deepspeech.cc

#include <algorithm>
#ifdef _MSC_VER
  #define _USE_MATH_DEFINES
#endif
#include <cmath>
#include <iostream>
#include <memory>
#include <string>
#include <utility>
#include <vector>

#include "deepspeech.h"
#include "alphabet.h"

#include "native_client/ds_version.h"

#ifndef USE_TFLITE
  #include "tensorflow/core/public/session.h"
  #include "tensorflow/core/platform/env.h"
  #include "tensorflow/core/util/memmapped_file_system.h"
#else // USE_TFLITE
  #include "tensorflow/lite/model.h"
  #include "tensorflow/lite/kernels/register.h"
#endif // USE_TFLITE

#include "c_speech_features.h"

#include "ctcdecode/ctc_beam_search_decoder.h"

#ifdef __ANDROID__
#include <android/log.h>
#define  LOG_TAG    "libdeepspeech"
#define  LOGD(...)  __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)
#define  LOGE(...)  __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
#else
#define  LOGD(...)
#define  LOGE(...)
#endif // __ANDROID__

//TODO: infer batch size from model/use dynamic batch size
constexpr unsigned int BATCH_SIZE = 1;

//TODO: use dynamic sample rate
constexpr unsigned int SAMPLE_RATE = 16000;

constexpr float AUDIO_WIN_LEN = 0.032f;
constexpr float AUDIO_WIN_STEP = 0.02f;
constexpr unsigned int AUDIO_WIN_LEN_SAMPLES = (unsigned int)(AUDIO_WIN_LEN * SAMPLE_RATE);
constexpr unsigned int AUDIO_WIN_STEP_SAMPLES = (unsigned int)(AUDIO_WIN_STEP * SAMPLE_RATE);

constexpr unsigned int MFCC_FEATURES = 26;

constexpr float PREEMPHASIS_COEFF = 0.97f;
constexpr unsigned int N_FFT = 512;
constexpr unsigned int N_FILTERS = 26;
constexpr unsigned int LOWFREQ = 0;
constexpr unsigned int CEP_LIFTER = 22;

constexpr size_t WINDOW_SIZE = AUDIO_WIN_LEN * SAMPLE_RATE;

std::array<float, WINDOW_SIZE> calc_hamming_window() {
  std::array<float, WINDOW_SIZE> a{0};
  for (int i = 0; i < WINDOW_SIZE; ++i) {
    a[i] = 0.54 - 0.46 * std::cos(2*M_PI*i/(WINDOW_SIZE-1));
  }
  return a;
}

std::array<float, WINDOW_SIZE> hamming_window = calc_hamming_window();

#ifndef USE_TFLITE
  using namespace tensorflow;
#else
  using namespace tflite;
#endif

using std::vector;

/* This is the actual implementation of the streaming inference API, with the
   Model class just forwarding the calls to this class.

   The streaming process uses three buffers that are fed eagerly as audio data
   is fed in. The buffers only hold the minimum amount of data needed to do a
   step in the acoustic model. The three buffers which live in StreamingContext
   are:

   - audio_buffer, used to buffer audio samples until there's enough data to
     compute input features for a single window.

   - mfcc_buffer, used to buffer input features until there's enough data for
     a single timestep. Remember there's overlap in the features, each timestep
     contains n_context past feature frames, the current feature frame, and
     n_context future feature frames, for a total of 2*n_context + 1 feature
     frames per timestep.

   - batch_buffer, used to buffer timesteps until there's enough data to compute
     a batch of n_steps.

   Data flows through all three buffers as audio samples are fed via the public
   API. When audio_buffer is full, features are computed from it and pushed to
   mfcc_buffer. When mfcc_buffer is full, the timestep is copied to batch_buffer.
   When batch_buffer is full, we do a single step through the acoustic model
   and accumulate results in StreamingState::accumulated_logits.

