music: add automatic rescanning

Add automatic rescanning, for real. This is the culmination of 6 months of work to make Auxio respond to music updates and to research the most versatile implementation of such. Is it the best system? No. It's actually a bit messy by necessity in order to prevent bugs. Does it work well? Yes. This will not be enabled by default, as it does require a battery draining foreground service and is generally not useful for most circumstances. So glad to be done with this. Resolves #72.
2022-07-08 16:35:45 -06:00 · 2022-07-08 16:35:45 -06:00 · 3a7768ad22
commit 3a7768ad22
parent 94f2d28936
28 changed files with 224 additions and 88 deletions
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@ -3,8 +3,10 @@
 ## dev

 #### What's New
+- Massively overhauled how music is loaded [#72]:
+	- Auxio can now reload music without requiring a restart
+	- Added a new option to reload music when device files change
 - Added direct metadata parsing, allowing more correct metadata at the cost of longer loading times
- Auxio can now reload music without requiring a restart
 - Added a shuffle shortcut
 - Widgets now have a more sleek and consistent button layout
 - "Rounded album covers" is now "Round mode"
--- a/app/src/main/java/org/oxycblt/auxio/detail/DetailViewModel.kt
+++ b/app/src/main/java/org/oxycblt/auxio/detail/DetailViewModel.kt
@ -33,9 +33,9 @@ import org.oxycblt.auxio.detail.recycler.SortHeader
 import org.oxycblt.auxio.music.Album
 import org.oxycblt.auxio.music.Artist
 import org.oxycblt.auxio.music.Genre
+import org.oxycblt.auxio.music.MimeType
 import org.oxycblt.auxio.music.MusicStore
 import org.oxycblt.auxio.music.Song
-import org.oxycblt.auxio.music.system.MimeType
 import org.oxycblt.auxio.settings.Settings
 import org.oxycblt.auxio.ui.Sort
 import org.oxycblt.auxio.ui.recycler.Header
--- a/app/src/main/java/org/oxycblt/auxio/home/HomeFragment.kt
+++ b/app/src/main/java/org/oxycblt/auxio/home/HomeFragment.kt
@ -46,10 +46,10 @@ import org.oxycblt.auxio.home.list.SongListFragment
 import org.oxycblt.auxio.music.Album
 import org.oxycblt.auxio.music.Artist
 import org.oxycblt.auxio.music.Genre
+import org.oxycblt.auxio.music.IndexerViewModel
 import org.oxycblt.auxio.music.Music
 import org.oxycblt.auxio.music.Song
 import org.oxycblt.auxio.music.system.Indexer
-import org.oxycblt.auxio.music.system.IndexerViewModel
 import org.oxycblt.auxio.playback.PlaybackViewModel
 import org.oxycblt.auxio.ui.DisplayMode
 import org.oxycblt.auxio.ui.MainNavigationAction
@ -313,7 +313,7 @@ class HomeFragment : ViewBindingFragment<FragmentHomeBinding>(), Toolbar.OnMenuI

        when (indexing) {
            is Indexer.Indexing.Indeterminate -> {
-                binding.homeIndexingStatus.textSafe = getString(R.string.lbl_indexing)
+                binding.homeIndexingStatus.textSafe = getString(R.string.lbl_indexing_desc)
                binding.homeIndexingProgress.isIndeterminate = true
            }
            is Indexer.Indexing.Songs -> {
--- a/app/src/main/java/org/oxycblt/auxio/music/system/IndexerViewModel.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/system/IndexerViewModel.kt
@ -15,15 +15,18 @@
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
-package org.oxycblt.auxio.music.system
+package org.oxycblt.auxio.music

 import androidx.lifecycle.ViewModel
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
+import org.oxycblt.auxio.music.system.Indexer

 /**
 * A ViewModel representing the current music indexing state.
 * @author OxygenCobalt
+ *
+ * TODO: Indeterminate state for Home + Settings
 */
 class IndexerViewModel : ViewModel(), Indexer.Callback {
    private val indexer = Indexer.getInstance()
--- a/app/src/main/java/org/oxycblt/auxio/music/Music.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/Music.kt
@ -23,8 +23,6 @@ import android.content.Context
 import android.net.Uri
 import android.provider.MediaStore
 import org.oxycblt.auxio.R
-import org.oxycblt.auxio.music.system.MimeType
-import org.oxycblt.auxio.music.system.Path
 import org.oxycblt.auxio.ui.recycler.Item
 import org.oxycblt.auxio.util.unlikelyToBeNull

