) {
+    float time = frame_shift_s * t;
+    r.timestamps.push_back(time);
+  }
+
+  return r;
+}
+
+class OnlineRecognizerTransducerImpl : public OnlineRecognizerImpl {
+ public:
+  explicit OnlineRecognizerTransducerImpl(const OnlineRecognizerConfig &config)
+      : config_(config),
+        model_(OnlineTransducerModel::Create(config.model_config)),
+        sym_(config.model_config.tokens),
+        endpoint_(config_.endpoint_config) {
+    if (config.decoding_method == "modified_beam_search") {
+      if (!config_.lm_config.model.empty()) {
+        lm_ = OnlineLM::Create(config.lm_config);
+      }
+
+      decoder_ = std::make_unique<OnlineTransducerModifiedBeamSearchDecoder>(
+          model_.get(), lm_.get(), config_.max_active_paths,
+          config_.lm_config.scale);
+    } else if (config.decoding_method == "greedy_search") {
+      decoder_ =
+          std::make_unique<OnlineTransducerGreedySearchDecoder>(model_.get());
+    } else {
+      SHERPA_ONNX_LOGE("Unsupported decoding method: %s",
+                       config.decoding_method.c_str());
+      exit(-1);
+    }
+  }
+
+#if __ANDROID_API__ >= 9
+  explicit OnlineRecognizerTransducerImpl(AAssetManager *mgr,
+                                          const OnlineRecognizerConfig &config)
+      : config_(config),
+        model_(OnlineTransducerModel::Create(mgr, config.model_config)),
+        sym_(mgr, config.model_config.tokens),
+        endpoint_(config_.endpoint_config) {
+    if (config.decoding_method == "modified_beam_search") {
+      decoder_ = std::make_unique<OnlineTransducerModifiedBeamSearchDecoder>(
+          model_.get(), lm_.get(), config_.max_active_paths,
+          config_.lm_config.scale);
+    } else if (config.decoding_method == "greedy_search") {
+      decoder_ =
+          std::make_unique<OnlineTransducerGreedySearchDecoder>(model_.get());
+    } else {
+      SHERPA_ONNX_LOGE("Unsupported decoding method: %s",
+                       config.decoding_method.c_str());
+      exit(-1);
+    }
+  }
+#endif
+
+  void InitOnlineStream(OnlineStream *stream) const override {
+    auto r = decoder_->GetEmptyResult();
+
+    if (config_.decoding_method == "modified_beam_search" &&
+        nullptr != stream->GetContextGraph()) {
+      // r.hyps has only one element.
+      for (auto it = r.hyps.begin(); it != r.hyps.end(); ++it) {
+        it->second.context_state = stream->GetContextGraph()->Root();
+      }
+    }
+
+    stream->SetResult(r);
+    stream->SetStates(model_->GetEncoderInitStates());
+  }
+
+  std::unique_ptr<OnlineStream> CreateStream() const override {
+    auto stream = std::make_unique<OnlineStream>(config_.feat_config);
+    InitOnlineStream(stream.get());
+    return stream;
+  }
+
+  std::unique_ptr<OnlineStream> CreateStream(
+      const std::vector<std::vector<int32_t>> &contexts) const override {
+    // We create context_graph at this level, because we might have default
+    // context_graph(will be added later if needed) that belongs to the whole
+    // model rather than each stream.
+    auto context_graph =
+        std::make_shared<ContextGraph>(contexts, config_.context_score);
+    auto stream =
+        std::make_unique<OnlineStream>(config_.feat_config, context_graph);
+    InitOnlineStream(stream.get());
+    return stream;
+  }
+
+  bool IsReady(OnlineStream *s) const override {
+    return s->GetNumProcessedFrames() + model_->ChunkSize() <
+           s->NumFramesReady();
+  }
+
+  void DecodeStreams(OnlineStream **ss, int32_t n) const override {
+    int32_t chunk_size = model_->ChunkSize();
+    int32_t chunk_shift = model_->ChunkShift();
+
+    int32_t feature_dim = ss[0]->FeatureDim();
+
+    std::vector<OnlineTransducerDecoderResult> results(n);
+    std::vector<float> features_vec(n * chunk_size * feature_dim);
+    std::vector<std::vector<Ort::Value>> states_vec(n);
+    std::vector<int64_t> all_processed_frames(n);
+    bool has_context_graph = false;
+
+    for (int32_t i = 0; i != n; ++i) {
+      if (!has_context_graph && ss[i]->GetContextGraph())
+        has_context_graph = true;
+
+      const auto num_processed_frames = ss[i]->GetNumProcessedFrames();
+      std::vector<float> features =
+          ss[i]->GetFrames(num_processed_frames, chunk_size);
+
+      // Question: should num_processed_frames include chunk_shift?
+      ss[i]->GetNumProcessedFrames() += chunk_shift;
+
+      std::copy(features.begin(), features.end(),
+                features_vec.data() + i * chunk_size * feature_dim);
+
+      results[i] = std::move(ss[i]->GetResult());
+      states_vec[i] = std::move(ss[i]->GetStates());
+      all_processed_frames[i] = num_processed_frames;
+    }
+
+    auto memory_info =
+        Ort::MemoryInfo::CreateCpu(OrtDeviceAllocator, OrtMemTypeDefault);
+
+    std::array<int64_t, 3> x_shape{n, chunk_size, feature_dim};
+
+    Ort::Value x = Ort::Value::CreateTensor(memory_info, features_vec.data(),
+                                            features_vec.size(), x_shape.data(),
+                                            x_shape.size());
+
+    std::array<int64_t, 1> processed_frames_shape{
+        static_cast<int64_t>(all_processed_frames.size())};
+
+    Ort::Value processed_frames = Ort::Value::CreateTensor(
+        memory_info, all_processed_frames.data(), all_processed_frames.size(),
+        processed_frames_shape.data(), processed_frames_shape.size());
+
+    auto states = model_->StackStates(states_vec);
+
+    auto pair = model_->RunEncoder(std::move(x), std::move(states),
+                                   std::move(processed_frames));
+
+    if (has_context_graph) {
+      decoder_->Decode(std::move(pair.first), ss, &results);
+    } else {
+      decoder_->Decode(std::move(pair.first), &results);
+    }
+
+    std::vector<std::vector<Ort::Value>> next_states =
+        model_->UnStackStates(pair.second);
+
+    for (int32_t i = 0; i != n; ++i) {
+      ss[i]->SetResult(results[i]);
+      ss[i]->SetStates(std::move(next_states[i]));
+    }
+  }
+
+  OnlineRecognizerResult GetResult(OnlineStream *s) const override {
+    OnlineTransducerDecoderResult decoder_result = s->GetResult();
+    decoder_->StripLeadingBlanks(&decoder_result);
+
+    // TODO(fangjun): Remember to change these constants if needed
+    int32_t frame_shift_ms = 10;
+    int32_t subsampling_factor = 4;
+    return Convert(decoder_result, sym_, frame_shift_ms, subsampling_factor);
+  }
+
+  bool IsEndpoint(OnlineStream *s) const override {
+    if (!config_.enable_endpoint) return false;
+    int32_t num_processed_frames = s->GetNumProcessedFrames();
+
+    // frame shift is 10 milliseconds
+    float frame_shift_in_seconds = 0.01;
+
+    // subsampling factor is 4
+    int32_t trailing_silence_frames = s->GetResult().num_trailing_blanks * 4;
+
+    return endpoint_.IsEndpoint(num_processed_frames, trailing_silence_frames,
+                                frame_shift_in_seconds);
+  }
+
+  void Reset(OnlineStream *s) const override {
+    // we keep the decoder_out
+    decoder_->UpdateDecoderOut(&s->GetResult());
+    Ort::Value decoder_out = std::move(s->GetResult().decoder_out);
+    s->SetResult(decoder_->GetEmptyResult());
+    s->GetResult().decoder_out = std::move(decoder_out);
+
+    // Note: We only update counters. The underlying audio samples
+    // are not discarded.
+    s->Reset();
+  }
+
+ private:
+  OnlineRecognizerConfig config_;
+  std::unique_ptr<OnlineTransducerModel> model_;
+  std::unique_ptr<OnlineLM> lm_;
+  std::unique_ptr<OnlineTransducerDecoder> decoder_;
+  SymbolTable sym_;
+  Endpoint endpoint_;
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_ONLINE_RECOGNIZER_TRANSDUCER_IMPL_H_