   When fininshStream() is called, we decode the accumulated logits and return
   the corresponding transcription.
*/
struct StreamingState {
  vector<float> accumulated_logits;
  vector<float> audio_buffer;
  float last_sample; // used for preemphasis
  vector<float> mfcc_buffer;
  vector<float> batch_buffer;
  ModelState* model;

  void feedAudioContent(const short* buffer, unsigned int buffer_size);
  char* intermediateDecode();
  char* finishStream();

  void processAudioWindow(const vector<float>& buf);
  void processMfccWindow(const vector<float>& buf);
  void pushMfccBuffer(const float* buf, unsigned int len);
  void addZeroMfccWindow();
  void processBatch(const vector<float>& buf, unsigned int n_steps);
};

struct ModelState {
#ifndef USE_TFLITE
  MemmappedEnv* mmap_env;
  Session* session;
  GraphDef graph_def;
#else // USE_TFLITE
  std::unique_ptr<Interpreter> interpreter;
  std::unique_ptr<FlatBufferModel> fbmodel;
#endif // USE_TFLITE
  unsigned int ncep;
  unsigned int ncontext;
  Alphabet* alphabet;
  Scorer* scorer;
  unsigned int beam_width;
  unsigned int n_steps;
  unsigned int mfcc_feats_per_timestep;
  unsigned int n_context;

#ifdef USE_TFLITE
  size_t previous_state_size;
  std::unique_ptr<float[]> previous_state_c_;
  std::unique_ptr<float[]> previous_state_h_;

  int input_node_idx;
  int previous_state_c_idx;
  int previous_state_h_idx;

  int logits_idx;
  int new_state_c_idx;
  int new_state_h_idx;
#endif

  ModelState();
  ~ModelState();

  /**
   * @brief Perform decoding of the logits, using basic CTC decoder or
   *        CTC decoder with KenLM enabled
   *
   * @param logits         Flat matrix of logits, of size:
   *                       n_frames * batch_size * num_classes
   *
   * @return String representing the decoded text.
   */
  char* decode(vector<float>& logits);

  /**
   * @brief Do a single inference step in the acoustic model, with:
   *          input=mfcc
   *          input_lengths=[n_frames]
   *
   * @param mfcc batch input data
   * @param n_frames number of timesteps in the data
   *
   * @param[out] output_logits Where to store computed logits.
   */
  void infer(const float* mfcc, unsigned int n_frames, vector<float>& output_logits);
};

ModelState::ModelState()
  :
#ifndef USE_TFLITE
    mmap_env(nullptr)
  , session(nullptr)
#else // USE_TFLITE
    interpreter(nullptr)
  , fbmodel(nullptr)
#endif // USE_TFLITE
  , ncep(0)
  , ncontext(0)
  , alphabet(nullptr)
  , scorer(nullptr)
  , beam_width(0)
  , n_steps(-1)
  , mfcc_feats_per_timestep(-1)
  , n_context(-1)
#ifdef USE_TFLITE
  , previous_state_size(0)
  , previous_state_c_(nullptr)
  , previous_state_h_(nullptr)
#endif
{
}

ModelState::~ModelState()
{
#ifndef USE_TFLITE
  if (session) {
    Status status = session->Close();
    if (!status.ok()) {
      std::cerr << "Error closing TensorFlow session: " << status << std::endl;
    }
  }
  delete mmap_env;
#endif // USE_TFLITE

  delete scorer;
  delete alphabet;
}

void
StreamingState::feedAudioContent(const short* buffer,
                                 unsigned int buffer_size)
{
  // Consume all the data that was passed in, processing full buffers if needed
  while (buffer_size > 0) {
    while (buffer_size > 0 && audio_buffer.size() < AUDIO_WIN_LEN_SAMPLES) {
      // Apply preemphasis to input sample and buffer it
      float sample = (float)(*buffer) - (PREEMPHASIS_COEFF * last_sample);
      audio_buffer.push_back(sample);
      last_sample = *buffer;
      ++buffer;
      --buffer_size;
    }

    // If the buffer is full, process and shift it
    if (audio_buffer.size() == AUDIO_WIN_LEN_SAMPLES) {
      processAudioWindow(audio_buffer);
      // Shift data by one step
      std::rotate(audio_buffer.begin(), audio_buffer.begin() + AUDIO_WIN_STEP_SAMPLES, audio_buffer.end());
      audio_buffer.resize(audio_buffer.size() - AUDIO_WIN_STEP_SAMPLES);
    }

    // Repeat until buffer empty
  }
}

char*
StreamingState::intermediateDecode()
{
  return model->decode(accumulated_logits);
}

char*
StreamingState::finishStream()
{
  // Flush audio buffer
  processAudioWindow(audio_buffer);

