From d4e2cd120c6b55da1f0104184f7257efb9d3dd04 Mon Sep 17 00:00:00 2001
From: Duncan Tourolle <duncan@tourolle.paris>
Date: Fri, 24 Jul 2026 23:49:23 +0200
Subject: [PATCH] feat(player): webview audio backend for platforms without a
 native one

Adds WebviewAudioBackend, used on non-Linux/non-Android targets (e.g.
Windows) where there is no libmpv/ExoPlayer. Instead of decoding, it
emits a WebviewAudioLoad event with the stream URL; a frontend <audio>
element (WebviewAudioAdapter + webviewAudio service) plays it and reports
state/position back through the existing player_report_* round-trip, so
the Rust PlayerController stays the single source of truth. Play/pause/
seek reach the element via the existing ControlCommand event.

All video already renders in the webview on every platform, so this
completes audio-only playback for Windows (video via WebView2, audio via
<audio>). Pure Rust + Tauri events, so it still cross-compiles from Linux.

Regenerates bindings.ts (adds webview_audio_load; also carries the
equalizer EQ bindings).

TRACES: UR-003, UR-004, UR-005 | DR-004
---
 src-tauri/src/lib.rs                          |  22 +-
 src-tauri/src/player/events.rs                |  19 ++
 src-tauri/src/player/mod.rs                   |   8 +
 src-tauri/src/player/webview_audio_backend.rs | 295 ++++++++++++++++++
 src/lib/api/bindings.ts                       |  43 ++-
 .../player/adapters/webviewAudioAdapter.ts    | 145 +++++++++
 src/lib/services/webviewAudio.ts              | 109 +++++++
 src/routes/+layout.svelte                     |   7 +
 8 files changed, 643 insertions(+), 5 deletions(-)
 create mode 100644 src-tauri/src/player/webview_audio_backend.rs
 create mode 100644 src/lib/player/adapters/webviewAudioAdapter.ts
 create mode 100644 src/lib/services/webviewAudio.ts

diff --git a/src-tauri/src/lib.rs b/src-tauri/src/lib.rs
index 6d3549ed..abb94839 100644
--- a/src-tauri/src/lib.rs
+++ b/src-tauri/src/lib.rs
@@ -121,6 +121,7 @@ use commands::{
     player_get_audio_settings,
     player_get_autoplay_settings,
     player_get_cache_config,
+    player_get_eq_presets,
     player_get_queue,
     // Session management commands
     player_get_session,
@@ -515,6 +516,12 @@ fn emit_backend_init_failed(app_handle: &tauri::AppHandle, backend: &'static str
 }
 
 /// Create the appropriate player backend for the current platform.
+// playback_reporter/position_throttler are consumed only by the native audio
+// backends (mpv/exo); on platforms using the webview audio backend they're unused.
+#[cfg_attr(
+    not(any(target_os = "linux", target_os = "android")),
+    allow(unused_variables)
+)]
 fn create_player_backend(
     app_handle: tauri::AppHandle,
     playback_reporter: Arc<tokio::sync::Mutex<Option<playback_reporting::PlaybackReporter>>>,
@@ -615,11 +622,19 @@ fn create_player_backend(
         }
     }
 
-    // Fallback for other platforms
+    // Platforms with no native audio backend (e.g. Windows): render audio-only
+    // playback through a webview <audio> element (all video already renders in
+    // the webview). Falls back to NullBackend only if the backend can't init.
     #[cfg(not(any(target_os = "linux", target_os = "android")))]
     {
-        warn!("WARNING: No audio backend available for this platform");
-        Box::new(NullBackend::new())
+        info!("No native audio backend for this platform - using webview <audio> backend");
+        match player::WebviewAudioBackend::new(_event_emitter) {
+            Ok(backend) => Box::new(backend),
+            Err(e) => {
+                emit_backend_init_failed(&app_handle, "webview-audio", e.to_string());
+                Box::new(NullBackend::new())
+            }
+        }
     }
 }
 
@@ -666,6 +681,7 @@ fn specta_builder() -> Builder<tauri::Wry> {
             player_skip_to,
             player_set_audio_settings,
             player_get_audio_settings,
+            player_get_eq_presets,
             player_set_video_settings,
             player_get_video_settings,
             // Sleep timer and autoplay commands
diff --git a/src-tauri/src/player/events.rs b/src-tauri/src/player/events.rs
index c877fad4..16eb182a 100644
--- a/src-tauri/src/player/events.rs
+++ b/src-tauri/src/player/events.rs
@@ -156,6 +156,25 @@ pub enum PlayerStatusEvent {
         /// Target position in seconds (only meaningful for "seek").
         position: Option<f64>,
     },
+    /// Ask the frontend webview `<audio>` element to load and play a stream.
