Limit the maximum segment length for VAD. (#990)

@@ -190,6 +190,14 @@ class SileroVadModel::Impl {
 
   int32_t MinSpeechDurationSamples() const { return min_speech_samples_; }
 
+  void SetMinSilenceDuration(float s) {
+    min_silence_samples_ = sample_rate_ * s;
+  }
+
+  void SetThreshold(float threshold) {
+    config_.silero_vad.threshold = threshold;
+  }
+
  private:
   void Init(void *model_data, size_t model_data_length) {
     sess_ = std::make_unique<Ort::Session>(env_, model_data, model_data_length,
@@ -306,4 +314,12 @@ int32_t SileroVadModel::MinSpeechDurationSamples() const {
   return impl_->MinSpeechDurationSamples();
 }
 
+void SileroVadModel::SetMinSilenceDuration(float s) {
+  impl_->SetMinSilenceDuration(s);
+}
+
+void SileroVadModel::SetThreshold(float threshold) {
+  impl_->SetThreshold(threshold);
+}
+
 }  // namespace sherpa_onnx

@@ -42,6 +42,9 @@ class SileroVadModel : public VadModel {
   int32_t MinSilenceDurationSamples() const override;
   int32_t MinSpeechDurationSamples() const override;
 
+  void SetMinSilenceDuration(float s) override;
+  void SetThreshold(float threshold) override;
+
  private:
   class Impl;
   std::unique_ptr<Impl> impl_;

@@ -42,6 +42,8 @@ class VadModel {
 
   virtual int32_t MinSilenceDurationSamples() const = 0;
   virtual int32_t MinSpeechDurationSamples() const = 0;
+  virtual void SetMinSilenceDuration(float s) = 0;
+  virtual void SetThreshold(float threshold) = 0;
 };
 
 }  // namespace sherpa_onnx

@@ -29,6 +29,14 @@ class VoiceActivityDetector::Impl {
 #endif
 
   void AcceptWaveform(const float *samples, int32_t n) {
+    if (buffer_.Size() > max_utterance_length_) {
+      model_->SetMinSilenceDuration(new_min_silence_duration_s_);
+      model_->SetThreshold(new_threshold_);
+    } else {
+      model_->SetMinSilenceDuration(config_.silero_vad.min_silence_duration);
+      model_->SetThreshold(config_.silero_vad.threshold);
+    }
+
     int32_t window_size = model_->WindowSize();
 
     // note n is usually window_size and there is no need to use
@@ -114,6 +122,10 @@ class VoiceActivityDetector::Impl {
   CircularBuffer buffer_;
   std::vector<float> last_;
 
+  int max_utterance_length_ = 16000 * 20;  // in samples
+  float new_min_silence_duration_s_ = 0.1;
+  float new_threshold_ = 1.10;
+
   int32_t start_ = -1;
 };