Add online transducer decoder (#27)

 function(download_kaldi_native_fbank)
   include(FetchContent)
 
-  set(kaldi_native_fbank_URL  "https://github.com/csukuangfj/kaldi-native-fbank/archive/refs/tags/v1.11.tar.gz")
-  set(kaldi_native_fbank_HASH "SHA256=e69ae25ef6f30566ef31ca949dd1b0b8ec3a827caeba93a61d82bb848dac5d69")
+  set(kaldi_native_fbank_URL  "https://github.com/csukuangfj/kaldi-native-fbank/archive/refs/tags/v1.12.tar.gz")
+  set(kaldi_native_fbank_HASH "SHA256=8f4dfc3f6ddb1adcd9ac0ae87743ebc6cbcae147aacf9d46e76fa54134e12b44")
 
   set(KALDI_NATIVE_FBANK_BUILD_TESTS OFF CACHE BOOL "" FORCE)
   set(KALDI_NATIVE_FBANK_BUILD_PYTHON OFF CACHE BOOL "" FORCE)
@@ -11,10 +11,11 @@ function(download_kaldi_native_fbank)
   # If you don't have access to the Internet,
   # please pre-download kaldi-native-fbank
   set(possible_file_locations
-    $ENV{HOME}/Downloads/kaldi-native-fbank-1.11.tar.gz
-    ${PROJECT_SOURCE_DIR}/kaldi-native-fbank-1.11.tar.gz
-    ${PROJECT_BINARY_DIR}/kaldi-native-fbank-1.11.tar.gz
-    /tmp/kaldi-native-fbank-1.11.tar.gz
+    $ENV{HOME}/Downloads/kaldi-native-fbank-1.12.tar.gz
+    ${PROJECT_SOURCE_DIR}/kaldi-native-fbank-1.12.tar.gz
+    ${PROJECT_BINARY_DIR}/kaldi-native-fbank-1.12.tar.gz
+    /tmp/kaldi-native-fbank-1.12.tar.gz
+    /star-fj/fangjun/download/github/kaldi-native-fbank-1.12.tar.gz
   )
 
   foreach(f IN LISTS possible_file_locations)

@@ -9,6 +9,7 @@ function(download_onnxruntime)
       ${PROJECT_SOURCE_DIR}/onnxruntime-linux-x64-1.14.0.tgz
       ${PROJECT_BINARY_DIR}/onnxruntime-linux-x64-1.14.0.tgz
       /tmp/onnxruntime-linux-x64-1.14.0.tgz
+      /star-fj/fangjun/download/github/onnxruntime-linux-x64-1.14.0.tgz
     )
 
     set(onnxruntime_URL  "https://github.com/microsoft/onnxruntime/releases/download/v1.14.0/onnxruntime-linux-x64-1.14.0.tgz")

 include_directories(${CMAKE_SOURCE_DIR})
 
 add_executable(sherpa-onnx
-  decode.cc
   features.cc
   online-lstm-transducer-model.cc
+  online-transducer-greedy-search-decoder.cc
   online-transducer-model-config.cc
   online-transducer-model.cc
   onnx-utils.cc

-// sherpa/csrc/decode.h
-//
-// Copyright (c)  2023  Xiaomi Corporation
-
-#ifndef SHERPA_ONNX_CSRC_DECODE_H_
-#define SHERPA_ONNX_CSRC_DECODE_H_
-
-#include <vector>
-
-#include "sherpa-onnx/csrc/online-transducer-model.h"
-
-namespace sherpa_onnx {
-
-/** Greedy search for non-streaming ASR.
- *
- * @TODO(fangjun) Support batch size > 1
- *
- * @param model  The RnntModel
- * @param encoder_out  Its shape is (1, num_frames, encoder_out_dim).
- */
-void GreedySearch(OnlineTransducerModel *model, Ort::Value encoder_out,
-                  std::vector<int64_t> *hyp);
-
-}  // namespace sherpa_onnx
-
-#endif  // SHERPA_ONNX_CSRC_DECODE_H_

@@ -15,16 +15,16 @@ namespace sherpa_onnx {
 
 class FeatureExtractor::Impl {
  public:
-  Impl(int32_t sampling_rate, int32_t feature_dim) {
+  explicit Impl(const FeatureExtractorConfig &config) {
     opts_.frame_opts.dither = 0;
     opts_.frame_opts.snip_edges = false;
-    opts_.frame_opts.samp_freq = sampling_rate;
+    opts_.frame_opts.samp_freq = config.sampling_rate;
 
