Prewarm audio to speed up mic publishing (#623)

* Prewarm audio to speed up mic publishing

* update cache action

* spotless and changeset

+---
+"client-sdk-android": minor
+---
+
+Prewarm audio to speed up mic publishing

@@ -35,7 +35,7 @@ jobs:
         java-version: '17'
         distribution: 'adopt'
 
-    - uses: actions/cache@v3.3.2
+    - uses: actions/cache@v4
       with:
         path: |
           ~/.gradle/caches

 [versions]
-webrtc = "125.6422.06.1"
+webrtc = "125.6422.07"
 
 androidJainSipRi = "1.3.0-91"
 androidx-activity = "1.9.0"

+/*
+ * Copyright 2025 LiveKit, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.livekit.android.audio
+
+import livekit.org.webrtc.audio.JavaAudioDeviceModule
+
+/**
+ * @suppress
+ */
+interface AudioRecordPrewarmer {
+    fun prewarm()
+    fun stop()
+}
+
+/**
+ * @suppress
+ */
+class NoAudioRecordPrewarmer : AudioRecordPrewarmer {
+    override fun prewarm() {
+        // nothing to do.
+    }
+
+    override fun stop() {
+        // nothing to do.
+    }
+}
+
+/**
+ * @suppress
+ */
+class JavaAudioRecordPrewarmer(private val audioDeviceModule: JavaAudioDeviceModule) : AudioRecordPrewarmer {
+    override fun prewarm() {
+        audioDeviceModule.prewarmRecording()
+    }
+
+    override fun stop() {
+        audioDeviceModule.requestStopRecording()
+    }
+}

@@ -27,8 +27,11 @@ import io.livekit.android.LiveKit
 import io.livekit.android.audio.AudioBufferCallbackDispatcher
 import io.livekit.android.audio.AudioProcessingController
 import io.livekit.android.audio.AudioProcessorOptions
+import io.livekit.android.audio.AudioRecordPrewarmer
 import io.livekit.android.audio.AudioRecordSamplesDispatcher
 import io.livekit.android.audio.CommunicationWorkaround
+import io.livekit.android.audio.JavaAudioRecordPrewarmer
+import io.livekit.android.audio.NoAudioRecordPrewarmer
 import io.livekit.android.memory.CloseableManager
 import io.livekit.android.util.LKLog
 import io.livekit.android.util.LoggingLevel
@@ -244,6 +247,15 @@ internal object RTCModule {
     }
 
     @Provides
+    fun audioPrewarmer(audioDeviceModule: AudioDeviceModule): AudioRecordPrewarmer {
+        return if (audioDeviceModule is JavaAudioDeviceModule) {
+            JavaAudioRecordPrewarmer(audioDeviceModule)
+        } else {
+            NoAudioRecordPrewarmer()
+        }
+    }
+
+    @Provides
     @Singleton
     fun eglBase(
         @Named(InjectionNames.OVERRIDE_EGL_BASE)

@@ -32,6 +32,7 @@ import io.livekit.android.RoomOptions
 import io.livekit.android.Version
 import io.livekit.android.audio.AudioHandler
 import io.livekit.android.audio.AudioProcessingController
+import io.livekit.android.audio.AudioRecordPrewarmer
 import io.livekit.android.audio.AudioSwitchHandler
 import io.livekit.android.audio.AuthedAudioProcessingController
 import io.livekit.android.audio.CommunicationWorkaround
@@ -104,6 +105,7 @@ constructor(
     private val audioDeviceModule: AudioDeviceModule,
     private val regionUrlProviderFactory: RegionUrlProvider.Factory,
     private val connectionWarmer: ConnectionWarmer,
+    private val audioRecordPrewarmer: AudioRecordPrewarmer,
 ) : RTCEngine.Listener, ParticipantListener {
 
     private lateinit var coroutineScope: CoroutineScope
@@ -177,6 +179,7 @@ constructor(
                 State.DISCONNECTED -> {
                     audioHandler.stop()
                     communicationWorkaround.stop()
+                    audioRecordPrewarmer.stop()
                 }
 
                 else -> {}
@@ -475,6 +478,7 @@ constructor(
             networkCallbackManager.registerCallback()
             if (options.audio) {
                 val audioTrack = localParticipant.createAudioTrack()
+                audioTrack.prewarm()
                 localParticipant.publishAudioTrack(audioTrack)
             }
             ensureActive()

@@ -317,6 +317,7 @@ internal constructor(
 
                         Track.Source.MICROPHONE -> {
                             val track = createAudioTrack()
+                            track.prewarm()
                             publishAudioTrack(track)
                         }
 