--- a/app/src/main/java/org/oxycblt/auxio/music/system/StorageFramework.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/system/StorageFramework.kt
@ -15,7 +15,7 @@
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
-package org.oxycblt.auxio.music.system
+package org.oxycblt.auxio.music

 import android.annotation.SuppressLint
 import android.content.Context
@ -109,7 +109,7 @@ val StorageVolume.directoryCompat: String?
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
            directory?.absolutePath
        } else {
-            // Replicate getDirectory: getPath if mounted, null if not
+            // Replicate API: getPath if mounted, null if not
            when (stateCompat) {
                Environment.MEDIA_MOUNTED,
                Environment.MEDIA_MOUNTED_READ_ONLY ->
--- a/app/src/main/java/org/oxycblt/auxio/music/dirs/MusicDirAdapter.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/dirs/MusicDirAdapter.kt
@ -19,7 +19,7 @@ package org.oxycblt.auxio.music.dirs

 import android.content.Context
 import org.oxycblt.auxio.databinding.ItemMusicDirBinding
-import org.oxycblt.auxio.music.system.Directory
+import org.oxycblt.auxio.music.Directory
 import org.oxycblt.auxio.ui.recycler.BackingData
 import org.oxycblt.auxio.ui.recycler.BindingViewHolder
 import org.oxycblt.auxio.ui.recycler.MonoAdapter
--- a/app/src/main/java/org/oxycblt/auxio/music/dirs/MusicDirs.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/dirs/MusicDirs.kt
@ -17,7 +17,7 @@
 
 package org.oxycblt.auxio.music.dirs

-import org.oxycblt.auxio.music.system.Directory
+import org.oxycblt.auxio.music.Directory

 /** Represents a the configuration for the "Folder Management" setting */
 data class MusicDirs(val dirs: List<Directory>, val shouldInclude: Boolean)
--- a/app/src/main/java/org/oxycblt/auxio/music/dirs/MusicDirsDialog.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/dirs/MusicDirsDialog.kt
@ -28,7 +28,7 @@ import androidx.core.view.isVisible
 import org.oxycblt.auxio.BuildConfig
 import org.oxycblt.auxio.R
 import org.oxycblt.auxio.databinding.DialogMusicDirsBinding
-import org.oxycblt.auxio.music.system.Directory
+import org.oxycblt.auxio.music.Directory
 import org.oxycblt.auxio.settings.Settings
 import org.oxycblt.auxio.ui.fragment.ViewBindingDialogFragment
 import org.oxycblt.auxio.util.context
--- a/app/src/main/java/org/oxycblt/auxio/music/backend/ExoPlayerBackend.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/backend/ExoPlayerBackend.kt
@ -15,7 +15,7 @@
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
-package org.oxycblt.auxio.music.backend
+package org.oxycblt.auxio.music.system

 import android.content.Context
 import android.database.Cursor
@ -29,7 +29,6 @@ import org.oxycblt.auxio.music.audioUri
 import org.oxycblt.auxio.music.id3GenreName
 import org.oxycblt.auxio.music.iso8601year
 import org.oxycblt.auxio.music.plainTrackNo
-import org.oxycblt.auxio.music.system.Indexer
 import org.oxycblt.auxio.music.trackDiscNo
 import org.oxycblt.auxio.music.year
 import org.oxycblt.auxio.util.logD
--- a/app/src/main/java/org/oxycblt/auxio/music/system/Indexer.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/system/Indexer.kt
@ -32,10 +32,6 @@ import org.oxycblt.auxio.music.Artist
 import org.oxycblt.auxio.music.Genre
 import org.oxycblt.auxio.music.MusicStore
 import org.oxycblt.auxio.music.Song
-import org.oxycblt.auxio.music.backend.Api21MediaStoreBackend
-import org.oxycblt.auxio.music.backend.Api29MediaStoreBackend
-import org.oxycblt.auxio.music.backend.Api30MediaStoreBackend
-import org.oxycblt.auxio.music.backend.ExoPlayerBackend
 import org.oxycblt.auxio.settings.Settings
 import org.oxycblt.auxio.ui.Sort
 import org.oxycblt.auxio.util.logD
@ -130,6 +126,10 @@ class Indexer {
        this.callback = null
    }

+    /**
+     * Start the indexing process. This should be done by [Controller] in a background thread. When
+     * complete, a new completion state will be pushed to each callback.
+     */
    suspend fun index(context: Context) {
        requireBackgroundThread()

@ -190,7 +190,7 @@ class Indexer {

    @Synchronized
    private fun emitIndexing(indexing: Indexing?, generation: Long) {
-        checkGenerationImpl(generation)
+        checkGeneration(generation)

        if (indexing == indexingState) {
            // Ignore redundant states used when the backends just want to check for
@ -211,7 +211,7 @@ class Indexer {

    private suspend fun emitCompletion(response: Response, generation: Long) {
        synchronized(this) {
-            checkGenerationImpl(generation)
+            checkGeneration(generation)