  // Add empty mfcc vectors at end of sample
  for (int i = 0; i < model->n_context; ++i) {
    addZeroMfccWindow();
  }

  // Process final batch
  if (batch_buffer.size() > 0) {
    processBatch(batch_buffer, batch_buffer.size()/model->mfcc_feats_per_timestep);
  }

  return model->decode(accumulated_logits);
}

void
StreamingState::processAudioWindow(const vector<float>& buf)
{
  // Compute MFCC features
  float* mfcc;
  int n_frames = csf_mfcc(buf.data(), buf.size(), SAMPLE_RATE,
                          AUDIO_WIN_LEN, AUDIO_WIN_STEP, MFCC_FEATURES, N_FILTERS, N_FFT,
                          LOWFREQ, SAMPLE_RATE/2, 0.f, CEP_LIFTER, 1, hamming_window.data(),
                          &mfcc);
  assert(n_frames == 1);

  pushMfccBuffer(mfcc, n_frames * MFCC_FEATURES);
  free(mfcc);
}

void
StreamingState::addZeroMfccWindow()
{
  static const float zero_buffer[MFCC_FEATURES] = {0.f};
  pushMfccBuffer(zero_buffer, MFCC_FEATURES);
}

void
StreamingState::pushMfccBuffer(const float* buf, unsigned int len)
{
  while (len > 0) {
    unsigned int next_copy_amount = std::min(len, (unsigned int)(model->mfcc_feats_per_timestep - mfcc_buffer.size()));
    mfcc_buffer.insert(mfcc_buffer.end(), buf, buf + next_copy_amount);
    buf += next_copy_amount;
    len -= next_copy_amount;
    assert(mfcc_buffer.size() <= model->mfcc_feats_per_timestep);

    if (mfcc_buffer.size() == model->mfcc_feats_per_timestep) {
      processMfccWindow(mfcc_buffer);
      // Shift data by one step of one mfcc feature vector
      std::rotate(mfcc_buffer.begin(), mfcc_buffer.begin() + MFCC_FEATURES, mfcc_buffer.end());
      mfcc_buffer.resize(mfcc_buffer.size() - MFCC_FEATURES);
    }
  }
}

void
StreamingState::processMfccWindow(const vector<float>& buf)
{
  auto start = buf.begin();
  auto end = buf.end();
  while (start != end) {
    unsigned int next_copy_amount = std::min<unsigned int>(std::distance(start, end), (unsigned int)(model->n_steps * model->mfcc_feats_per_timestep - batch_buffer.size()));
    batch_buffer.insert(batch_buffer.end(), start, start + next_copy_amount);
    start += next_copy_amount;
    assert(batch_buffer.size() <= model->n_steps * model->mfcc_feats_per_timestep);

    if (batch_buffer.size() == model->n_steps * model->mfcc_feats_per_timestep) {
      processBatch(batch_buffer, model->n_steps);
      batch_buffer.resize(0);
    }
  }
}

void
StreamingState::processBatch(const vector<float>& buf, unsigned int n_steps)
{
  model->infer(buf.data(), n_steps, accumulated_logits);
}

void
ModelState::infer(const float* aMfcc, unsigned int n_frames, vector<float>& logits_output)
{
  const size_t num_classes = alphabet->GetSize() + 1; // +1 for blank

#ifndef USE_TFLITE
  Tensor input(DT_FLOAT, TensorShape({BATCH_SIZE, n_steps, 2*n_context+1, MFCC_FEATURES}));

  auto input_mapped = input.flat<float>();
  int i;
  for (i = 0; i < n_frames*mfcc_feats_per_timestep; ++i) {
    input_mapped(i) = aMfcc[i];
  }
  for (; i < n_steps*mfcc_feats_per_timestep; ++i) {
    input_mapped(i) = 0;
  }

