Support specifying max speech duration for VAD. (#1348)

sherpa-onnx/csrc/silero-vad-model-config.h

@@ -27,6 +27,11 @@ struct SileroVadModelConfig {
   // 256, 512, 768 samples for 800 Hz
   int32_t window_size = 512;  // in samples
 
+  // If a speech segment is longer than this value, then we increase
+  // the threshold to 0.9. After finishing detecting the segment,
+  // the threshold value is reset to its original value.
+  float max_speech_duration = 20;  // in seconds
+
   SileroVadModelConfig() = default;
 
   void Register(ParseOptions *po);