            // Do not check for redundancy here, as we actually need to notify a switch
            // from Indexing -> Complete and not Indexing -> Indexing or Complete -> Complete.
@ -230,7 +230,7 @@ class Indexer {
        }
    }

-    private fun checkGenerationImpl(generation: Long) {
+    private fun checkGeneration(generation: Long) {
        if (currentGeneration != generation) {
            // Not the running task anymore, cancel this co-routine. This allows a yield-like
            // behavior to be implemented in a far cheaper manner for each backend.
--- a/app/src/main/java/org/oxycblt/auxio/music/system/IndexerNotifications.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/system/IndexerNotifications.kt
@ -30,7 +30,7 @@ import org.oxycblt.auxio.util.logD
 import org.oxycblt.auxio.util.newMainPendingIntent

 /** The notification responsible for showing the indexer state. */
-class IndexerNotification(private val context: Context) :
+class IndexingNotification(private val context: Context) :
    NotificationCompat.Builder(context, CHANNEL_ID) {
    private val notificationManager = context.getSystemServiceSafe(NotificationManager::class)

@ -52,7 +52,7 @@ class IndexerNotification(private val context: Context) :
        setContentIntent(context.newMainPendingIntent())
        setVisibility(NotificationCompat.VISIBILITY_PUBLIC)
        setContentTitle(context.getString(R.string.info_indexer_channel_name))
-        setContentText(context.getString(R.string.lbl_indexing))
+        setContentText(context.getString(R.string.lbl_indexing_desc))
        setProgress(0, 0, true)
    }

@ -64,7 +64,7 @@ class IndexerNotification(private val context: Context) :
        when (indexing) {
            is Indexer.Indexing.Indeterminate -> {
                logD("Updating state to $indexing")
-                setContentText(context.getString(R.string.lbl_indexing))
+                setContentText(context.getString(R.string.lbl_indexing_desc))
                setProgress(0, 0, true)
                return true
            }
@ -87,3 +87,37 @@ class IndexerNotification(private val context: Context) :
        const val CHANNEL_ID = BuildConfig.APPLICATION_ID + ".channel.INDEXER"
    }
 }
+
+/** The notification responsible for showing the indexer state. */
+class ObservingNotification(context: Context) : NotificationCompat.Builder(context, CHANNEL_ID) {
+    private val notificationManager = context.getSystemServiceSafe(NotificationManager::class)
+
+    init {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+            val channel =
+                NotificationChannel(
+                    CHANNEL_ID,
+                    context.getString(R.string.info_indexer_channel_name),
+                    NotificationManager.IMPORTANCE_LOW)
+
+            notificationManager.createNotificationChannel(channel)
+        }
+
+        setSmallIcon(R.drawable.ic_indexer_24)
+        setCategory(NotificationCompat.CATEGORY_SERVICE)
+        setShowWhen(false)
+        setSilent(true)
+        setContentIntent(context.newMainPendingIntent())
+        setVisibility(NotificationCompat.VISIBILITY_PUBLIC)
+        setContentTitle(context.getString(R.string.lbl_observing))
+        setContentText(context.getString(R.string.lbl_observing_desc))
+    }
+
+    fun renotify() {
+        notificationManager.notify(IntegerTable.INDEXER_NOTIFICATION_CODE, build())
+    }
+
+    companion object {
+        const val CHANNEL_ID = BuildConfig.APPLICATION_ID + ".channel.INDEXER"
+    }
+}
--- a/app/src/main/java/org/oxycblt/auxio/music/system/IndexerService.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/system/IndexerService.kt
@ -17,9 +17,14 @@
 
 package org.oxycblt.auxio.music.system

+import android.app.Notification
 import android.app.Service
 import android.content.Intent
+import android.database.ContentObserver
+import android.os.Handler
 import android.os.IBinder
+import android.os.Looper
+import android.provider.MediaStore
 import androidx.core.app.ServiceCompat
 import coil.imageLoader
 import kotlinx.coroutines.CoroutineScope
@ -31,6 +36,7 @@ import org.oxycblt.auxio.R
 import org.oxycblt.auxio.music.MusicStore
 import org.oxycblt.auxio.playback.state.PlaybackStateManager
 import org.oxycblt.auxio.settings.Settings
+import org.oxycblt.auxio.util.contentResolverSafe
 import org.oxycblt.auxio.util.logD