@@ -15,14 +15,7 @@
 #include <vector>
 
 #include "nlohmann/json.hpp"
-#include "sherpa-onnx/csrc/file-utils.h"
-#include "sherpa-onnx/csrc/macros.h"
-#include "sherpa-onnx/csrc/online-lm.h"
-#include "sherpa-onnx/csrc/online-transducer-decoder.h"
-#include "sherpa-onnx/csrc/online-transducer-greedy-search-decoder.h"
-#include "sherpa-onnx/csrc/online-transducer-model.h"
-#include "sherpa-onnx/csrc/online-transducer-modified-beam-search-decoder.h"
-#include "sherpa-onnx/csrc/symbol-table.h"
+#include "sherpa-onnx/csrc/online-recognizer-impl.h"
 
 namespace sherpa_onnx {
 
@@ -54,30 +47,6 @@ std::string OnlineRecognizerResult::AsJsonString() const {
   return j.dump();
 }
 
-static OnlineRecognizerResult Convert(const OnlineTransducerDecoderResult &src,
-                                      const SymbolTable &sym_table,
-                                      int32_t frame_shift_ms,
-                                      int32_t subsampling_factor) {
-  OnlineRecognizerResult r;
-  r.tokens.reserve(src.tokens.size());
-  r.timestamps.reserve(src.tokens.size());
-
-  for (auto i : src.tokens) {
-    auto sym = sym_table[i];
-
-    r.text.append(sym);
-    r.tokens.push_back(std::move(sym));
-  }
-
-  float frame_shift_s = frame_shift_ms / 1000. * subsampling_factor;
-  for (auto t : src.timestamps) {
-    float time = frame_shift_s * t;
-    r.timestamps.push_back(time);
-  }
-
-  return r;
-}
-
 void OnlineRecognizerConfig::Register(ParseOptions *po) {
   feat_config.Register(po);
   model_config.Register(po);
@@ -124,210 +93,13 @@ std::string OnlineRecognizerConfig::ToString() const {
   return os.str();
 }
 