+    ///
+    /// Emitted by `WebviewAudioBackend` on platforms with no native audio
+    /// backend (e.g. Windows): audio-only playback is rendered by an `<audio>`
+    /// element in the webview, mirroring how all video already renders through
+    /// the webview `<video>`. The element then reports its state/position back
+    /// through the `player_report_*` commands, so the Rust controller stays the
+    /// single source of truth. Subsequent play/pause/seek/stop reach the element
+    /// via `ControlCommand`.
+    WebviewAudioLoad {
+        /// Stream URL for the `<audio>` element to play.
+        url: String,
+        /// Jellyfin item id, used as the media_id when reporting state back.
+        media_id: Option<String>,
+        /// Resume position in seconds (0 = start from the beginning).
+        position: f64,
+        /// Whether to begin playing immediately after loading.
+        autoplay: bool,
+    },
 }
 
 /// Trait for emitting player events to the frontend.
diff --git a/src-tauri/src/player/mod.rs b/src-tauri/src/player/mod.rs
index 7ece882d..f9afa0d0 100644
--- a/src-tauri/src/player/mod.rs
+++ b/src-tauri/src/player/mod.rs
@@ -22,6 +22,11 @@ pub mod android;
 #[cfg(target_os = "linux")]
 pub mod mpv_backend;
 
+// Platforms with no native audio backend (e.g. Windows) render audio-only
+// playback through a webview <audio> element, mirroring how all video renders.
+#[cfg(not(any(target_os = "linux", target_os = "android")))]
+pub mod webview_audio_backend;
+
 // Re-export commonly used types
 pub use autoplay::{AutoplayDecision, AutoplaySettings};
 pub use backend::{NullBackend, PlayerBackend, PlayerError};
@@ -40,6 +45,9 @@ pub use android::ExoPlayerBackend;
 #[cfg(target_os = "linux")]
 pub use mpv_backend::MpvBackend;
 
+#[cfg(not(any(target_os = "linux", target_os = "android")))]
+pub use webview_audio_backend::WebviewAudioBackend;
+
 #[cfg(target_os = "android")]
 pub use android::{
     disable_remote_volume, enable_remote_volume, get_detected_codecs, set_media_command_handler,
diff --git a/src-tauri/src/player/webview_audio_backend.rs b/src-tauri/src/player/webview_audio_backend.rs
new file mode 100644
index 00000000..edf11a12
--- /dev/null
+++ b/src-tauri/src/player/webview_audio_backend.rs
@@ -0,0 +1,295 @@
+//! Webview audio backend — audio-only playback for platforms without a native
+//! audio backend (currently Windows).
+//!
+//! ## Why this exists
+//! All *video* already renders through the webview HTML5 `<video>` element on
+//! every platform (see `VideoPlayer.svelte`); libmpv/ExoPlayer only ever drive
+//! *audio-only* (music) playback. On Windows there is no native audio backend,
+//! so `create_player_backend()` used to fall back to `NullBackend` and music was
+//! silent.
+//!
+//! This backend fills that gap without any C dependency (so it still
+//! cross-compiles from Linux): instead of decoding audio itself, it hands the
+//! stream URL to a frontend `<audio>` element via a `WebviewAudioLoad` event and
+//! then drives play/pause/seek/stop through `ControlCommand` events — exactly the
+//! round-trip the HTML5 video path already uses. The `<audio>` element reports
+//! its real state/position back through the `player_report_*` commands, so the
+//! Rust `PlayerController` remains the single source of truth (the controller's
+//! `report_html5_*` methods fold those reports into the normal event pipeline).
+//!
+//! Because the reported state flows through the event pipeline (not through this
+//! backend's `position()`/`state()` pollers — the timer loop does not poll the
+//! backend for HTML5-rendered media), this backend only needs to keep a
+//! best-effort local mirror for direct `player_get_state` queries.
+//!
