fix(audio): stabilize loudness normalization and streaming startup behavior

Improve normalization consistency by separating cache refresh for non-playing tracks, hardening track-id cache lookups, and keeping UI gain state aligned with actual playback. Also reduce startup stalls by preferring non-seekable streaming when format hints are missing and by tuning ALSA/analysis paths to avoid underrun-prone churn.

src-tauri/Cargo.lock

@@ -944,6 +944,15 @@ dependencies = [
  "syn 2.0.117",
 ]
 
+[[package]]
+name = "dasp_frame"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b2a3937f5fe2135702897535c8d4a5553f8b116f76c1529088797f2eee7c5cd6"
+dependencies = [
+ "dasp_sample",
+]
+
 [[package]]
 name = "dasp_sample"
 version = "0.11.0"
@@ -1169,6 +1178,18 @@ version = "1.0.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d0881ea181b1df73ff77ffaaf9c7544ecc11e82fba9b5f27b262a3c73a332555"
 
+[[package]]
+name = "ebur128"
+version = "0.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e227cc62d64d6fe01abbef48134b9c1f17d470cef1e7a56337ad05b1f81df7f9"
+dependencies = [
+ "bitflags 1.3.2",
+ "dasp_frame",
+ "dasp_sample",
+ "smallvec",
+]
+
 [[package]]
 name = "either"
 version = "1.15.0"
@@ -1302,6 +1323,18 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "af9673d8203fcb076b19dfd17e38b3d4ae9f44959416ea532ce72415a6020365"
 
+[[package]]
+name = "fallible-iterator"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2acce4a10f12dc2fb14a218589d4f1f62ef011b2d0cc4b3cb1bba8e94da14649"
+
+[[package]]
+name = "fallible-streaming-iterator"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7360491ce676a36bf9bb3c56c1aa791658183a54d2744120f27285738d90465a"
+
 [[package]]
 name = "fastrand"
 version = "1.9.0"
@@ -1908,6 +1941,15 @@ version = "0.17.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4f467dd6dccf739c208452f8014c75c18bb8301b050ad1cfb27153803edb0f51"
 
+[[package]]
+name = "hashlink"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7382cf6263419f2d8df38c55d7da83da5c18aef87fc7a7fc1fb1e344edfe14c1"
+dependencies = [
+ "hashbrown 0.15.5",
+]
+
 [[package]]
 name = "heck"
 version = "0.4.1"
@@ -2548,6 +2590,17 @@ dependencies = [
  "redox_syscall 0.7.4",
 ]
 
+[[package]]
+name = "libsqlite3-sys"
+version = "0.35.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "133c182a6a2c87864fe97778797e46c7e999672690dc9fa3ee8e241aa4a9c13f"
+dependencies = [
+ "cc",
+ "pkg-config",
+ "vcpkg",
+]
+
 [[package]]
 name = "linux-raw-sys"
 version = "0.3.8"
@@ -3657,6 +3710,7 @@ version = "1.43.0"
 dependencies = [
  "biquad",
  "discord-rich-presence",
+ "ebur128",
  "futures-util",
  "id3",
  "libc",
@@ -3665,6 +3719,7 @@ dependencies = [
  "reqwest 0.12.28",
  "ringbuf",
  "rodio",
+ "rusqlite",
  "serde",
  "serde_json",
  "souvlaki",
@@ -4116,6 +4171,20 @@ dependencies = [
  "thiserror 1.0.69",
 ]
 
+[[package]]
+name = "rusqlite"
+version = "0.37.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "165ca6e57b20e1351573e3729b958bc62f0e48025386970b6e4d29e7a7e71f3f"
+dependencies = [
+ "bitflags 2.11.1",
+ "fallible-iterator",
+ "fallible-streaming-iterator",
+ "hashlink",
+ "libsqlite3-sys",
+ "smallvec",
+]
+
 [[package]]
 name = "rustc-hash"
 version = "2.1.2"
@@ -6115,6 +6184,12 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "vcpkg"
+version = "0.2.15"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "accd4ea62f7bb7a82fe23066fb0957d48ef677f6eeb8215f372f52e48bb32426"
+
 [[package]]
 name = "version-compare"
 version = "0.2.1"

src-tauri/Cargo.toml

@@ -49,6 +49,8 @@ lofty = "0.22"
 sysinfo = { version = "0.33", default-features = false, features = ["disk"] }
 id3 = "1.16.4"
 symphonia-adapter-libopus = "0.2.7"
+rusqlite = { version = "0.37", features = ["bundled"] }
+ebur128 = "0.1"
 
 [target.'cfg(unix)'.dependencies]
 libc = "0.2"

src-tauri/patches/cpal-0.15.3/src/host/alsa/mod.rs

@@ -1063,10 +1063,11 @@ fn set_hw_params_from_format(
             hw_params.set_buffer_size(v as alsa::pcm::Frames)?;
         }
         BufferSize::Default => {
-            // These values together represent a moderate latency and wakeup interval.
-            // Without them, we are at the mercy of the device
-            hw_params.set_period_time_near(25_000, alsa::ValueOr::Nearest)?;
-            hw_params.set_buffer_time_near(100_000, alsa::ValueOr::Nearest)?;
+            // Larger buffer than upstream cpal default: after Symphonia seeks or CPU
+            // spikes (analysis, demux) the mixer needs more margin before ALSA underruns.
+            // ~40 ms period, ~200 ms total buffer (device may round to nearest supported).
+            hw_params.set_period_time_near(40_000, alsa::ValueOr::Nearest)?;
+            hw_params.set_buffer_time_near(200_000, alsa::ValueOr::Nearest)?;
         }
     }
 

src-tauri/src/analysis_cache.rs

@@ -0,0 +1,559 @@
+use std::path::PathBuf;
+use std::io::Cursor;
+use std::sync::Mutex;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use ebur128::{EbuR128, Mode as Ebur128Mode};
+use rusqlite::{params, Connection, OptionalExtension};
+use symphonia::core::audio::SampleBuffer;
+use symphonia::core::codecs::{CODEC_TYPE_NULL, DecoderOptions};
+use symphonia::core::errors::Error as SymphoniaError;
+use symphonia::core::formats::FormatOptions;
+use symphonia::core::io::MediaSourceStream;
+use symphonia::core::meta::MetadataOptions;
+use symphonia::core::probe::Hint;
+use tauri::Manager;
+
+pub const WAVEFORM_ALGO_VERSION: i64 = 1;
+pub const LOUDNESS_ALGO_VERSION: i64 = 1;
+
+#[derive(Debug, Clone)]
+pub struct TrackKey {
+    pub track_id: String,
+    pub md5_16kb: String,
+}
+
+#[derive(Debug, Clone)]
+pub struct WaveformEntry {
+    pub bins: Vec<u8>,
+    pub bin_count: i64,
+    pub is_partial: bool,
+    pub known_until_sec: f64,
+    pub duration_sec: f64,
+    pub updated_at: i64,
+}
+
+#[allow(dead_code)]
+#[derive(Debug, Clone)]
+pub struct LoudnessEntry {
+    pub integrated_lufs: f64,
+    pub true_peak: f64,
+    pub recommended_gain_db: f64,
+    pub target_lufs: f64,
+    pub updated_at: i64,
+}
+
+#[allow(dead_code)]
+#[derive(Debug, Clone)]
+pub struct LoudnessSnapshot {
+    pub integrated_lufs: f64,
+    pub true_peak: f64,
+    pub recommended_gain_db: f64,
+    pub target_lufs: f64,
+    pub updated_at: i64,
+}
+
+pub struct AnalysisCache {
+    conn: Mutex<Connection>,
+}
+
+/// Ranged HTTP seeding uses `stream:<subsonicId>` (see `playback_identity`); backfill
+/// and IPC often use the bare `<subsonicId>`. Rows may exist under either key.
+fn track_id_cache_variants(id: &str) -> Vec<String> {
+    let mut out = vec![id.to_string()];
+    if let Some(bare) = id.strip_prefix("stream:") {
+        if !bare.is_empty() {
+            out.push(bare.to_string());
+        }
+    } else {
+        out.push(format!("stream:{id}"));
+    }
+    out
+}
+
+impl AnalysisCache {
+    pub fn init(app: &tauri::AppHandle) -> Result<Self, String> {
+        let db_path = analysis_db_path(app)?;
+        if let Some(parent) = db_path.parent() {
+            std::fs::create_dir_all(parent).map_err(|e| e.to_string())?;
+        }
+        let conn = Connection::open(db_path).map_err(|e| e.to_string())?;
+        configure_connection(&conn).map_err(|e| e.to_string())?;
+        migrate_schema(&conn).map_err(|e| e.to_string())?;
+        Ok(Self { conn: Mutex::new(conn) })
+    }
+
+    pub fn touch_track_status(&self, key: &TrackKey, status: &str) -> Result<(), String> {
+        let now = now_unix_ts();
+        let conn = self.conn.lock().map_err(|_| "analysis_cache lock poisoned".to_string())?;
+        conn.execute(
+            r#"
+            INSERT INTO analysis_track (
+                track_id, md5_16kb, status, waveform_algo_version, loudness_algo_version, updated_at
+            ) VALUES (?1, ?2, ?3, ?4, ?5, ?6)
+            ON CONFLICT(track_id, md5_16kb) DO UPDATE SET
+                status = excluded.status,
+                waveform_algo_version = excluded.waveform_algo_version,
+                loudness_algo_version = excluded.loudness_algo_version,
+                updated_at = excluded.updated_at
+            "#,
+            params![
+                key.track_id,
+                key.md5_16kb,
+                status,
+                WAVEFORM_ALGO_VERSION,
+                LOUDNESS_ALGO_VERSION,
+                now
+            ],
+        )
+        .map_err(|e| e.to_string())?;
+        Ok(())
+    }
+
+    pub fn upsert_waveform(&self, key: &TrackKey, entry: &WaveformEntry) -> Result<(), String> {
+        let conn = self.conn.lock().map_err(|_| "analysis_cache lock poisoned".to_string())?;
+        conn.execute(
+            r#"
+            INSERT INTO waveform_cache (
+                track_id, md5_16kb, bins, bin_count, is_partial, known_until_sec, duration_sec, updated_at
+            ) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8)
+            ON CONFLICT(track_id, md5_16kb) DO UPDATE SET
+                bins = excluded.bins,
+                bin_count = excluded.bin_count,
+                is_partial = excluded.is_partial,
+                known_until_sec = excluded.known_until_sec,
+                duration_sec = excluded.duration_sec,
+                updated_at = excluded.updated_at
+            "#,
+            params![
+                key.track_id,
+                key.md5_16kb,
+                entry.bins,
+                entry.bin_count,
+                if entry.is_partial { 1 } else { 0 },
+                entry.known_until_sec,
+                entry.duration_sec,
+                entry.updated_at
+            ],
+        )
+        .map_err(|e| e.to_string())?;
+        Ok(())
+    }
+
+    pub fn upsert_loudness(&self, key: &TrackKey, entry: &LoudnessEntry) -> Result<(), String> {
+        let conn = self.conn.lock().map_err(|_| "analysis_cache lock poisoned".to_string())?;
+        conn.execute(
+            r#"
+            INSERT INTO loudness_cache (
+                track_id, md5_16kb, integrated_lufs, true_peak, recommended_gain_db, target_lufs, updated_at
+            ) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7)
+            ON CONFLICT(track_id, md5_16kb, target_lufs) DO UPDATE SET
+                integrated_lufs = excluded.integrated_lufs,
+                true_peak = excluded.true_peak,
+                recommended_gain_db = excluded.recommended_gain_db,
+                updated_at = excluded.updated_at
+            "#,
+            params![
+                key.track_id,
+                key.md5_16kb,
+                entry.integrated_lufs,
+                entry.true_peak,
+                entry.recommended_gain_db,
+                entry.target_lufs,
+                entry.updated_at
+            ],
+        )
+        .map_err(|e| e.to_string())?;
+        Ok(())
+    }
+
+    pub fn get_waveform(&self, key: &TrackKey) -> Result<Option<WaveformEntry>, String> {
+        let conn = self.conn.lock().map_err(|_| "analysis_cache lock poisoned".to_string())?;
+        conn.query_row(
+            r#"
+            SELECT w.bins, w.bin_count, w.is_partial, w.known_until_sec, w.duration_sec, w.updated_at
+            FROM waveform_cache w
+            JOIN analysis_track a
+              ON a.track_id = w.track_id
+             AND a.md5_16kb = w.md5_16kb
+            WHERE w.track_id = ?1
+              AND w.md5_16kb = ?2
+              AND a.waveform_algo_version = ?3
+            "#,
+            params![key.track_id, key.md5_16kb, WAVEFORM_ALGO_VERSION],
+            |row| {
+                Ok(WaveformEntry {
+                    bins: row.get(0)?,
+                    bin_count: row.get(1)?,
+                    is_partial: row.get::<_, i64>(2)? != 0,
+                    known_until_sec: row.get(3)?,
+                    duration_sec: row.get(4)?,
+                    updated_at: row.get(5)?,
+                })
+            },
+        )
+        .optional()
+        .map_err(|e| e.to_string())
+    }
+
+    pub fn get_latest_waveform_for_track(&self, track_id: &str) -> Result<Option<WaveformEntry>, String> {
+        let conn = self.conn.lock().map_err(|_| "analysis_cache lock poisoned".to_string())?;
+        const SQL: &str = r#"
+            SELECT w.bins, w.bin_count, w.is_partial, w.known_until_sec, w.duration_sec, w.updated_at
+            FROM waveform_cache w
+            JOIN analysis_track a
+              ON a.track_id = w.track_id
+             AND a.md5_16kb = w.md5_16kb
+            WHERE w.track_id = ?1
+              AND a.waveform_algo_version = ?2
+            ORDER BY w.updated_at DESC
+            LIMIT 1
+            "#;
+        for tid in track_id_cache_variants(track_id) {
+            let row = conn
+                .query_row(
+                    SQL,
+                    params![tid, WAVEFORM_ALGO_VERSION],
+                    |row| {
+                        Ok(WaveformEntry {
+                            bins: row.get(0)?,
+                            bin_count: row.get(1)?,
+                            is_partial: row.get::<_, i64>(2)? != 0,
+                            known_until_sec: row.get(3)?,
+                            duration_sec: row.get(4)?,
+                            updated_at: row.get(5)?,
+                        })
+                    },
+                )
+                .optional()
+                .map_err(|e| e.to_string())?;
+            if row.is_some() {
+                return Ok(row);
+            }
+        }
+        Ok(None)
+    }
+
+    pub fn get_latest_loudness_for_track(&self, track_id: &str) -> Result<Option<LoudnessSnapshot>, String> {
+        let conn = self.conn.lock().map_err(|_| "analysis_cache lock poisoned".to_string())?;
+        const SQL: &str = r#"
+            SELECT l.integrated_lufs, l.true_peak, l.recommended_gain_db, l.target_lufs, l.updated_at
+            FROM loudness_cache l
+            JOIN analysis_track a
+              ON a.track_id = l.track_id
+             AND a.md5_16kb = l.md5_16kb
+            WHERE l.track_id = ?1
+              AND a.loudness_algo_version = ?2
+            ORDER BY l.updated_at DESC
+            LIMIT 1
+            "#;
+        for tid in track_id_cache_variants(track_id) {
+            let row = conn
+                .query_row(
+                    SQL,
+                    params![tid, LOUDNESS_ALGO_VERSION],
+                    |row| {
+                        Ok(LoudnessSnapshot {
+                            integrated_lufs: row.get(0)?,
+                            true_peak: row.get(1)?,
+                            recommended_gain_db: row.get(2)?,
+                            target_lufs: row.get(3)?,
+                            updated_at: row.get(4)?,
+                        })
+                    },
+                )
+                .optional()
+                .map_err(|e| e.to_string())?;
+            if row.is_some() {
+                return Ok(row);
+            }
+        }
+        Ok(None)
+    }
+}
+
+pub fn recommended_gain_for_target(integrated_lufs: f64, true_peak: f64, target_lufs: f64) -> f64 {
+    let mut recommended_gain_db = target_lufs - integrated_lufs;
+    if true_peak > 0.0 {
+        let true_peak_dbtp = 20.0 * true_peak.log10();
+        let max_gain_db = -1.0 - true_peak_dbtp;
+        if recommended_gain_db > max_gain_db {
+            recommended_gain_db = max_gain_db;
+        }
+    }
+    recommended_gain_db.clamp(-24.0, 24.0)
+}
+
+pub fn seed_from_bytes(app: &tauri::AppHandle, track_id: &str, bytes: &[u8]) -> Result<(), String> {
+    let Some(cache) = app.try_state::<AnalysisCache>() else {
+        return Ok(());
+    };
+    let key = TrackKey {
+        track_id: track_id.to_string(),
+        md5_16kb: md5_first_16kb(bytes),
+    };
+    cache.touch_track_status(&key, "queued")?;
+
+    let waveform = WaveformEntry {
+        bins: derive_waveform_bins(bytes, 500),
+        bin_count: 500,
+        is_partial: false,
+        known_until_sec: 0.0,
+        duration_sec: 0.0,
+        updated_at: now_unix_ts(),
+    };
+    cache.upsert_waveform(&key, &waveform)?;
+
+    if let Some((integrated_lufs, true_peak, recommended_gain_db, target_lufs)) =
+        analyze_loudness_from_audio_bytes(bytes, -16.0)
+    {
+        let loudness = LoudnessEntry {
+            integrated_lufs,
+            true_peak,
+            recommended_gain_db,
+            target_lufs,
+            updated_at: now_unix_ts(),
+        };
+        cache.upsert_loudness(&key, &loudness)?;
+    }
+
+    cache.touch_track_status(&key, "ready")?;
+    Ok(())
+}
+
+fn now_unix_ts() -> i64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_secs() as i64)
+        .unwrap_or(0)
+}
+
+fn md5_first_16kb(bytes: &[u8]) -> String {
+    let n = bytes.len().min(16 * 1024);
+    format!("{:x}", md5::compute(&bytes[..n]))
+}
+
+fn derive_waveform_bins(bytes: &[u8], bin_count: usize) -> Vec<u8> {
+    if bin_count == 0 || bytes.is_empty() {
+        return Vec::new();
+    }
+    let mut out = vec![0u8; bin_count];
+    for (i, slot) in out.iter_mut().enumerate() {
+        let start = i * bytes.len() / bin_count;
+        let end = ((i + 1) * bytes.len() / bin_count).max(start + 1).min(bytes.len());
+        let mut peak: u8 = 0;
+        for &b in &bytes[start..end] {
+            let centered = if b >= 128 { b - 128 } else { 128 - b };
+            if centered > peak {
+                peak = centered;
+            }
+        }
+        *slot = ((peak as f32 / 127.0).sqrt().clamp(0.0, 1.0) * 255.0) as u8;
+    }
+    out
+}
+
+fn analyze_loudness_from_audio_bytes(bytes: &[u8], target_lufs: f64) -> Option<(f64, f64, f64, f64)> {
+    if bytes.is_empty() {
+        return None;
+    }
+
+    let source = Box::new(Cursor::new(bytes.to_vec()));
+    let mss = MediaSourceStream::new(source, Default::default());
+    let hint = Hint::new();
+    let probed = symphonia::default::get_probe()
+        .format(&hint, mss, &FormatOptions::default(), &MetadataOptions::default())
+        .ok()?;
+    let mut format = probed.format;
+    let track = format
+        .default_track()
+        .filter(|t| t.codec_params.codec != CODEC_TYPE_NULL)
+        .or_else(|| {
+            format
+                .tracks()
+                .iter()
+                .find(|t| {
+                    t.codec_params.codec != CODEC_TYPE_NULL
+                        && t.codec_params.sample_rate.is_some()
+                        && t.codec_params.channels.is_some()
+                })
+        })
+        .or_else(|| format.tracks().iter().find(|t| t.codec_params.codec != CODEC_TYPE_NULL))?;
+    let track_id = track.id;
+    let codec_params = track.codec_params.clone();
+
+    let mut decoder = match symphonia::default::get_codecs()
+        .make(&codec_params, &DecoderOptions::default())
+    {
+        Ok(v) => v,
+        Err(e) => {
+            crate::app_deprintln!("[analysis] decoder make failed: {}", e);
+            return None;
+        }
+    };
+    let mut ebu: Option<EbuR128> = None;
+    let mut ebu_channels: u32 = 0;
+    let mut sample_peak_abs = 0.0_f64;
+    let mut fed_any_frames = false;
+    let mut loop_i: u32 = 0;
+
+    loop {
+        let packet = match format.next_packet() {
+            Ok(packet) => packet,
+            Err(_) => break,
+        };
+        if packet.track_id() != track_id {
+            continue;
+        }
+
+        let decoded = match decoder.decode(&packet) {
+            Ok(buf) => buf,
+            Err(SymphoniaError::DecodeError(_)) => continue,
+            Err(SymphoniaError::ResetRequired) => break,
+            Err(_) => break,
+        };
+
+        let spec = *decoded.spec();
+        if ebu.is_none() {
+            let ch = spec.channels.count() as u32;
+            let sr = spec.rate;
+            match EbuR128::new(ch, sr, Ebur128Mode::I | Ebur128Mode::TRUE_PEAK) {
+                Ok(v) => {
+                    ebu = Some(v);
+                    ebu_channels = ch;
+                }
+                Err(e) => {
+                    crate::app_deprintln!(
+                        "[analysis] EbuR128 init failed: channels={} sample_rate={} err={}",
+                        ch,
+                        sr,
+                        e
+                    );
+                    return None;
+                }
+            }
+        }
+        let mut samples = SampleBuffer::<f32>::new(decoded.capacity() as u64, spec);
+        samples.copy_interleaved_ref(decoded);
+        for &s in samples.samples() {
+            let v = (s as f64).abs();
+            if v.is_finite() && v > sample_peak_abs {
+                sample_peak_abs = v;
+            }
+        }
+        let Some(ref mut ebu) = ebu else {
+            crate::app_deprintln!("[analysis] loudness failed: ebu not initialized");
+            return None;
+        };
+        match ebu.add_frames_f32(samples.samples()) {
+            Ok(_) => fed_any_frames = true,
+            Err(e) => {
+                crate::app_deprintln!("[analysis] loudness add_frames failed: {}", e);
+                return None;
+            }
+        }
+        loop_i = loop_i.wrapping_add(1);
+        if loop_i % 128 == 0 {
+            std::thread::yield_now();
+        }
+    }
+
+    if !fed_any_frames {
+        crate::app_deprintln!("[analysis] loudness failed: no decoded frames");
+        return None;
+    }
+    let Some(ebu) = ebu else {
+        crate::app_deprintln!("[analysis] loudness failed: no decoder output");
+        return None;
+    };
+    let integrated_lufs = match ebu.loudness_global() {
+        Ok(v) => v,
+        Err(e) => {
+            crate::app_deprintln!("[analysis] loudness_global failed: {}", e);
+            return None;
+        }
+    };
+    if !integrated_lufs.is_finite() {
+        crate::app_deprintln!("[analysis] loudness failed: integrated_lufs not finite");
+        return None;
+    }
+    let mut true_peak = 0.0_f64;
+    let mut true_peak_ok = true;
+    for ch in 0..ebu_channels {
+        match ebu.true_peak(ch) {
+            Ok(v) if v.is_finite() && v > true_peak => true_peak = v,
+            Ok(_) => {}
+            Err(e) => {
+                true_peak_ok = false;
+                crate::app_deprintln!("[analysis] true_peak unavailable: {}", e);
+                break;
+            }
+        }
+    }
+    if !true_peak_ok {
+        // Fallback to sample peak if true-peak is not available for this stream/codec.
+        true_peak = sample_peak_abs;
+    }
+
+    let recommended_gain_db = recommended_gain_for_target(integrated_lufs, true_peak, target_lufs);
+    Some((integrated_lufs, true_peak, recommended_gain_db, target_lufs))
+}
+
+fn analysis_db_path(app: &tauri::AppHandle) -> Result<PathBuf, String> {
+    let base = app
+        .path()
+        .app_config_dir()
+        .map_err(|e| e.to_string())?;
+    Ok(base.join("audio-analysis.sqlite"))
+}
+
+fn configure_connection(conn: &Connection) -> rusqlite::Result<()> {
+    conn.pragma_update(None, "journal_mode", "WAL")?;
+    conn.pragma_update(None, "synchronous", "NORMAL")?;
+    conn.pragma_update(None, "temp_store", "MEMORY")?;
+    conn.pragma_update(None, "foreign_keys", "ON")?;
+    Ok(())
+}
+
+fn migrate_schema(conn: &Connection) -> rusqlite::Result<()> {
+    conn.execute_batch(
+        r#"
+        CREATE TABLE IF NOT EXISTS analysis_track (
+            track_id TEXT NOT NULL,
+            md5_16kb TEXT NOT NULL,
+            status TEXT NOT NULL,
+            waveform_algo_version INTEGER NOT NULL,
+            loudness_algo_version INTEGER NOT NULL,
+            updated_at INTEGER NOT NULL,
+            PRIMARY KEY (track_id, md5_16kb)
+        );
+
+        CREATE TABLE IF NOT EXISTS waveform_cache (
+            track_id TEXT NOT NULL,
+            md5_16kb TEXT NOT NULL,
+            bins BLOB NOT NULL,
+            bin_count INTEGER NOT NULL,
+            is_partial INTEGER NOT NULL,
+            known_until_sec REAL NOT NULL,
+            duration_sec REAL NOT NULL,
+            updated_at INTEGER NOT NULL,
+            PRIMARY KEY (track_id, md5_16kb)
+        );
+
+        CREATE TABLE IF NOT EXISTS loudness_cache (
+            track_id TEXT NOT NULL,
+            md5_16kb TEXT NOT NULL,
+            integrated_lufs REAL NOT NULL,
+            true_peak REAL NOT NULL,
+            recommended_gain_db REAL NOT NULL,
+            target_lufs REAL NOT NULL,
+            updated_at INTEGER NOT NULL,
+            PRIMARY KEY (track_id, md5_16kb, target_lufs)
+        );
+
+        CREATE INDEX IF NOT EXISTS idx_analysis_track_status
+            ON analysis_track(status);
+        "#,
+    )?;
+    Ok(())
+}

