update vad config

model.py

@@ -251,9 +251,11 @@ def get_vad() -> sherpa_onnx.VoiceActivityDetector:
 
     config = sherpa_onnx.VadModelConfig()
     config.silero_vad.model = vad_model
-    config.silero_vad.min_silence_duration = 0.15
+    config.silero_vad.threshold = 0.5
+    config.silero_vad.min_silence_duration = 0.25
     config.silero_vad.min_speech_duration = 0.25
     config.sample_rate = sample_rate
+    config.silero_vad.max_speech_duration = 20  # seconds
 
     vad = sherpa_onnx.VoiceActivityDetector(
         config,