diff --git a/sherpa-onnx/kotlin-api/KeywordSpotter.kt b/sherpa-onnx/kotlin-api/KeywordSpotter.kt
index 803762e5..ea214361 100644
--- a/sherpa-onnx/kotlin-api/KeywordSpotter.kt
+++ b/sherpa-onnx/kotlin-api/KeywordSpotter.kt
@@ -24,7 +24,7 @@ class KeywordSpotter(
     assetManager: AssetManager? = null,
     val config: KeywordSpotterConfig,
 ) {
-    private val ptr: Long
+    private var ptr: Long
 
     init {
         ptr = if (assetManager != null) {
@@ -35,7 +35,10 @@ class KeywordSpotter(
     }
 
     protected fun finalize() {
-        delete(ptr)
+        if (ptr != 0L) {
+            delete(ptr)
+            ptr = 0
+        }
     }
 
     fun release() = finalize()
diff --git a/sherpa-onnx/kotlin-api/OfflinePunctuation.kt b/sherpa-onnx/kotlin-api/OfflinePunctuation.kt
index ec6aa08f..8dfcbd63 100644
--- a/sherpa-onnx/kotlin-api/OfflinePunctuation.kt
+++ b/sherpa-onnx/kotlin-api/OfflinePunctuation.kt
@@ -18,7 +18,7 @@ class OfflinePunctuation(
     assetManager: AssetManager? = null,
     config: OfflinePunctuationConfig,
 ) {
-    private val ptr: Long
+    private var ptr: Long
 
     init {
         ptr = if (assetManager != null) {
@@ -29,7 +29,10 @@ class OfflinePunctuation(
     }
 
     protected fun finalize() {
-        delete(ptr)
+        if (ptr != 0L) {
+            delete(ptr)
+            ptr = 0
+        }
     }
 
     fun release() = finalize()
diff --git a/sherpa-onnx/kotlin-api/OfflineRecognizer.kt b/sherpa-onnx/kotlin-api/OfflineRecognizer.kt
index 0003eb42..f48cc3fd 100644
--- a/sherpa-onnx/kotlin-api/OfflineRecognizer.kt
+++ b/sherpa-onnx/kotlin-api/OfflineRecognizer.kt
@@ -72,7 +72,7 @@ class OfflineRecognizer(
     assetManager: AssetManager? = null,
     config: OfflineRecognizerConfig,
 ) {
-    private val ptr: Long
+    private var ptr: Long
 
     init {
         ptr = if (assetManager != null) {
@@ -83,7 +83,10 @@ class OfflineRecognizer(
     }
 
     protected fun finalize() {
-        delete(ptr)
+        if (ptr != 0L) {
+            delete(ptr)
+            ptr = 0
+        }
     }
 
     fun release() = finalize()
@@ -102,7 +105,14 @@ class OfflineRecognizer(
         val lang = objArray[3] as String
         val emotion = objArray[4] as String
         val event = objArray[5] as String
-        return OfflineRecognizerResult(text = text, tokens = tokens, timestamps = timestamps, lang = lang, emotion = emotion, event = event)
+        return OfflineRecognizerResult(
+            text = text,
+            tokens = tokens,
+            timestamps = timestamps,
+            lang = lang,
+            emotion = emotion,
+            event = event
+        )
     }
 
     fun decode(stream: OfflineStream) = decode(ptr, stream.ptr)
diff --git a/sherpa-onnx/kotlin-api/OfflineStream.kt b/sherpa-onnx/kotlin-api/OfflineStream.kt
index 49652e72..ab316c52 100644
--- a/sherpa-onnx/kotlin-api/OfflineStream.kt
+++ b/sherpa-onnx/kotlin-api/OfflineStream.kt
@@ -13,6 +13,14 @@ class OfflineStream(var ptr: Long) {
 
     fun release() = finalize()
 
+    fun use(block: (OfflineStream) -> Unit) {
+        try {
+            block(this)
+        } finally {
+            release()
+        }
+    }
+
     private external fun acceptWaveform(ptr: Long, samples: FloatArray, sampleRate: Int)
     private external fun delete(ptr: Long)
 
diff --git a/sherpa-onnx/kotlin-api/OnlineRecognizer.kt b/sherpa-onnx/kotlin-api/OnlineRecognizer.kt
index 4750e232..7ddefdf3 100644
--- a/sherpa-onnx/kotlin-api/OnlineRecognizer.kt
+++ b/sherpa-onnx/kotlin-api/OnlineRecognizer.kt
@@ -62,7 +62,7 @@ data class OnlineRecognizerConfig(
     var featConfig: FeatureConfig = FeatureConfig(),
     var modelConfig: OnlineModelConfig,
     var lmConfig: OnlineLMConfig = OnlineLMConfig(),
-    var ctcFstDecoderConfig : OnlineCtcFstDecoderConfig = OnlineCtcFstDecoderConfig(),
+    var ctcFstDecoderConfig: OnlineCtcFstDecoderConfig = OnlineCtcFstDecoderConfig(),
     var endpointConfig: EndpointConfig = EndpointConfig(),
     var enableEndpoint: Boolean = true,
     var decodingMethod: String = "greedy_search",
@@ -85,7 +85,7 @@ class OnlineRecognizer(
     assetManager: AssetManager? = null,
     val config: OnlineRecognizerConfig,
 ) {
-    private val ptr: Long
+    private var ptr: Long
 