src-tauri/src/audio.rs

@@ -21,7 +21,41 @@ use symphonia::core::{
     units::{self, Time},
 };
 use futures_util::StreamExt;
-use tauri::{AppHandle, Emitter, State};
+use tauri::{AppHandle, Emitter, Manager, State};
+#[derive(Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+struct PartialWaveformPayload {
+    track_id: Option<String>,
+    bins: Vec<u8>,
+    known_until_sec: f64,
+    duration_sec: f64,
+    is_partial: bool,
+}
+
+#[derive(Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+struct PartialLoudnessPayload {
+    track_id: Option<String>,
+    gain_db: f32,
+    target_lufs: f32,
+    is_partial: bool,
+}
+
+#[derive(Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+struct WaveformUpdatedPayload {
+    track_id: String,
+    is_partial: bool,
+}
+
+#[derive(Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+struct NormalizationStatePayload {
+    engine: String,
+    current_gain_db: Option<f32>,
+    target_lufs: f32,
+}
+
 
 // ─── 10-Band Graphic Equalizer ────────────────────────────────────────────────
 
@@ -1021,17 +1055,20 @@ async fn track_download_task(
     gen: u64,
     gen_arc: Arc<AtomicU64>,
     http_client: reqwest::Client,
+    app: AppHandle,
     url: String,
     initial_response: reqwest::Response,
     mut prod: HeapProducer<u8>,
     done: Arc<AtomicBool>,
     promote_cache_slot: Arc<Mutex<Option<PreloadedTrack>>>,
+    normalization_target_lufs: Arc<AtomicU32>,
 ) {
     let mut downloaded: u64 = 0;
     let mut reconnects: u32 = 0;
     let mut next_response: Option<reqwest::Response> = Some(initial_response);
     let mut capture: Vec<u8> = Vec::new();
     let mut capture_over_limit = false;
+    let mut last_partial_loudness_emit = Instant::now() - Duration::from_secs(5);
     'outer: loop {
         let response = if let Some(r) = next_response.take() {
             r
@@ -1120,12 +1157,29 @@ async fn track_download_task(
                             capture_over_limit = true;
                         }
                     }
+                    if !capture_over_limit
+                        && last_partial_loudness_emit.elapsed() >= Duration::from_millis(PARTIAL_LOUDNESS_EMIT_INTERVAL_MS)
+                    {
+                        let target_lufs = f32::from_bits(normalization_target_lufs.load(Ordering::Relaxed));
+                        emit_partial_loudness_from_bytes(&app, &url, &capture, target_lufs);
+                        last_partial_loudness_emit = Instant::now();
+                    }
                     offset += pushed;
                     downloaded += pushed as u64;
                 }
             }
         }
         if !capture_over_limit && !capture.is_empty() {
+            if let Some(track_id) = playback_identity(&url) {
+                if let Err(e) = crate::analysis_cache::seed_from_bytes(&app, &track_id, &capture) {
+                    crate::app_eprintln!("[analysis] track seed failed for {}: {}", track_id, e);
+                } else {
+                    let _ = app.emit(
+                        "analysis:waveform-updated",
+                        WaveformUpdatedPayload { track_id, is_partial: false },
+                    );
+                }
+            }
             *promote_cache_slot.lock().unwrap() = Some(PreloadedTrack {
                 url: url.clone(),
                 data: capture,
@@ -1144,12 +1198,15 @@ async fn ranged_download_task(
     gen: u64,
     gen_arc: Arc<AtomicU64>,
     http_client: reqwest::Client,
+    app: AppHandle,
+    duration_hint: f64,
     url: String,
     initial_response: reqwest::Response,
     buf: Arc<Mutex<Vec<u8>>>,
     downloaded_to: Arc<AtomicUsize>,
     done: Arc<AtomicBool>,
     promote_cache_slot: Arc<Mutex<Option<PreloadedTrack>>>,
+    normalization_target_lufs: Arc<AtomicU32>,
 ) {
     let total_size = buf.lock().unwrap().len();
     let mut downloaded: usize = 0;
@@ -1157,6 +1214,8 @@ async fn ranged_download_task(
     let mut next_response: Option<reqwest::Response> = Some(initial_response);
     let dl_started = Instant::now();
     let mut next_progress_mb: usize = 1;
+    let mut last_partial_emit = Instant::now();
+    let mut last_partial_loudness_emit = Instant::now() - Duration::from_secs(5);
 