  Tensor input_lengths(DT_INT32, TensorShape({1}));
  input_lengths.scalar<int>()() = n_frames;

  vector<Tensor> outputs;
  Status status = session->Run(
    {{"input_node", input}, {"input_lengths", input_lengths}},
    {"logits"}, {}, &outputs);

  if (!status.ok()) {
    std::cerr << "Error running session: " << status << "\n";
    return;
  }

  auto logits_mapped = outputs[0].flat<float>();
  // The CTCDecoder works with log-probs.
  for (int t = 0; t < n_frames * BATCH_SIZE * num_classes; ++t) {
    logits_output.push_back(logits_mapped(t));
  }
#else // USE_TFLITE
  // Feeding input_node
  float* input_node = interpreter->typed_tensor<float>(input_node_idx);
  {
    int i;
    for (i = 0; i < n_frames*mfcc_feats_per_timestep; ++i) {
      input_node[i] = aMfcc[i];
    }
    for (; i < n_steps*mfcc_feats_per_timestep; ++i) {
      input_node[i] = 0;
    }
  }

  assert(previous_state_size > 0);

  // Feeding previous_state_c, previous_state_h
  memcpy(interpreter->typed_tensor<float>(previous_state_c_idx), previous_state_c_.get(), sizeof(float) * previous_state_size);
  memcpy(interpreter->typed_tensor<float>(previous_state_h_idx), previous_state_h_.get(), sizeof(float) * previous_state_size);

  TfLiteStatus status = interpreter->Invoke();
  if (status != kTfLiteOk) {
    std::cerr << "Error running session: " << status << "\n";
    return;
  }

  float* outputs = interpreter->typed_tensor<float>(logits_idx);

  // The CTCDecoder works with log-probs.
  for (int t = 0; t < n_frames * BATCH_SIZE * num_classes; ++t) {
    logits_output.push_back(outputs[t]);
  }

  memcpy(previous_state_c_.get(), interpreter->typed_tensor<float>(new_state_c_idx), sizeof(float) * previous_state_size);
  memcpy(previous_state_h_.get(), interpreter->typed_tensor<float>(new_state_h_idx), sizeof(float) * previous_state_size);
#endif // USE_TFLITE
}

char*
ModelState::decode(vector<float>& logits)
{
  const int cutoff_top_n = 40;
  const double cutoff_prob = 1.0;
  const size_t num_classes = alphabet->GetSize() + 1; // +1 for blank
  const int n_frames = logits.size() / (BATCH_SIZE * num_classes);

  // Convert logits to double
  vector<double> inputs(logits.begin(), logits.end());

  // Vector of <probability, Output> pairs
  vector<Output> out = ctc_beam_search_decoder(
    inputs.data(), n_frames, num_classes, *alphabet, beam_width,
    cutoff_prob, cutoff_top_n, scorer);

  return strdup(alphabet->LabelsToString(out[0].tokens).c_str());
}

#ifdef USE_TFLITE
int tflite_get_tensor_by_name(const ModelState* ctx, const vector<int>& list, const char* name)
{
  int rv = -1;

  for (int i = 0; i < list.size(); ++i) {
    const string& node_name = ctx->interpreter->tensor(list[i])->name;
    if (node_name.compare(string(name)) == 0) {
      rv = i;
    }
  }

  assert(rv >= 0);
  return rv;
}

int tflite_get_input_tensor_by_name(const ModelState* ctx, const char* name)
{
  return ctx->interpreter->inputs()[tflite_get_tensor_by_name(ctx, ctx->interpreter->inputs(), name)];
}

int tflite_get_output_tensor_by_name(const ModelState* ctx, const char* name)
{
  return ctx->interpreter->outputs()[tflite_get_tensor_by_name(ctx, ctx->interpreter->outputs(), name)];
}
#endif

int
DS_CreateModel(const char* aModelPath,
               unsigned int aNCep,
               unsigned int aNContext,
               const char* aAlphabetConfigPath,
               unsigned int aBeamWidth,
               ModelState** retval)
{
  std::unique_ptr<ModelState> model(new ModelState());
#ifndef USE_TFLITE
  model->mmap_env   = new MemmappedEnv(Env::Default());
#endif // USE_TFLITE
  model->ncep       = aNCep;
  model->ncontext   = aNContext;
  model->alphabet   = new Alphabet(aAlphabetConfigPath);
  model->beam_width = aBeamWidth;

  *retval = nullptr;

  DS_PrintVersions();

  if (!aModelPath || strlen(aModelPath) < 1) {
    std::cerr << "No model specified, cannot continue." << std::endl;
    return DS_ERR_NO_MODEL;
  }