-class OnlineRecognizer::Impl {
- public:
-  explicit Impl(const OnlineRecognizerConfig &config)
-      : config_(config),
-        model_(OnlineTransducerModel::Create(config.model_config)),
-        sym_(config.model_config.tokens),
-        endpoint_(config_.endpoint_config) {
-    if (config.decoding_method == "modified_beam_search") {
-      if (!config_.lm_config.model.empty()) {
-        lm_ = OnlineLM::Create(config.lm_config);
-      }
-
-      decoder_ = std::make_unique<OnlineTransducerModifiedBeamSearchDecoder>(
-          model_.get(), lm_.get(), config_.max_active_paths,
-          config_.lm_config.scale);
-    } else if (config.decoding_method == "greedy_search") {
-      decoder_ =
-          std::make_unique<OnlineTransducerGreedySearchDecoder>(model_.get());
-    } else {
-      SHERPA_ONNX_LOGE("Unsupported decoding method: %s",
-                       config.decoding_method.c_str());
-      exit(-1);
-    }
-  }
-
-#if __ANDROID_API__ >= 9
-  explicit Impl(AAssetManager *mgr, const OnlineRecognizerConfig &config)
-      : config_(config),
-        model_(OnlineTransducerModel::Create(mgr, config.model_config)),
-        sym_(mgr, config.model_config.tokens),
-        endpoint_(config_.endpoint_config) {
-    if (config.decoding_method == "modified_beam_search") {
-      decoder_ = std::make_unique<OnlineTransducerModifiedBeamSearchDecoder>(
-          model_.get(), lm_.get(), config_.max_active_paths,
-          config_.lm_config.scale);
-    } else if (config.decoding_method == "greedy_search") {
-      decoder_ =
-          std::make_unique<OnlineTransducerGreedySearchDecoder>(model_.get());
-    } else {
-      SHERPA_ONNX_LOGE("Unsupported decoding method: %s",
-                       config.decoding_method.c_str());
-      exit(-1);
-    }
-  }
-#endif
-
-  void InitOnlineStream(OnlineStream *stream) const {
-    auto r = decoder_->GetEmptyResult();
-
-    if (config_.decoding_method == "modified_beam_search" &&
-        nullptr != stream->GetContextGraph()) {
-      // r.hyps has only one element.
-      for (auto it = r.hyps.begin(); it != r.hyps.end(); ++it) {
-        it->second.context_state = stream->GetContextGraph()->Root();
-      }
-    }
-
-    stream->SetResult(r);
-    stream->SetStates(model_->GetEncoderInitStates());
-  }
-
-  std::unique_ptr<OnlineStream> CreateStream() const {
-    auto stream = std::make_unique<OnlineStream>(config_.feat_config);
-    InitOnlineStream(stream.get());
-    return stream;
-  }
-
-  std::unique_ptr<OnlineStream> CreateStream(
-      const std::vector<std::vector<int32_t>> &contexts) const {
-    // We create context_graph at this level, because we might have default
-    // context_graph(will be added later if needed) that belongs to the whole
-    // model rather than each stream.
-    auto context_graph =
-        std::make_shared<ContextGraph>(contexts, config_.context_score);
-    auto stream =
-        std::make_unique<OnlineStream>(config_.feat_config, context_graph);
-    InitOnlineStream(stream.get());
-    return stream;
-  }
-
-  bool IsReady(OnlineStream *s) const {
-    return s->GetNumProcessedFrames() + model_->ChunkSize() <
-           s->NumFramesReady();
-  }
-
-  void DecodeStreams(OnlineStream **ss, int32_t n) const {
-    int32_t chunk_size = model_->ChunkSize();
-    int32_t chunk_shift = model_->ChunkShift();
-
-    int32_t feature_dim = ss[0]->FeatureDim();
-
-    std::vector<OnlineTransducerDecoderResult> results(n);
-    std::vector<float> features_vec(n * chunk_size * feature_dim);
-    std::vector<std::vector<Ort::Value>> states_vec(n);
-    std::vector<int64_t> all_processed_frames(n);
-    bool has_context_graph = false;
-
-    for (int32_t i = 0; i != n; ++i) {
-      if (!has_context_graph && ss[i]->GetContextGraph())
-        has_context_graph = true;
-
-      const auto num_processed_frames = ss[i]->GetNumProcessedFrames();
-      std::vector<float> features =
-          ss[i]->GetFrames(num_processed_frames, chunk_size);
-
-      // Question: should num_processed_frames include chunk_shift?
-      ss[i]->GetNumProcessedFrames() += chunk_shift;
-
-      std::copy(features.begin(), features.end(),
-                features_vec.data() + i * chunk_size * feature_dim);
-
-      results[i] = std::move(ss[i]->GetResult());
-      states_vec[i] = std::move(ss[i]->GetStates());
-      all_processed_frames[i] = num_processed_frames;
-    }
-
-    auto memory_info =
-        Ort::MemoryInfo::CreateCpu(OrtDeviceAllocator, OrtMemTypeDefault);
-
-    std::array<int64_t, 3> x_shape{n, chunk_size, feature_dim};
-
-    Ort::Value x = Ort::Value::CreateTensor(memory_info, features_vec.data(),
-                                            features_vec.size(), x_shape.data(),
-                                            x_shape.size());
-
-    std::array<int64_t, 1> processed_frames_shape{
-        static_cast<int64_t>(all_processed_frames.size())};
-
-    Ort::Value processed_frames = Ort::Value::CreateTensor(
-        memory_info, all_processed_frames.data(), all_processed_frames.size(),
-        processed_frames_shape.data(), processed_frames_shape.size());
-
-    auto states = model_->StackStates(states_vec);
-
-    auto pair = model_->RunEncoder(std::move(x), std::move(states),
-                                   std::move(processed_frames));
-
-    if (has_context_graph) {
-      decoder_->Decode(std::move(pair.first), ss, &results);
-    } else {
-      decoder_->Decode(std::move(pair.first), &results);
-    }
-
-    std::vector<std::vector<Ort::Value>> next_states =
-        model_->UnStackStates(pair.second);
-
-    for (int32_t i = 0; i != n; ++i) {
-      ss[i]->SetResult(results[i]);
-      ss[i]->SetStates(std::move(next_states[i]));
-    }
-  }
-
-  OnlineRecognizerResult GetResult(OnlineStream *s) const {
-    OnlineTransducerDecoderResult decoder_result = s->GetResult();
-    decoder_->StripLeadingBlanks(&decoder_result);
-
-    // TODO(fangjun): Remember to change these constants if needed
-    int32_t frame_shift_ms = 10;
-    int32_t subsampling_factor = 4;
-    return Convert(decoder_result, sym_, frame_shift_ms, subsampling_factor);
-  }
-
-  bool IsEndpoint(OnlineStream *s) const {
-    if (!config_.enable_endpoint) return false;
-    int32_t num_processed_frames = s->GetNumProcessedFrames();
-
-    // frame shift is 10 milliseconds
-    float frame_shift_in_seconds = 0.01;
-
-    // subsampling factor is 4
-    int32_t trailing_silence_frames = s->GetResult().num_trailing_blanks * 4;
-
-    return endpoint_.IsEndpoint(num_processed_frames, trailing_silence_frames,
-                                frame_shift_in_seconds);
-  }
-
-  void Reset(OnlineStream *s) const {
-    // we keep the decoder_out
-    decoder_->UpdateDecoderOut(&s->GetResult());
-    Ort::Value decoder_out = std::move(s->GetResult().decoder_out);
-    s->SetResult(decoder_->GetEmptyResult());
-    s->GetResult().decoder_out = std::move(decoder_out);
-
-    // Note: We only update counters. The underlying audio samples
-    // are not discarded.
-    s->Reset();
-  }
-
- private:
-  OnlineRecognizerConfig config_;
-  std::unique_ptr<OnlineTransducerModel> model_;
-  std::unique_ptr<OnlineLM> lm_;
-  std::unique_ptr<OnlineTransducerDecoder> decoder_;
-  SymbolTable sym_;
-  Endpoint endpoint_;
-};
-
 OnlineRecognizer::OnlineRecognizer(const OnlineRecognizerConfig &config)
-    : impl_(std::make_unique<Impl>(config)) {}
+    : impl_(OnlineRecognizerImpl::Create(config)) {}
 
 #if __ANDROID_API__ >= 9
 OnlineRecognizer::OnlineRecognizer(AAssetManager *mgr,
                                    const OnlineRecognizerConfig &config)
-    : impl_(std::make_unique<Impl>(mgr, config)) {}
+    : impl_(OnlineRecognizerImpl::Create(mgr, config)) {}
 #endif
 
 OnlineRecognizer::~OnlineRecognizer() = default;

@@ -17,6 +17,7 @@
 #include "sherpa-onnx/csrc/endpoint.h"
 #include "sherpa-onnx/csrc/features.h"
 #include "sherpa-onnx/csrc/online-lm-config.h"
+#include "sherpa-onnx/csrc/online-model-config.h"
 #include "sherpa-onnx/csrc/online-stream.h"
 #include "sherpa-onnx/csrc/online-transducer-model-config.h"
 #include "sherpa-onnx/csrc/parse-options.h"
@@ -67,7 +68,7 @@ struct OnlineRecognizerResult {
 
 struct OnlineRecognizerConfig {
   FeatureExtractorConfig feat_config;
-  OnlineTransducerModelConfig model_config;
+  OnlineModelConfig model_config;
   OnlineLMConfig lm_config;
   EndpointConfig endpoint_config;
   bool enable_endpoint = true;
@@ -83,7 +84,7 @@ struct OnlineRecognizerConfig {
   OnlineRecognizerConfig() = default;
 
   OnlineRecognizerConfig(const FeatureExtractorConfig &feat_config,
-                         const OnlineTransducerModelConfig &model_config,
+                         const OnlineModelConfig &model_config,
                          const OnlineLMConfig &lm_config,
                          const EndpointConfig &endpoint_config,
                          bool enable_endpoint,
@@ -103,6 +104,8 @@ struct OnlineRecognizerConfig {
   std::string ToString() const;
 };
 