     'outer: loop {
         let response = if let Some(r) = next_response.take() {
@@ -1231,6 +1290,51 @@ async fn ranged_download_task(
             }
             downloaded += n;
             downloaded_to.store(downloaded, Ordering::SeqCst);
+            if downloaded >= 4096
+                && total_size > 0
+                && last_partial_emit.elapsed() >= partial_waveform_emit_min_interval(downloaded)
+            {
+                let bins =
+                    derive_partial_waveform_bins_short_locks(&buf, downloaded, 500);
+                if last_partial_loudness_emit.elapsed() >= Duration::from_millis(PARTIAL_LOUDNESS_EMIT_INTERVAL_MS) {
+                    let target_lufs = f32::from_bits(normalization_target_lufs.load(Ordering::Relaxed));
+                    if let Some(provisional_db) = provisional_loudness_gain_from_progress(downloaded, total_size, target_lufs) {
+                        let _ = app.emit(
+                            "analysis:loudness-partial",
+                            PartialLoudnessPayload {
+                                track_id: playback_identity(&url),
+                                gain_db: provisional_db,
+                                target_lufs,
+                                is_partial: true,
+                            },
+                        );
+                        crate::app_deprintln!(
+                            "[normalization] partial-loudness provisional progress={:.2}% gain_db={:.2} target_lufs={:.2} track_id={:?}",
+                            (downloaded as f32 / total_size as f32) * 100.0,
+                            provisional_db,
+                            target_lufs,
+                            playback_identity(&url)
+                        );
+                    }
+                    last_partial_loudness_emit = Instant::now();
+                };
+                let known_until_sec = if duration_hint > 0.0 {
+                    (duration_hint * downloaded as f64 / total_size as f64).clamp(0.0, duration_hint)
+                } else {
+                    0.0
+                };
+                let _ = app.emit(
+                    "analysis:waveform-partial",
+                    PartialWaveformPayload {
+                        track_id: playback_identity(&url),
+                        bins,
+                        known_until_sec,
+                        duration_sec: duration_hint.max(0.0),
+                        is_partial: true,
+                    },
+                );
+                last_partial_emit = Instant::now();
+            }
             let mb = downloaded / (1024 * 1024);
             if mb >= next_progress_mb {
                 let pct = (downloaded as f64 / total_size as f64 * 100.0) as u32;
@@ -1262,11 +1366,144 @@ async fn ranged_download_task(
 
     if downloaded == total_size && total_size > 0 && total_size <= TRACK_STREAM_PROMOTE_MAX_BYTES {
         let data = buf.lock().unwrap().clone();
+        if let Some(track_id) = playback_identity(&url) {
+            if let Err(e) = crate::analysis_cache::seed_from_bytes(&app, &track_id, &data) {
+                crate::app_eprintln!("[analysis] ranged seed failed for {}: {}", track_id, e);
+            } else {
+                let _ = app.emit(
+                    "analysis:waveform-updated",
+                    WaveformUpdatedPayload { track_id, is_partial: false },
+                );
+            }
+        }
         *promote_cache_slot.lock().unwrap() = Some(PreloadedTrack { url, data });
         crate::app_deprintln!("[stream] promoted to stream_completed_cache for replay");
     }
 }
 
+/// Wall-clock spacing for `analysis:waveform-partial` — larger buffers cost more
+/// to summarize, so we slow emits and keep UI responsive without CPU spikes.
+fn partial_waveform_emit_min_interval(downloaded: usize) -> Duration {
+    const MB: usize = 1024 * 1024;
+    if downloaded <= 3 * MB {
+        Duration::from_millis(280)
+    } else if downloaded <= 10 * MB {
+        Duration::from_millis(650)
+    } else {
+        Duration::from_millis(1100)
+    }
+}
+
+/// Max centered-byte samples examined per bin for partial waveforms (full track
+/// analysis still uses dense scans elsewhere). Keeps work O(bin_count × cap).
+const PARTIAL_WAVEFORM_SAMPLES_PER_BIN_CAP: usize = 2048;
+
+fn peak_centered_byte_sampled(region: &[u8]) -> u8 {
+    if region.is_empty() {
+        return 0;
+    }
+    let cap = PARTIAL_WAVEFORM_SAMPLES_PER_BIN_CAP;
+    let mut peak: u8 = 0;
+    if region.len() <= cap {
+        for &b in region {
+            let centered = if b >= 128 { b - 128 } else { 128 - b };
+            if centered > peak {
+                peak = centered;
+            }
+        }
+    } else {
+        let step = (region.len() / cap).max(1);
+        let mut i = 0;
+        while i < region.len() {
+            let b = region[i];
+            let centered = if b >= 128 { b - 128 } else { 128 - b };
+            if centered > peak {
+                peak = centered;
+            }
+            i = i.saturating_add(step);
+        }
+        let b = region[region.len() - 1];
+        let centered = if b >= 128 { b - 128 } else { 128 - b };
+        if centered > peak {
+            peak = centered;
+        }
+    }
+    peak
+}
+
+/// Partial waveform without cloning the whole download buffer and without
+/// holding `buf` locked across all bins (that would stall the decoder's `read()`).
+fn derive_partial_waveform_bins_short_locks(
+    buf: &Arc<Mutex<Vec<u8>>>,
+    downloaded: usize,
+    bin_count: usize,
+) -> Vec<u8> {
+    if downloaded == 0 || bin_count == 0 {
+        return Vec::new();
+    }
+    let len = downloaded;
+    let mut out = vec![0u8; bin_count];
+    for (i, slot) in out.iter_mut().enumerate() {
+        let start = i * len / bin_count;
+        let end = ((i + 1) * len / bin_count).max(start + 1).min(len);
+        let peak = {
+            let b = buf.lock().unwrap();
+            if start >= b.len() {
+                0u8
+            } else {
+                let end = end.min(b.len());
+                peak_centered_byte_sampled(&b[start..end])
+            }
+        };
+        *slot = ((peak as f32 / 127.0).sqrt().clamp(0.0, 1.0) * 255.0) as u8;
+    }
+    out
+}
+
+fn emit_partial_loudness_from_bytes(app: &AppHandle, url: &str, bytes: &[u8], target_lufs: f32) {
+    if bytes.len() < PARTIAL_LOUDNESS_MIN_BYTES {
+        crate::app_deprintln!(
+            "[normalization] partial-loudness skip reason=insufficient-bytes bytes={} min_bytes={}",
+            bytes.len(),
+            PARTIAL_LOUDNESS_MIN_BYTES
+        );
+        return;
+    }
+    // Lightweight fallback based on buffered bytes count to keep CPU low.
+    let mb = bytes.len() as f32 / (1024.0 * 1024.0);
+    let floor_db = (target_lufs + 11.0).clamp(-6.0, -1.5);
+    let gain_db = (-(mb * 0.7)).max(floor_db).min(0.0);
+    crate::app_deprintln!(
+        "[normalization] partial-loudness emit bytes={} gain_db={:.2} target_lufs={:.2} track_id={:?}",
+        bytes.len(),
+        gain_db,
+        target_lufs,
+        playback_identity(url)
+    );
+    let _ = app.emit(
+        "analysis:loudness-partial",
+        PartialLoudnessPayload {
+            track_id: playback_identity(url),
+            gain_db: gain_db as f32,
+            target_lufs,
+            is_partial: true,
+        },
+    );
+}
+
+fn provisional_loudness_gain_from_progress(downloaded: usize, total_size: usize, target_lufs: f32) -> Option<f32> {
+    if total_size == 0 || downloaded == 0 {
+        return None;
+    }
+    let progress = (downloaded as f32 / total_size as f32).clamp(0.0, 1.0);
+    // Move from startup attenuation toward a more realistic late-stream level.
+    // This avoids staying near -2 dB and then jumping hard when final LUFS lands.
+    let start_db = LOUDNESS_STARTUP_ATTENUATION_DB.min(0.0);
+    let end_db = (target_lufs + 6.0).clamp(-10.0, -3.0).min(0.0);
+    let shaped = progress.powf(0.75);
+    Some(start_db + (end_db - start_db) * shaped)
+}
+
 fn content_type_to_hint(ct: &str) -> Option<String> {
     let ct = ct.to_ascii_lowercase();
     if ct.contains("mpeg") || ct.contains("mp3") { Some("mp3".into()) }
@@ -1999,6 +2236,10 @@ pub struct AudioEngine {
     /// When true, audio_play chains sources to the existing Sink instead of
     /// creating a new one, achieving sample-accurate gapless transitions.
     pub gapless_enabled: Arc<AtomicBool>,
+    /// 0=off, 1=replaygain, 2=loudness (future runtime loudness engine).
+    pub normalization_engine: Arc<AtomicU32>,
+    /// Target loudness in LUFS for loudness engine (future use).
+    pub normalization_target_lufs: Arc<AtomicU32>,
     /// Info about the next-up chained track (gapless mode).
     /// The progress task reads this when `current_source_done` fires.
     pub(crate) chained_info: Arc<Mutex<Option<ChainedInfo>>>,
@@ -2015,6 +2256,10 @@ pub struct AudioEngine {
     /// Active radio session state.  None for regular (non-radio) tracks.
     /// Dropping the value aborts the HTTP download task via RadioLiveState::Drop.
     pub(crate) radio_state: Mutex<Option<RadioLiveState>>,
+    /// URL last committed to `AudioCurrent` — used so `audio_update_replay_gain` can
+    /// resolve LUFS / startup trim when the frontend passes `loudnessGainDb: null`
+    /// (otherwise `compute_gain` would treat that as unity gain and playback "jumps").
+    pub(crate) current_playback_url: Arc<Mutex<Option<String>>>,
 }
 
 pub struct AudioCurrent {
@@ -2190,11 +2435,13 @@ pub fn create_engine() -> (AudioEngine, std::thread::JoinHandle<()>) {
             // Set PipeWire / PulseAudio latency hints before the first open.
             #[cfg(target_os = "linux")]
             {
+                // Match cpal ALSA ~200 ms headroom: larger quantum reduces underruns when
+                // the decoder thread catches up after seek or competes with other work.
                 if std::env::var("PIPEWIRE_LATENCY").is_err() {
-                    std::env::set_var("PIPEWIRE_LATENCY", "4096/48000");
+                    std::env::set_var("PIPEWIRE_LATENCY", "8192/48000");
                 }
                 if std::env::var("PULSE_LATENCY_MSEC").is_err() {
-                    std::env::set_var("PULSE_LATENCY_MSEC", "85");
+                    std::env::set_var("PULSE_LATENCY_MSEC", "170");
                 }
             }
 
@@ -2276,12 +2523,15 @@ pub fn create_engine() -> (AudioEngine, std::thread::JoinHandle<()>) {
         crossfade_secs: Arc::new(AtomicU32::new(3.0f32.to_bits())),
         fading_out_sink: Arc::new(Mutex::new(None)),
         gapless_enabled: Arc::new(AtomicBool::new(false)),
+        normalization_engine: Arc::new(AtomicU32::new(0)),
+        normalization_target_lufs: Arc::new(AtomicU32::new((-16.0f32).to_bits())),
         chained_info: Arc::new(Mutex::new(None)),
         samples_played: Arc::new(AtomicU64::new(0)),
         current_sample_rate: Arc::new(AtomicU32::new(0)),
         current_channels: Arc::new(AtomicU32::new(2)),
         gapless_switch_at: Arc::new(AtomicU64::new(0)),
         radio_state: Mutex::new(None),
+        current_playback_url: Arc::new(Mutex::new(None)),
     };
 
     (engine, thread)
@@ -2343,6 +2593,101 @@ fn same_playback_target(a_url: &str, b_url: &str) -> bool {
     }
 }
 
+fn resolve_loudness_gain_from_cache(
+    app: &AppHandle,
+    url: &str,
+    target_lufs: f32,
+    requested_loudness_gain_db: Option<f32>,
+) -> Option<f32> {
+    // Never trust `requested` alone: the frontend may pass the *next* track's gain
+    // while `current_playback_url` still lags one play behind. Always prefer a
+    // cache row for **this** URL's track_id; use `requested` only on cache miss
+    // (provisional / pre-seed from JS).
+    let Some(track_id) = playback_identity(url) else {
+        if let Some(r) = requested_loudness_gain_db {
+            crate::app_deprintln!(
+                "[normalization] resolve_loudness_gain source=request-no-identity arg={:.4}",
+                r
+            );
+        }
+        return requested_loudness_gain_db;
+    };
+    let Some(cache) = app.try_state::<crate::analysis_cache::AnalysisCache>() else {
+        if let Some(r) = requested_loudness_gain_db {
+            crate::app_deprintln!(
+                "[normalization] resolve_loudness_gain source=request-no-cache arg={:.4} track_id={}",
+                r,
+                track_id
+            );
+        }
+        return requested_loudness_gain_db;
+    };
+    // Also touch waveform row here so playback path verifies current context is present.
+    let _ = cache.get_latest_waveform_for_track(&track_id);
+    match cache.get_latest_loudness_for_track(&track_id) {
+        Ok(Some(row)) if row.integrated_lufs.is_finite() => {
+            let recommended = crate::analysis_cache::recommended_gain_for_target(
+                row.integrated_lufs,
+                row.true_peak,
+                target_lufs as f64,
+            ) as f32;
+            crate::app_deprintln!(
+                "[normalization] resolve_loudness_gain source=cache track_id={} gain_db={:.2} target_lufs={:.2} integrated_lufs={:.2} updated_at={}",
+                track_id,
+                recommended,
+                target_lufs,
+                row.integrated_lufs,
+                row.updated_at
+            );
+            Some(recommended)
+        }
+        Ok(Some(row)) => {
+            crate::app_deprintln!(
+                "[normalization] resolve_loudness_gain source=cache-invalid track_id={} integrated_lufs={}",
+                track_id,
+                row.integrated_lufs
+            );
+            None
+        }
+        Ok(None) => {
+            crate::app_deprintln!(
+                "[normalization] resolve_loudness_gain source=cache-miss track_id={}",
+                track_id
+            );
+            if let Some(r) = requested_loudness_gain_db {
+                crate::app_deprintln!(
+                    "[normalization] resolve_loudness_gain source=request-fallback track_id={} arg={:.4}",
+                    track_id,
+                    r
+                );
+                Some(r)
+            } else {
+                None
+            }
+        }
+        Err(e) => {
+            crate::app_deprintln!(
+                "[normalization] resolve_loudness_gain source=cache-error track_id={} err={}",
+                track_id,
+                e
+            );
+            None
+        }
+    }
+}
+
+/// LUFS mode: use cache / explicit `requested`, else a **conservative** trim until
+/// analysis exists — must never return `None` here or `compute_gain` uses unity.
+fn loudness_gain_db_or_startup(
+    app: &AppHandle,
+    url: &str,
+    target_lufs: f32,
+    requested: Option<f32>,
+) -> Option<f32> {
+    resolve_loudness_gain_from_cache(app, url, target_lufs, requested)
+        .or(Some(LOUDNESS_STARTUP_ATTENUATION_DB))
+}
+
 /// Take (consume) completed manual-stream bytes if they correspond to `url`.
 pub(crate) fn take_stream_completed_for_url(state: &AudioEngine, url: &str) -> Option<Vec<u8>> {
     let mut guard = state.stream_completed_cache.lock().unwrap();
@@ -2439,23 +2784,104 @@ async fn fetch_data(
 /// can produce inter-sample peaks slightly above ±1.0 → audible distortion.
 /// 10^(-1/20) ≈ 0.891 — inaudible volume difference, eliminates clipping.
 const MASTER_HEADROOM: f32 = 0.891_254;
+const PARTIAL_LOUDNESS_MIN_BYTES: usize = 256 * 1024;
+const PARTIAL_LOUDNESS_EMIT_INTERVAL_MS: u64 = 350;
+/// Until integrated LUFS is known, stay clearly below "full" level so a follow-up
+/// `audio_update_replay_gain(null)` cannot briefly blast louder than this anchor.
+const LOUDNESS_STARTUP_ATTENUATION_DB: f32 = -6.0;
 
 fn compute_gain(
+    normalization_engine: u32,
     replay_gain_db: Option<f32>,
     replay_gain_peak: Option<f32>,
+    loudness_gain_db: Option<f32>,
     pre_gain_db: f32,
     fallback_db: f32,
     volume: f32,
 ) -> (f32, f32) {
-    let gain_linear = replay_gain_db
-        .map(|db| 10f32.powf((db + pre_gain_db) / 20.0))
-        .unwrap_or_else(|| 10f32.powf(fallback_db / 20.0));
-    let peak = replay_gain_peak.unwrap_or(1.0).max(0.001);
+    let gain_linear = match normalization_engine {
+        2 => loudness_gain_db
+            .map(|db| 10f32.powf(db / 20.0))
+            .unwrap_or(1.0),
+        1 => replay_gain_db
+            .map(|db| 10f32.powf((db + pre_gain_db) / 20.0))
+            .unwrap_or_else(|| 10f32.powf(fallback_db / 20.0)),
+        _ => 1.0,
+    };
+    let peak = if normalization_engine == 1 {
+        replay_gain_peak.unwrap_or(1.0).max(0.001)
+    } else {
+        1.0
+    };
     let gain_linear = gain_linear.min(1.0 / peak);
     let effective = (volume.clamp(0.0, 1.0) * gain_linear * MASTER_HEADROOM).clamp(0.0, 1.0);
     (gain_linear, effective)
 }
 