     // cache 100 seconds of feature frames, which is more than enough
     // for real needs
     opts_.frame_opts.max_feature_vectors = 100 * 100;
 
-    opts_.mel_opts.num_bins = feature_dim;
+    opts_.mel_opts.num_bins = config.feature_dim;
 
     fbank_ = std::make_unique<knf::OnlineFbank>(opts_);
   }
@@ -80,9 +80,8 @@ class FeatureExtractor::Impl {
   mutable std::mutex mutex_;
 };
 
-FeatureExtractor::FeatureExtractor(int32_t sampling_rate /*=16000*/,
-                                   int32_t feature_dim /*=80*/)
-    : impl_(std::make_unique<Impl>(sampling_rate, feature_dim)) {}
+FeatureExtractor::FeatureExtractor(const FeatureExtractorConfig &config /*={}*/)
+    : impl_(std::make_unique<Impl>(config)) {}
 
 FeatureExtractor::~FeatureExtractor() = default;
 

@@ -10,14 +10,18 @@
 
 namespace sherpa_onnx {
 
+struct FeatureExtractorConfig {
+  int32_t sampling_rate = 16000;
+  int32_t feature_dim = 80;
+};
+
 class FeatureExtractor {
  public:
   /**
    * @param sampling_rate  Sampling rate of the data used to train the model.
    * @param feature_dim    Dimension of the features used to train the model.
    */
-  explicit FeatureExtractor(int32_t sampling_rate = 16000,
-                            int32_t feature_dim = 80);
+  explicit FeatureExtractor(const FeatureExtractorConfig &config = {});
   ~FeatureExtractor();
 
   /**

+// sherpa/csrc/online-transducer-decoder.h
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#ifndef SHERPA_ONNX_CSRC_ONLINE_TRANSDUCER_DECODER_H_
+#define SHERPA_ONNX_CSRC_ONLINE_TRANSDUCER_DECODER_H_
+
+#include <vector>
+
+#include "onnxruntime_cxx_api.h"  // NOLINT
+
+namespace sherpa_onnx {
+
+struct OnlineTransducerDecoderResult {
+  /// The decoded token IDs so far
+  std::vector<int64_t> tokens;
+};
+
+class OnlineTransducerDecoder {
+ public:
+  virtual ~OnlineTransducerDecoder() = default;
+
+  /* Return an empty result.
+   *
+   * To simplify the decoding code, we add `context_size` blanks
+   * to the beginning of the decoding result, which will be
+   * stripped by calling `StripPrecedingBlanks()`.
+   */
+  virtual OnlineTransducerDecoderResult GetEmptyResult() = 0;
+
+  /** Strip blanks added by `GetEmptyResult()`.
+   *
+   * @param r It is changed in-place.
+   */
+  virtual void StripLeadingBlanks(OnlineTransducerDecoderResult * /*r*/) {}
+
+  /** Run transducer beam search given the output from the encoder model.
+   *
+   * @param encoder_out A 3-D tensor of shape (N, T, joiner_dim)
+   * @param result  It is modified in-place.
+   *
+   * @note There is no need to pass encoder_out_length here since for the
+   * online decoding case, each utterance has the same number of frames
+   * and there are no paddings.
+   */
+  virtual void Decode(Ort::Value encoder_out,
+                      std::vector<OnlineTransducerDecoderResult> *result) = 0;
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_ONLINE_TRANSDUCER_DECODER_H_

-// sherpa/csrc/decode.cc
+// sherpa/csrc/online-transducer-greedy-search-decoder.cc
 //
 // Copyright (c)  2023  Xiaomi Corporation
 
-#include "sherpa-onnx/csrc/decode.h"
+#include "sherpa-onnx/csrc/online-transducer-greedy-search-decoder.h"
 
 #include <assert.h>
 
@@ -10,19 +10,9 @@
 #include <utility>
 #include <vector>
 
-namespace sherpa_onnx {
-
-static Ort::Value Clone(Ort::Value *v) {
-  auto type_and_shape = v->GetTensorTypeAndShapeInfo();
-  std::vector<int64_t> shape = type_and_shape.GetShape();
-
-  auto memory_info =
-      Ort::MemoryInfo::CreateCpu(OrtDeviceAllocator, OrtMemTypeDefault);
+#include "sherpa-onnx/csrc/onnx-utils.h"
 