#ifndef USE_TFLITE
  Status status;
  SessionOptions options;

  bool is_mmap = std::string(aModelPath).find(".pbmm") != std::string::npos;
  if (!is_mmap) {
    std::cerr << "Warning: reading entire model file into memory. Transform model file into an mmapped graph to reduce heap usage." << std::endl;
  } else {
    status = model->mmap_env->InitializeFromFile(aModelPath);
    if (!status.ok()) {
      std::cerr << status << std::endl;
      return DS_ERR_FAIL_INIT_MMAP;
    }

    options.config.mutable_graph_options()
      ->mutable_optimizer_options()
      ->set_opt_level(::OptimizerOptions::L0);
    options.env = model->mmap_env;
  }

  status = NewSession(options, &model->session);
  if (!status.ok()) {
    std::cerr << status << std::endl;
    return DS_ERR_FAIL_INIT_SESS;
  }

  if (is_mmap) {
    status = ReadBinaryProto(model->mmap_env,
                             MemmappedFileSystem::kMemmappedPackageDefaultGraphDef,
                             &model->graph_def);
  } else {
    status = ReadBinaryProto(Env::Default(), aModelPath, &model->graph_def);
  }
  if (!status.ok()) {
    std::cerr << status << std::endl;
    return DS_ERR_FAIL_READ_PROTOBUF;
  }

  status = model->session->Create(model->graph_def);
  if (!status.ok()) {
    std::cerr << status << std::endl;
    return DS_ERR_FAIL_CREATE_SESS;
  }

  for (int i = 0; i < model->graph_def.node_size(); ++i) {
    NodeDef node = model->graph_def.node(i);
    if (node.name() == "input_node") {
      const auto& shape = node.attr().at("shape").shape();
      model->n_steps = shape.dim(1).size();
      model->n_context = (shape.dim(2).size()-1)/2;
      model->mfcc_feats_per_timestep = shape.dim(2).size() * shape.dim(3).size();
    } else if (node.name() == "logits_shape") {
      Tensor logits_shape = Tensor(DT_INT32, TensorShape({3}));
      if (!logits_shape.FromProto(node.attr().at("value").tensor())) {
        continue;
      }

      int final_dim_size = logits_shape.vec<int>()(2) - 1;
      if (final_dim_size != model->alphabet->GetSize()) {
        std::cerr << "Error: Alphabet size does not match loaded model: alphabet "
                  << "has size " << model->alphabet->GetSize()
                  << ", but model has " << final_dim_size
                  << " classes in its output. Make sure you're passing an alphabet "
                  << "file with the same size as the one used for training."
                  << std::endl;
        return DS_ERR_INVALID_ALPHABET;
      }
    }
  }

  if (model->n_context == -1) {
    std::cerr << "Error: Could not infer context window size from model file. "
              << "Make sure input_node is a 3D tensor with the last dimension "
              << "of size MFCC_FEATURES * ((2 * context window) + 1). If you "
              << "changed the number of features in the input, adjust the "
              << "MFCC_FEATURES constant in " __FILE__
              << std::endl;
    return DS_ERR_INVALID_SHAPE;
  }

  *retval = model.release();
  return DS_ERR_OK;
#else // USE_TFLITE
  TfLiteStatus status;

  model->fbmodel = tflite::FlatBufferModel::BuildFromFile(aModelPath);
  if (!model->fbmodel) {
    std::cerr << "Error at reading model file " << aModelPath << std::endl;
    return DS_ERR_FAIL_INIT_MMAP;
  }


  tflite::ops::builtin::BuiltinOpResolver resolver;
  tflite::InterpreterBuilder(*model->fbmodel, resolver)(&model->interpreter);
  if (!model->interpreter) {
    std::cerr << "Error at InterpreterBuilder for model file " << aModelPath << std::endl;
    return DS_ERR_FAIL_INTERPRETER;
  }

  model->interpreter->AllocateTensors();
  model->interpreter->SetNumThreads(4);