+fn normalization_engine_name(mode: u32) -> &'static str {
+    match mode {
+        1 => "replaygain",
+        2 => "loudness",
+        _ => "off",
+    }
+}
+
+fn gain_linear_to_db(gain_linear: f32) -> Option<f32> {
+    if gain_linear.is_finite() && gain_linear > 0.0 {
+        Some(20.0 * gain_linear.log10())
+    } else {
+        None
+    }
+}
+
+/// `audio:normalization-state` “Now dB” for the UI: omit a number while loudness
+/// mode is still on the **startup safety trim** only (no cache row / no explicit
+/// requested gain from analysis), so users do not read `-6 dB` as measured LUFS.
+fn loudness_ui_current_gain_db(
+    norm_mode: u32,
+    resolved_loudness_gain_db: Option<f32>,
+    gain_linear: f32,
+) -> Option<f32> {
+    if norm_mode == 2 && resolved_loudness_gain_db.is_none() {
+        None
+    } else {
+        gain_linear_to_db(gain_linear)
+    }
+}
+
+fn ramp_sink_volume(sink: Arc<Sink>, from: f32, to: f32) {
+    let from = from.clamp(0.0, 1.0);
+    let to = to.clamp(0.0, 1.0);
+    if (to - from).abs() < 0.002 {
+        sink.set_volume(to);
+        return;
+    }
+    static RAMP_GEN: AtomicU64 = AtomicU64::new(0);
+    let my_gen = RAMP_GEN.fetch_add(1, Ordering::SeqCst) + 1;
+    std::thread::spawn(move || {
+        let delta = (to - from).abs();
+        // Stretch large corrections to avoid audible "step down" moments.
+        let (steps, step_ms): (usize, u64) = if delta > 0.30 {
+            (24, 35)
+        } else if delta > 0.18 {
+            (18, 30)
+        } else if delta > 0.10 {
+            (14, 24)
+        } else {
+            (8, 16)
+        };
+        for i in 1..=steps {
+            if RAMP_GEN.load(Ordering::SeqCst) != my_gen {
+                return;
+            }
+            let t = i as f32 / steps as f32;
+            let v = from + (to - from) * t;
+            sink.set_volume(v.clamp(0.0, 1.0));
+            std::thread::sleep(Duration::from_millis(step_ms));
+        }
+    });
+}
+
 // ─── Commands ─────────────────────────────────────────────────────────────────
 
 #[tauri::command]
@@ -2465,6 +2891,7 @@ pub async fn audio_play(
     duration_hint: f64,
     replay_gain_db: Option<f32>,
     replay_gain_peak: Option<f32>,
+    loudness_gain_db: Option<f32>,
     pre_gain_db: f32,
     fallback_db: f32,
     manual: bool, // true = user-initiated skip → bypass crossfade, start immediately
@@ -2541,6 +2968,11 @@ pub async fn audio_play(
         old.stop();
     }
 
+    // Pin the logical playback URL immediately so `audio_update_replay_gain` (e.g. from
+    // a fast `refreshLoudness` after `playTrack`) resolves LUFS for **this** track, not
+    // the previous URL still stored until the sink swap completes.
+    *state.current_playback_url.lock().unwrap() = Some(url.clone());
+
     // Extract format hint from URL for better symphonia probing. Strip the
     // query string first so Subsonic-style URLs (`stream.view?...&v=1.16.1&...`)
     // don't latch onto random query-param substrings; only accept short
@@ -2646,7 +3078,11 @@ pub async fn audio_play(
                 .is_some_and(|v| v.to_ascii_lowercase().contains("bytes"));
             let total_size = response.content_length();
 
-            if let (true, Some(total)) = (supports_range, total_size) {
+            // Guardrail: when format/container hint is unknown, some demuxers may
+            // seek near EOF during probe. With a progressively downloaded ranged
+            // source that can delay first audible samples until most/all bytes are
+            // fetched. Prefer sequential streaming in that case for faster start.
+            if let (true, Some(total), true) = (supports_range, total_size, stream_hint.is_some()) {
                 let total_usize = total as usize;
                 crate::app_deprintln!(
                     "[stream] RangedHttpSource selected — total={} KB, hint={:?}",
@@ -2660,12 +3096,15 @@ pub async fn audio_play(
                     gen,
                     state.generation.clone(),
                     audio_http_client(&state),
+                    app.clone(),
+                    duration_hint,
                     url.clone(),
                     response,
                     buf.clone(),
                     downloaded_to.clone(),
                     done.clone(),
                     state.stream_completed_cache.clone(),
+                    state.normalization_target_lufs.clone(),
                 ));
                 let reader = RangedHttpSource {
                     buf,
@@ -2683,8 +3122,8 @@ pub async fn audio_play(
                 }
             } else {
                 crate::app_deprintln!(
-                    "[stream] legacy AudioStreamReader (non-seekable) — accept-ranges={}, content-length={:?}",
-                    supports_range, total_size
+                    "[stream] legacy AudioStreamReader (non-seekable) — accept-ranges={}, content-length={:?}, hint={:?}",
+                    supports_range, total_size, stream_hint
                 );
                 let buffer_cap = total_size
                     .map(|n| n as usize)
@@ -2697,11 +3136,13 @@ pub async fn audio_play(
                     gen,
                     state.generation.clone(),
                     audio_http_client(&state),
+                    app.clone(),
                     url.clone(),
                     response,
                     prod,
                     done.clone(),
                     state.stream_completed_cache.clone(),
+                    state.normalization_target_lufs.clone(),
                 ));
 
                 let (_new_cons_tx, new_cons_rx) = std::sync::mpsc::channel::<HeapConsumer<u8>>();
@@ -2735,7 +3176,45 @@ pub async fn audio_play(
         return Ok(());
     }
 
-    let (gain_linear, effective_volume) = compute_gain(replay_gain_db, replay_gain_peak, pre_gain_db, fallback_db, volume);
+    let target_lufs = f32::from_bits(state.normalization_target_lufs.load(Ordering::Relaxed));
+    let resolved_loudness_gain_db = resolve_loudness_gain_from_cache(&app, &url, target_lufs, loudness_gain_db);
+    let norm_mode = state.normalization_engine.load(Ordering::Relaxed);
+    let startup_loudness_gain_db = if norm_mode == 2 {
+        loudness_gain_db_or_startup(&app, &url, target_lufs, loudness_gain_db)
+    } else {
+        resolved_loudness_gain_db
+    };
+    let (gain_linear, effective_volume) = compute_gain(
+        norm_mode,
+        replay_gain_db,
+        replay_gain_peak,
+        startup_loudness_gain_db,
+        pre_gain_db,
+        fallback_db,
+        volume,
+    );
+    let current_gain_db = loudness_ui_current_gain_db(norm_mode, resolved_loudness_gain_db, gain_linear);
+    crate::app_deprintln!(
+        "[normalization] audio_play track_id={:?} engine={} replay_gain_db={:?} replay_gain_peak={:?} loudness_gain_db={:?} gain_linear={:.4} current_gain_db={:?} target_lufs={:.2} volume={:.3} effective_volume={:.3}",
+        playback_identity(&url),
+        normalization_engine_name(norm_mode),
+        replay_gain_db,
+        replay_gain_peak,
+        resolved_loudness_gain_db,
+        gain_linear,
+        current_gain_db,
+        target_lufs,
+        volume,
+        effective_volume
+    );
+    let _ = app.emit(
+        "audio:normalization-state",
+        NormalizationStatePayload {
+            engine: normalization_engine_name(norm_mode).to_string(),
+            current_gain_db,
+            target_lufs,
+        },
+    );
 
     // Manual skips (user-initiated) bypass crossfade — the track should start immediately.
     let crossfade_enabled = state.crossfade_enabled.load(Ordering::Relaxed) && !manual;
@@ -2999,6 +3478,7 @@ pub async fn audio_play(
         state.current_sample_rate.clone(),
         state.current_channels.clone(),
         state.gapless_switch_at.clone(),
+        state.current_playback_url.clone(),
     );
 
     Ok(())
@@ -3020,9 +3500,11 @@ pub async fn audio_chain_preload(
     duration_hint: f64,
     replay_gain_db: Option<f32>,
     replay_gain_peak: Option<f32>,
+    loudness_gain_db: Option<f32>,
     pre_gain_db: f32,
     fallback_db: f32,
     hi_res_enabled: bool,
+    app: AppHandle,
     state: State<'_, AudioEngine>,
 ) -> Result<(), String> {
     // Idempotent: already chained this track → nothing to do.
@@ -3087,7 +3569,22 @@ pub async fn audio_chain_preload(
     // current track ends, and `Sink::set_volume` affects the WHOLE Sink (incl.
     // the still-playing current source). Volume for the chained track is
     // applied at the gapless transition in `spawn_progress_task`, not here.
-    let (gain_linear, _effective_volume) = compute_gain(replay_gain_db, replay_gain_peak, pre_gain_db, fallback_db, volume);
+    let target_lufs = f32::from_bits(state.normalization_target_lufs.load(Ordering::Relaxed));
+    let norm_mode = state.normalization_engine.load(Ordering::Relaxed);
+    let chain_loudness_db = if norm_mode == 2 {
+        loudness_gain_db_or_startup(&app, &url, target_lufs, loudness_gain_db)
+    } else {
+        resolve_loudness_gain_from_cache(&app, &url, target_lufs, loudness_gain_db)
+    };
+    let (gain_linear, _effective_volume) = compute_gain(
+        norm_mode,
+        replay_gain_db,
+        replay_gain_peak,
+        chain_loudness_db,
+        pre_gain_db,
+        fallback_db,
+        volume,
+    );
 
     let done_next = Arc::new(AtomicBool::new(false));
     // Use a dedicated counter for the chained source — it will be swapped into
@@ -3189,6 +3686,7 @@ fn spawn_progress_task(
     sample_rate_arc: Arc<AtomicU32>,
     channels_arc: Arc<AtomicU32>,
     gapless_switch_at: Arc<AtomicU64>,
+    current_playback_url: Arc<Mutex<Option<String>>>,
 ) {
     tokio::spawn(async move {
         let mut near_end_ticks: u32 = 0;
@@ -3239,6 +3737,7 @@ fn spawn_progress_task(
                     // must only be called at the boundary, not at preload.
                     {
                         let mut cur = current_arc.lock().unwrap();
+                        let prev_effective = (cur.base_volume * cur.replay_gain_linear * MASTER_HEADROOM).clamp(0.0, 1.0);
                         cur.replay_gain_linear = info.replay_gain_linear;
                         cur.base_volume = info.base_volume;
                         cur.duration_secs = info.duration_secs;
@@ -3246,10 +3745,12 @@ fn spawn_progress_task(
                         cur.play_started = Some(Instant::now());
                         if let Some(sink) = &cur.sink {
                             let effective = (cur.base_volume * cur.replay_gain_linear * MASTER_HEADROOM).clamp(0.0, 1.0);
-                            sink.set_volume(effective);
+                            ramp_sink_volume(Arc::clone(sink), prev_effective, effective);
                         }
                     }
 
+                    *current_playback_url.lock().unwrap() = Some(info.url.clone());
+
                     // Record the gapless switch timestamp for ghost-command guard.
                     let switch_ts = std::time::SystemTime::now()
                         .duration_since(std::time::UNIX_EPOCH)
@@ -3411,6 +3912,7 @@ pub async fn audio_resume(state: State<'_, AudioEngine>, app: AppHandle) -> Resu
 #[tauri::command]
 pub fn audio_stop(state: State<'_, AudioEngine>) {
     state.generation.fetch_add(1, Ordering::SeqCst);
+    *state.current_playback_url.lock().unwrap() = None;
     *state.chained_info.lock().unwrap() = None;
     *state.stream_completed_cache.lock().unwrap() = None;
     // Drop RadioLiveState → triggers Drop → task.abort() → TCP released.
@@ -3525,9 +4027,11 @@ pub fn audio_seek(seconds: f64, state: State<'_, AudioEngine>) -> Result<(), Str
 #[tauri::command]
 pub fn audio_set_volume(volume: f32, state: State<'_, AudioEngine>) {
     let mut cur = state.current.lock().unwrap();
+    let prev_effective = (cur.base_volume * cur.replay_gain_linear * MASTER_HEADROOM).clamp(0.0, 1.0);
     cur.base_volume = volume.clamp(0.0, 1.0);
     if let Some(sink) = &cur.sink {
-        sink.set_volume((cur.base_volume * cur.replay_gain_linear * MASTER_HEADROOM).clamp(0.0, 1.0));
+        let next_effective = (cur.base_volume * cur.replay_gain_linear * MASTER_HEADROOM).clamp(0.0, 1.0);
+        ramp_sink_volume(Arc::clone(sink), prev_effective, next_effective);
     }
 }
 
@@ -3536,17 +4040,67 @@ pub fn audio_update_replay_gain(
     volume: f32,
     replay_gain_db: Option<f32>,
     replay_gain_peak: Option<f32>,
+    loudness_gain_db: Option<f32>,
     pre_gain_db: f32,
     fallback_db: f32,
+    app: AppHandle,
     state: State<'_, AudioEngine>,
 ) {
-    let (gain_linear, effective) = compute_gain(replay_gain_db, replay_gain_peak, pre_gain_db, fallback_db, volume);
+    let norm_mode = state.normalization_engine.load(Ordering::Relaxed);
+    let target_lufs = f32::from_bits(state.normalization_target_lufs.load(Ordering::Relaxed));
+    let url_for_loudness = if norm_mode == 2 {
+        state.current_playback_url.lock().unwrap().clone()
+    } else {
+        None
+    };
+    let resolved_loudness_gain_db = url_for_loudness
+        .as_deref()
+        .and_then(|u| resolve_loudness_gain_from_cache(&app, u, target_lufs, loudness_gain_db));
+    let effective_loudness_db = if norm_mode == 2 {
+        match url_for_loudness.as_deref() {
+            Some(u) => loudness_gain_db_or_startup(&app, u, target_lufs, loudness_gain_db),
+            None => loudness_gain_db.or(Some(LOUDNESS_STARTUP_ATTENUATION_DB)),
+        }
+    } else {
+        loudness_gain_db
+    };
+    let (gain_linear, effective) = compute_gain(
+        norm_mode,
+        replay_gain_db,
+        replay_gain_peak,
+        effective_loudness_db,
+        pre_gain_db,
+        fallback_db,
+        volume,
+    );
+    let current_gain_db = loudness_ui_current_gain_db(norm_mode, resolved_loudness_gain_db, gain_linear);
+    crate::app_deprintln!(
+        "[normalization] audio_update_replay_gain engine={} replay_gain_db={:?} replay_gain_peak={:?} loudness_gain_db={:?} gain_linear={:.4} current_gain_db={:?} target_lufs={:.2} volume={:.3} effective={:.3}",
+        normalization_engine_name(norm_mode),
+        replay_gain_db,
+        replay_gain_peak,
+        loudness_gain_db,
+        gain_linear,
+        current_gain_db,
+        target_lufs,
+        volume,
+        effective
+    );
     let mut cur = state.current.lock().unwrap();
+    let prev_effective = (cur.base_volume * cur.replay_gain_linear * MASTER_HEADROOM).clamp(0.0, 1.0);
     cur.replay_gain_linear = gain_linear;
     cur.base_volume = volume.clamp(0.0, 1.0);
     if let Some(sink) = &cur.sink {
-        sink.set_volume(effective);
+        ramp_sink_volume(Arc::clone(sink), prev_effective, effective);
     }
+    let _ = app.emit(
+        "audio:normalization-state",
+        NormalizationStatePayload {
+            engine: normalization_engine_name(norm_mode).to_string(),
+            current_gain_db,
+            target_lufs,
+        },
+    );
 }
 
 /// Proxy: fetches https://autoeq.app/entries via Rust to bypass WebView CORS restrictions.
@@ -3636,6 +4190,16 @@ pub async fn audio_preload(
         response.bytes().await.map_err(|e| e.to_string())?.into()
     };
     let _ = duration_hint; // kept in API for compatibility
+    if let Some(track_id) = playback_identity(&url) {
+        if let Err(e) = crate::analysis_cache::seed_from_bytes(&app, &track_id, &data) {
+            crate::app_eprintln!("[analysis] preload seed failed for {}: {}", track_id, e);
+        } else {
+            let _ = app.emit(
+                "analysis:waveform-updated",
+                WaveformUpdatedPayload { track_id, is_partial: false },
+            );
+        }
+    }
     let url_for_emit = url.clone();
     *state.preloaded.lock().unwrap() = Some(PreloadedTrack { url, data });
     let _ = app.emit("audio:preload-ready", url_for_emit);
@@ -3780,6 +4344,8 @@ pub async fn audio_play_radio(
         cur.fadeout_samples   = Some(fadeout_samples);
     }
 