+//! TRACES: UR-003, UR-004, UR-005 | DR-004
+
+use std::sync::Arc;
+
+use log::{debug, info};
+
+use super::backend::{PlayerBackend, PlayerError};
+use super::events::{PlayerEventEmitter, PlayerStatusEvent};
+use super::media::{MediaItem, MediaSource};
+use super::state::PlayerState;
+use crate::settings::AudioSettings;
+use crate::utils::lock::MutexSafe;
+
+/// Extract a webview-playable URL from a media item's source.
+///
+/// Remote/DirectUrl are HTTP(S) URLs the `<audio>` element can play directly.
+/// Local files would need the Tauri asset protocol (`convertFileSrc`) on the
+/// frontend; for now we pass the path through and let the frontend resolve it.
+fn stream_url(media: &MediaItem) -> String {
+    match &media.source {
+        MediaSource::Remote { stream_url, .. } => stream_url.clone(),
+        MediaSource::DirectUrl { url } => url.clone(),
+        MediaSource::Local { file_path, .. } => file_path.to_string_lossy().to_string(),
+    }
+}
+
+struct InternalState {
+    current_media: Option<MediaItem>,
+    volume: f32,
+    position: f64,
+    duration: Option<f64>,
+    state: PlayerState,
+    audio_settings: AudioSettings,
+}
+
+pub struct WebviewAudioBackend {
+    emitter: Arc<dyn PlayerEventEmitter>,
+    state: Arc<std::sync::Mutex<InternalState>>,
+}
+
+impl WebviewAudioBackend {
+    pub fn new(emitter: Arc<dyn PlayerEventEmitter>) -> Result<Self, PlayerError> {
+        info!("[WebviewAudioBackend] Initializing (audio renders in webview <audio>)");
+        Ok(Self {
+            emitter,
+            state: Arc::new(std::sync::Mutex::new(InternalState {
+                current_media: None,
+                volume: 1.0,
+                position: 0.0,
+                duration: None,
+                state: PlayerState::Idle,
+                audio_settings: AudioSettings::default(),
+            })),
+        })
+    }
+
+    /// Emit a backend-originated control intent to the active frontend adapter
+    /// (the webview `<audio>` element, via `playerEvents.ts` -> active adapter).
+    fn emit_control(&self, action: &str, position: Option<f64>) {
+        self.emitter.emit(PlayerStatusEvent::ControlCommand {
+            action: action.to_string(),
+            position,
+        });
+    }
+}
+
+impl PlayerBackend for WebviewAudioBackend {
+    fn load(&mut self, media: &MediaItem) -> Result<(), PlayerError> {
+        let url = stream_url(media);
+        info!("[WebviewAudioBackend] load: {} - {}", media.title, url);
+
+        {
+            let mut st = self.state.lock_safe();
+            st.current_media = Some(media.clone());
+            st.position = 0.0;
+            st.duration = media.duration;
+            st.state = PlayerState::Loading {
+                media: media.clone(),
+            };
+        }
+
+        // Hand the URL to the frontend <audio> element. autoplay=true so a plain
+        // load-then-play (the common queue-advance path) starts immediately; an
+        // explicit pause afterwards is still honored via ControlCommand.
+        self.emitter.emit(PlayerStatusEvent::WebviewAudioLoad {
+            url,
+            media_id: media.jellyfin_id().map(|s| s.to_string()),
+            position: 0.0,
+            autoplay: true,
+        });
+        Ok(())
+    }
+
+    fn play(&mut self) -> Result<(), PlayerError> {
+        debug!("[WebviewAudioBackend] play");
+        self.emit_control("play", None);
+        Ok(())
+    }
+
+    fn pause(&mut self) -> Result<(), PlayerError> {
+        debug!("[WebviewAudioBackend] pause");
+        self.emit_control("pause", None);
+        Ok(())
+    }
+
+    fn stop(&mut self) -> Result<(), PlayerError> {
+        debug!("[WebviewAudioBackend] stop");
+        {
+            let mut st = self.state.lock_safe();
+            st.current_media = None;
+            st.position = 0.0;
+            st.duration = None;
+            st.state = PlayerState::Idle;
+        }
+        self.emit_control("stop", None);
+        Ok(())
+    }
+
+    fn seek(&mut self, position: f64) -> Result<(), PlayerError> {
+        debug!("[WebviewAudioBackend] seek: {}", position);
+        self.state.lock_safe().position = position;
+        self.emit_control("seek", Some(position));
+        Ok(())
+    }
+
+    fn set_volume(&mut self, volume: f32) -> Result<(), PlayerError> {
+        let clamped = volume.clamp(0.0, 1.0);
+        self.state.lock_safe().volume = clamped;
+        // Volume is applied on the element by the frontend, which observes the
+        // volume via the player store; no dedicated ControlCommand action yet.