+class OnlineRecognizerImpl;
+
 class OnlineRecognizer {
  public:
   explicit OnlineRecognizer(const OnlineRecognizerConfig &config);
@@ -151,8 +154,7 @@ class OnlineRecognizer {
   void Reset(OnlineStream *s) const;
 
  private:
-  class Impl;
-  std::unique_ptr<Impl> impl_;
+  std::unique_ptr<OnlineRecognizerImpl> impl_;
 };
 
 }  // namespace sherpa_onnx

@@ -11,46 +11,24 @@
 namespace sherpa_onnx {
 
 void OnlineTransducerModelConfig::Register(ParseOptions *po) {
-  po->Register("encoder", &encoder_filename, "Path to encoder.onnx");
-  po->Register("decoder", &decoder_filename, "Path to decoder.onnx");
-  po->Register("joiner", &joiner_filename, "Path to joiner.onnx");
-  po->Register("tokens", &tokens, "Path to tokens.txt");
-  po->Register("num_threads", &num_threads,
-               "Number of threads to run the neural network");
-  po->Register("provider", &provider,
-               "Specify a provider to use: cpu, cuda, coreml");
-
-  po->Register("debug", &debug,
-               "true to print model information while loading it.");
-  po->Register("model-type", &model_type,
-               "Specify it to reduce model initialization time. "
-               "Valid values are: conformer, lstm, zipformer, zipformer2. "
-               "All other values lead to loading the model twice.");
+  po->Register("encoder", &encoder, "Path to encoder.onnx");
+  po->Register("decoder", &decoder, "Path to decoder.onnx");
+  po->Register("joiner", &joiner, "Path to joiner.onnx");
 }
 
 bool OnlineTransducerModelConfig::Validate() const {
-  if (!FileExists(tokens)) {
-    SHERPA_ONNX_LOGE("tokens: %s does not exist", tokens.c_str());
-    return false;
-  }
-
-  if (!FileExists(encoder_filename)) {
-    SHERPA_ONNX_LOGE("encoder: %s does not exist", encoder_filename.c_str());
-    return false;
-  }
-
-  if (!FileExists(decoder_filename)) {
-    SHERPA_ONNX_LOGE("decoder: %s does not exist", decoder_filename.c_str());
+  if (!FileExists(encoder)) {
+    SHERPA_ONNX_LOGE("transducer encoder: %s does not exist", encoder.c_str());
     return false;
   }
 
-  if (!FileExists(joiner_filename)) {
-    SHERPA_ONNX_LOGE("joiner: %s does not exist", joiner_filename.c_str());
+  if (!FileExists(decoder)) {
+    SHERPA_ONNX_LOGE("transducer decoder: %s does not exist", decoder.c_str());
     return false;
   }
 
-  if (num_threads < 1) {
-    SHERPA_ONNX_LOGE("num_threads should be > 0. Given %d", num_threads);
+  if (!FileExists(joiner)) {
+    SHERPA_ONNX_LOGE("joiner: %s does not exist", joiner.c_str());
     return false;
   }
 
@@ -61,14 +39,9 @@ std::string OnlineTransducerModelConfig::ToString() const {
   std::ostringstream os;
 
   os << "OnlineTransducerModelConfig(";
-  os << "encoder_filename=\"" << encoder_filename << "\", ";
-  os << "decoder_filename=\"" << decoder_filename << "\", ";
-  os << "joiner_filename=\"" << joiner_filename << "\", ";
-  os << "tokens=\"" << tokens << "\", ";
-  os << "num_threads=" << num_threads << ", ";
-  os << "provider=\"" << provider << "\", ";
-  os << "model_type=\"" << model_type << "\", ";
-  os << "debug=" << (debug ? "True" : "False") << ")";
+  os << "encoder=\"" << encoder << "\", ";
+  os << "decoder=\"" << decoder << "\", ";
+  os << "joiner=\"" << joiner << "\")";
 
   return os.str();
 }

@@ -11,41 +11,15 @@
 namespace sherpa_onnx {
 
 struct OnlineTransducerModelConfig {
-  std::string encoder_filename;
-  std::string decoder_filename;
-  std::string joiner_filename;
-  std::string tokens;
-  int32_t num_threads = 2;
-  bool debug = false;
-  std::string provider = "cpu";
-
-  // With the help of this field, we only need to load the model once
-  // instead of twice; and therefore it reduces initialization time.
-  //
-  // Valid values:
-  //  - conformer
-  //  - lstm
-  //  - zipformer
-  //  - zipformer2
-  //
-  // All other values are invalid and lead to loading the model twice.
-  std::string model_type;
+  std::string encoder;
+  std::string decoder;
+  std::string joiner;
 
   OnlineTransducerModelConfig() = default;
-  OnlineTransducerModelConfig(const std::string &encoder_filename,
-                              const std::string &decoder_filename,
-                              const std::string &joiner_filename,
-                              const std::string &tokens, int32_t num_threads,
-                              bool debug, const std::string &provider,
-                              const std::string &model_type)
-      : encoder_filename(encoder_filename),
-        decoder_filename(decoder_filename),
-        joiner_filename(joiner_filename),
-        tokens(tokens),
-        num_threads(num_threads),
-        debug(debug),
-        provider(provider),
-        model_type(model_type) {}
+  OnlineTransducerModelConfig(const std::string &encoder,
+                              const std::string &decoder,
+                              const std::string &joiner)
+      : encoder(encoder), decoder(decoder), joiner(joiner) {}
 
   void Register(ParseOptions *po);
   bool Validate() const;

@@ -76,7 +76,7 @@ static ModelType GetModelType(char *model_data, size_t model_data_length,
 }
 
 std::unique_ptr<OnlineTransducerModel> OnlineTransducerModel::Create(
-    const OnlineTransducerModelConfig &config) {
+    const OnlineModelConfig &config) {
   if (!config.model_type.empty()) {
     const auto &model_type = config.model_type;
     if (model_type == "conformer") {
@@ -96,7 +96,7 @@ std::unique_ptr<OnlineTransducerModel> OnlineTransducerModel::Create(
   ModelType model_type = ModelType::kUnkown;
 
   {
-    auto buffer = ReadFile(config.encoder_filename);
+    auto buffer = ReadFile(config.transducer.encoder);
 
     model_type = GetModelType(buffer.data(), buffer.size(), config.debug);
   }
@@ -155,7 +155,7 @@ Ort::Value OnlineTransducerModel::BuildDecoderInput(
 
 #if __ANDROID_API__ >= 9
 std::unique_ptr<OnlineTransducerModel> OnlineTransducerModel::Create(
-    AAssetManager *mgr, const OnlineTransducerModelConfig &config) {
+    AAssetManager *mgr, const OnlineModelConfig &config) {
   if (!config.model_type.empty()) {
     const auto &model_type = config.model_type;
     if (model_type == "conformer") {
@@ -173,7 +173,7 @@ std::unique_ptr<OnlineTransducerModel> OnlineTransducerModel::Create(
     }
   }
 