+    *state.current_playback_url.lock().unwrap() = Some(url.clone());
+
     state.current_sample_rate.store(sample_rate, Ordering::Relaxed);
     state.current_channels.store(channels as u32, Ordering::Relaxed);
 
@@ -3798,6 +4364,7 @@ pub async fn audio_play_radio(
         state.current_sample_rate.clone(),
         state.current_channels.clone(),
         state.gapless_switch_at.clone(),
+        state.current_playback_url.clone(),
     );
 
     Ok(())
@@ -3980,6 +4547,36 @@ pub fn audio_set_gapless(enabled: bool, state: State<'_, AudioEngine>) {
     state.gapless_enabled.store(enabled, Ordering::Relaxed);
 }
 
+#[tauri::command]
+pub fn audio_set_normalization(engine: String, target_lufs: f32, app: AppHandle, state: State<'_, AudioEngine>) {
+    let mode = match engine.as_str() {
+        "replaygain" => 1,
+        "loudness" => 2,
+        _ => 0,
+    };
+    state.normalization_engine.store(mode, Ordering::Relaxed);
+    let target = target_lufs.clamp(-30.0, -8.0);
+    state
+        .normalization_target_lufs
+        .store(target.to_bits(), Ordering::Relaxed);
+    crate::app_deprintln!(
+        "[normalization] audio_set_normalization requested_engine={} resolved_engine={} target_lufs={:.2}",
+        engine,
+        normalization_engine_name(mode),
+        target
+    );
+    let _ = app.emit(
+        "audio:normalization-state",
+        NormalizationStatePayload {
+            engine: normalization_engine_name(mode).to_string(),
+            // At mode-switch time the effective track gain may not be recalculated yet.
+            // Emit `None` and let audio_play/audio_update_replay_gain publish actual value.
+            current_gain_db: None,
+            target_lufs: target,
+        },
+    );
+}
+
 // ─── Device-change watcher ────────────────────────────────────────────────────
 //
 // Polls every 3 s for two conditions:

src-tauri/src/lib.rs

@@ -2,6 +2,7 @@
 #![cfg_attr(not(debug_assertions), windows_subsystem = "windows")]
 
 mod audio;
+mod analysis_cache;
 pub mod cli;
 mod discord;
 pub(crate) mod logging;
@@ -59,6 +60,12 @@ fn sync_cancel_flags() -> &'static Mutex<HashMap<String, Arc<AtomicBool>>> {
     FLAGS.get_or_init(|| Mutex::new(HashMap::new()))
 }
 
+/// Tracks analysis backfill jobs already running per track_id.
+fn analysis_backfill_inflight() -> &'static Mutex<std::collections::HashSet<String>> {
+    static SET: OnceLock<Mutex<std::collections::HashSet<String>>> = OnceLock::new();
+    SET.get_or_init(|| Mutex::new(std::collections::HashSet::new()))
+}
+
 /// Holds the live system-tray icon handle.  `None` means the tray is currently hidden/removed.
 /// Dropping the inner `TrayIcon` fully removes it from the OS notification area on all platforms.
 type TrayState = Mutex<Option<TrayIcon>>;
@@ -67,6 +74,34 @@ type TrayState = Mutex<Option<TrayIcon>>;
 /// `None` if souvlaki failed to initialize (e.g. no D-Bus session on Linux).
 type MprisControls = Mutex<Option<souvlaki::MediaControls>>;
 
+#[derive(serde::Serialize)]
+#[serde(rename_all = "camelCase")]
+struct WaveformCachePayload {
+    bins: Vec<u8>,
+    bin_count: i64,
+    is_partial: bool,
+    known_until_sec: f64,
+    duration_sec: f64,
+    updated_at: i64,
+}
+
+#[derive(Clone, serde::Serialize)]
+#[serde(rename_all = "camelCase")]
+struct WaveformUpdatedPayload {
+    track_id: String,
+    is_partial: bool,
+}
+
+#[derive(serde::Serialize)]
+#[serde(rename_all = "camelCase")]
+struct LoudnessCachePayload {
+    integrated_lufs: f64,
+    true_peak: f64,
+    recommended_gain_db: f64,
+    target_lufs: f64,
+    updated_at: i64,
+}
+
 #[tauri::command]
 fn greet(name: &str) -> String {
     format!("Hello, {}!", name)
@@ -1131,6 +1166,126 @@ fn check_dir_accessible(path: String) -> bool {
     std::path::Path::new(&path).is_dir()
 }
 
+#[tauri::command]
+fn analysis_get_waveform(
+    track_id: String,
+    md5_16kb: String,
+    cache: tauri::State<'_, analysis_cache::AnalysisCache>,
+) -> Result<Option<WaveformCachePayload>, String> {
+    let key = analysis_cache::TrackKey { track_id, md5_16kb };
+    let row = cache.get_waveform(&key)?;
+    Ok(row.map(|v| WaveformCachePayload {
+        bins: v.bins,
+        bin_count: v.bin_count,
+        is_partial: v.is_partial,
+        known_until_sec: v.known_until_sec,
+        duration_sec: v.duration_sec,
+        updated_at: v.updated_at,
+    }))
+}
+
+#[tauri::command]
+fn analysis_get_waveform_for_track(
+    track_id: String,
+    cache: tauri::State<'_, analysis_cache::AnalysisCache>,
+) -> Result<Option<WaveformCachePayload>, String> {
+    let row = cache.get_latest_waveform_for_track(&track_id)?;
+    Ok(row.map(|v| WaveformCachePayload {
+        bins: v.bins,
+        bin_count: v.bin_count,
+        is_partial: v.is_partial,
+        known_until_sec: v.known_until_sec,
+        duration_sec: v.duration_sec,
+        updated_at: v.updated_at,
+    }))
+}
+
+#[tauri::command]
+fn analysis_get_loudness_for_track(
+    track_id: String,
+    target_lufs: Option<f64>,
+    cache: tauri::State<'_, analysis_cache::AnalysisCache>,
+) -> Result<Option<LoudnessCachePayload>, String> {
+    let row = cache.get_latest_loudness_for_track(&track_id)?;
+    Ok(row.map(|v| {
+        let requested_target = target_lufs.unwrap_or(v.target_lufs).clamp(-30.0, -8.0);
+        let recommended_gain_db = analysis_cache::recommended_gain_for_target(
+            v.integrated_lufs,
+            v.true_peak,
+            requested_target,
+        );
+        LoudnessCachePayload {
+        integrated_lufs: v.integrated_lufs,
+        true_peak: v.true_peak,
+        recommended_gain_db,
+        target_lufs: requested_target,
+        updated_at: v.updated_at,
+    }}))
+}
+
+#[tauri::command]
+fn analysis_enqueue_seed_from_url(
+    track_id: String,
+    url: String,
+    app: tauri::AppHandle,
+) -> Result<(), String> {
+    if track_id.trim().is_empty() || url.trim().is_empty() {
+        return Ok(());
+    }
+    if let Some(cache) = app.try_state::<analysis_cache::AnalysisCache>() {
+        if cache.get_latest_loudness_for_track(&track_id)?.is_some() {
+            crate::app_deprintln!(
+                "[analysis] backfill skip (already cached): {}",
+                track_id
+            );
+            return Ok(());
+        }
+    }
+    {
+        let mut inflight = analysis_backfill_inflight()
+            .lock()
+            .map_err(|_| "analysis backfill lock poisoned".to_string())?;
+        if inflight.contains(&track_id) {
+            return Ok(());
+        }
+        inflight.insert(track_id.clone());
+    }
+    let app_clone = app.clone();
+    tauri::async_runtime::spawn(async move {
+        crate::app_deprintln!("[analysis] backfill queued: {}", track_id);
+        let result = async {
+            let client = reqwest::Client::builder()
+                .user_agent(subsonic_wire_user_agent())
+                .timeout(std::time::Duration::from_secs(120))
+                .build()
+                .map_err(|e| e.to_string())?;
+            let response = client.get(&url).send().await.map_err(|e| e.to_string())?;
+            if !response.status().is_success() {
+                return Err(format!("HTTP {}", response.status().as_u16()));
+            }
+            let bytes = response.bytes().await.map_err(|e| e.to_string())?;
+            if bytes.is_empty() {
+                return Err("empty response".to_string());
+            }
+            let has_loudness = enqueue_analysis_seed(&app_clone, &track_id, &bytes)?;
+            Ok::<bool, String>(has_loudness)
+        }
+        .await;
+        match result {
+            Ok(has_loudness) => crate::app_deprintln!(
+                "[analysis] backfill ready: {} (has_loudness={})",
+                track_id,
+                has_loudness
+            ),
+            Err(e) => crate::app_eprintln!("[analysis] backfill failed for {}: {}", track_id, e),
+        }
+        if let Ok(mut inflight) = analysis_backfill_inflight().lock() {
+            inflight.remove(&track_id);
+        }
+    });
+    Ok(())
+}
+
 // ─── Offline Track Cache ──────────────────────────────────────────────────────
 
 /// Streams an HTTP response body directly to `dest_path` in small chunks.
@@ -1151,6 +1306,47 @@ async fn stream_to_file(response: reqwest::Response, dest_path: &std::path::Path
     Ok(())
 }
 
+fn enqueue_analysis_seed(app: &tauri::AppHandle, track_id: &str, bytes: &[u8]) -> Result<bool, String> {
+    analysis_cache::seed_from_bytes(app, track_id, bytes)
+        .map_err(|e| {
+            crate::app_eprintln!("[analysis] failed to seed {}: {}", track_id, e);
+            e
+        })?;
+    let _ = app.emit(
+        "analysis:waveform-updated",
+        WaveformUpdatedPayload {
+            track_id: track_id.to_string(),
+            is_partial: false,
+        },
+    );
+    let has_loudness = app
+        .try_state::<analysis_cache::AnalysisCache>()
+        .and_then(|cache| cache.get_latest_loudness_for_track(track_id).ok().flatten())
+        .is_some();
+    crate::app_deprintln!(
+        "[analysis] seed result track_id={} bytes={} has_loudness={}",
+        track_id,
+        bytes.len(),
+        has_loudness
+    );
+    Ok(has_loudness)
+}
+
+async fn enqueue_analysis_seed_from_file(
+    app: &tauri::AppHandle,
+    track_id: &str,
+    file_path: &std::path::Path,
+) {
+    let bytes = match tokio::fs::read(file_path).await {
+        Ok(v) => v,
+        Err(_) => return,
+    };
+    if bytes.is_empty() {
+        return;
+    }
+    let _ = enqueue_analysis_seed(app, track_id, &bytes);
+}
+
 /// Downloads a single track to the app's offline cache directory.
 /// Returns the absolute file path so TypeScript can store it and later
 /// construct a `psysonic-local://<path>` URL for the audio engine.
@@ -1217,6 +1413,8 @@ async fn download_track_offline(
         .await
         .map_err(|e| e.to_string())?;
 
+    enqueue_analysis_seed_from_file(&app, &track_id, &file_path).await;
+
     Ok(path_str)
 }
 
@@ -1765,6 +1963,8 @@ async fn download_track_hot_cache(
         .await
         .map_err(|e| e.to_string())?;
 
+    enqueue_analysis_seed_from_file(&app, &track_id, &file_path).await;
+
     let size = tokio::fs::metadata(&file_path)
         .await
         .map(|m| m.len())
@@ -1818,6 +2018,8 @@ async fn promote_stream_cache_to_hot_cache(
         .await
         .map_err(|e| e.to_string())?;
 
+    let _ = enqueue_analysis_seed(&app, &track_id, &bytes);
+
     let size = tokio::fs::metadata(&file_path)
         .await
         .map(|m| m.len())
@@ -3582,6 +3784,13 @@ pub fn run() {
         }))
 
         .setup(|app| {
+            // ── Analysis cache (SQLite) ───────────────────────────────────
+            {
+                let cache = analysis_cache::AnalysisCache::init(&app.handle())
+                    .map_err(|e| format!("analysis cache init failed: {e}"))?;
+                app.manage(cache);
+            }
+
             // ── Custom title bar on Linux ─────────────────────────────────
             // Remove OS window decorations on all Linux so the React TitleBar
             // can take over.  The frontend checks is_tiling_wm() to decide
@@ -3820,6 +4029,7 @@ pub fn run() {
             audio::audio_play_radio,
             audio::audio_set_crossfade,
             audio::audio_set_gapless,
+            audio::audio_set_normalization,
             audio::audio_list_devices,
             audio::audio_canonicalize_selected_device,
             audio::audio_default_output_device_name,
@@ -3850,6 +4060,10 @@ pub fn run() {
             fetch_json_url,
             fetch_icy_metadata,
             resolve_stream_url,
+            analysis_get_waveform,
+            analysis_get_waveform_for_track,
+            analysis_get_loudness_for_track,
+            analysis_enqueue_seed_from_url,
             download_track_offline,
             delete_offline_track,
             get_offline_cache_size,

src/components/QueuePanel.tsx

@@ -258,6 +258,9 @@ export default function QueuePanel() {
   const contextMenu = usePlayerStore(s => s.contextMenu);
 
   const playbackSource = usePlayerStore(s => s.currentPlaybackSource);
+  const normalizationNowDb = usePlayerStore(s => s.normalizationNowDb);
+  const normalizationTargetLufs = usePlayerStore(s => s.normalizationTargetLufs);
+  const normalizationEngineLive = usePlayerStore(s => s.normalizationEngineLive);
 
   const crossfadeEnabled = useAuthStore(s => s.crossfadeEnabled);
   const crossfadeSecs = useAuthStore(s => s.crossfadeSecs);
@@ -267,6 +270,8 @@ export default function QueuePanel() {
   const setCrossfadeSecs = useAuthStore(s => s.setCrossfadeSecs);
   const setGaplessEnabled = useAuthStore(s => s.setGaplessEnabled);
   const setInfiniteQueueEnabled = useAuthStore(s => s.setInfiniteQueueEnabled);
+  const normalizationEngine = useAuthStore(s => s.normalizationEngine);
+  const replayGainMode = useAuthStore(s => s.replayGainMode);
 
   const activeTab  = useLyricsStore(s => s.activeTab);
   const setTab     = useLyricsStore(s => s.setTab);
@@ -478,6 +483,14 @@ export default function QueuePanel() {
             const rgParts = formatQueueReplayGainParts(currentTrack, t);
             const baseLine = baseParts.join(' · ');
             const rgLine = rgParts.join(' · ');
+            const liveGainLabel = normalizationNowDb != null
+              ? `${normalizationNowDb >= 0 ? '+' : ''}${normalizationNowDb.toFixed(2)} dB`
+              : '—';
+            const targetLabel = normalizationEngineLive === 'loudness'
+              ? (normalizationTargetLufs != null ? `${normalizationTargetLufs} LUFS` : '-16 LUFS')
+              : normalizationEngineLive === 'replaygain'
+                ? `ReplayGain (${replayGainMode})`
+                : t('queue.normOff', { defaultValue: 'Off' });
             if (!baseLine && !rgLine && !playbackSource) return null;
             const showRgLine = expandReplayGain && !!rgLine;
             return (
@@ -522,6 +535,15 @@ export default function QueuePanel() {
                       {' · '}{rgLine}
                     </span>
                   )}
+                  {(normalizationEngine === 'loudness' || normalizationEngineLive === 'loudness') && (
+                    <span className="queue-current-tech-rg">
+                      <span className="queue-current-tech-rg-label">{t('queue.normNow', { defaultValue: 'Now' })}</span>
+                      {' · '}{liveGainLabel}
+                      {' · '}
+                      <span className="queue-current-tech-rg-label">{t('queue.normTarget', { defaultValue: 'Target' })}</span>
+                      {' · '}{targetLabel}
+                    </span>
+                  )}
                 </div>
               </div>
             );

src/components/WaveformSeek.tsx

@@ -824,6 +824,7 @@ export default function WaveformSeek({ trackId }: Props) {
   const SEEK_COMMIT_PROGRESS_EPS = 0.02;
   const canvasRef    = useRef<HTMLCanvasElement>(null);
   const heightsRef   = useRef<Float32Array | null>(null);
+  const lastHeightsTrackIdRef = useRef<string | undefined>(undefined);
   const progressRef  = useRef(usePlayerStore.getState().progress);
   const bufferedRef  = useRef(usePlayerStore.getState().buffered);
   const isDragging   = useRef(false);
@@ -832,6 +833,10 @@ export default function WaveformSeek({ trackId }: Props) {
   const [hoverPct, setHoverPct] = useState<number | null>(null);
 
   const seek         = usePlayerStore(s => s.seek);
+  const waveformBins = usePlayerStore(s => s.waveformBins);
+  const waveformIsPartial = usePlayerStore(s => s.waveformIsPartial);
+  const waveformKnownUntilSec = usePlayerStore(s => s.waveformKnownUntilSec);
+  const waveformDurationSec = usePlayerStore(s => s.waveformDurationSec);
   const duration     = usePlayerStore(s => s.currentTrack?.duration ?? 0);
   const seekbarStyle = useAuthStore(s => s.seekbarStyle);
 