 /*
- * Copyright 2023-2024 LiveKit, Inc.
+ * Copyright 2023-2025 LiveKit, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,6 +26,7 @@ import dagger.assisted.AssistedInject
 import io.livekit.android.audio.AudioBufferCallback
 import io.livekit.android.audio.AudioBufferCallbackDispatcher
 import io.livekit.android.audio.AudioProcessingController
+import io.livekit.android.audio.AudioRecordPrewarmer
 import io.livekit.android.audio.AudioRecordSamplesDispatcher
 import io.livekit.android.audio.MixerAudioBufferCallback
 import io.livekit.android.dagger.InjectionNames
@@ -70,6 +71,7 @@ constructor(
     private val audioRecordSamplesDispatcher: AudioRecordSamplesDispatcher,
     @Named(InjectionNames.LOCAL_AUDIO_BUFFER_CALLBACK_DISPATCHER)
     private val audioBufferCallbackDispatcher: AudioBufferCallbackDispatcher,
+    private val audioRecordPrewarmer: AudioRecordPrewarmer,
 ) : AudioTrack(name, mediaTrack) {
     /**
      * To only be used for flow delegate scoping, and should not be cancelled.
@@ -83,6 +85,17 @@ constructor(
     private val trackSinks = mutableSetOf<AudioTrackSink>()
 
     /**
+     * Prewarms the audio stack if needed by starting the recording regardless of whether it's being published.
+     */
+    fun prewarm() {
+        audioRecordPrewarmer.prewarm()
+    }
+
+    fun stopPrewarm() {
+        audioRecordPrewarmer.stop()
+    }
+
+    /**
      * Note: This function relies on us setting
      * [JavaAudioDeviceModule.Builder.setSamplesReadyCallback].
      * If you provide your own [AudioDeviceModule], or set your own

 /*
- * Copyright 2023-2024 LiveKit, Inc.
+ * Copyright 2023-2025 LiveKit, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,7 +22,9 @@ import dagger.Module
 import dagger.Provides
 import io.livekit.android.audio.AudioBufferCallbackDispatcher
 import io.livekit.android.audio.AudioProcessingController
+import io.livekit.android.audio.AudioRecordPrewarmer
 import io.livekit.android.audio.AudioRecordSamplesDispatcher
+import io.livekit.android.audio.NoAudioRecordPrewarmer
 import io.livekit.android.dagger.CapabilitiesGetter
 import io.livekit.android.dagger.InjectionNames
 import io.livekit.android.test.mock.MockAudioDeviceModule
@@ -75,6 +77,11 @@ object TestRTCModule {
     }
 
     @Provides
+    fun audioPrewarmer(): AudioRecordPrewarmer {
+        return NoAudioRecordPrewarmer()
+    }
+
+    @Provides
     @Singleton
     fun peerConnectionFactory(
         appContext: Context,

 /*
- * Copyright 2024 LiveKit, Inc.
+ * Copyright 2024-2025 LiveKit, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,7 +18,9 @@ package io.livekit.android.test.mock.room.track
 
 import io.livekit.android.audio.AudioBufferCallbackDispatcher
 import io.livekit.android.audio.AudioProcessingController
+import io.livekit.android.audio.AudioRecordPrewarmer
 import io.livekit.android.audio.AudioRecordSamplesDispatcher
+import io.livekit.android.audio.NoAudioRecordPrewarmer
 import io.livekit.android.room.track.LocalAudioTrack
 import io.livekit.android.room.track.LocalAudioTrackOptions
 import io.livekit.android.test.MockE2ETest
@@ -38,6 +40,7 @@ fun MockE2ETest.createMockLocalAudioTrack(
     dispatcher: CoroutineDispatcher = coroutineRule.dispatcher,
     audioRecordSamplesDispatcher: AudioRecordSamplesDispatcher = AudioRecordSamplesDispatcher(),
     audioBufferCallbackDispatcher: AudioBufferCallbackDispatcher = AudioBufferCallbackDispatcher(),
+    audioRecordPrewarmer: AudioRecordPrewarmer = NoAudioRecordPrewarmer(),
 ): LocalAudioTrack {
     return LocalAudioTrack(
         name = name,
@@ -47,5 +50,6 @@ fun MockE2ETest.createMockLocalAudioTrack(
         dispatcher = dispatcher,
         audioRecordSamplesDispatcher = audioRecordSamplesDispatcher,
         audioBufferCallbackDispatcher = audioBufferCallbackDispatcher,
+        audioRecordPrewarmer = audioRecordPrewarmer,
     )
 }

 /*
- * Copyright 2023-2024 LiveKit, Inc.
+ * Copyright 2023-2025 LiveKit, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@ import android.net.ConnectivityManager.NetworkCallback
 import android.net.Network
 import androidx.test.core.app.ApplicationProvider
 import io.livekit.android.audio.NoAudioHandler
+import io.livekit.android.audio.NoAudioRecordPrewarmer
 import io.livekit.android.audio.NoopCommunicationWorkaround
 import io.livekit.android.e2ee.E2EEManager
 import io.livekit.android.events.DisconnectReason
@@ -131,6 +132,7 @@ class RoomTest {
             audioDeviceModule = MockAudioDeviceModule(),
             regionUrlProviderFactory = regionUrlProviderFactory,
             connectionWarmer = MockConnectionWarmer(),
+            audioRecordPrewarmer = NoAudioRecordPrewarmer(),
         )
     }