-  auto buffer = ReadFile(mgr, config.encoder_filename);
+  auto buffer = ReadFile(mgr, config.transducer.encoder);
   auto model_type = GetModelType(buffer.data(), buffer.size(), config.debug);
 
   switch (model_type) {

@@ -15,6 +15,7 @@
 
 #include "onnxruntime_cxx_api.h"  // NOLINT
 #include "sherpa-onnx/csrc/hypothesis.h"
+#include "sherpa-onnx/csrc/online-model-config.h"
 #include "sherpa-onnx/csrc/online-transducer-decoder.h"
 #include "sherpa-onnx/csrc/online-transducer-model-config.h"
 
@@ -27,11 +28,11 @@ class OnlineTransducerModel {
   virtual ~OnlineTransducerModel() = default;
 
   static std::unique_ptr<OnlineTransducerModel> Create(
-      const OnlineTransducerModelConfig &config);
+      const OnlineModelConfig &config);
 
 #if __ANDROID_API__ >= 9
   static std::unique_ptr<OnlineTransducerModel> Create(
-      AAssetManager *mgr, const OnlineTransducerModelConfig &config);
+      AAssetManager *mgr, const OnlineModelConfig &config);
 #endif
 
   /** Stack a list of individual states into a batch.
@@ -64,15 +65,15 @@ class OnlineTransducerModel {
    *
    * @param features  A tensor of shape (N, T, C). It is changed in-place.
    * @param states  Encoder state of the previous chunk. It is changed in-place.
-   * @param processed_frames  Processed frames before subsampling. It is a 1-D tensor with data type int64_t.
+   * @param processed_frames  Processed frames before subsampling. It is a 1-D
+   * tensor with data type int64_t.
    *
    * @return Return a tuple containing:
    *           - encoder_out, a tensor of shape (N, T', encoder_out_dim)
    *           - next_states  Encoder state for the next chunk.
    */
   virtual std::pair<Ort::Value, std::vector<Ort::Value>> RunEncoder(
-      Ort::Value features,
-      std::vector<Ort::Value> states,
+      Ort::Value features, std::vector<Ort::Value> states,
       Ort::Value processed_frames) = 0;  // NOLINT
 
   /** Run the decoder network.

@@ -30,46 +30,46 @@
 namespace sherpa_onnx {
 
 OnlineZipformerTransducerModel::OnlineZipformerTransducerModel(
-    const OnlineTransducerModelConfig &config)
+    const OnlineModelConfig &config)
     : env_(ORT_LOGGING_LEVEL_WARNING),
       config_(config),
       sess_opts_(GetSessionOptions(config)),
       allocator_{} {
   {
-    auto buf = ReadFile(config.encoder_filename);
+    auto buf = ReadFile(config.transducer.encoder);
     InitEncoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(config.decoder_filename);
+    auto buf = ReadFile(config.transducer.decoder);
     InitDecoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(config.joiner_filename);
+    auto buf = ReadFile(config.transducer.joiner);
     InitJoiner(buf.data(), buf.size());
   }
 }
 
 #if __ANDROID_API__ >= 9
 OnlineZipformerTransducerModel::OnlineZipformerTransducerModel(
-    AAssetManager *mgr, const OnlineTransducerModelConfig &config)
+    AAssetManager *mgr, const OnlineModelConfig &config)
     : env_(ORT_LOGGING_LEVEL_WARNING),
       config_(config),
       sess_opts_(GetSessionOptions(config)),
       allocator_{} {
   {
-    auto buf = ReadFile(mgr, config.encoder_filename);
+    auto buf = ReadFile(mgr, config.transducer.encoder);
     InitEncoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(mgr, config.decoder_filename);
+    auto buf = ReadFile(mgr, config.transducer.decoder);
     InitDecoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(mgr, config.joiner_filename);
+    auto buf = ReadFile(mgr, config.transducer.joiner);
     InitJoiner(buf.data(), buf.size());
   }
 }

@@ -15,19 +15,18 @@
 #endif
 
 #include "onnxruntime_cxx_api.h"  // NOLINT
-#include "sherpa-onnx/csrc/online-transducer-model-config.h"
+#include "sherpa-onnx/csrc/online-model-config.h"
 #include "sherpa-onnx/csrc/online-transducer-model.h"
 
 namespace sherpa_onnx {
 
 class OnlineZipformerTransducerModel : public OnlineTransducerModel {
  public:
-  explicit OnlineZipformerTransducerModel(
-      const OnlineTransducerModelConfig &config);
+  explicit OnlineZipformerTransducerModel(const OnlineModelConfig &config);
 
 #if __ANDROID_API__ >= 9
   OnlineZipformerTransducerModel(AAssetManager *mgr,
-                                 const OnlineTransducerModelConfig &config);
+                                 const OnlineModelConfig &config);
 #endif
 
   std::vector<Ort::Value> StackStates(
@@ -87,7 +86,7 @@ class OnlineZipformerTransducerModel : public OnlineTransducerModel {
   std::vector<std::string> joiner_output_names_;
   std::vector<const char *> joiner_output_names_ptr_;
 
-  OnlineTransducerModelConfig config_;
+  OnlineModelConfig config_;
 
   std::vector<int32_t> encoder_dims_;
   std::vector<int32_t> attention_dims_;

@@ -32,46 +32,46 @@
 namespace sherpa_onnx {
 
 OnlineZipformer2TransducerModel::OnlineZipformer2TransducerModel(
-    const OnlineTransducerModelConfig &config)
+    const OnlineModelConfig &config)
     : env_(ORT_LOGGING_LEVEL_WARNING),
       config_(config),
       sess_opts_(GetSessionOptions(config)),
       allocator_{} {
   {
-    auto buf = ReadFile(config.encoder_filename);
+    auto buf = ReadFile(config.transducer.encoder);
     InitEncoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(config.decoder_filename);
+    auto buf = ReadFile(config.transducer.decoder);
     InitDecoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(config.joiner_filename);
+    auto buf = ReadFile(config.transducer.joiner);
     InitJoiner(buf.data(), buf.size());
   }
 }
 
 #if __ANDROID_API__ >= 9
 OnlineZipformer2TransducerModel::OnlineZipformer2TransducerModel(
-    AAssetManager *mgr, const OnlineTransducerModelConfig &config)
+    AAssetManager *mgr, const OnlineModelConfig &config)
     : env_(ORT_LOGGING_LEVEL_WARNING),
       config_(config),
       sess_opts_(GetSessionOptions(config)),
       allocator_{} {
   {
-    auto buf = ReadFile(mgr, config.encoder_filename);
+    auto buf = ReadFile(mgr, config.transducer.encoder);
     InitEncoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(mgr, config.decoder_filename);
+    auto buf = ReadFile(mgr, config.transducer.decoder);
     InitDecoder(buf.data(), buf.size());
   }
 
   {
-    auto buf = ReadFile(mgr, config.joiner_filename);
+    auto buf = ReadFile(mgr, config.transducer.joiner);
     InitJoiner(buf.data(), buf.size());
   }
 }