@@ -843,10 +848,44 @@ export default function WaveformSeek({ trackId }: Props) {
   useEffect(() => {
     if (!trackId) {
       heightsRef.current = null;
+      lastHeightsTrackIdRef.current = undefined;
+      return;
+    }
+    if (waveformBins && waveformBins.length > 0) {
+      const src = waveformBins;
+      const h = new Float32Array(BAR_COUNT);
+      const effectiveDur = waveformDurationSec > 0 ? waveformDurationSec : duration;
+      const knownFrac = waveformIsPartial && effectiveDur > 0
+        ? Math.max(0, Math.min(1, waveformKnownUntilSec / effectiveDur))
+        : 1;
+      const knownBars = Math.max(0, Math.min(BAR_COUNT, Math.floor(knownFrac * BAR_COUNT)));
+      for (let i = 0; i < BAR_COUNT; i++) {
+        if (i >= knownBars) {
+          h[i] = 0.08; // unknown tail baseline while partial waveform is still loading
+          continue;
+        }
+        const idx = Math.min(src.length - 1, Math.floor((i / BAR_COUNT) * src.length));
+        const v = src[idx];
+        h[i] = Math.max(0.08, Math.min(1, (Number(v) / 255)));
+      }
+      // Partial -> full handoff: blend with previous heights for a smoother
+      // visual transition and avoid a hard "jump" in the waveform shape.
+      if (lastHeightsTrackIdRef.current === trackId && heightsRef.current && heightsRef.current.length === BAR_COUNT) {
+        const prev = heightsRef.current;
+        const mixed = new Float32Array(BAR_COUNT);
+        for (let i = 0; i < BAR_COUNT; i++) {
+          mixed[i] = prev[i] * 0.45 + h[i] * 0.55;
+        }
+        heightsRef.current = mixed;
+      } else {
+        heightsRef.current = h;
+      }
+      lastHeightsTrackIdRef.current = trackId;
       return;
     }
     heightsRef.current = makeHeights(trackId);
-  }, [trackId]);
+    lastHeightsTrackIdRef.current = trackId;
+  }, [trackId, waveformBins, waveformIsPartial, waveformKnownUntilSec, waveformDurationSec, duration]);
 
   // Imperative subscription — no React re-renders from progress changes.
   // Static styles draw here; animated styles only update refs.

src/pages/Settings.tsx

@@ -2224,12 +2224,71 @@ export default function Settings() {
                   <div style={{ fontSize: 12, color: 'var(--text-muted)' }}>{t('settings.replayGainDesc')}</div>
                 </div>
                 <label className="toggle-switch" aria-label={t('settings.replayGain')}>
-                  <input type="checkbox" checked={auth.replayGainEnabled} onChange={e => auth.setReplayGainEnabled(e.target.checked)} id="replay-gain-toggle" />
+                  <input
+                    type="checkbox"
+                    checked={auth.replayGainEnabled}
+                    onChange={e => {
+                      const on = e.target.checked;
+                      auth.setReplayGainEnabled(on);
+                      if (!on) auth.setNormalizationEngine('off');
+                      else if (auth.normalizationEngine === 'off') auth.setNormalizationEngine('replaygain');
+                    }}
+                    id="replay-gain-toggle"
+                  />
                   <span className="toggle-track" />
                 </label>
               </div>
               {auth.replayGainEnabled && (
                 <div style={{ paddingLeft: '1rem', marginTop: '0.5rem', display: 'flex', flexDirection: 'column', gap: '0.4rem' }}>
+                  <div style={{ display: 'flex', alignItems: 'center', gap: '0.75rem', flexWrap: 'wrap' }}>
+                    <span style={{ fontSize: 13, color: 'var(--text-secondary)' }}>Engine:</span>
+                    <button
+                      className={`btn ${auth.normalizationEngine === 'replaygain' ? 'btn-primary' : 'btn-ghost'}`}
+                      style={{ fontSize: 12, padding: '3px 12px' }}
+                      onClick={() => auth.setNormalizationEngine('replaygain')}
+                    >
+                      ReplayGain
+                    </button>
+                    <button
+                      className={`btn ${auth.normalizationEngine === 'loudness' ? 'btn-primary' : 'btn-ghost'}`}
+                      style={{ fontSize: 12, padding: '3px 12px' }}
+                      onClick={() => auth.setNormalizationEngine('loudness')}
+                    >
+                      Loudness
+                    </button>
+                  </div>
+                  {auth.normalizationEngine === 'loudness' && (
+                    <>
+                      <div style={{ fontSize: 12, color: 'var(--text-muted)' }}>
+                        Apple-like automatic normalization. ReplayGain tags are ignored in this mode.
+                      </div>
+                      <div style={{ display: 'flex', alignItems: 'center', gap: '0.75rem', flexWrap: 'wrap' }}>
+                        <span style={{ fontSize: 13, color: 'var(--text-secondary)' }}>Target LUFS:</span>
+                        <button
+                          className={`btn ${auth.loudnessTargetLufs === -16 ? 'btn-primary' : 'btn-ghost'}`}
+                          style={{ fontSize: 12, padding: '3px 12px' }}
+                          onClick={() => auth.setLoudnessTargetLufs(-16)}
+                        >
+                          -16
+                        </button>
+                        <button
+                          className={`btn ${auth.loudnessTargetLufs === -14 ? 'btn-primary' : 'btn-ghost'}`}
+                          style={{ fontSize: 12, padding: '3px 12px' }}
+                          onClick={() => auth.setLoudnessTargetLufs(-14)}
+                        >
+                          -14
+                        </button>
+                        <button
+                          className={`btn ${auth.loudnessTargetLufs === -12 ? 'btn-primary' : 'btn-ghost'}`}
+                          style={{ fontSize: 12, padding: '3px 12px' }}
+                          onClick={() => auth.setLoudnessTargetLufs(-12)}
+                        >
+                          -12
+                        </button>
+                      </div>
+                    </>
+                  )}
+                  {auth.normalizationEngine === 'replaygain' && (
                   <div style={{ display: 'flex', alignItems: 'center', gap: '0.75rem', flexWrap: 'wrap' }}>
                     <span style={{ fontSize: 13, color: 'var(--text-secondary)' }}>{t('settings.replayGainMode')}:</span>
                     <button
@@ -2254,14 +2313,15 @@ export default function Settings() {
                       {t('settings.replayGainAlbum')}
                     </button>
                   </div>
-                  {auth.replayGainMode === 'auto' && (
+                  )}
+                  {auth.normalizationEngine === 'replaygain' && auth.replayGainMode === 'auto' && (
                     <div style={{ fontSize: 12, color: 'var(--text-muted)' }}>
                       {t('settings.replayGainAutoDesc')}
                     </div>
                   )}
                 </div>
               )}
-              {auth.replayGainEnabled && (
+              {auth.replayGainEnabled && auth.normalizationEngine === 'replaygain' && (
                 <div style={{ paddingLeft: '1rem', marginTop: '0.75rem', display: 'flex', flexDirection: 'column', gap: '0.6rem' }}>
                   <div style={{ display: 'flex', alignItems: 'center', gap: '0.75rem', flexWrap: 'wrap' }}>
                     <span style={{ fontSize: 13, color: 'var(--text-secondary)', minWidth: 100 }}>

src/store/analysisSync.ts

@@ -0,0 +1,29 @@
+export type AnalysisStorageChangedReason =
+  | 'offline-delete'
+  | 'hotcache-delete'
+  | 'hotcache-purge';
+
+export type AnalysisStorageChangedDetail = {
+  trackId?: string | null;
+  reason: AnalysisStorageChangedReason;
+};
+
+const EVENT_NAME = 'psysonic:analysis-storage-changed';
+
+export function emitAnalysisStorageChanged(detail: AnalysisStorageChangedDetail): void {
+  if (typeof window === 'undefined') return;
+  window.dispatchEvent(new CustomEvent<AnalysisStorageChangedDetail>(EVENT_NAME, { detail }));
+}
+
+export function onAnalysisStorageChanged(
+  listener: (detail: AnalysisStorageChangedDetail) => void,
+): () => void {
+  if (typeof window === 'undefined') return () => {};
+  const wrapped = (evt: Event) => {
+    const ce = evt as CustomEvent<AnalysisStorageChangedDetail>;
+    if (!ce?.detail) return;
+    listener(ce.detail);
+  };
+  window.addEventListener(EVENT_NAME, wrapped as EventListener);
+  return () => window.removeEventListener(EVENT_NAME, wrapped as EventListener);
+}

src/store/authStore.ts

@@ -20,6 +20,7 @@ export interface ServerProfile {
 
 export type SeekbarStyle = 'waveform' | 'linedot' | 'bar' | 'thick' | 'segmented' | 'neon' | 'pulsewave' | 'particletrail' | 'liquidfill' | 'retrotape';
 export type LoggingMode = 'off' | 'normal' | 'debug';
+export type NormalizationEngine = 'off' | 'replaygain' | 'loudness';
 
 export type LyricsSourceId = 'server' | 'lrclib' | 'netease';
 export interface LyricsSourceConfig { id: LyricsSourceId; enabled: boolean; }
@@ -49,6 +50,8 @@ interface AuthState {
   excludeAudiobooks: boolean;
   customGenreBlacklist: string[];
   replayGainEnabled: boolean;
+  normalizationEngine: NormalizationEngine;
+  loudnessTargetLufs: -16 | -14 | -12;
   replayGainMode: 'track' | 'album' | 'auto';
   replayGainPreGainDb: number;   // added to RG gain for tagged files (0…+6 dB)
   replayGainFallbackDb: number;  // gain for untagged files / radio (-6…0 dB)
@@ -205,6 +208,8 @@ interface AuthState {
   setExcludeAudiobooks: (v: boolean) => void;
   setCustomGenreBlacklist: (v: string[]) => void;
   setReplayGainEnabled: (v: boolean) => void;
+  setNormalizationEngine: (v: NormalizationEngine) => void;
+  setLoudnessTargetLufs: (v: -16 | -14 | -12) => void;
   setReplayGainMode: (v: 'track' | 'album' | 'auto') => void;
   setReplayGainPreGainDb: (v: number) => void;
   setReplayGainFallbackDb: (v: number) => void;
@@ -315,6 +320,8 @@ export const useAuthStore = create<AuthState>()(
       excludeAudiobooks: false,
       customGenreBlacklist: [],
       replayGainEnabled: false,
+      normalizationEngine: 'off',
+      loudnessTargetLufs: -14,
       replayGainMode: 'auto',
       replayGainPreGainDb: 0,
       replayGainFallbackDb: 0,
@@ -442,6 +449,14 @@ export const useAuthStore = create<AuthState>()(
         set({ replayGainEnabled: v });
         usePlayerStore.getState().updateReplayGainForCurrentTrack();
       },
+      setNormalizationEngine: (v) => {
+        set({ normalizationEngine: v });
+        usePlayerStore.getState().updateReplayGainForCurrentTrack();
+      },
+      setLoudnessTargetLufs: (v) => {
+        set({ loudnessTargetLufs: v });
+        usePlayerStore.getState().updateReplayGainForCurrentTrack();
+      },
       setReplayGainMode: (v) => {
         set({ replayGainMode: v });
         usePlayerStore.getState().updateReplayGainForCurrentTrack();

src/store/hotCacheStore.ts

@@ -3,6 +3,7 @@ import { persist, createJSONStorage } from 'zustand/middleware';
 import { invoke } from '@tauri-apps/api/core';
 import { isHotCachePreviousTrackUnderGrace } from '../utils/hotCacheGate';
 import type { Track } from './playerStore';
+import { emitAnalysisStorageChanged } from './analysisSync';
 
 /** How many queue slots after the current index are eviction-protected (1 = current + next only). */
 export const HOT_CACHE_PROTECT_AFTER_CURRENT = 1;
@@ -96,6 +97,7 @@ export const useHotCacheStore = create<HotCacheState>()(
           delete next[entryKey(serverId, trackId)];
           return { entries: next };
         });
+        emitAnalysisStorageChanged({ trackId, reason: 'hotcache-delete' });
       },
 
       totalBytes: () =>
@@ -167,6 +169,7 @@ export const useHotCacheStore = create<HotCacheState>()(
           }).catch(() => {});
           sum -= meta.sizeBytes || 0;
           delete entries[key];
+          emitAnalysisStorageChanged({ trackId: parsed.trackId, reason: 'hotcache-delete' });
         }
 
         set({ entries });
@@ -175,6 +178,7 @@ export const useHotCacheStore = create<HotCacheState>()(
       clearAllDisk: async (customDir: string | null) => {
         await invoke('purge_hot_cache', { customDir: customDir || null }).catch(() => {});
         set({ entries: {} });
+        emitAnalysisStorageChanged({ trackId: null, reason: 'hotcache-purge' });
       },
     }),
     {

src/store/offlineStore.ts

@@ -6,6 +6,7 @@ import type { SubsonicSong } from '../api/subsonic';
 import { useAuthStore } from './authStore';
 import { showToast } from '../utils/toast';
 import { useOfflineJobStore, cancelledDownloads } from './offlineJobStore';
+import { emitAnalysisStorageChanged } from './analysisSync';
 
 export interface OfflineTrackMeta {
   id: string;
@@ -299,6 +300,9 @@ export const useOfflineStore = create<OfflineState>()(
             }).catch(() => {});
           }),
         );
+        for (const trackId of album.trackIds) {
+          emitAnalysisStorageChanged({ trackId, reason: 'offline-delete' });
+        }
 
         set(state => {
           const tracks = { ...state.tracks };

src/store/playerStore.ts

@@ -10,6 +10,7 @@ import { lastfmScrobble, lastfmUpdateNowPlaying, lastfmLoveTrack, lastfmUnloveTr
 import { useAuthStore } from './authStore';
 import { useOfflineStore } from './offlineStore';
 import { useHotCacheStore } from './hotCacheStore';
+import { onAnalysisStorageChanged } from './analysisSync';
 
 export interface Track {
   id: string;
@@ -143,6 +144,19 @@ async function buildInfiniteQueueCandidates(
 
 interface PlayerState {
   currentTrack: Track | null;
+  waveformBins: number[] | null;
+  waveformIsPartial: boolean;
+  waveformKnownUntilSec: number;
+  waveformDurationSec: number;
+  normalizationNowDb: number | null;
+  normalizationTargetLufs: number | null;
+  normalizationEngineLive: 'off' | 'replaygain' | 'loudness';
+  normalizationDbgSource: string | null;
+  normalizationDbgTrackId: string | null;
+  normalizationDbgCacheGainDb: number | null;
+  normalizationDbgCacheTargetLufs: number | null;
+  normalizationDbgCacheUpdatedAt: number | null;
+  normalizationDbgLastEventAt: number | null;
   currentRadio: InternetRadioStation | null;
   /** Latches the source used to start the currently playing track. */
   currentPlaybackSource: PlaybackSourceKind | null;
@@ -241,6 +255,29 @@ interface PlayerState {
   closeSongInfo: () => void;
 }
 