 /**
@ -43,8 +49,6 @@ import org.oxycblt.auxio.util.logD
 * boilerplate you skip is not worth the insanity of androidx.
 *
 * @author OxygenCobalt
- *
- * TODO: Add file observing
 */
 class IndexerService : Service(), Indexer.Controller, Settings.Callback {
    private val indexer = Indexer.getInstance()
@ -52,18 +56,23 @@ class IndexerService : Service(), Indexer.Controller, Settings.Callback {

    private val serviceJob = Job()
    private val indexScope = CoroutineScope(serviceJob + Dispatchers.IO)
+    private lateinit var indexerContentObserver: SystemContentObserver

    private val playbackManager = PlaybackStateManager.getInstance()
    private lateinit var settings: Settings

    private var isForeground = false
-    private lateinit var notification: IndexerNotification
+    private lateinit var indexingNotification: IndexingNotification
+    private lateinit var observingNotification: ObservingNotification

    override fun onCreate() {
        super.onCreate()

-        notification = IndexerNotification(this)
        settings = Settings(this, this)
+        indexerContentObserver = SystemContentObserver()
+
+        indexingNotification = IndexingNotification(this)
+        observingNotification = ObservingNotification(this)

        indexer.registerController(this)
        if (musicStore.library == null && indexer.isIndeterminate) {
@ -81,12 +90,14 @@ class IndexerService : Service(), Indexer.Controller, Settings.Callback {
    override fun onDestroy() {
        super.onDestroy()

-        // cancelLast actually stops foreground for us as it updates the loading state to
-        // null or completed.
-        indexer.cancelLast()
-        indexer.unregisterController(this)
-        serviceJob.cancel()
+        // De-initialize the components first to prevent stray reloading events
        settings.release()
+        indexerContentObserver.release()
+        indexer.unregisterController(this)
+
+        // Then cancel the other components.
+        indexer.cancelLast()
+        serviceJob.cancel()
    }

    // --- CONTROLLER CALLBACKS ---
@ -109,7 +120,7 @@ class IndexerService : Service(), Indexer.Controller, Settings.Callback {
                    val newLibrary = state.response.library

                    if (musicStore.library != null) {
-                        // This is a new library to replace a pre-existing one.
+                        // This is a new library to replace an existing one.

                        // Wipe possibly-invalidated album covers
                        imageLoader.memoryCache?.clear()
@ -127,46 +138,115 @@ class IndexerService : Service(), Indexer.Controller, Settings.Callback {
                // error, in practice that comes into conflict with the upcoming Android 13
                // notification permission, and there is no point implementing permission
                // on-boarding for such when it will only be used for this.
-                stopForegroundSession()
+                updateIdleSession()
            }
            is Indexer.State.Indexing -> {
-                // When loading, we want to enter the foreground state so that android does
-                // not shut off the loading process. Note that while we will always post the
-                // notification when initially starting, we will not update the notification
-                // unless it indicates that we have changed it.
-                val changed = notification.updateIndexingState(state.indexing)
-                if (!isForeground) {
-                    logD("Starting foreground session")
-                    startForeground(IntegerTable.INDEXER_NOTIFICATION_CODE, notification.build())
-                    isForeground = true
-                } else if (changed) {
-                    logD("Notification changed, re-posting notification")
-                    notification.renotify()
-                }
+                updateActiveSession(state.indexing)
            }
            null -> {
                // Null is the indeterminate state that occurs on app startup or after
                // the cancellation of a load, so in that case we want to stop foreground
                // since (technically) nothing is loading.
-                stopForegroundSession()
+                updateIdleSession()
            }
        }
    }

+    // --- INTERNAL ---
+
+    private fun updateActiveSession(state: Indexer.Indexing) {
+        // When loading, we want to enter the foreground state so that android does
+        // not shut off the loading process. Note that while we will always post the
+        // notification when initially starting, we will not update the notification
+        // unless it indicates that we have changed it.
+        val changed = indexingNotification.updateIndexingState(state)
+        if (!tryStartForeground(indexingNotification.build()) && changed) {
+            logD("Notification changed, re-posting notification")
+            indexingNotification.renotify()
+        }
+    }
+
+    private fun updateIdleSession() {
+        if (settings.shouldBeObserving) {
+            // There are a few reasons why we stay in the foreground with automatic rescanning:
+            // 1. Newer versions of Android have become more and more restrictive regarding
+            // how a foreground service starts. Thus, it's best to go foreground now so that
+            // we can go foreground later.
+            // 2. If a non-foreground service is killed, the app will probably still be alive,
+            // and thus the music library will not be updated at all.
+            if (!tryStartForeground(observingNotification.build())) {
+                observingNotification.renotify()
+            }
+        } else {
+            tryStopForeground()
+        }
+    }
+
+    private fun tryStartForeground(notification: Notification): Boolean {
+        if (isForeground) {
+            return false
+        }
+
+        startForeground(IntegerTable.INDEXER_NOTIFICATION_CODE, notification)
+        isForeground = true
+
+        return true
+    }
+
+    private fun tryStopForeground() {
+        if (!isForeground) {
+            return
+        }
+
+        ServiceCompat.stopForeground(this, ServiceCompat.STOP_FOREGROUND_REMOVE)
+        isForeground = false
+    }
+
    // --- SETTING CALLBACKS ---