@@ -15,19 +15,18 @@
 #endif
 
 #include "onnxruntime_cxx_api.h"  // NOLINT
-#include "sherpa-onnx/csrc/online-transducer-model-config.h"
+#include "sherpa-onnx/csrc/online-model-config.h"
 #include "sherpa-onnx/csrc/online-transducer-model.h"
 
 namespace sherpa_onnx {
 
 class OnlineZipformer2TransducerModel : public OnlineTransducerModel {
  public:
-  explicit OnlineZipformer2TransducerModel(
-      const OnlineTransducerModelConfig &config);
+  explicit OnlineZipformer2TransducerModel(const OnlineModelConfig &config);
 
 #if __ANDROID_API__ >= 9
   OnlineZipformer2TransducerModel(AAssetManager *mgr,
-                                 const OnlineTransducerModelConfig &config);
+                                  const OnlineModelConfig &config);
 #endif
 
   std::vector<Ort::Value> StackStates(
@@ -87,7 +86,7 @@ class OnlineZipformer2TransducerModel : public OnlineTransducerModel {
   std::vector<std::string> joiner_output_names_;
   std::vector<const char *> joiner_output_names_ptr_;
 
-  OnlineTransducerModelConfig config_;
+  OnlineModelConfig config_;
 
   std::vector<int32_t> encoder_dims_;
   std::vector<int32_t> query_head_dims_;

@@ -60,8 +60,7 @@ static Ort::SessionOptions GetSessionOptionsImpl(int32_t num_threads,
   return sess_opts;
 }
 
-Ort::SessionOptions GetSessionOptions(
-    const OnlineTransducerModelConfig &config) {
+Ort::SessionOptions GetSessionOptions(const OnlineModelConfig &config) {
   return GetSessionOptionsImpl(config.num_threads, config.provider);
 }
 

@@ -9,12 +9,11 @@
 #include "sherpa-onnx/csrc/offline-lm-config.h"
 #include "sherpa-onnx/csrc/offline-model-config.h"
 #include "sherpa-onnx/csrc/online-lm-config.h"
-#include "sherpa-onnx/csrc/online-transducer-model-config.h"
+#include "sherpa-onnx/csrc/online-model-config.h"
 
 namespace sherpa_onnx {
 
-Ort::SessionOptions GetSessionOptions(
-    const OnlineTransducerModelConfig &config);
+Ort::SessionOptions GetSessionOptions(const OnlineModelConfig &config);
 
 Ort::SessionOptions GetSessionOptions(const OfflineModelConfig &config);
 

@@ -12,6 +12,7 @@
 #include "sherpa-onnx/csrc/alsa.h"
 #include "sherpa-onnx/csrc/display.h"
 #include "sherpa-onnx/csrc/online-recognizer.h"
+#include "sherpa-onnx/csrc/parse-options.h"
 
 bool stop = false;
 
@@ -21,19 +22,19 @@ static void Handler(int sig) {
 }
 
 int main(int32_t argc, char *argv[]) {
-  if (argc < 6 || argc > 8) {
-    const char *usage = R"usage(
+  signal(SIGINT, Handler);
+
+  const char *kUsageMessage = R"usage(
 Usage:
   ./bin/sherpa-onnx-alsa \
-    /path/to/tokens.txt \
-    /path/to/encoder.onnx \
-    /path/to/decoder.onnx \
-    /path/to/joiner.onnx \
+    --tokens=/path/to/tokens.txt \
+    --encoder=/path/to/encoder.onnx \
+    --decoder=/path/to/decoder.onnx \
+    --joiner=/path/to/joiner.onnx \
+    --provider=cpu \
+    --num-threads=2 \
+    --decoding-method=greedy_search \
     device_name \
-    [num_threads [decoding_method]]
-
-Default value for num_threads is 2.
-Valid values for decoding_method: greedy_search (default), modified_beam_search.
 
 Please refer to
 https://k2-fsa.github.io/sherpa/onnx/pretrained_models/index.html
@@ -55,44 +56,24 @@ and if you want to select card 3 and the device 0 on that card, please use:
 
   hw:3,0
 
-as the device_name.
-)usage";
+or
 
-    fprintf(stderr, "%s\n", usage);
-    fprintf(stderr, "argc, %d\n", argc);
-
-    return 0;
-  }
-
-  signal(SIGINT, Handler);
+  plughw:3,0
 
+as the device_name.
+)usage";
+  sherpa_onnx::ParseOptions po(kUsageMessage);
   sherpa_onnx::OnlineRecognizerConfig config;
 
-  config.model_config.tokens = argv[1];
-
-  config.model_config.debug = false;
-  config.model_config.encoder_filename = argv[2];
-  config.model_config.decoder_filename = argv[3];
-  config.model_config.joiner_filename = argv[4];
-
-  const char *device_name = argv[5];
+  config.Register(&po);
 
-  config.model_config.num_threads = 2;
-  if (argc == 7 && atoi(argv[6]) > 0) {
-    config.model_config.num_threads = atoi(argv[6]);
+  po.Read(argc, argv);
+  if (po.NumArgs() != 1) {
+    fprintf(stderr, "Please provide only 1 argument: the device name\n");
+    po.PrintUsage();
+    exit(EXIT_FAILURE);
   }
 
-  if (argc == 8) {
-    config.decoding_method = argv[7];
-  }
-  config.max_active_paths = 4;
-
-  config.enable_endpoint = true;
-
-  config.endpoint_config.rule1.min_trailing_silence = 2.4;
-  config.endpoint_config.rule2.min_trailing_silence = 1.2;
-  config.endpoint_config.rule3.min_utterance_length = 300;
-
   fprintf(stderr, "%s\n", config.ToString().c_str());
 
   if (!config.Validate()) {
@@ -103,8 +84,9 @@ as the device_name.
 
   int32_t expected_sample_rate = config.feat_config.sampling_rate;
 
-  sherpa_onnx::Alsa alsa(device_name);
-  fprintf(stderr, "Use recording device: %s\n", device_name);
+  std::string device_name = po.GetArg(1);
+  sherpa_onnx::Alsa alsa(device_name.c_str());
+  fprintf(stderr, "Use recording device: %s\n", device_name.c_str());
 
   if (alsa.GetExpectedSampleRate() != expected_sample_rate) {
     fprintf(stderr, "sample rate: %d != %d\n", alsa.GetExpectedSampleRate(),

@@ -4,6 +4,7 @@
 // Copyright      2023  Xiaomi Corporation
 #ifndef SHERPA_ONNX_CSRC_TEXT_UTILS_H_
 #define SHERPA_ONNX_CSRC_TEXT_UTILS_H_
+#include <errno.h>.
 #include <stdlib.h>
 