-  return Ort::Value::CreateTensor(memory_info, v->GetTensorMutableData<float>(),
-                                  type_and_shape.GetElementCount(),
-                                  shape.data(), shape.size());
-}
+namespace sherpa_onnx {
 
 static Ort::Value GetFrame(Ort::Value *encoder_out, int32_t t) {
   std::vector<int64_t> encoder_out_shape =
@@ -42,26 +32,58 @@ static Ort::Value GetFrame(Ort::Value *encoder_out, int32_t t) {
       encoder_out_dim, shape.data(), shape.size());
 }
 
-void GreedySearch(OnlineTransducerModel *model, Ort::Value encoder_out,
-                  std::vector<int64_t> *hyp) {
+OnlineTransducerDecoderResult
+OnlineTransducerGreedySearchDecoder::GetEmptyResult() {
+  int32_t context_size = model_->ContextSize();
+  int32_t blank_id = 0;  // always 0
+  OnlineTransducerDecoderResult r;
+  r.tokens.resize(context_size, blank_id);
+
+  return r;
+}
+
+void OnlineTransducerGreedySearchDecoder::StripLeadingBlanks(
+    OnlineTransducerDecoderResult *r) {
+  int32_t context_size = model_->ContextSize();
+
+  auto start = r->tokens.begin() + context_size;
+  auto end = r->tokens.end();
+
+  r->tokens = std::vector<int64_t>(start, end);
+}
+
+void OnlineTransducerGreedySearchDecoder::Decode(
+    Ort::Value encoder_out,
+    std::vector<OnlineTransducerDecoderResult> *result) {
   std::vector<int64_t> encoder_out_shape =
       encoder_out.GetTensorTypeAndShapeInfo().GetShape();
 
-  if (encoder_out_shape[0] > 1) {
-    fprintf(stderr, "Only batch_size=1 is implemented. Given: %d\n",
-            static_cast<int32_t>(encoder_out_shape[0]));
+  if (encoder_out_shape[0] != result->size()) {
+    fprintf(stderr,
+            "Size mismatch! encoder_out.size(0) %d, result.size(0): %d\n",
+            static_cast<int32_t>(encoder_out_shape[0]),
+            static_cast<int32_t>(result->size()));
+    exit(-1);
+  }
+
+  if (result->size() != 1) {
+    fprintf(stderr, "only batch size == 1 is implemented. Given: %d",
+            static_cast<int32_t>(result->size()));
+    exit(-1);
   }
 
+  auto &hyp = (*result)[0].tokens;
+
   int32_t num_frames = encoder_out_shape[1];
-  int32_t vocab_size = model->VocabSize();
+  int32_t vocab_size = model_->VocabSize();
 
-  Ort::Value decoder_input = model->BuildDecoderInput(*hyp);
-  Ort::Value decoder_out = model->RunDecoder(std::move(decoder_input));
+  Ort::Value decoder_input = model_->BuildDecoderInput(hyp);
+  Ort::Value decoder_out = model_->RunDecoder(std::move(decoder_input));
 
   for (int32_t t = 0; t != num_frames; ++t) {
     Ort::Value cur_encoder_out = GetFrame(&encoder_out, t);
     Ort::Value logit =
-        model->RunJoiner(std::move(cur_encoder_out), Clone(&decoder_out));
+        model_->RunJoiner(std::move(cur_encoder_out), Clone(&decoder_out));
     const float *p_logit = logit.GetTensorData<float>();
 
     auto y = static_cast<int32_t>(std::distance(
@@ -69,9 +91,9 @@ void GreedySearch(OnlineTransducerModel *model, Ort::Value encoder_out,
         std::max_element(static_cast<const float *>(p_logit),
                          static_cast<const float *>(p_logit) + vocab_size)));
     if (y != 0) {
-      hyp->push_back(y);
-      decoder_input = model->BuildDecoderInput(*hyp);
-      decoder_out = model->RunDecoder(std::move(decoder_input));
+      hyp.push_back(y);
+      decoder_input = model_->BuildDecoderInput(hyp);
+      decoder_out = model_->RunDecoder(std::move(decoder_input));
     }
   }
 }