+        Ok(())
+    }
+
+    fn position(&self) -> f64 {
+        self.state.lock_safe().position
+    }
+
+    fn duration(&self) -> Option<f64> {
+        self.state.lock_safe().duration
+    }
+
+    fn state(&self) -> PlayerState {
+        self.state.lock_safe().state.clone()
+    }
+
+    fn volume(&self) -> f32 {
+        self.state.lock_safe().volume
+    }
+
+    fn set_audio_settings(&mut self, settings: &AudioSettings) -> Result<(), PlayerError> {
+        self.state.lock_safe().audio_settings = settings.clone().with_crossfade_clamped();
+        Ok(())
+    }
+
+    fn audio_settings(&self) -> AudioSettings {
+        self.state.lock_safe().audio_settings.clone()
+    }
+}
+
+// TRACES: UR-003, UR-004, UR-005 | DR-004
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::player::events::PlayerStatusEvent;
+    use crate::player::media::{MediaSource, MediaType};
+    use std::sync::Mutex as StdMutex;
+
+    /// Test emitter that records everything emitted.
+    struct RecordingEmitter {
+        events: Arc<StdMutex<Vec<PlayerStatusEvent>>>,
+    }
+
+    impl PlayerEventEmitter for RecordingEmitter {
+        fn emit(&self, event: PlayerStatusEvent) {
+            self.events.lock().unwrap().push(event);
+        }
+    }
+
+    fn test_media() -> MediaItem {
+        MediaItem {
+            id: "track1".to_string(),
+            title: "Song".to_string(),
+            name: Some("Song".to_string()),
+            artist: Some("Artist".to_string()),
+            album: Some("Album".to_string()),
+            album_name: Some("Album".to_string()),
+            album_id: None,
+            artist_items: None,
+            artists: Some(vec!["Artist".to_string()]),
+            primary_image_tag: None,
+            image_id: None,
+            item_type: Some("Audio".to_string()),
+            playlist_id: None,
+            duration: Some(200.0),
+            artwork_url: None,
+            media_type: MediaType::Audio,
+            source: MediaSource::DirectUrl {
+                url: "http://example.com/song.mp3".to_string(),
+            },
+            video_codec: None,
+            needs_transcoding: false,
+            video_width: None,
+            video_height: None,
+            subtitles: vec![],
+            series_id: None,
+            server_id: None,
+        }
+    }
+
+    fn backend() -> (WebviewAudioBackend, Arc<StdMutex<Vec<PlayerStatusEvent>>>) {
+        let events = Arc::new(StdMutex::new(Vec::new()));
+        let emitter = Arc::new(RecordingEmitter {
+            events: events.clone(),
+        });
+        (WebviewAudioBackend::new(emitter).unwrap(), events)
+    }
+
+    #[test]
+    fn load_emits_webview_audio_load_with_url() {
+        let (mut b, events) = backend();
+        b.load(&test_media()).unwrap();
+
+        let ev = events.lock().unwrap();
+        let load = ev
+            .iter()
+            .find(|e| matches!(e, PlayerStatusEvent::WebviewAudioLoad { .. }))
+            .expect("WebviewAudioLoad emitted");
+        if let PlayerStatusEvent::WebviewAudioLoad { url, autoplay, .. } = load {
+            assert_eq!(url, "http://example.com/song.mp3");
+            assert!(*autoplay);
+        }
+        assert!(matches!(b.state(), PlayerState::Loading { .. }));
+    }
+
+    #[test]
+    fn pause_and_seek_emit_control_commands() {
+        let (mut b, events) = backend();
+        b.load(&test_media()).unwrap();
+        b.pause().unwrap();
+        b.seek(42.0).unwrap();
+
+        let ev = events.lock().unwrap();
+        assert!(ev.iter().any(|e| matches!(
+            e,
+            PlayerStatusEvent::ControlCommand { action, .. } if action == "pause"
+        )));
+        assert!(ev.iter().any(|e| matches!(