 #include <limits>

@@ -159,47 +159,47 @@ static OnlineRecognizerConfig GetConfig(JNIEnv *env, jobject config) {
   //---------- model config ----------
   fid = env->GetFieldID(cls, "modelConfig",
                         "Lcom/k2fsa/sherpa/onnx/OnlineTransducerModelConfig;");
-  jobject model_config = env->GetObjectField(config, fid);
-  jclass model_config_cls = env->GetObjectClass(model_config);
+  jobject transducer_config = env->GetObjectField(config, fid);
+  jclass model_config_cls = env->GetObjectClass(transducer_config);
 
   fid = env->GetFieldID(model_config_cls, "encoder", "Ljava/lang/String;");
-  s = (jstring)env->GetObjectField(model_config, fid);
+  s = (jstring)env->GetObjectField(transducer_config, fid);
   p = env->GetStringUTFChars(s, nullptr);
-  ans.model_config.encoder_filename = p;
+  ans.model_config.transducer.encoder = p;
   env->ReleaseStringUTFChars(s, p);
 
   fid = env->GetFieldID(model_config_cls, "decoder", "Ljava/lang/String;");
-  s = (jstring)env->GetObjectField(model_config, fid);
+  s = (jstring)env->GetObjectField(transducer_config, fid);
   p = env->GetStringUTFChars(s, nullptr);
-  ans.model_config.decoder_filename = p;
+  ans.model_config.transducer.decoder = p;
   env->ReleaseStringUTFChars(s, p);
 
   fid = env->GetFieldID(model_config_cls, "joiner", "Ljava/lang/String;");
-  s = (jstring)env->GetObjectField(model_config, fid);
+  s = (jstring)env->GetObjectField(transducer_config, fid);
   p = env->GetStringUTFChars(s, nullptr);
-  ans.model_config.joiner_filename = p;
+  ans.model_config.transducer.joiner = p;
   env->ReleaseStringUTFChars(s, p);
 
   fid = env->GetFieldID(model_config_cls, "tokens", "Ljava/lang/String;");
-  s = (jstring)env->GetObjectField(model_config, fid);
+  s = (jstring)env->GetObjectField(transducer_config, fid);
   p = env->GetStringUTFChars(s, nullptr);
   ans.model_config.tokens = p;
   env->ReleaseStringUTFChars(s, p);
 
   fid = env->GetFieldID(model_config_cls, "numThreads", "I");
-  ans.model_config.num_threads = env->GetIntField(model_config, fid);
+  ans.model_config.num_threads = env->GetIntField(transducer_config, fid);
 
   fid = env->GetFieldID(model_config_cls, "debug", "Z");
-  ans.model_config.debug = env->GetBooleanField(model_config, fid);
+  ans.model_config.debug = env->GetBooleanField(transducer_config, fid);
 
   fid = env->GetFieldID(model_config_cls, "provider", "Ljava/lang/String;");
-  s = (jstring)env->GetObjectField(model_config, fid);
+  s = (jstring)env->GetObjectField(transducer_config, fid);
   p = env->GetStringUTFChars(s, nullptr);
   ans.model_config.provider = p;
   env->ReleaseStringUTFChars(s, p);
 
   fid = env->GetFieldID(model_config_cls, "modelType", "Ljava/lang/String;");
-  s = (jstring)env->GetObjectField(model_config, fid);
+  s = (jstring)env->GetObjectField(transducer_config, fid);
   p = env->GetStringUTFChars(s, nullptr);
   ans.model_config.model_type = p;
   env->ReleaseStringUTFChars(s, p);
@@ -328,7 +328,7 @@ JNIEXPORT jobjectArray JNICALL Java_com_k2fsa_sherpa_onnx_SherpaOnnx_getTokens(
   jobjectArray result = env->NewObjectArray(size, stringClass, NULL);
   for (int i = 0; i < size; i++) {
     // Convert the C++ string to a C string
-    const char* cstr = tokens[i].c_str();
+    const char *cstr = tokens[i].c_str();
 
     // Convert the C string to a jstring
     jstring jstr = env->NewStringUTF(cstr);

@@ -13,6 +13,7 @@ pybind11_add_module(_sherpa_onnx
   offline-transducer-model-config.cc
   offline-whisper-model-config.cc
   online-lm-config.cc
+  online-model-config.cc
   online-recognizer.cc
   online-stream.cc
   online-transducer-model-config.cc

+// sherpa-onnx/python/csrc/online-model-config.cc
+//
+// Copyright (c)  2023 by manyeyes
+
+#include "sherpa-onnx/python/csrc/online-model-config.h"
+
+#include <string>
+#include <vector>
+
+#include "sherpa-onnx/csrc/online-model-config.h"
+#include "sherpa-onnx/csrc/online-transducer-model-config.h"
+#include "sherpa-onnx/python/csrc/online-transducer-model-config.h"
+
+namespace sherpa_onnx {
+
+void PybindOnlineModelConfig(py::module *m) {
+  PybindOnlineTransducerModelConfig(m);
+
+  using PyClass = OnlineModelConfig;
+  py::class_<PyClass>(*m, "OnlineModelConfig")
+      .def(py::init<const OnlineTransducerModelConfig &, std::string &, int32_t,
+                    bool, const std::string &, const std::string &>(),
+           py::arg("transducer") = OnlineTransducerModelConfig(),
+           py::arg("tokens"), py::arg("num_threads"), py::arg("debug") = false,
+           py::arg("provider") = "cpu", py::arg("model_type") = "")
+      .def_readwrite("transducer", &PyClass::transducer)
+      .def_readwrite("tokens", &PyClass::tokens)
+      .def_readwrite("num_threads", &PyClass::num_threads)
+      .def_readwrite("debug", &PyClass::debug)
+      .def_readwrite("provider", &PyClass::provider)
+      .def_readwrite("model_type", &PyClass::model_type)
+      .def("__str__", &PyClass::ToString);
+}
+
+}  // namespace sherpa_onnx

+// sherpa-onnx/python/csrc/online-model-config.h
+//
+// Copyright (c)  2023 by manyeyes
+
+#ifndef SHERPA_ONNX_PYTHON_CSRC_ONLINE_MODEL_CONFIG_H_
+#define SHERPA_ONNX_PYTHON_CSRC_ONLINE_MODEL_CONFIG_H_
+
+#include "sherpa-onnx/python/csrc/sherpa-onnx.h"
+
+namespace sherpa_onnx {
+
+void PybindOnlineModelConfig(py::module *m);
+
+}
+
+#endif  // SHERPA_ONNX_PYTHON_CSRC_ONLINE_MODEL_CONFIG_H_

@@ -27,10 +27,9 @@ static void PybindOnlineRecognizerResult(py::module *m) {
 static void PybindOnlineRecognizerConfig(py::module *m) {
   using PyClass = OnlineRecognizerConfig;
   py::class_<PyClass>(*m, "OnlineRecognizerConfig")
-      .def(py::init<const FeatureExtractorConfig &,
-                    const OnlineTransducerModelConfig &, const OnlineLMConfig &,
-                    const EndpointConfig &, bool, const std::string &, int32_t,
-                    float>(),
+      .def(py::init<const FeatureExtractorConfig &, const OnlineModelConfig &,
+                    const OnlineLMConfig &, const EndpointConfig &, bool,
+                    const std::string &, int32_t, float>(),
            py::arg("feat_config"), py::arg("model_config"),
            py::arg("lm_config") = OnlineLMConfig(), py::arg("endpoint_config"),
            py::arg("enable_endpoint"), py::arg("decoding_method"),