    override fun onSettingChanged(key: String) {
-        if (key == getString(R.string.set_key_music_dirs) ||
-            key == getString(R.string.set_key_music_dirs_include) ||
-            key == getString(R.string.set_key_quality_tags)) {
-            onStartIndexing()
+        when (key) {
+            getString(R.string.set_key_music_dirs),
+            getString(R.string.set_key_music_dirs_include),
+            getString(R.string.set_key_quality_tags) -> onStartIndexing()
+            getString(R.string.set_key_observing) -> {
+                if (!indexer.isIndexing) {
+                    updateIdleSession()
+                }
+            }
        }
    }

-    private fun stopForegroundSession() {
-        if (isForeground) {
-            ServiceCompat.stopForeground(this, ServiceCompat.STOP_FOREGROUND_REMOVE)
-            isForeground = false
+    /** Internal content observer intended to work with the automatic reloading framework. */
+    private inner class SystemContentObserver(
+        private val handler: Handler = Handler(Looper.getMainLooper())
+    ) : ContentObserver(handler), Runnable {
+        init {
+            contentResolverSafe.registerContentObserver(
+                MediaStore.Audio.Media.EXTERNAL_CONTENT_URI, true, this)
+        }
+
+        fun release() {
+            contentResolverSafe.unregisterContentObserver(this)
+        }
+
+        override fun onChange(selfChange: Boolean) {
+            // Batch rapid-fire updates to the library into a single call to run after an
+            // arbitrary amount of time.
+            handler.removeCallbacks(this)
+            handler.postDelayed(this, REINDEX_DELAY)
+        }
+
+        override fun run() {
+            // Check here if we should even start a reindex. This is much less bug-prone than
+            // registering and de-registering this component as this setting changes.
+            if (settings.shouldBeObserving) {
+                onStartIndexing()
+            }
        }
    }
+
+    companion object {
+        const val REINDEX_DELAY = 500L
+    }
 }
--- a/app/src/main/java/org/oxycblt/auxio/music/backend/MediaStoreBackend.kt
+++ b/app/src/main/java/org/oxycblt/auxio/music/backend/MediaStoreBackend.kt
@ -15,7 +15,7 @@
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
-package org.oxycblt.auxio.music.backend
+package org.oxycblt.auxio.music.system

 import android.content.Context
 import android.database.Cursor
@ -27,20 +27,19 @@ import androidx.annotation.RequiresApi
 import androidx.core.database.getIntOrNull
 import androidx.core.database.getStringOrNull
 import java.io.File
+import org.oxycblt.auxio.music.Directory
+import org.oxycblt.auxio.music.MimeType
+import org.oxycblt.auxio.music.Path
 import org.oxycblt.auxio.music.Song
 import org.oxycblt.auxio.music.albumCoverUri
 import org.oxycblt.auxio.music.audioUri
+import org.oxycblt.auxio.music.directoryCompat
 import org.oxycblt.auxio.music.id3GenreName
+import org.oxycblt.auxio.music.mediaStoreVolumeNameCompat
 import org.oxycblt.auxio.music.packedDiscNo
 import org.oxycblt.auxio.music.packedTrackNo
 import org.oxycblt.auxio.music.queryCursor
-import org.oxycblt.auxio.music.system.Directory
-import org.oxycblt.auxio.music.system.Indexer
-import org.oxycblt.auxio.music.system.MimeType
-import org.oxycblt.auxio.music.system.Path
-import org.oxycblt.auxio.music.system.directoryCompat
-import org.oxycblt.auxio.music.system.mediaStoreVolumeNameCompat
-import org.oxycblt.auxio.music.system.storageVolumesCompat
+import org.oxycblt.auxio.music.storageVolumesCompat
 import org.oxycblt.auxio.music.trackDiscNo
 import org.oxycblt.auxio.music.useQuery
 import org.oxycblt.auxio.settings.Settings
@ -182,6 +181,8 @@ abstract class MediaStoreBackend : Indexer.Backend {
            audios.add(buildAudio(context, cursor))
            if (cursor.position % 50 == 0) {
                // Only check for a cancellation every 50 songs or so (~20ms).
+                // While this seems redundant, each call to emitIndexing checks for a
+                // cancellation of the co-routine this loading task is running on.
                emitIndexing(Indexer.Indexing.Indeterminate)
            }
        }
@ -462,8 +463,8 @@ class Api21MediaStoreBackend : MediaStoreBackend() {
 }