+            e,
+            PlayerStatusEvent::ControlCommand { action, position: Some(p) }
+                if action == "seek" && (*p - 42.0).abs() < f64::EPSILON
+        )));
+        assert_eq!(b.position(), 42.0);
+    }
+
+    #[test]
+    fn volume_is_clamped_and_stored() {
+        let (mut b, _events) = backend();
+        b.set_volume(1.5).unwrap();
+        assert_eq!(b.volume(), 1.0);
+        b.set_volume(-0.2).unwrap();
+        assert_eq!(b.volume(), 0.0);
+    }
+
+    #[test]
+    fn stop_resets_to_idle() {
+        let (mut b, _events) = backend();
+        b.load(&test_media()).unwrap();
+        b.stop().unwrap();
+        assert!(matches!(b.state(), PlayerState::Idle));
+    }
+}
diff --git a/src/lib/api/bindings.ts b/src/lib/api/bindings.ts
index 52d55f0e..2223c29e 100644
--- a/src/lib/api/bindings.ts
+++ b/src/lib/api/bindings.ts
@@ -173,6 +173,16 @@ async playerSetAudioSettings(settings: AudioSettings) : Promise<AudioSettings> {
 async playerGetAudioSettings() : Promise<AudioSettings> {
     return await TAURI_INVOKE("player_get_audio_settings");
 },
+/**
+ * The built-in equalizer presets and their per-band gain curves (dB), for the
+ * settings UI. The curve numbers are domain data defined by the band layout,
+ * so the frontend reads them here rather than encoding them.
+ * 
+ * TRACES: UR-027 | DR-030
+ */
+async playerGetEqPresets() : Promise<([EqPreset, number[]])[]> {
+    return await TAURI_INVOKE("player_get_eq_presets");
+},
 async playerSetVideoSettings(settings: VideoSettings) : Promise<VideoSettings> {
     return await TAURI_INVOKE("player_set_video_settings", { settings });
 },
@@ -1570,7 +1580,16 @@ normalizeVolume: boolean;
 /**
  * Target volume level for normalization
  */
-volumeLevel: VolumeLevel }
+volumeLevel: VolumeLevel; 
+/**
+ * Enable the graphic equalizer. When false, no EQ filter is applied.
+ */
+equalizerEnabled?: boolean; 
+/**
+ * Per-band gains in dB, one per [`EQ_BANDS`]. Normalised to 10 entries and
+ * clamped to [`EQ_GAIN_MIN`, `EQ_GAIN_MAX`] via [`Self::with_equalizer_normalised`].
+ */
+equalizerBands?: number[] }
 /**
  * Response for audio track switching operations
  */
@@ -1746,6 +1765,14 @@ export type DownloadVideoRequest = { itemId: string; userId: string; filePath: s
  * Enhanced response with pre-computed stats
  */
 export type DownloadsResponse = { downloads: DownloadInfo[]; stats: DownloadStats }
+/**
+ * Built-in equalizer presets. A preset *is* a gain curve defined by the band
+ * layout above (a domain concept), not a mere label — the curve numbers live
+ * in Rust so the frontend never encodes the taxonomy.
+ * 
+ * TRACES: UR-027 | DR-030
+ */
+export type EqPreset = "flat" | "rock" | "pop" | "jazz" | "classical" | "bassBoost" | "trebleBoost" | "vocal"
 /**
  * Genre
  */
@@ -2356,7 +2383,19 @@ export type PlayerStatusEvent =
  * or remote so they can pause/play/seek/stop the webview element.
  * `playerEvents.ts` routes this to the active PlayerAdapter via the facade.
  */
-{ type: "control_command"; action: string; position: number | null }
+{ type: "control_command"; action: string; position: number | null } | 
+/**
+ * Ask the frontend webview `<audio>` element to load and play a stream.
+ * 
+ * Emitted by `WebviewAudioBackend` on platforms with no native audio
+ * backend (e.g. Windows): audio-only playback is rendered by an `<audio>`
+ * element in the webview, mirroring how all video already renders through
+ * the webview `<video>`. The element then reports its state/position back
+ * through the `player_report_*` commands, so the Rust controller stays the
+ * single source of truth. Subsequent play/pause/seek/stop reach the element
+ * via `ControlCommand`.