@@ -14,20 +14,11 @@ void PybindOnlineTransducerModelConfig(py::module *m) {
   using PyClass = OnlineTransducerModelConfig;
   py::class_<PyClass>(*m, "OnlineTransducerModelConfig")
       .def(py::init<const std::string &, const std::string &,
-                    const std::string &, const std::string &, int32_t, bool,
-                    const std::string &, const std::string &>(),
-           py::arg("encoder_filename"), py::arg("decoder_filename"),
-           py::arg("joiner_filename"), py::arg("tokens"),
-           py::arg("num_threads"), py::arg("debug") = false,
-           py::arg("provider") = "cpu", py::arg("model_type") = "")
-      .def_readwrite("encoder_filename", &PyClass::encoder_filename)
-      .def_readwrite("decoder_filename", &PyClass::decoder_filename)
-      .def_readwrite("joiner_filename", &PyClass::joiner_filename)
-      .def_readwrite("tokens", &PyClass::tokens)
-      .def_readwrite("num_threads", &PyClass::num_threads)
-      .def_readwrite("debug", &PyClass::debug)
-      .def_readwrite("provider", &PyClass::provider)
-      .def_readwrite("model_type", &PyClass::model_type)
+                    const std::string &>(),
+           py::arg("encoder"), py::arg("decoder"), py::arg("joiner"))
+      .def_readwrite("encoder", &PyClass::encoder)
+      .def_readwrite("decoder", &PyClass::decoder)
+      .def_readwrite("joiner", &PyClass::joiner)
       .def("__str__", &PyClass::ToString);
 }
 

@@ -12,9 +12,9 @@
 #include "sherpa-onnx/python/csrc/offline-recognizer.h"
 #include "sherpa-onnx/python/csrc/offline-stream.h"
 #include "sherpa-onnx/python/csrc/online-lm-config.h"
+#include "sherpa-onnx/python/csrc/online-model-config.h"
 #include "sherpa-onnx/python/csrc/online-recognizer.h"
 #include "sherpa-onnx/python/csrc/online-stream.h"
-#include "sherpa-onnx/python/csrc/online-transducer-model-config.h"
 
 namespace sherpa_onnx {
 
@@ -22,7 +22,7 @@ PYBIND11_MODULE(_sherpa_onnx, m) {
   m.doc() = "pybind11 binding of sherpa-onnx";
 
   PybindFeatures(&m);
-  PybindOnlineTransducerModelConfig(&m);
+  PybindOnlineModelConfig(&m);
   PybindOnlineLMConfig(&m);
   PybindOnlineStream(&m);
   PybindEndpoint(&m);

@@ -5,6 +5,7 @@ from typing import List, Optional
 from _sherpa_onnx import (
     EndpointConfig,
     FeatureExtractorConfig,
+    OnlineModelConfig,
     OnlineRecognizer as _Recognizer,
     OnlineRecognizerConfig,
     OnlineStream,
@@ -24,8 +25,9 @@ class OnlineRecognizer(object):
      - https://github.com/k2-fsa/sherpa-onnx/blob/master/python-api-examples/online-decode-files.py
     """
 
-    def __init__(
-        self,
+    @classmethod
+    def from_transducer(
+        cls,
         tokens: str,
         encoder: str,
         decoder: str,
@@ -95,6 +97,7 @@ class OnlineRecognizer(object):
             Online transducer model type. Valid values are: conformer, lstm,
             zipformer, zipformer2. All other values lead to loading the model twice.
         """
+        self = cls.__new__(cls)
         _assert_file_exists(tokens)
         _assert_file_exists(encoder)
         _assert_file_exists(decoder)
@@ -102,10 +105,14 @@ class OnlineRecognizer(object):
 
         assert num_threads > 0, num_threads
 
-        model_config = OnlineTransducerModelConfig(
-            encoder_filename=encoder,
-            decoder_filename=decoder,
-            joiner_filename=joiner,
+        transducer_config = OnlineTransducerModelConfig(
+            encoder=encoder,
+            decoder=decoder,
+            joiner=joiner,
+        )
+
+        model_config = OnlineModelConfig(
+            transducer=transducer_config,
             tokens=tokens,
             num_threads=num_threads,
             provider=provider,
@@ -135,6 +142,7 @@ class OnlineRecognizer(object):
 
         self.recognizer = _Recognizer(recognizer_config)
         self.config = recognizer_config
+        return self
 
     def create_stream(self, contexts_list: Optional[List[List[int]]] = None):
         if contexts_list is None:

@@ -65,7 +65,7 @@ class TestOnlineRecognizer(unittest.TestCase):
                 return
 
             for decoding_method in ["greedy_search", "modified_beam_search"]:
-                recognizer = sherpa_onnx.OnlineRecognizer(
+                recognizer = sherpa_onnx.OnlineRecognizer.from_transducer(
                     encoder=encoder,
                     decoder=decoder,
                     joiner=joiner,
@@ -109,7 +109,7 @@ class TestOnlineRecognizer(unittest.TestCase):
                 return
 
             for decoding_method in ["greedy_search", "modified_beam_search"]:
-                recognizer = sherpa_onnx.OnlineRecognizer(
+                recognizer = sherpa_onnx.OnlineRecognizer.from_transducer(
                     encoder=encoder,
                     decoder=decoder,
                     joiner=joiner,

@@ -14,19 +14,13 @@ import _sherpa_onnx
 class TestOnlineTransducerModelConfig(unittest.TestCase):
     def test_constructor(self):
         config = _sherpa_onnx.OnlineTransducerModelConfig(
-            encoder_filename="encoder.onnx",
-            decoder_filename="decoder.onnx",
-            joiner_filename="joiner.onnx",
-            tokens="tokens.txt",
-            num_threads=8,
-            debug=True,
+            encoder="encoder.onnx",
+            decoder="decoder.onnx",
+            joiner="joiner.onnx",
         )
-        assert config.encoder_filename == "encoder.onnx", config.encoder_filename
-        assert config.decoder_filename == "decoder.onnx", config.decoder_filename
-        assert config.joiner_filename == "joiner.onnx", config.joiner_filename
-        assert config.tokens == "tokens.txt", config.tokens
-        assert config.num_threads == 8, config.num_threads
-        assert config.debug is True, config.debug
+        assert config.encoder == "encoder.onnx", config.encoder
+        assert config.decoder == "decoder.onnx", config.decoder
+        assert config.joiner == "joiner.onnx", config.joiner
         print(config)