 /**
- * A [MediaStoreBackend] that selects directories and builds paths using the modern volume
- * primitives available from API 29 onwards.
+ * A [MediaStoreBackend] that selects directories and builds paths using the modern volume fields
+ * available from API 29 onwards.
 * @author OxygenCobalt
 */
@RequiresApi(Build.VERSION_CODES.Q)
@ -503,7 +504,7 @@ open class VolumeAwareMediaStoreBackend : MediaStoreBackend() {
        val relativePath = cursor.getString(relativePathIndex)

        // Find the StorageVolume whose MediaStore name corresponds to this song.
-        // This is what we use for the Directory.
+        // This is what we use for the Directory's volume.
        val volume = volumes.find { it.mediaStoreVolumeNameCompat == volumeName }
        if (volume != null) {
            audio.dir = Directory(volume, relativePath.removeSuffix(File.separator))
@ -532,7 +533,7 @@ open class Api29MediaStoreBackend : VolumeAwareMediaStoreBackend() {
            trackIndex = cursor.getColumnIndexOrThrow(MediaStore.Audio.AudioColumns.TRACK)
        }

-        // This backend is volume-aware, but does not support the modern track primitives.
+        // This backend is volume-aware, but does not support the modern track fields.
        // Use the packed utilities instead.
        val rawTrack = cursor.getIntOrNull(trackIndex)
        if (rawTrack != null) {
--- a/app/src/main/java/org/oxycblt/auxio/settings/Settings.kt
+++ b/app/src/main/java/org/oxycblt/auxio/settings/Settings.kt
@ -25,8 +25,8 @@ import androidx.core.content.edit
 import androidx.preference.PreferenceManager
 import org.oxycblt.auxio.R
 import org.oxycblt.auxio.home.tabs.Tab
+import org.oxycblt.auxio.music.Directory
 import org.oxycblt.auxio.music.dirs.MusicDirs
-import org.oxycblt.auxio.music.system.Directory
 import org.oxycblt.auxio.playback.replaygain.ReplayGainMode
 import org.oxycblt.auxio.playback.replaygain.ReplayGainPreAmp
 import org.oxycblt.auxio.playback.state.PlaybackMode
@ -185,6 +185,10 @@ class Settings(private val context: Context, private val callback: Callback? = n
    val pauseOnRepeat: Boolean
        get() = inner.getBoolean(context.getString(R.string.set_key_repeat_pause), false)