+type WaveformCachePayload = {
+  bins: number[];
+  binCount: number;
+  isPartial: boolean;
+  knownUntilSec: number;
+  durationSec: number;
+  updatedAt: number;
+};
+
+type LoudnessCachePayload = {
+  integratedLufs: number;
+  truePeak: number;
+  recommendedGainDb: number;
+  targetLufs: number;
+  updatedAt: number;
+};
+
+type NormalizationStatePayload = {
+  engine: 'off' | 'replaygain' | 'loudness' | string;
+  currentGainDb: number | null;
+  targetLufs: number;
+};
+
 // ─── Module-level playback primitives ─────────────────────────────────────────
 
 // isAudioPaused — true when the Rust audio engine has a loaded-but-paused track.
@@ -259,6 +296,66 @@ let radioFetching = false;
 // Artist ID used to start the current radio session — persists across track
 // advances so proactive loading works even when songs lack artistId.
 let currentRadioArtistId: string | null = null;
+let cachedLoudnessGainByTrackId: Record<string, number> = {};
+let stableLoudnessGainByTrackId: Record<string, true> = {};
+let lastNormalizationUiUpdateAtMs = 0;
+
+function emitNormalizationDebug(step: string, details?: Record<string, unknown>) {
+  if (useAuthStore.getState().loggingMode !== 'debug') return;
+  void invoke('frontend_debug_log', {
+    scope: 'normalization',
+    message: JSON.stringify({ step, details }),
+  }).catch(() => {});
+}
+
+function normalizeAnalysisTrackId(trackId?: string | null): string | null {
+  if (!trackId) return null;
+  if (trackId.startsWith('stream:')) return trackId.slice('stream:'.length);
+  return trackId;
+}
+
+function normalizationAlmostEqual(a: number | null, b: number | null, eps = 0.12): boolean {
+  if (a == null && b == null) return true;
+  if (a == null || b == null) return false;
+  return Math.abs(a - b) <= eps;
+}
+
+function deriveNormalizationSnapshot(
+  track: Track,
+  queue: Track[],
+  queueIndex: number,
+): Pick<
+  PlayerState,
+  'normalizationNowDb' | 'normalizationTargetLufs' | 'normalizationEngineLive'
+> {
+  const auth = useAuthStore.getState();
+  const engine = auth.normalizationEngine;
+  if (engine === 'loudness') {
+    const target = auth.loudnessTargetLufs;
+    return {
+      // Clears stale UI until `audio:normalization-state` / refresh catches up.
+      normalizationNowDb: null,
+      normalizationTargetLufs: target,
+      normalizationEngineLive: 'loudness',
+    };
+  }
+  if (engine === 'replaygain' && auth.replayGainEnabled) {
+    const prev = queueIndex > 0 ? queue[queueIndex - 1] : null;
+    const next = queueIndex + 1 < queue.length ? queue[queueIndex + 1] : null;
+    const resolved = resolveReplayGainDb(track, prev, next, true, auth.replayGainMode);
+    const nowDb = resolved != null ? (resolved + auth.replayGainPreGainDb) : auth.replayGainFallbackDb;
+    return {
+      normalizationNowDb: nowDb,
+      normalizationTargetLufs: null,
+      normalizationEngineLive: 'replaygain',
+    };
+  }
+  return {
+    normalizationNowDb: null,
+    normalizationTargetLufs: null,
+    normalizationEngineLive: 'off',
+  };
+}
 
 // Debounce timer for seek slider drags.
 let seekDebounce: ReturnType<typeof setTimeout> | null = null;
@@ -267,6 +364,9 @@ let seekDebounce: ReturnType<typeof setTimeout> | null = null;
 let seekTarget: number | null = null;
 let seekTargetSetAt = 0;
 const SEEK_TARGET_GUARD_TIMEOUT_MS = 5000;
+const analysisBackfillInFlightByTrackId: Record<string, true> = {};
+const analysisBackfillAttemptsByTrackId: Record<string, number> = {};
+const MAX_BACKFILL_ATTEMPTS_PER_TRACK = 2;
 // Streaming fallback seek guard: coalesce repeated "not seekable" recoveries.
 let seekFallbackRetryTimer: ReturnType<typeof setTimeout> | null = null;
 let seekFallbackRetryStartedAt = 0;
@@ -481,6 +581,102 @@ function touchHotCacheOnPlayback(trackId: string, serverId: string) {
   useHotCacheStore.getState().touchPlayed(trackId, serverId);
 }
 
+function isReplayGainActive() {
+  const a = useAuthStore.getState();
+  return a.normalizationEngine === 'replaygain' && a.replayGainEnabled;
+}
+
+async function refreshWaveformForTrack(trackId: string) {
+  if (!trackId) return;
+  try {
+    const row = await invoke<WaveformCachePayload | null>('analysis_get_waveform_for_track', { trackId });
+    if (!row || !Array.isArray(row.bins) || row.bins.length === 0) {
+      usePlayerStore.setState({
+        waveformBins: null,
+        waveformIsPartial: false,
+        waveformKnownUntilSec: 0,
+        waveformDurationSec: 0,
+      });
+      return;
+    }
+    usePlayerStore.setState({
+      waveformBins: row.bins,
+      waveformIsPartial: !!row.isPartial,
+      waveformKnownUntilSec: Number.isFinite(row.knownUntilSec) ? row.knownUntilSec : 0,
+      waveformDurationSec: Number.isFinite(row.durationSec) ? row.durationSec : 0,
+    });
+  } catch {
+    // best-effort; seekbar falls back to placeholder waveform
+  }
+}
+
+/** When `syncPlayingEngine` is false, only update `cachedLoudnessGainByTrackId` (e.g. queue neighbour) — do not call `audio_update_replay_gain` for the already-playing track. */
+async function refreshLoudnessForTrack(
+  trackId: string,
+  opts?: { syncPlayingEngine?: boolean },
+) {
+  if (!trackId) return;
+  const syncEngine = opts?.syncPlayingEngine !== false;
+  emitNormalizationDebug('refresh:start', { trackId });
+  usePlayerStore.setState({ normalizationDbgSource: 'refresh:start', normalizationDbgTrackId: trackId });
+  try {
+    const row = await invoke<LoudnessCachePayload | null>('analysis_get_loudness_for_track', {
+      trackId,
+      targetLufs: useAuthStore.getState().loudnessTargetLufs,
+    });
+    if (!row || !Number.isFinite(row.recommendedGainDb)) {
+      delete cachedLoudnessGainByTrackId[trackId];
+      delete stableLoudnessGainByTrackId[trackId];
+      emitNormalizationDebug('refresh:miss', { trackId, row: row ?? null });
+      const auth = useAuthStore.getState();
+      const attempts = analysisBackfillAttemptsByTrackId[trackId] ?? 0;
+      if (auth.normalizationEngine === 'loudness'
+        && !analysisBackfillInFlightByTrackId[trackId]
+        && attempts < MAX_BACKFILL_ATTEMPTS_PER_TRACK) {
+        analysisBackfillInFlightByTrackId[trackId] = true;
+        analysisBackfillAttemptsByTrackId[trackId] = attempts + 1;
+        const url = buildStreamUrl(trackId);
+        emitNormalizationDebug('backfill:enqueue', { trackId, url, attempt: attempts + 1 });
+        void invoke('analysis_enqueue_seed_from_url', { trackId, url })
+          .then(() => emitNormalizationDebug('backfill:queued', { trackId, attempt: attempts + 1 }))
+          .catch((e) => emitNormalizationDebug('backfill:error', { trackId, error: String(e) }))
+          .finally(() => {
+            delete analysisBackfillInFlightByTrackId[trackId];
+          });
+      } else if (auth.normalizationEngine === 'loudness' && attempts >= MAX_BACKFILL_ATTEMPTS_PER_TRACK) {
+        emitNormalizationDebug('backfill:throttled', { trackId, attempts });
+      }
+      usePlayerStore.setState({
+        normalizationDbgSource: 'refresh:miss',
+        normalizationDbgTrackId: trackId,
+        normalizationDbgCacheGainDb: null,
+        normalizationDbgCacheTargetLufs: Number.isFinite(row?.targetLufs as number) ? (row?.targetLufs as number) : null,
+        normalizationDbgCacheUpdatedAt: Number.isFinite(row?.updatedAt as number) ? (row?.updatedAt as number) : null,
+      });
+      return;
+    }
+    cachedLoudnessGainByTrackId[trackId] = row.recommendedGainDb;
+    stableLoudnessGainByTrackId[trackId] = true;
+    analysisBackfillAttemptsByTrackId[trackId] = 0;
+    emitNormalizationDebug('refresh:hit', { trackId, row });
+    usePlayerStore.setState({
+      normalizationDbgSource: 'refresh:hit',
+      normalizationDbgTrackId: trackId,
+      normalizationDbgCacheGainDb: row.recommendedGainDb,
+      normalizationDbgCacheTargetLufs: Number.isFinite(row.targetLufs) ? row.targetLufs : null,
+      normalizationDbgCacheUpdatedAt: Number.isFinite(row.updatedAt) ? row.updatedAt : null,
+    });
+    if (syncEngine) {
+      usePlayerStore.getState().updateReplayGainForCurrentTrack();
+    }
+  } catch {
+    delete cachedLoudnessGainByTrackId[trackId];
+    delete stableLoudnessGainByTrackId[trackId];
+    emitNormalizationDebug('refresh:error', { trackId });
+    usePlayerStore.setState({ normalizationDbgSource: 'refresh:error', normalizationDbgTrackId: trackId });
+  }
+}
+
 async function promoteCompletedStreamToHotCache(track: Track, serverId: string, customDir: string | null) {
   try {
     const res = await invoke<{ path: string; size: number } | null>(
@@ -567,7 +763,19 @@ function handleAudioProgress(current_time: number, duration: number) {
   const dur = duration > 0 ? duration : track.duration;
   if (dur <= 0) return;
   const progress = displayTime / dur;
-  usePlayerStore.setState({ currentTime: displayTime, progress, buffered: 0 });
+  const stateNow = usePlayerStore.getState();
+  if (stateNow.waveformIsPartial) {
+    usePlayerStore.setState({
+      currentTime: displayTime,
+      progress,
+      buffered: 0,
+      // Keep known span aligned with playback position during partial stage:
+      // if playback moved forward, this part is definitely known already.
+      waveformKnownUntilSec: Math.max(stateNow.waveformKnownUntilSec || 0, displayTime),
+    });
+  } else {
+    usePlayerStore.setState({ currentTime: displayTime, progress, buffered: 0 });
+  }
 
   // Scrobble at 50%: Last.fm + Navidrome (updates play_date / recently played)
   if (progress >= 0.5 && !store.scrobbled) {
@@ -641,6 +849,9 @@ function handleAudioProgress(current_time: number, duration: number) {
     // Byte pre-download — runs early so bytes are cached by chain time.
     if ((shouldBytePreload || shouldBytePreloadForGaplessBackup) && nextTrack.id !== bytePreloadingId) {
       bytePreloadingId = nextTrack.id;
+      // Keep analysis context warm for the upcoming track before any source swap.
+      void refreshWaveformForTrack(nextTrack.id);
+      void refreshLoudnessForTrack(nextTrack.id, { syncPlayingEngine: false });
       if (import.meta.env.DEV) {
         console.info('[psysonic][preload-request]', {
           nextTrackId: nextTrack.id,
@@ -657,6 +868,8 @@ function handleAudioProgress(current_time: number, duration: number) {
     // Gapless chain — decode + chain into Sink 30s before track boundary.
     if (shouldChainGapless && nextTrack.id !== gaplessPreloadingId) {
       gaplessPreloadingId = nextTrack.id;
+      // Ensure loudness gain is already cached for the chained request payload.
+      void refreshLoudnessForTrack(nextTrack.id, { syncPlayingEngine: false });
       const authState = useAuthStore.getState();
       // Auto-mode neighbours for the *next* track: current track on its left,
       // queue[nextIdx+1] on its right.
@@ -665,9 +878,9 @@ function handleAudioProgress(current_time: number, duration: number) {
         : (repeatMode === 'all' && queue.length > 0 ? queue[0] : null);
       const replayGainDb = resolveReplayGainDb(
         nextTrack, track, nextNeighbour,
-        authState.replayGainEnabled, authState.replayGainMode,
+        isReplayGainActive(), authState.replayGainMode,
       );
-      const replayGainPeak = authState.replayGainEnabled
+      const replayGainPeak = isReplayGainActive()
         ? (nextTrack.replayGainPeak ?? null)
         : null;
       invoke('audio_chain_preload', {
@@ -676,6 +889,7 @@ function handleAudioProgress(current_time: number, duration: number) {
         durationHint: nextTrack.duration,
         replayGainDb,
         replayGainPeak,
+        loudnessGainDb: cachedLoudnessGainByTrackId[nextTrack.id] ?? null,
         preGainDb: authState.replayGainPreGainDb,
         fallbackDb: authState.replayGainFallbackDb,
         hiResEnabled: authState.enableHiRes,
@@ -700,7 +914,14 @@ function handleAudioEnded() {
 
   const { repeatMode, currentTrack, queue } = usePlayerStore.getState();
   isAudioPaused = false;
-  usePlayerStore.setState({ isPlaying: false, progress: 0, currentTime: 0, buffered: 0 });
+  usePlayerStore.setState({
+    isPlaying: false,
+    progress: 0,
+    currentTime: 0,
+    buffered: 0,
+    waveformIsPartial: false,
+    waveformKnownUntilSec: 0,
+  });
   setTimeout(() => {
     if (repeatMode === 'one' && currentTrack) {
       usePlayerStore.getState().playTrack(currentTrack, queue, false);
@@ -744,6 +965,13 @@ function handleAudioTrackSwitched(duration: number) {
 
   usePlayerStore.setState({
     currentTrack: nextTrack,
+    waveformBins: null,
+    waveformIsPartial: false,
+    waveformKnownUntilSec: 0,
+    waveformDurationSec: 0,
+    ...deriveNormalizationSnapshot(nextTrack, queue, newIndex),
+    normalizationDbgSource: 'track-switched',
+    normalizationDbgTrackId: nextTrack.id,
     queueIndex: newIndex,
     isPlaying: true,
     progress: 0,
@@ -752,6 +980,14 @@ function handleAudioTrackSwitched(duration: number) {
     scrobbled: false,
     lastfmLoved: false,
   });
+  emitNormalizationDebug('track-switched', {
+    trackId: nextTrack.id,
+    queueIndex: newIndex,
+    engineRequested: useAuthStore.getState().normalizationEngine,
+  });
+  void refreshWaveformForTrack(nextTrack.id);
+  void refreshLoudnessForTrack(nextTrack.id);
+  usePlayerStore.getState().updateReplayGainForCurrentTrack();
 