  // Query all the index once
  model->input_node_idx       = tflite_get_input_tensor_by_name(model.get(), "input_node");
  model->previous_state_c_idx = tflite_get_input_tensor_by_name(model.get(), "previous_state_c");
  model->previous_state_h_idx = tflite_get_input_tensor_by_name(model.get(), "previous_state_h");
  model->logits_idx           = tflite_get_output_tensor_by_name(model.get(), "logits");
  model->new_state_c_idx      = tflite_get_output_tensor_by_name(model.get(), "new_state_c");
  model->new_state_h_idx      = tflite_get_output_tensor_by_name(model.get(), "new_state_h");

  TfLiteIntArray* dims_input_node = model->interpreter->tensor(model->input_node_idx)->dims;

  model->n_steps = dims_input_node->data[1];
  model->n_context = (dims_input_node->data[2] - 1 ) / 2;
  model->mfcc_feats_per_timestep = dims_input_node->data[2] * dims_input_node->data[3];

  TfLiteIntArray* dims_logits = model->interpreter->tensor(model->logits_idx)->dims;
  const int final_dim_size = dims_logits->data[1] - 1;
  if (final_dim_size != model->alphabet->GetSize()) {
    std::cerr << "Error: Alphabet size does not match loaded model: alphabet "
              << "has size " << model->alphabet->GetSize()
              << ", but model has " << final_dim_size
              << " classes in its output. Make sure you're passing an alphabet "
              << "file with the same size as the one used for training."
              << std::endl;
    return DS_ERR_INVALID_ALPHABET;
  }

  TfLiteIntArray* dims_c = model->interpreter->tensor(model->previous_state_c_idx)->dims;
  TfLiteIntArray* dims_h = model->interpreter->tensor(model->previous_state_h_idx)->dims;
  assert(dims_c->data[1] == dims_h->data[1]);

  model->previous_state_size = dims_c->data[1];
  model->previous_state_c_.reset(new float[model->previous_state_size]());
  model->previous_state_h_.reset(new float[model->previous_state_size]());

  // Set initial values for previous_state_c and previous_state_h
  memset(model->previous_state_c_.get(), 0, sizeof(float) * model->previous_state_size);
  memset(model->previous_state_h_.get(), 0, sizeof(float) * model->previous_state_size);

  *retval = model.release();
  return DS_ERR_OK;
#endif // USE_TFLITE
}

void
DS_DestroyModel(ModelState* ctx)
{
  delete ctx;
}

int
DS_EnableDecoderWithLM(ModelState* aCtx,
                       const char* aAlphabetConfigPath,
                       const char* aLMPath,
                       const char* aTriePath,
                       float aLMAlpha,
                       float aLMBeta)
{
  try {
    aCtx->scorer = new Scorer(aLMAlpha, aLMBeta,
                              aLMPath ? aLMPath : "",
                              aTriePath ? aTriePath : "",
                              *aCtx->alphabet);
    return DS_ERR_OK;
  } catch (...) {
    return DS_ERR_INVALID_LM;
  }
}

char*
DS_SpeechToText(ModelState* aCtx,
                const short* aBuffer,
                unsigned int aBufferSize,
                unsigned int aSampleRate)
{
  StreamingState* ctx;
  int status = DS_SetupStream(aCtx, 0, aSampleRate, &ctx);
  if (status != DS_ERR_OK) {
    return nullptr;
  }
  DS_FeedAudioContent(ctx, aBuffer, aBufferSize);
  return DS_FinishStream(ctx);
}

int
DS_SetupStream(ModelState* aCtx,
               unsigned int aPreAllocFrames,
               unsigned int aSampleRate,
               StreamingState** retval)
{
  *retval = nullptr;

#ifndef USE_TFLITE
  Status status = aCtx->session->Run({}, {}, {"initialize_state"}, nullptr);
  if (!status.ok()) {
    std::cerr << "Error running session: " << status << std::endl;
    return DS_ERR_FAIL_RUN_SESS;
  }
#endif // USE_TFLITE

  std::unique_ptr<StreamingState> ctx(new StreamingState());
  if (!ctx) {
    std::cerr << "Could not allocate streaming state." << std::endl;
    return DS_ERR_FAIL_CREATE_STREAM;
  }

  const size_t num_classes = aCtx->alphabet->GetSize() + 1; // +1 for blank

  // Default initial allocation = 3 seconds.
  if (aPreAllocFrames == 0) {
    aPreAllocFrames = 150;
  }

  ctx->accumulated_logits.reserve(aPreAllocFrames * BATCH_SIZE * num_classes);

  ctx->audio_buffer.reserve(AUDIO_WIN_LEN_SAMPLES);
  ctx->last_sample = 0;
  ctx->mfcc_buffer.reserve(aCtx->mfcc_feats_per_timestep);
  ctx->mfcc_buffer.resize(MFCC_FEATURES*aCtx->n_context, 0.f);
  ctx->batch_buffer.reserve(aCtx->n_steps * aCtx->mfcc_feats_per_timestep);

  ctx->model = aCtx;