     init {
         ptr = if (assetManager != null) {
@@ -96,7 +96,10 @@ class OnlineRecognizer(
     }
 
     protected fun finalize() {
-        delete(ptr)
+        if (ptr != 0L) {
+            delete(ptr)
+            ptr = 0
+        }
     }
 
     fun release() = finalize()
diff --git a/sherpa-onnx/kotlin-api/OnlineStream.kt b/sherpa-onnx/kotlin-api/OnlineStream.kt
index 6057fabd..cb15a9a4 100644
--- a/sherpa-onnx/kotlin-api/OnlineStream.kt
+++ b/sherpa-onnx/kotlin-api/OnlineStream.kt
@@ -15,10 +15,19 @@ class OnlineStream(var ptr: Long = 0) {
 
     fun release() = finalize()
 
+    fun use(block: (OnlineStream) -> Unit) {
+        try {
+            block(this)
+        } finally {
+            release()
+        }
+    }
+
     private external fun acceptWaveform(ptr: Long, samples: FloatArray, sampleRate: Int)
     private external fun inputFinished(ptr: Long)
     private external fun delete(ptr: Long)
 
+
     companion object {
         init {
             System.loadLibrary("sherpa-onnx-jni")
diff --git a/sherpa-onnx/kotlin-api/Vad.kt b/sherpa-onnx/kotlin-api/Vad.kt
index c842e035..182a23d5 100644
--- a/sherpa-onnx/kotlin-api/Vad.kt
+++ b/sherpa-onnx/kotlin-api/Vad.kt
@@ -19,11 +19,13 @@ data class VadModelConfig(
     var debug: Boolean = false,
 )
 
+class SpeechSegment(val start: Int, val samples: FloatArray)
+
 class Vad(
     assetManager: AssetManager? = null,
     var config: VadModelConfig,
 ) {
-    private val ptr: Long
+    private var ptr: Long
 
     init {
         if (assetManager != null) {
@@ -34,17 +36,23 @@ class Vad(
     }
 
     protected fun finalize() {
-        delete(ptr)
+        if (ptr != 0L) {
+            delete(ptr)
+            ptr = 0
+        }
     }
 
+    fun release() = finalize()
+
     fun acceptWaveform(samples: FloatArray) = acceptWaveform(ptr, samples)
 
     fun empty(): Boolean = empty(ptr)
     fun pop() = pop(ptr)
 
-    // return an array containing
-    // [start: Int, samples: FloatArray]
-    fun front() = front(ptr)
+    fun front(): SpeechSegment {
+        val segment = front(ptr)
+        return SpeechSegment(segment[0] as Int, segment[1] as FloatArray)
+    }
 
     fun clear() = clear(ptr)
 
diff --git a/sherpa-onnx/kotlin-api/WaveReader.kt b/sherpa-onnx/kotlin-api/WaveReader.kt
index dca39984..9e4f5fbd 100644
--- a/sherpa-onnx/kotlin-api/WaveReader.kt
+++ b/sherpa-onnx/kotlin-api/WaveReader.kt
@@ -3,8 +3,49 @@ package com.k2fsa.sherpa.onnx
 
 import android.content.res.AssetManager
 
+data class WaveData(
+    val samples: FloatArray,
+    val sampleRate: Int,
+) {
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (javaClass != other?.javaClass) return false
+
+        other as WaveData
+
+        if (!samples.contentEquals(other.samples)) return false
+        if (sampleRate != other.sampleRate) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        var result = samples.contentHashCode()
+        result = 31 * result + sampleRate
+        return result
+    }
+}
+
 class WaveReader {
     companion object {
+
+        fun readWave(
+            assetManager: AssetManager,
+            filename: String,
+        ): WaveData {
+            return readWaveFromAsset(assetManager, filename).let {
+                WaveData(it[0] as FloatArray, it[1] as Int)
+            }
+        }
+
+        fun readWave(
+            filename: String,
+        ): WaveData {
+            return readWaveFromFile(filename).let {
+                WaveData(it[0] as FloatArray, it[1] as Int)
+            }
+        }
+
         // Read a mono wave file asset
         // The returned array has two entries:
         //  - the first entry contains an 1-D float array