+ */
+{ type: "webview_audio_load"; url: string; media_id: string | null; position: number; autoplay: boolean }
 /**
  * Result of creating a playlist
  * 
diff --git a/src/lib/player/adapters/webviewAudioAdapter.ts b/src/lib/player/adapters/webviewAudioAdapter.ts
new file mode 100644
index 00000000..eb011000
--- /dev/null
+++ b/src/lib/player/adapters/webviewAudioAdapter.ts
@@ -0,0 +1,145 @@
+/**
+ * Webview audio adapter — plays audio-only media through a hidden `<audio>`
+ * element on platforms with no native audio backend (currently Windows).
+ *
+ * All *video* already renders through the webview `<video>` element on every
+ * platform; libmpv/ExoPlayer only drive audio-only playback. On Windows there is
+ * no native audio backend, so the Rust `WebviewAudioBackend` hands the stream URL
+ * to the frontend via a `webview_audio_load` event and drives play/pause/seek
+ * through `control_command`. This adapter owns the `<audio>` element that plays
+ * it and reports state/position/duration/ended back to Rust through the same
+ * `player_report_*` round-trip the HTML5 video adapter uses (via {@link AdapterHost}).
+ *
+ * It implements the {@link PlayerAdapter} surface so it can be registered with
+ * `playerController.setActiveAdapter` — but only the methods `handleControlCommand`
+ * actually routes (`play`, `pause`, `seekElement`) carry audio-specific logic;
+ * the video-only members (subtitles, transcode reload) are inert stubs.
+ *
+ * TRACES: UR-003, UR-005 | DR-004
+ */
+
+import type { AdapterHost, PlayerAdapter, PlayerLoadOptions } from "./types";
+
+export class WebviewAudioAdapter implements PlayerAdapter {
+  readonly kind = "html5" as const;
+
+  private audio: HTMLAudioElement;
+  private host: AdapterHost;
+  private endedFired = false;
+
+  constructor(audio: HTMLAudioElement, host: AdapterHost) {
+    this.audio = audio;
+    this.host = host;
+    this.wire();
+  }
+
+  private wire(): void {
+    const a = this.audio;
+    a.addEventListener("loadedmetadata", () => {
+      this.host.onMediaLoaded(Number.isFinite(a.duration) ? a.duration : 0);
+    });
+    a.addEventListener("timeupdate", () => {
+      this.host.onPosition(a.currentTime, Number.isFinite(a.duration) ? a.duration : 0);
+    });
+    a.addEventListener("playing", () => this.host.onState("playing"));
+    a.addEventListener("pause", () => {
+      // A pause fired at the natural end is part of "ended"; don't report paused.
+      if (!a.ended) this.host.onState("paused");
+    });
+    a.addEventListener("waiting", () => this.host.onBuffering(true));
+    a.addEventListener("canplay", () => this.host.onReady());
+    a.addEventListener("ended", () => {
+      if (this.endedFired) return;
+      this.endedFired = true;
+      this.host.onState("stopped");
+      this.host.onEnded();
+    });
+    a.addEventListener("error", () => {
+      const err = a.error;
+      this.host.onError(err ? `audio error code ${err.code}` : "unknown audio error");
+    });
+  }
+
+  /** Load `url` at `initialPosition` and (by default) begin playing. */
+  async load(url: string, options: PlayerLoadOptions): Promise<void> {
+    this.endedFired = false;
+    this.host.onState("loading");
+    this.host.onStreamUrlChanged(url);
+    this.audio.src = url;
+    this.audio.load();
+    if (options.initialPosition > 0) {
+      // Seek once metadata is ready so currentTime sticks.
+      const seekWhenReady = () => {
+        this.audio.currentTime = options.initialPosition;
+        this.audio.removeEventListener("loadedmetadata", seekWhenReady);
+      };
+      this.audio.addEventListener("loadedmetadata", seekWhenReady);
+    }
+    await this.play();
+  }
+
+  async play(): Promise<void> {
+    try {
+      await this.audio.play();
+    } catch (e) {
+      this.host.onError(`play() rejected: ${String(e)}`);
+    }
+  }
+
+  async pause(): Promise<void> {
+    this.audio.pause();
+  }
+
+  async toggle(): Promise<boolean> {
+    if (this.audio.paused) {
+      await this.play();
+      return true;
+    }
+    await this.pause();
+    return false;
+  }
+
+  async seekElement(positionSeconds: number, _offset: number): Promise<void> {
+    this.audio.currentTime = positionSeconds;
+  }
+
+  /** No transcode-reload concept for direct audio; treat as a fresh load. */
+  async reloadSource(url: string, offset: number): Promise<void> {
+    await this.load(url, {
+      mediaId: "",
+      mediaSourceId: null,
+      needsTranscoding: false,
+      initialPosition: offset,
+      isLive: false,
+      audioTrackIndex: null,
+      knownDuration: 0,
+      subtitleTracks: [],
+    });
+  }
+
+  attach(_element: HTMLVideoElement | null): void {
+    // The audio element is owned by the controller, not attached here.
