playback: add replaygain support

Add ReplayGain support leveraging ExoPlayer. This was a widely
requested feature, but since I thought I needed MediaStore to
expose the fields, I never considered it. Turns out ExoPlayer
automatically exposes metadata for ID3v2 and Xiph tags, so we
can implement it just fine.

Resolves #7.

app/src/main/java/org/oxycblt/auxio/playback/PlaybackLayout.kt

@@ -44,8 +44,6 @@ import kotlin.math.min
  * of state and view magic. I tried my best to document it, but it's probably not the most friendly
  * or extendable. You have been warned.
  *
- * TODO: Add the queue view into this layout.
- *
  * @author OxygenCobalt (With help from Umano and Hai Zhang)
  */
 class PlaybackLayout @JvmOverloads constructor(

app/src/main/java/org/oxycblt/auxio/playback/system/PlaybackService.kt

@@ -36,6 +36,7 @@ import com.google.android.exoplayer2.MediaItem
 import com.google.android.exoplayer2.PlaybackException
 import com.google.android.exoplayer2.Player
 import com.google.android.exoplayer2.RenderersFactory
+import com.google.android.exoplayer2.TracksInfo
 import com.google.android.exoplayer2.audio.AudioAttributes
 import com.google.android.exoplayer2.audio.MediaCodecAudioRenderer
 import com.google.android.exoplayer2.extractor.DefaultExtractorsFactory
@@ -234,6 +235,29 @@ class PlaybackService : Service(), Player.Listener, PlaybackStateManager.Callbac
         }
     }
 
+    override fun onTracksInfoChanged(tracksInfo: TracksInfo) {
+        super.onTracksInfoChanged(tracksInfo)
+
+        for (info in tracksInfo.trackGroupInfos) {
+            if (info.isSelected) {
+                for (i in 0 until info.trackGroup.length) {
+                    if (info.isTrackSelected(i)) {
+                        val metadata = info.trackGroup.getFormat(i).metadata
+
+                        if (metadata != null) {
+                            player.volume = calculateReplayGain(metadata)
+                            logD("Applied ReplayGain adjustment: ${player.volume}")
+                        }
+
+                        break
+                    }
+                }
+
+                break
+            }
+        }
+    }
+
     // --- PLAYBACK STATE CALLBACK OVERRIDES ---
 
     override fun onSongUpdate(song: Song?) {
@@ -501,7 +525,6 @@ class PlaybackService : Service(), Player.Listener, PlaybackStateManager.Callbac
     companion object {
         private const val DISCONNECTED = 0
         private const val CONNECTED = 1
-        private const val WAKELOCK_TIME = 25000L
         private const val POS_POLL_INTERVAL = 500L
 
         const val ACTION_LOOP = BuildConfig.APPLICATION_ID + ".action.LOOP"
@@ -510,5 +533,10 @@ class PlaybackService : Service(), Player.Listener, PlaybackStateManager.Callbac
         const val ACTION_PLAY_PAUSE = BuildConfig.APPLICATION_ID + ".action.PLAY_PAUSE"
         const val ACTION_SKIP_NEXT = BuildConfig.APPLICATION_ID + ".action.NEXT"
         const val ACTION_EXIT = BuildConfig.APPLICATION_ID + ".action.EXIT"
+
+        const val RG_TRACK = "REPLAYGAIN_TRACK_GAIN"
+        const val RG_ALBUM = "REPLAYGAIN_ALBUM_GAIN"
+        const val R128_TRACK = "R128_TRACK_GAIN"
+        const val R128_ALBUM = "R128_ALBUM_GAIN"
     }
 }