+// sherpa/csrc/online-transducer-greedy-search-decoder.h
+//
+// Copyright (c)  2023  Xiaomi Corporation
+
+#ifndef SHERPA_ONNX_CSRC_ONLINE_TRANSDUCER_GREEDY_SEARCH_DECODER_H_
+#define SHERPA_ONNX_CSRC_ONLINE_TRANSDUCER_GREEDY_SEARCH_DECODER_H_
+
+#include <vector>
+
+#include "sherpa-onnx/csrc/online-transducer-decoder.h"
+#include "sherpa-onnx/csrc/online-transducer-model.h"
+
+namespace sherpa_onnx {
+
+class OnlineTransducerGreedySearchDecoder : public OnlineTransducerDecoder {
+ public:
+  explicit OnlineTransducerGreedySearchDecoder(OnlineTransducerModel *model)
+      : model_(model) {}
+
+  OnlineTransducerDecoderResult GetEmptyResult() override;
+
+  void StripLeadingBlanks(OnlineTransducerDecoderResult *r) override;
+
+  void Decode(Ort::Value encoder_out,
+              std::vector<OnlineTransducerDecoderResult> *result) override;
+
+ private:
+  OnlineTransducerModel *model_;  // Not owned
+};
+
+}  // namespace sherpa_onnx
+
+#endif  // SHERPA_ONNX_CSRC_ONLINE_TRANSDUCER_GREEDY_SEARCH_DECODER_H_

@@ -46,4 +46,16 @@ void PrintModelMetadata(std::ostream &os, const Ort::ModelMetadata &meta_data) {
   }
 }
 
+Ort::Value Clone(Ort::Value *v) {
+  auto type_and_shape = v->GetTensorTypeAndShapeInfo();
+  std::vector<int64_t> shape = type_and_shape.GetShape();
+
+  auto memory_info =
+      Ort::MemoryInfo::CreateCpu(OrtDeviceAllocator, OrtMemTypeDefault);
+
+  return Ort::Value::CreateTensor(memory_info, v->GetTensorMutableData<float>(),
+                                  type_and_shape.GetElementCount(),
+                                  shape.data(), shape.size());
+}
+
 }  // namespace sherpa_onnx

@@ -55,6 +55,9 @@ void GetOutputNames(Ort::Session *sess, std::vector<std::string> *output_names,
 void PrintModelMetadata(std::ostream &os,
                         const Ort::ModelMetadata &meta_data);  // NOLINT
 
+// Return a shallow copy of v
+Ort::Value Clone(Ort::Value *v);
+
 }  // namespace sherpa_onnx
 
 #endif  // SHERPA_ONNX_CSRC_ONNX_UTILS_H_

@@ -9,8 +9,8 @@
 #include <vector>
 
 #include "kaldi-native-fbank/csrc/online-feature.h"
-#include "sherpa-onnx/csrc/decode.h"
 #include "sherpa-onnx/csrc/features.h"
+#include "sherpa-onnx/csrc/online-transducer-greedy-search-decoder.h"
 #include "sherpa-onnx/csrc/online-transducer-model-config.h"
 #include "sherpa-onnx/csrc/online-transducer-model.h"
 #include "sherpa-onnx/csrc/symbol-table.h"
@@ -64,8 +64,6 @@ for a list of pre-trained models to download.
 
   std::vector<Ort::Value> states = model->GetEncoderInitStates();
 
-  std::vector<int64_t> hyp(model->ContextSize(), 0);
-
   int32_t expected_sampling_rate = 16000;
 
   bool is_ok = false;
@@ -100,6 +98,10 @@ for a list of pre-trained models to download.
 
   std::array<int64_t, 3> x_shape{1, chunk_size, feature_dim};
 
+  sherpa_onnx::OnlineTransducerGreedySearchDecoder decoder(model.get());
+  std::vector<sherpa_onnx::OnlineTransducerDecoderResult> result = {
+      decoder.GetEmptyResult()};
+
   for (int32_t start = 0; start + chunk_size < num_frames;
        start += chunk_shift) {
     std::vector<float> features = feat_extractor.GetFrames(start, chunk_size);
@@ -109,8 +111,10 @@ for a list of pre-trained models to download.
                                  x_shape.data(), x_shape.size());
     auto pair = model->RunEncoder(std::move(x), states);
     states = std::move(pair.second);
-    sherpa_onnx::GreedySearch(model.get(), std::move(pair.first), &hyp);
+    decoder.Decode(std::move(pair.first), &result);
   }
+  decoder.StripLeadingBlanks(&result[0]);
+  const auto &hyp = result[0].tokens;
   std::string text;
   for (size_t i = model->ContextSize(); i != hyp.size(); ++i) {
     text += sym[hyp[i]];