MPV: Adjust subtitle delay/offset (#470)

**This is for MPV playback backend only!** Since this only works in MPV
for now, the option is not shown if using ExoPlayer.

Adds a setting (the gear icon during playback) to adjust the subtitle
delay.

A negative delay shows subtitles sooner. A positive delay shows them
later. For example, if a subtitle is supposed to show between
1000ms-2000ms, a negative 250ms delay will show it at 750ms-1750ms
instead.

The delay is persisted between plays of the same media & subtitle track.

Ref: #12 


![subtitle_delay](https://github.com/user-attachments/assets/824e3a28-650a-4619-9535-b67addaabf1e)

app/src/main/java/com/github/damontecres/wholphin/data/AppDatabase.kt

@@ -9,6 +9,7 @@ import androidx.room.migration.Migration
 import androidx.sqlite.db.SupportSQLiteDatabase
 import com.github.damontecres.wholphin.data.model.GetItemsFilter
 import com.github.damontecres.wholphin.data.model.ItemPlayback
+import com.github.damontecres.wholphin.data.model.ItemTrackModification
 import com.github.damontecres.wholphin.data.model.JellyfinServer
 import com.github.damontecres.wholphin.data.model.JellyfinUser
 import com.github.damontecres.wholphin.data.model.LibraryDisplayInfo
@@ -30,8 +31,9 @@ import java.util.UUID
         NavDrawerPinnedItem::class,
         LibraryDisplayInfo::class,
         PlaybackLanguageChoice::class,
+        ItemTrackModification::class,
     ],
-    version = 11,
+    version = 12,
     exportSchema = true,
     autoMigrations = [
         AutoMigration(3, 4),
@@ -42,6 +44,7 @@ import java.util.UUID
         AutoMigration(8, 9),
         AutoMigration(9, 10),
         AutoMigration(10, 11),
+        AutoMigration(11, 12),
     ],
 )
 @TypeConverters(Converters::class)

app/src/main/java/com/github/damontecres/wholphin/data/ItemPlaybackDao.kt

@@ -5,6 +5,7 @@ import androidx.room.Insert
 import androidx.room.OnConflictStrategy
 import androidx.room.Query
 import com.github.damontecres.wholphin.data.model.ItemPlayback
+import com.github.damontecres.wholphin.data.model.ItemTrackModification
 import com.github.damontecres.wholphin.data.model.JellyfinUser
 import java.util.UUID
 
@@ -26,4 +27,20 @@ interface ItemPlaybackDao {
 
     @Query("SELECT * from ItemPlayback WHERE userId=:userId")
     fun getItems(userId: Int): List<ItemPlayback>
+
+    @Query("SELECT * FROM ItemTrackModification WHERE userId=:userId AND itemId=:itemId")
+    suspend fun getTrackModifications(
+        userId: Int,
+        itemId: UUID,
+    ): List<ItemTrackModification>
+
+    @Query("SELECT * FROM ItemTrackModification WHERE userId=:userId AND itemId=:itemId AND trackIndex=:trackIndex")
+    suspend fun getTrackModifications(
+        userId: Int,
+        itemId: UUID,
+        trackIndex: Int,
+    ): ItemTrackModification
+
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    suspend fun saveItem(item: ItemTrackModification): Long
 }

app/src/main/java/com/github/damontecres/wholphin/data/ItemPlaybackRepository.kt

@@ -2,6 +2,7 @@ package com.github.damontecres.wholphin.data
 
 import com.github.damontecres.wholphin.data.model.BaseItem
 import com.github.damontecres.wholphin.data.model.ItemPlayback
+import com.github.damontecres.wholphin.data.model.ItemTrackModification
 import com.github.damontecres.wholphin.data.model.PlaybackLanguageChoice
 import com.github.damontecres.wholphin.data.model.TrackIndex
 import com.github.damontecres.wholphin.preferences.UserPreferences
@@ -16,6 +17,7 @@ import timber.log.Timber
 import java.util.UUID
 import javax.inject.Inject
 import javax.inject.Singleton
+import kotlin.time.Duration
 
 @Singleton
 class ItemPlaybackRepository
@@ -179,6 +181,32 @@ class ItemPlaybackRepository
             val id = itemPlaybackDao.saveItem(toSave)
             return toSave.copy(rowId = id)
         }
+
+        suspend fun getTrackModifications(
+            itemId: UUID,
+            trackIndex: Int,
+        ): ItemTrackModification? =
+            serverRepository.currentUser.value?.rowId?.let { userId ->
+                itemPlaybackDao.getTrackModifications(userId, itemId, trackIndex)
+            }
+
+        suspend fun saveTrackModifications(
+            itemId: UUID,
+            trackIndex: Int,
+            delay: Duration,
+        ) {
+            serverRepository.currentUser.value?.rowId?.let { userId ->
+                Timber.v("Saving track mod item=%s, track=%s, delay=%s", itemId, trackIndex, delay)
+                itemPlaybackDao.saveItem(
+                    ItemTrackModification(
+                        userId,
+                        itemId,
+                        trackIndex,
+                        delay.inWholeMilliseconds,
+                    ),
+                )
+            }
+        }
     }
 
 data class ChosenStreams(

app/src/main/java/com/github/damontecres/wholphin/data/model/ItemTrackModification.kt

@@ -0,0 +1,30 @@
+@file:UseSerializers(UUIDSerializer::class)
+
+package com.github.damontecres.wholphin.data.model
+
+import androidx.room.Entity
+import androidx.room.ForeignKey
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.UseSerializers
+import org.jellyfin.sdk.model.serializer.UUIDSerializer
+import java.util.UUID
+
+@Entity(
+    foreignKeys = [
+        ForeignKey(
+            entity = JellyfinUser::class,
+            parentColumns = arrayOf("rowId"),
+            childColumns = arrayOf("userId"),
+            onDelete = ForeignKey.CASCADE,
+            onUpdate = ForeignKey.CASCADE,
+        ),
+    ],
+    primaryKeys = ["userId", "itemId", "trackIndex"],
+)
+@Serializable
+data class ItemTrackModification(
+    val userId: Int,
+    val itemId: UUID,
+    val trackIndex: Int,
+    val delayMs: Long,
+)