+    /** Whether to be actively watching for changes in the music library. */
+    val shouldBeObserving: Boolean
+        get() = inner.getBoolean(context.getString(R.string.set_key_observing), false)
+
    /** Whether to parse metadata directly with ExoPlayer. */
    val useQualityTags: Boolean
        get() = inner.getBoolean(context.getString(R.string.set_key_quality_tags), false)
--- a/app/src/main/java/org/oxycblt/auxio/settings/SettingsCompat.kt
+++ b/app/src/main/java/org/oxycblt/auxio/settings/SettingsCompat.kt
@ -27,10 +27,10 @@ import android.util.Log
 import androidx.core.content.edit
 import java.io.File
 import org.oxycblt.auxio.R
-import org.oxycblt.auxio.music.system.Directory
-import org.oxycblt.auxio.music.system.directoryCompat
-import org.oxycblt.auxio.music.system.isInternalCompat
-import org.oxycblt.auxio.music.system.storageVolumesCompat
+import org.oxycblt.auxio.music.Directory
+import org.oxycblt.auxio.music.directoryCompat
+import org.oxycblt.auxio.music.isInternalCompat
+import org.oxycblt.auxio.music.storageVolumesCompat
 import org.oxycblt.auxio.ui.accent.Accent
 import org.oxycblt.auxio.util.logD
 import org.oxycblt.auxio.util.queryAll
--- a/app/src/main/java/org/oxycblt/auxio/settings/SettingsListFragment.kt
+++ b/app/src/main/java/org/oxycblt/auxio/settings/SettingsListFragment.kt
@ -31,8 +31,8 @@ import androidx.recyclerview.widget.RecyclerView
 import coil.Coil
 import org.oxycblt.auxio.R
 import org.oxycblt.auxio.home.tabs.TabCustomizeDialog
+import org.oxycblt.auxio.music.IndexerViewModel
 import org.oxycblt.auxio.music.dirs.MusicDirsDialog
-import org.oxycblt.auxio.music.system.IndexerViewModel
 import org.oxycblt.auxio.playback.PlaybackViewModel
 import org.oxycblt.auxio.playback.replaygain.PreAmpCustomizeDialog
 import org.oxycblt.auxio.settings.ui.IntListPreference
--- a/app/src/main/res/values-cs/strings.xml
+++ b/app/src/main/res/values-cs/strings.xml
@ -6,7 +6,7 @@
    <string name="info_indexer_channel_name">Načítání hudby</string>
    <string name="info_widget_desc">Zobrazení a ovládání přehrávání hudby</string>
    <!-- Label Namespace | Static Labels -->
-    <string name="lbl_indexing">Načítání vaší hudební knihovny…</string>
+    <string name="lbl_indexing_desc">Načítání vaší hudební knihovny…</string>
    <string name="lbl_retry">Zkusit znovu</string>
    <string name="lbl_grant">Udělit</string>
    <string name="lbl_genres">Žánry</string>
--- a/app/src/main/res/values-de/strings.xml
+++ b/app/src/main/res/values-de/strings.xml
@ -192,7 +192,7 @@
    <string name="lbl_shuffle_shortcut_short">Mischen</string>
    <string name="lbl_shuffle_shortcut_long">Alle mischen</string>
    <string name="info_indexer_channel_name">Musik wird geladen</string>
-    <string name="lbl_indexing">Lade deine Musikbibliothek…</string>
+    <string name="lbl_indexing_desc">Lade deine Musikbibliothek…</string>
    <string name="lbl_sample_rate">Abtastrate</string>
    <string name="lbl_song_detail">Zeige Eigenschaften an</string>
    <string name="lbl_props">Lied-Eigenschaften</string>
--- a/app/src/main/res/values-fr/strings.xml
+++ b/app/src/main/res/values-fr/strings.xml
@ -101,7 +101,7 @@
    <string name="info_playback_channel_name">Lecture de musique</string>
    <string name="info_indexer_channel_name">Chargement de musique</string>
    <string name="info_widget_desc">Afficher et contrôler la lecture de la musique</string>
-    <string name="lbl_indexing">Chargement de votre bibliothèque musicale…</string>
+    <string name="lbl_indexing_desc">Chargement de votre bibliothèque musicale…</string>
    <string name="lbl_sort_name">Nom</string>
    <string name="lbl_sort_artist">Artiste</string>
    <string name="lbl_sort_album">Album</string>
--- a/app/src/main/res/values-in/strings.xml
+++ b/app/src/main/res/values-in/strings.xml
@ -73,7 +73,7 @@
    <string name="lbl_size">Ukuran</string>
    <string name="lbl_sample_rate">Tingkat sampel</string>
    <string name="set_lib_tabs">Tab Pustaka</string>
-    <string name="lbl_indexing">Memuat perpustakaan musik Anda…</string>
+    <string name="lbl_indexing_desc">Memuat perpustakaan musik Anda…</string>
    <string name="lbl_sort_name">Nama</string>
    <string name="lbl_sort_artist">Artis</string>
    <string name="lbl_sort_album">Album</string>
--- a/app/src/main/res/values-it/strings.xml
+++ b/app/src/main/res/values-it/strings.xml
@ -185,7 +185,7 @@
    <string name="def_sample_rate">Nessuna frequenza di campionamento</string>
    <string name="fmt_db_neg">-%.1f dB</string>
    <string name="info_indexer_channel_name">Caricamento musica</string>
-    <string name="lbl_indexing">Caricamento libreria musicale…</string>
+    <string name="lbl_indexing_desc">Caricamento libreria musicale…</string>
    <string name="lbl_sort_duration">Durata</string>
    <string name="lbl_sort_count">Conteggio canzoni</string>
    <string name="lbl_sort_disc">Disco</string>
--- a/app/src/main/res/values-pt-rBR/strings.xml
+++ b/app/src/main/res/values-pt-rBR/strings.xml
@ -102,7 +102,7 @@
    <string name="set_dirs_mode">Modo</string>
    <string name="err_no_perms">O Auxio precisa de permissão para ler sua biblioteca de músicas</string>
    <string name="info_app_desc">Um leitor de música simples e racional para android.</string>
-    <string name="lbl_indexing">Carregando sua biblioteca de músicas…</string>
+    <string name="lbl_indexing_desc">Carregando sua biblioteca de músicas…</string>
    <string name="lbl_sort_year">Ano</string>
    <string name="lbl_sort_duration">Duração</string>
    <string name="lbl_sort_count">Contagem de Músicas</string>
--- a/app/src/main/res/values-tr/strings.xml
+++ b/app/src/main/res/values-tr/strings.xml
@ -76,7 +76,7 @@
    <string name="info_widget_desc">Müzik çalmayı görüntüle ve kontrol et</string>
    <string name="info_app_desc">Android için basit, rasyonel bir müzik çalar.</string>
    <string name="info_indexer_channel_name">Müzik Yükleniyor</string>
-    <string name="lbl_indexing">Müzik kitaplığınız yükleniyor…</string>
+    <string name="lbl_indexing_desc">Müzik kitaplığınız yükleniyor…</string>
    <string name="lbl_sort_name">İsim</string>
    <string name="lbl_sort_artist">Sanatçı</string>
    <string name="lbl_sort_album">Albüm</string>
--- a/app/src/main/res/values-zh-rCN/strings.xml
+++ b/app/src/main/res/values-zh-rCN/strings.xml
@ -185,7 +185,7 @@
    <string name="fmt_lib_album_count">已加载专辑数量：%d</string>
    <string name="def_sample_rate">没有采样率信息</string>
    <string name="info_indexer_channel_name">音乐加载中</string>
-    <string name="lbl_indexing">正在加载您的音乐库……</string>
+    <string name="lbl_indexing_desc">正在加载您的音乐库……</string>
    <string name="lbl_sort_disc">碟片</string>
    <string name="lbl_sort_duration">时长</string>
    <string name="lbl_sort_count">歌曲计数</string>
--- a/app/src/main/res/values/settings.xml
+++ b/app/src/main/res/values/settings.xml
@ -28,7 +28,8 @@
    <string name="set_key_reindex" translatable="false">auxio_reindex</string>
    <string name="set_key_music_dirs" translatable="false">auxio_music_dirs</string>
    <string name="set_key_music_dirs_include" translatable="false">auxio_include_dirs</string>
-    <string name="set_key_quality_tags">auxio_quality_tags</string>
+    <string name="set_key_observing">auxio_observing</string>
+    <string name="set_key_quality_tags" translatable="false">auxio_quality_tags</string>