  *retval = ctx.release();
  return DS_ERR_OK;
}

void
DS_FeedAudioContent(StreamingState* aSctx,
                    const short* aBuffer,
                    unsigned int aBufferSize)
{
  aSctx->feedAudioContent(aBuffer, aBufferSize);
}

char*
DS_IntermediateDecode(StreamingState* aSctx)
{
  return aSctx->intermediateDecode();
}

char*
DS_FinishStream(StreamingState* aSctx)
{
  char* str = aSctx->finishStream();
  DS_DiscardStream(aSctx);
  return str;
}

void
DS_DiscardStream(StreamingState* aSctx)
{
  delete aSctx;
}

void
DS_AudioToInputVector(const short* aBuffer,
                      unsigned int aBufferSize,
                      unsigned int aSampleRate,
                      unsigned int aNCep,
                      unsigned int aNContext,
                      float** aMfcc,
                      int* aNFrames,
                      int* aFrameLen)
{
  const int contextSize = aNCep * aNContext;
  const int frameSize = aNCep + (2 * aNCep * aNContext);

  // Compute MFCC features
  float* mfcc;
  int n_frames = csf_mfcc(aBuffer, aBufferSize, aSampleRate,
                          AUDIO_WIN_LEN, AUDIO_WIN_STEP, aNCep, N_FILTERS, N_FFT,
                          LOWFREQ, aSampleRate/2, PREEMPHASIS_COEFF, CEP_LIFTER,
                          1, NULL, &mfcc);

  // Take every other frame (BiRNN stride of 2) and add past/future context
  int ds_input_length = (n_frames + 1) / 2;
  // TODO: Use MFCC of silence instead of zero
  float* ds_input = (float*)calloc(ds_input_length * frameSize, sizeof(float));
  for (int i = 0, idx = 0, mfcc_idx = 0; i < ds_input_length;
       i++, idx += frameSize, mfcc_idx += aNCep * 2) {
    // Past context
    for (int j = aNContext; j > 0; j--) {
      int frame_index = (i - j) * 2;
      if (frame_index < 0) { continue; }
      int mfcc_base = frame_index * aNCep;
      int base = (aNContext - j) * aNCep;
      for (int k = 0; k < aNCep; k++) {
        ds_input[idx + base + k] = mfcc[mfcc_base + k];
      }
    }

    // Present context
    for (int j = 0; j < aNCep; j++) {
      ds_input[idx + j + contextSize] = mfcc[mfcc_idx + j];
    }

    // Future context
    for (int j = 1; j <= aNContext; j++) {
      int frame_index = (i + j) * 2;
      if (frame_index >= n_frames) { break; }
      int mfcc_base = frame_index * aNCep;
      int base = contextSize + aNCep + ((j - 1) * aNCep);
      for (int k = 0; k < aNCep; k++) {
        ds_input[idx + base + k] = mfcc[mfcc_base + k];
      }
    }
  }

  // Free mfcc array
  free(mfcc);

  if (aMfcc) {
    *aMfcc = ds_input;
  }
  if (aNFrames) {
    *aNFrames = ds_input_length;
  }
  if (aFrameLen) {
    *aFrameLen = frameSize;
  }
}

void
DS_PrintVersions() {
  std::cerr << "TensorFlow: " << tf_local_git_version() << std::endl;
  std::cerr << "DeepSpeech: " << ds_git_version() << std::endl;
#ifdef __ANDROID__
  LOGE("TensorFlow: %s", tf_local_git_version());
  LOGD("TensorFlow: %s", tf_local_git_version());
  LOGE("DeepSpeech: %s", ds_git_version());
  LOGD("DeepSpeech: %s", ds_git_version());
#endif
}