   // Report Now Playing to Navidrome + Last.fm
   const { nowPlayingEnabled, scrobblingEnabled, lastfmSessionKey } = useAuthStore.getState();
@@ -817,6 +1053,90 @@ export function initAudioListeners(): () => void {
     listen<void>('audio:ended', () => handleAudioEnded()),
     listen<string>('audio:error', ({ payload }) => handleAudioError(payload)),
     listen<number>('audio:track_switched', ({ payload }) => handleAudioTrackSwitched(payload)),
+    listen<{ trackId?: string | null; bins: number[]; knownUntilSec: number; durationSec: number; isPartial: boolean }>('analysis:waveform-partial', ({ payload }) => {
+      const current = usePlayerStore.getState().currentTrack;
+      if (!current || !payload) return;
+      const payloadTrackId = normalizeAnalysisTrackId(payload.trackId);
+      if (payloadTrackId && payloadTrackId !== current.id) return;
+      if (!payload.isPartial || !payload?.bins?.length) {
+        usePlayerStore.setState({ waveformIsPartial: false, waveformKnownUntilSec: 0 });
+        return;
+      }
+      usePlayerStore.setState({
+        waveformBins: payload.bins,
+        waveformIsPartial: true,
+        waveformKnownUntilSec: Number.isFinite(payload.knownUntilSec) ? payload.knownUntilSec : 0,
+        waveformDurationSec: Number.isFinite(payload.durationSec) ? payload.durationSec : (current.duration || 0),
+      });
+    }),
+    listen<{ trackId?: string | null; gainDb: number; targetLufs: number; isPartial: boolean }>('analysis:loudness-partial', ({ payload }) => {
+      const current = usePlayerStore.getState().currentTrack;
+      if (!current || !payload) return;
+      const payloadTrackId = normalizeAnalysisTrackId(payload.trackId);
+      if (payloadTrackId && payloadTrackId !== current.id) return;
+      if (!Number.isFinite(payload.gainDb)) return;
+      if (stableLoudnessGainByTrackId[current.id]) return;
+      cachedLoudnessGainByTrackId[current.id] = payload.gainDb;
+      emitNormalizationDebug('partial-loudness:apply', {
+        trackId: current.id,
+        gainDb: payload.gainDb,
+        targetLufs: payload.targetLufs,
+      });
+      usePlayerStore.getState().updateReplayGainForCurrentTrack();
+    }),
+    listen<{ trackId: string; isPartial: boolean }>('analysis:waveform-updated', ({ payload }) => {
+      if (!payload?.trackId) return;
+      const payloadTrackId = normalizeAnalysisTrackId(payload.trackId);
+      if (!payloadTrackId) return;
+      const currentId = usePlayerStore.getState().currentTrack?.id;
+      if (currentId && payloadTrackId === currentId) {
+        void refreshWaveformForTrack(currentId);
+        void refreshLoudnessForTrack(currentId);
+        emitNormalizationDebug('backfill:applied', { trackId: currentId });
+        return;
+      }
+      // Backfill finished for another id (e.g. next in queue): refresh loudness cache only
+      // so `cachedLoudnessGainByTrackId` is ready before `audio_play` / gapless chain.
+      void refreshLoudnessForTrack(payloadTrackId, { syncPlayingEngine: false });
+      emitNormalizationDebug('backfill:applied', { trackId: payloadTrackId });
+    }),
+    listen<NormalizationStatePayload>('audio:normalization-state', ({ payload }) => {
+      if (!payload) return;
+      const engine =
+        payload.engine === 'loudness' || payload.engine === 'replaygain'
+          ? payload.engine
+          : 'off';
+      const nowDb = Number.isFinite(payload.currentGainDb as number) ? (payload.currentGainDb as number) : null;
+      const targetLufs = Number.isFinite(payload.targetLufs) ? payload.targetLufs : null;
+      const prev = usePlayerStore.getState();
+      // Avoid UI flicker from noisy duplicate emits and transient nulls.
+      if (
+        engine === prev.normalizationEngineLive
+        && normalizationAlmostEqual(nowDb, prev.normalizationNowDb)
+        && normalizationAlmostEqual(targetLufs, prev.normalizationTargetLufs, 0.02)
+      ) {
+        return;
+      }
+      if (engine === 'loudness' && nowDb == null && prev.normalizationNowDb != null) {
+        return;
+      }
+      const nowMs = Date.now();
+      if (nowMs - lastNormalizationUiUpdateAtMs < 120 && engine === prev.normalizationEngineLive) {
+        return;
+      }
+      lastNormalizationUiUpdateAtMs = nowMs;
+      emitNormalizationDebug('event:audio:normalization-state', {
+        trackId: usePlayerStore.getState().currentTrack?.id ?? null,
+        payload,
+      });
+      usePlayerStore.setState({
+        normalizationEngineLive: engine,
+        normalizationNowDb: nowDb,
+        normalizationTargetLufs: targetLufs,
+        normalizationDbgSource: 'event:audio:normalization-state',
+        normalizationDbgLastEventAt: Date.now(),
+      });
+    }),
     listen<string>('audio:preload-ready', ({ payload }) => {
       const tid = streamUrlTrackId(payload);
       if (import.meta.env.DEV) {
@@ -840,17 +1160,83 @@ export function initAudioListeners(): () => void {
   const { crossfadeEnabled, crossfadeSecs, gaplessEnabled, audioOutputDevice } = useAuthStore.getState();
   invoke('audio_set_crossfade', { enabled: crossfadeEnabled, secs: crossfadeSecs }).catch(() => {});
   invoke('audio_set_gapless', { enabled: gaplessEnabled }).catch(() => {});
+  const normCfg = useAuthStore.getState();
+  usePlayerStore.setState({
+    normalizationEngineLive: normCfg.normalizationEngine,
+    normalizationTargetLufs: normCfg.normalizationEngine === 'loudness' ? normCfg.loudnessTargetLufs : null,
+    normalizationNowDb: null,
+    normalizationDbgSource: 'init:set-normalization',
+  });
+  emitNormalizationDebug('init:set-normalization', {
+    engine: normCfg.normalizationEngine,
+    targetLufs: normCfg.loudnessTargetLufs,
+    currentTrackId: usePlayerStore.getState().currentTrack?.id ?? null,
+  });
+  invoke('audio_set_normalization', {
+    engine: normCfg.normalizationEngine,
+    targetLufs: normCfg.loudnessTargetLufs,
+  }).catch(() => {});
+  if (normCfg.normalizationEngine === 'loudness') {
+    const currentId = usePlayerStore.getState().currentTrack?.id;
+    if (currentId) {
+      void refreshLoudnessForTrack(currentId).finally(() => {
+        usePlayerStore.getState().updateReplayGainForCurrentTrack();
+      });
+    }
+  }
   if (audioOutputDevice) {
     invoke('audio_set_device', { deviceName: audioOutputDevice }).catch(() => {});
   }
 
   // Keep audio settings in sync whenever auth store changes.
+  let prevNormEngine = normCfg.normalizationEngine;
+  let prevNormTarget = normCfg.loudnessTargetLufs;
   const unsubAuth = useAuthStore.subscribe((state) => {
     invoke('audio_set_crossfade', {
       enabled: state.crossfadeEnabled,
       secs: state.crossfadeSecs,
     }).catch(() => {});
     invoke('audio_set_gapless', { enabled: state.gaplessEnabled }).catch(() => {});
+    const normChanged =
+      state.normalizationEngine !== prevNormEngine
+      || state.loudnessTargetLufs !== prevNormTarget;
+    if (!normChanged) return;
+    prevNormEngine = state.normalizationEngine;
+    prevNormTarget = state.loudnessTargetLufs;
+    usePlayerStore.setState({
+      normalizationEngineLive: state.normalizationEngine,
+      normalizationTargetLufs: state.normalizationEngine === 'loudness' ? state.loudnessTargetLufs : null,
+      normalizationNowDb: state.normalizationEngine === 'loudness'
+        ? usePlayerStore.getState().normalizationNowDb
+        : null,
+      normalizationDbgSource: 'auth:normalization-changed',
+    });
+    emitNormalizationDebug('auth:normalization-changed', {
+      engine: state.normalizationEngine,
+      targetLufs: state.loudnessTargetLufs,
+      currentTrackId: usePlayerStore.getState().currentTrack?.id ?? null,
+    });
+    invoke('audio_set_normalization', {
+      engine: state.normalizationEngine,
+      targetLufs: state.loudnessTargetLufs,
+    }).catch(() => {});
+    if (state.normalizationEngine === 'loudness') {
+      const currentId = usePlayerStore.getState().currentTrack?.id;
+      if (currentId) {
+        void refreshLoudnessForTrack(currentId).finally(() => {
+          usePlayerStore.getState().updateReplayGainForCurrentTrack();
+        });
+      }
+    } else {
+      usePlayerStore.getState().updateReplayGainForCurrentTrack();
+    }
+  });
+  const unsubAnalysisSync = onAnalysisStorageChanged(detail => {
+    const currentId = usePlayerStore.getState().currentTrack?.id;
+    if (!currentId) return;
+    if (detail.trackId && detail.trackId !== currentId) return;
+    void refreshWaveformForTrack(currentId);
+    void refreshLoudnessForTrack(currentId);
   });
 
   // ── MPRIS / OS media controls sync ───────────────────────────────────────
@@ -1012,6 +1398,7 @@ export function initAudioListeners(): () => void {
 
   return () => {
     unsubAuth();
+    unsubAnalysisSync();
     unsubMpris();
     unsubDiscordPlayer();
     unsubDiscordAuth();
@@ -1026,6 +1413,19 @@ export const usePlayerStore = create<PlayerState>()(
   persist(
     (set, get) => ({
       currentTrack: null,
+      waveformBins: null,
+      waveformIsPartial: false,
+      waveformKnownUntilSec: 0,
+      waveformDurationSec: 0,
+      normalizationNowDb: null,
+      normalizationTargetLufs: null,
+      normalizationEngineLive: 'off',
+      normalizationDbgSource: null,
+      normalizationDbgTrackId: null,
+      normalizationDbgCacheGainDb: null,
+      normalizationDbgCacheTargetLufs: null,
+      normalizationDbgCacheUpdatedAt: null,
+      normalizationDbgLastEventAt: null,
       currentRadio: null,
       currentPlaybackSource: null,
       enginePreloadedTrackId: null,
@@ -1152,6 +1552,13 @@ export const usePlayerStore = create<PlayerState>()(
           buffered: 0,
           currentTime: 0,
           currentRadio: null,
+          waveformBins: null,
+          waveformIsPartial: false,
+          waveformKnownUntilSec: 0,
+          waveformDurationSec: 0,
+          normalizationNowDb: null,
+          normalizationTargetLufs: null,
+          normalizationEngineLive: 'off',
           currentPlaybackSource: null,
           enginePreloadedTrackId: null,
           scheduledPauseAtMs: null,
@@ -1192,6 +1599,13 @@ export const usePlayerStore = create<PlayerState>()(
         set({
           currentRadio: station,
           currentTrack: null,
+          waveformBins: null,
+          waveformIsPartial: false,
+          waveformKnownUntilSec: 0,
+          waveformDurationSec: 0,
+          normalizationNowDb: null,
+          normalizationTargetLufs: null,
+          normalizationEngineLive: 'off',
           currentPlaybackSource: null,
           queue: [],
           queueIndex: 0,
@@ -1271,6 +1685,11 @@ export const usePlayerStore = create<PlayerState>()(
         set({
           currentTrack: track,
           currentRadio: null,
+          waveformBins: null,
+          waveformIsPartial: false,
+          waveformKnownUntilSec: 0,
+          waveformDurationSec: 0,
+          ...deriveNormalizationSnapshot(track, newQueue, idx >= 0 ? idx : 0),
           queue: newQueue,
           queueIndex: idx >= 0 ? idx : 0,
           progress: initialProgress,
@@ -1295,20 +1714,23 @@ export const usePlayerStore = create<PlayerState>()(
             authState.hotCacheDownloadDir || null,
           );
         }
+        void refreshWaveformForTrack(track.id);
+        void refreshLoudnessForTrack(track.id);
         setDeferHotCachePrefetch(true);
         const playIdx = idx >= 0 ? idx : 0;
         const nextNeighbour = playIdx + 1 < newQueue.length ? newQueue[playIdx + 1] : null;
         const replayGainDb = resolveReplayGainDb(
           track, prevTrack, nextNeighbour,
-          authState.replayGainEnabled, authState.replayGainMode,
+          isReplayGainActive(), authState.replayGainMode,
         );
-        const replayGainPeak = authState.replayGainEnabled ? (track.replayGainPeak ?? null) : null;
+        const replayGainPeak = isReplayGainActive() ? (track.replayGainPeak ?? null) : null;
         invoke('audio_play', {
           url,
           volume: state.volume,
           durationHint: track.duration,
           replayGainDb,
           replayGainPeak,
+          loudnessGainDb: cachedLoudnessGainByTrackId[track.id] ?? null,
           preGainDb: authState.replayGainPreGainDb,
           fallbackDb: authState.replayGainFallbackDb,
           manual,
@@ -1432,9 +1854,9 @@ export const usePlayerStore = create<PlayerState>()(
             const authStateCold = useAuthStore.getState();
             const replayGainDbCold = resolveReplayGainDb(
               trackToPlay, coldPrev, coldNext,
-              authStateCold.replayGainEnabled, authStateCold.replayGainMode,
+              isReplayGainActive(), authStateCold.replayGainMode,
             );
-            const replayGainPeakCold = authStateCold.replayGainEnabled ? (trackToPlay.replayGainPeak ?? null) : null;
+            const replayGainPeakCold = isReplayGainActive() ? (trackToPlay.replayGainPeak ?? null) : null;
             const coldServerId = useAuthStore.getState().activeServerId ?? '';
             setDeferHotCachePrefetch(true);
             const coldUrl = resolvePlaybackUrl(trackToPlay.id, coldServerId);
@@ -1445,6 +1867,7 @@ export const usePlayerStore = create<PlayerState>()(
               durationHint: trackToPlay.duration,
               replayGainDb: replayGainDbCold,
               replayGainPeak: replayGainPeakCold,
+              loudnessGainDb: cachedLoudnessGainByTrackId[trackToPlay.id] ?? null,
               preGainDb: authStateCold.replayGainPreGainDb,
               fallbackDb: authStateCold.replayGainFallbackDb,
               manual: false,
@@ -1466,9 +1889,9 @@ export const usePlayerStore = create<PlayerState>()(
              const authStateCold = useAuthStore.getState();
              const replayGainDbCold = resolveReplayGainDb(
                currentTrack, coldPrev, coldNext,
-               authStateCold.replayGainEnabled, authStateCold.replayGainMode,
+               isReplayGainActive(), authStateCold.replayGainMode,
              );
-             const replayGainPeakCold = authStateCold.replayGainEnabled ? (currentTrack.replayGainPeak ?? null) : null;
+             const replayGainPeakCold = isReplayGainActive() ? (currentTrack.replayGainPeak ?? null) : null;
              const coldServerId = useAuthStore.getState().activeServerId ?? '';
              setDeferHotCachePrefetch(true);
              const coldUrl = resolvePlaybackUrl(currentTrack.id, coldServerId);
@@ -1479,6 +1902,7 @@ export const usePlayerStore = create<PlayerState>()(
                durationHint: currentTrack.duration,
                replayGainDb: replayGainDbCold,
                replayGainPeak: replayGainPeakCold,
+               loudnessGainDb: cachedLoudnessGainByTrackId[currentTrack.id] ?? null,
                preGainDb: authStateCold.replayGainPreGainDb,
                fallbackDb: authStateCold.replayGainFallbackDb,
                manual: false,
@@ -1895,16 +2319,26 @@ export const usePlayerStore = create<PlayerState>()(
          const next = queueIndex + 1 < queue.length ? queue[queueIndex + 1] : null;
          const replayGainDb = resolveReplayGainDb(
            currentTrack, prev, next,
-           authState.replayGainEnabled, authState.replayGainMode,
+           isReplayGainActive(), authState.replayGainMode,
          );
-         const replayGainPeak = authState.replayGainEnabled
+         const replayGainPeak = isReplayGainActive()
            ? (currentTrack.replayGainPeak ?? null)
            : null;
          
-         invoke('audio_update_replay_gain', {
+        const normalization = deriveNormalizationSnapshot(currentTrack, queue, queueIndex);
+        set(prevState => ({
+          normalizationNowDb:
+            normalization.normalizationEngineLive === 'loudness'
+              ? prevState.normalizationNowDb
+              : normalization.normalizationNowDb,
+          normalizationTargetLufs: normalization.normalizationTargetLufs,
+          normalizationEngineLive: normalization.normalizationEngineLive,
+        }));
+        invoke('audio_update_replay_gain', {
            volume,
            replayGainDb,
            replayGainPeak,
+           loudnessGainDb: currentTrack ? (cachedLoudnessGainByTrackId[currentTrack.id] ?? null) : null,
            preGainDb: authState.replayGainPreGainDb,
            fallbackDb: authState.replayGainFallbackDb,
          }).catch(console.error);