Android: fix Cast volume to control receiver

- Route hardware volume keys to Cast via MediaSession VolumeProvider
- Use CastSession.volume (0–1) mapped to 0–100; clamp and step by 1
- Update provider with actual device volume after each change (prevents stalls)
- Drop stream-volume/polling attempts and other leftovers
- Expose get/set/adjust device volume commands to the player

android/app/src/main/java/com/audiobookshelf/app/player/CastPlayer.kt

@@ -76,7 +76,10 @@ class CastPlayer(var castContext: CastContext) : BasePlayer() {
       COMMAND_GET_MEDIA_ITEMS_METADATA,
       COMMAND_SET_MEDIA_ITEMS_METADATA,
       COMMAND_CHANGE_MEDIA_ITEMS,
-      COMMAND_GET_TRACKS)
+      COMMAND_GET_TRACKS,
+      COMMAND_GET_DEVICE_VOLUME,
+      COMMAND_SET_DEVICE_VOLUME,
+      COMMAND_ADJUST_DEVICE_VOLUME)
     .build()
 
   var currentPlaybackState = Player.STATE_IDLE
@@ -861,27 +864,48 @@ class CastPlayer(var castContext: CastContext) : BasePlayer() {
   }
 
   override fun getDeviceVolume(): Int {
-   return 0
+    val session = castContext.sessionManager.currentCastSession
+    return if (session != null && !session.isMute) {
+      (session.volume * 100).toInt()
+    } else {
+      0
+    }
   }
 
   override fun isDeviceMuted(): Boolean {
-   return false
+    val session = castContext.sessionManager.currentCastSession
+    return session?.isMute ?: false
   }
 
   override fun setDeviceVolume(volume: Int) {
-
+    val session = castContext.sessionManager.currentCastSession
+    try {
+      val clamped = volume.coerceIn(0, 100)
+      session?.volume = clamped / 100.0
+    } catch (e: Exception) {
+      Log.e(tag, "Failed to set cast device volume", e)
+    }
   }
 
   override fun increaseDeviceVolume() {
-
+    val currentVolume = getDeviceVolume()
+    val newVolume = (currentVolume + 1).coerceAtMost(100)
+    setDeviceVolume(newVolume)
   }
 
   override fun decreaseDeviceVolume() {
-
+    val currentVolume = getDeviceVolume()
+    val newVolume = (currentVolume - 1).coerceAtLeast(0)
+    setDeviceVolume(newVolume)
   }
 
   override fun setDeviceMuted(muted: Boolean) {
-
+    val session = castContext.sessionManager.currentCastSession
+    try {
+      session?.isMute = muted
+    } catch (e: Exception) {
+      Log.e(tag, "Failed to set cast device mute state", e)
+    }
   }
 
   inner class StatusListener() : RemoteMediaClient.Callback(), SessionManagerListener<CastSession>, RemoteMediaClient.ProgressListener {

android/app/src/main/java/com/audiobookshelf/app/player/PlayerNotificationService.kt

@@ -18,6 +18,8 @@ import android.support.v4.media.MediaDescriptionCompat
 import android.support.v4.media.MediaMetadataCompat
 import android.support.v4.media.session.MediaControllerCompat
 import android.support.v4.media.session.MediaSessionCompat
+import androidx.media.VolumeProviderCompat
+import android.media.AudioManager
 import android.support.v4.media.session.PlaybackStateCompat
 import android.util.Log
 import androidx.annotation.RequiresApi
@@ -94,6 +96,7 @@ class PlayerNotificationService : MediaBrowserServiceCompat() {
   private lateinit var mediaSessionConnector: MediaSessionConnector
   private lateinit var playerNotificationManager: PlayerNotificationManager
   lateinit var mediaSession: MediaSessionCompat
+  private var remoteVolumeProvider: VolumeProviderCompat? = null
   private lateinit var transportControls: MediaControllerCompat.TransportControls
 
   lateinit var mediaManager: MediaManager
@@ -705,11 +708,13 @@ class PlayerNotificationService : MediaBrowserServiceCompat() {
               Log.d(tag, "switchToPlayer: Using Cast Player " + castPlayer?.deviceInfo)
               mediaSessionConnector.setPlayer(castPlayer)
               playerNotificationManager.setPlayer(castPlayer)
+              setMediaSessionToCastVolume()
               castPlayer as CastPlayer
             } else {
               Log.d(tag, "switchToPlayer: Using ExoPlayer")
               mediaSessionConnector.setPlayer(mPlayer)
               playerNotificationManager.setPlayer(mPlayer)
+              setMediaSessionToLocalVolume()
               mPlayer
             }
 
@@ -726,6 +731,44 @@ class PlayerNotificationService : MediaBrowserServiceCompat() {
     }
   }
 
+  private fun setMediaSessionToCastVolume() {
+    val currentVol = try { castPlayer?.getDeviceVolume() ?: 0 } catch (e: Exception) { 0 }
+    val provider = object : VolumeProviderCompat(VolumeProviderCompat.VOLUME_CONTROL_ABSOLUTE, 100, currentVol) {
+      override fun onSetVolumeTo(volume: Int) {
+        val clamped = volume.coerceIn(0, 100)
+        try {
+          castPlayer?.setDeviceVolume(clamped)
+          val actual = castPlayer?.getDeviceVolume() ?: clamped
+          setCurrentVolume(actual)
+        } catch (_: Exception) {}
+      }
+      override fun onAdjustVolume(direction: Int) {
+        val current = try { castPlayer?.getDeviceVolume() ?: currentVolume } catch (_: Exception) { currentVolume }
+        val step = if (direction > 0) 1 else if (direction < 0) -1 else 0
+        if (step == 0) return
+        var target = (current + step).coerceIn(0, 100)
+        try {
+          castPlayer?.setDeviceVolume(target)
+          var actual = castPlayer?.getDeviceVolume() ?: current
+          // If device ignored tiny step, try nudging up to 3 steps total.
+          if (actual == current) {
+            target = (current + step * 3).coerceIn(0, 100)
+            castPlayer?.setDeviceVolume(target)
+            actual = castPlayer?.getDeviceVolume() ?: current
+          }
+          setCurrentVolume(actual)
+        } catch (_: Exception) {}
+      }
+    }
+    remoteVolumeProvider = provider
+    mediaSession.setPlaybackToRemote(provider)
+  }
+
+  private fun setMediaSessionToLocalVolume() {
+    mediaSession.setPlaybackToLocal(AudioManager.STREAM_MUSIC)
+    remoteVolumeProvider = null
+  }
+
   fun getCurrentTrackStartOffsetMs(): Long {
     return if (currentPlayer.mediaItemCount > 1) {
       val windowIndex = currentPlayer.currentMediaItemIndex