app/src/main/java/org/oxycblt/auxio/playback/system/ReplayGain.kt

@@ -0,0 +1,107 @@
+package org.oxycblt.auxio.playback.system
+
+import androidx.core.math.MathUtils
+import com.google.android.exoplayer2.metadata.Metadata
+import com.google.android.exoplayer2.metadata.flac.VorbisComment
+import com.google.android.exoplayer2.metadata.id3.TextInformationFrame
+import kotlin.math.pow
+
+const val RG_TRACK = "REPLAYGAIN_TRACK_GAIN"
+const val RG_ALBUM = "REPLAYGAIN_ALBUM_GAIN"
+const val R128_TRACK = "R128_TRACK_GAIN"
+const val R128_ALBUM = "R128_ALBUM_GAIN"
+
+val replayGainTags = arrayOf(
+    RG_TRACK,
+    RG_ALBUM,
+    R128_ALBUM,
+    R128_TRACK
+)
+
+data class Gain(val track: Float, val album: Float)
+
+/**
+ * Calculates the rough volume adjustment for [Metadata] with ReplayGain tags.
+ * This is based off Vanilla Music's implementation.
+ */
+fun calculateReplayGain(metadata: Metadata): Float {
+    val gain = parseReplayGain(metadata)
+
+    // Currently we consider both the album and the track gain. One might want to add
+    // configuration to handle more cases.
+    var adjust = 0f
+
+    if (gain != null) {
+        adjust = if (gain.album != 0f) {
+            gain.album
+        } else {
+            gain.track
+        }
+    }
+
+    // Final adjustment along the volume curve.
+    // Ensure this is clamped to 0 or 1 so that it can be used as a volume.
+    return MathUtils.clamp((10f.pow((adjust / 20f))), 0f, 1f)
+}
+
+private fun parseReplayGain(metadata: Metadata): Gain? {
+    data class GainTag(val key: String, val value: Float)
+
+    var trackGain = 0f
+    var albumGain = 0f
+    var found = false
+
+    val tags = mutableListOf<GainTag>()
+
+    for (i in 0 until metadata.length()) {
+        val entry = metadata.get(i)
+
+        // Sometimes the ReplayGain keys will be lowercase, so make them uppercase.
+        if (entry is TextInformationFrame && entry.description?.uppercase() in replayGainTags) {
+            tags.add(GainTag(entry.description!!.uppercase(), parseReplayGainFloat(entry.value)))
+            continue
+        }
+
+        if (entry is VorbisComment && entry.key.uppercase() in replayGainTags) {
+            tags.add(GainTag(entry.key.uppercase(), parseReplayGainFloat(entry.value)))
+        }
+    }
+
+    // Case 1: Normal ReplayGain, most commonly found on MPEG files.
+    tags.findLast { tag -> tag.key == RG_TRACK }?.let { tag ->
+        trackGain = tag.value
+        found = true
+    }
+
+    tags.findLast { tag -> tag.key == RG_ALBUM }?.let { tag ->
+        albumGain = tag.value
+        found = true
+    }
+
+    // Case 2: R128 ReplayGain, most commonly found on FLAC files.
+    // While technically there is the R128 base gain in Opus files, ExoPlayer doesn't
+    // have metadata parsing functionality for those, so we just ignore it.
+    tags.findLast { tag -> tag.key == R128_TRACK }?.let { tag ->
+        trackGain += tag.value / 256f
+        found = true
+    }
+
+    tags.findLast { tag -> tag.key == R128_ALBUM }?.let { tag ->
+        albumGain += tag.value / 256f
+        found = true
+    }
+
+    return if (found) {
+        Gain(trackGain, albumGain)
+    } else {
+        null
+    }
+}
+
+private fun parseReplayGainFloat(raw: String): Float {
+    return try {
+        raw.replace(Regex("[^0-9.-]"), "").toFloat()
+    } catch (e: Exception) {
+        0f
+    }
+}

app/src/main/java/org/oxycblt/auxio/util/LogUtil.kt

@@ -59,7 +59,7 @@ private fun Any.getName(): String = "Auxio.${this::class.simpleName ?: "Anonymou
  * I know that this will not stop you, but consider what you are doing with your life, copycats.
  * Do you want to live a fulfilling existence on this planet? Or do you want to spend your life
  * taking work others did and making it objectively worse so you could arbitrage a fraction of a
- * penny on every AdMob impression you get. You could do so many great things if you simply had
+ * penny on every AdMob impression you get? You could do so many great things if you simply had
  * the courage to come up with an idea of your own. Be better.
  */
 private fun basedCopyleftNotice() {