    <string name="set_key_search_filter" translatable="false">KEY_SEARCH_FILTER</string>

--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@ -2,14 +2,16 @@
 <resources xmlns:tools="http://schemas.android.com/tools" tools:ignore="MissingTranslation">
    <!-- Info namespace | App labels -->
    <string name="info_app_desc">A simple, rational music player for android.</string>
-    <string name="info_playback_channel_name">Music Playback</string>
-    <string name="info_indexer_channel_name">Music Loading</string>
+    <string name="info_playback_channel_name">Music playback</string>
+    <string name="info_indexer_channel_name">Music loading</string>
    <string name="info_widget_desc">View and control music playback</string>

    <!-- Label Namespace | Static Labels -->
-    <string name="lbl_indexing">Loading your music library…</string>
    <string name="lbl_retry">Retry</string>
    <string name="lbl_grant">Grant</string>
+    <string name="lbl_indexing_desc">Loading your music library…</string>
+    <string name="lbl_observing">Automatic reloading</string>
+    <string name="lbl_observing_desc">Monitoring your music library for changes… (You can disable this in settings)</string>

    <string name="lbl_genres">Genres</string>
    <string name="lbl_artists">Artists</string>
@ -146,7 +148,9 @@
    <string name="set_dirs_mode_include">Include</string>
    <string name="set_dirs_mode_include_desc">Music will <b>only</b> be loaded from the folders you add.</string>
    <string name="set_quality_tags">Ignore MediaStore tags</string>
-    <string name="set_quality_tags_desc">Increases tag quality, but requires longer loading times</string>
+    <string name="set_quality_tags_desc">Increases tag quality, but requires longer loading times (Experimental)</string>
+    <string name="set_observing">Automatic reloading</string>
+    <string name="set_observing_desc">Reload music whenever your audio files change (Experimental)</string>

    <!-- Error Namespace | Error Labels -->
    <string name="err_no_music">No music found</string>
@ -227,6 +231,7 @@
    <string name="clr_orange">Orange</string>
    <string name="clr_brown">Brown</string>
    <string name="clr_grey">Grey</string>
+    <!-- As in "Dynamic Colors"/Material You theming -->
    <string name="clr_dynamic">Dynamic</string>

    <!-- Format Namespace | Value formatting/plurals -->
@ -247,6 +252,7 @@
    <string name="fmt_lib_album_count">Albums loaded: %d</string>
    <string name="fmt_lib_artist_count">Artists loaded: %d</string>
    <string name="fmt_lib_genre_count">Genres loaded: %d</string>
+    <!-- AS in the total duration of all songs in the music library -->
    <string name="fmt_lib_total_duration">Total duration: %s</string>

    <plurals name="fmt_song_count">
--- a/app/src/main/res/xml/prefs_main.xml
+++ b/app/src/main/res/xml/prefs_main.xml
@ -187,5 +187,13 @@
            app:summary="@string/set_quality_tags_desc"
            app:title="@string/set_quality_tags" />

+        <org.oxycblt.auxio.settings.ui.M3SwitchPreference
+            app:allowDividerBelow="false"
+            app:defaultValue="false"
+            app:iconSpaceReserved="false"
+            app:key="@string/set_key_observing"
+            app:summary="@string/set_observing_desc"
+            app:title="@string/set_observing" />
+
    </PreferenceCategory>
 </PreferenceScreen>