From 26cfc8158819791b907aa16c313789907339baef Mon Sep 17 00:00:00 2001
From: junkerderprovinz <jdp@braethoria.com>
Date: Sun, 9 Aug 2026 14:14:01 +0200
Subject: [PATCH] fix(ui): fall back to track ReplayGain when album gain is
 missing

Signed-off-by: junkerderprovinz <jdp@braethoria.com>
---
 ui/src/utils/calculateReplayGain.js      | 10 ++++++
 ui/src/utils/calculateReplayGain.test.js | 46 ++++++++++++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 ui/src/utils/calculateReplayGain.test.js

diff --git a/ui/src/utils/calculateReplayGain.js b/ui/src/utils/calculateReplayGain.js
index 0ce69fa4b..e73ab5559 100644
--- a/ui/src/utils/calculateReplayGain.js
+++ b/ui/src/utils/calculateReplayGain.js
@@ -11,6 +11,16 @@ const calculateReplayGain = (preAmp, gain, peak) => {
 export const calculateGain = (gainInfo, song) => {
   switch (gainInfo.gainMode) {
     case 'album': {
+      // Fall back to track gain when the album gain is missing (singles, or
+      // tracks without album ReplayGain tags), matching common ReplayGain
+      // players instead of applying no adjustment at all.
+      if (song.rgAlbumGain === undefined || song.rgAlbumPeak === undefined) {
+        return calculateReplayGain(
+          gainInfo.preAmp,
+          song.rgTrackGain,
+          song.rgTrackPeak,
+        )
+      }
       return calculateReplayGain(
         gainInfo.preAmp,
         song.rgAlbumGain,
diff --git a/ui/src/utils/calculateReplayGain.test.js b/ui/src/utils/calculateReplayGain.test.js
new file mode 100644
index 000000000..dc3e54196
--- /dev/null
+++ b/ui/src/utils/calculateReplayGain.test.js
@@ -0,0 +1,46 @@
+import { describe, it, expect } from 'vitest'
+import { calculateGain } from './calculateReplayGain'
+
+describe('calculateGain', () => {
+  const preAmp = 0
+
+  const albumSong = {
+    rgAlbumGain: -6,
+    rgAlbumPeak: 1,
+    rgTrackGain: -3,
+    rgTrackPeak: 1,
+  }
+  const trackOnlySong = {
+    rgTrackGain: -3,
+    rgTrackPeak: 1,
+  }
+  const noGainSong = {}
+
+  it('uses album gain in album mode when it is present', () => {
+    const result = calculateGain({ gainMode: 'album', preAmp }, albumSong)
+    expect(result).toBeCloseTo(10 ** (-6 / 20))
+  })
+
+  it('falls back to track gain in album mode when the album gain is missing', () => {
+    const result = calculateGain({ gainMode: 'album', preAmp }, trackOnlySong)
+    // Without the fallback this returned 1 (no adjustment). It should now use
+    // the track gain instead.
+    expect(result).toBeCloseTo(10 ** (-3 / 20))
+    expect(result).not.toBe(1)
+  })
+
+  it('returns 1 in album mode when neither album nor track gain is present', () => {
+    const result = calculateGain({ gainMode: 'album', preAmp }, noGainSong)
+    expect(result).toBe(1)
+  })
+
+  it('uses track gain in track mode', () => {
+    const result = calculateGain({ gainMode: 'track', preAmp }, albumSong)
+    expect(result).toBeCloseTo(10 ** (-3 / 20))
+  })
+
+  it('returns 1 when gain is disabled', () => {
+    const result = calculateGain({ gainMode: 'none', preAmp }, albumSong)
+    expect(result).toBe(1)
+  })
+})