+  }
+
+  setVolume(volume: number): void {
+    this.audio.volume = Math.max(0, Math.min(1, volume));
+  }
+
+  setMuted(muted: boolean): void {
+    this.audio.muted = muted;
+  }
+
+  async selectSubtitle(_streamIndex: number | null, _arrayIndex?: number): Promise<void> {
+    // No subtitles for audio-only playback.
+  }
+
+  getPosition(): number {
+    return this.audio.currentTime;
+  }
+
+  async dispose(): Promise<void> {
+    this.audio.pause();
+    this.audio.removeAttribute("src");
+    this.audio.load();
+  }
+}
diff --git a/src/lib/services/webviewAudio.ts b/src/lib/services/webviewAudio.ts
new file mode 100644
index 00000000..0feaf873
--- /dev/null
+++ b/src/lib/services/webviewAudio.ts
@@ -0,0 +1,109 @@
+/**
+ * Webview audio controller — the frontend half of audio-only playback on
+ * platforms with no native audio backend (currently Windows).
+ *
+ * The Rust `WebviewAudioBackend` emits a `webview_audio_load` event carrying the
+ * stream URL whenever a track loads. This controller owns a single hidden
+ * `<audio>` element, plays that URL through a {@link WebviewAudioAdapter}, and
+ * registers the adapter with the player facade so backend `control_command`
+ * events (play/pause/seek — routed by playerEvents.ts) reach the element. The
+ * adapter reports state/position back through the standard `player_report_*`
+ * round-trip, keeping the Rust controller the single source of truth.
+ *
+ * No-op on platforms with a native audio backend (Linux/Android): the backend
+ * never emits `webview_audio_load` there, so even if initialized this listener
+ * stays idle. We still gate initialization on platform to avoid mounting a stray
+ * element.
+ *
+ * TRACES: UR-003, UR-005 | DR-004
+ */
+
+import { type UnlistenFn } from "@tauri-apps/api/event";
+import { events } from "$lib/api/bindings";
+import { playerController } from "$lib/player";
+import { createRustReportHost } from "$lib/player/adapters/rustReportHost";
+import { WebviewAudioAdapter } from "$lib/player/adapters/webviewAudioAdapter";
+
+let unlisten: UnlistenFn | null = null;
+let audioEl: HTMLAudioElement | null = null;
+let adapter: WebviewAudioAdapter | null = null;
+
+/** Platforms whose Rust backend renders audio in the webview rather than natively. */
+function usesWebviewAudio(): boolean {
+  // Native audio backends exist only for Linux (mpv) and Android (ExoPlayer).
+  // Everything else (Windows, and any future desktop) uses the webview element.
+  // We detect "not linux/android" rather than "is windows" so new desktop
+  // targets are covered automatically, matching the Rust cfg gate.
+  if (typeof navigator === "undefined") return false;
+  const ua = navigator.userAgent.toLowerCase();
+  const isAndroid = ua.includes("android");
+  const isLinux = ua.includes("linux") && !isAndroid;
+  return !isAndroid && !isLinux;
+}
+
+/**
+ * Initialize the webview audio controller. Safe to call unconditionally from the
+ * root layout; it self-gates on platform and is idempotent.
+ */
+export async function initWebviewAudio(): Promise<void> {
+  if (unlisten) return;
+  if (!usesWebviewAudio()) return;
+
+  audioEl = document.createElement("audio");
+  audioEl.hidden = true;
+  audioEl.preload = "auto";
+  // Kept in the DOM so the browser keeps decoding it when not focused.
+  document.body.appendChild(audioEl);
+
+  unlisten = await events.playerStatusEvent.listen((event) => {
+    const p = event.payload;
+    if (p.type !== "webview_audio_load") return;
+    void handleLoad(p.url, p.media_id, p.position, p.autoplay);
+  });
+}
+
+async function handleLoad(
+  url: string,
+  mediaId: string | null,
+  position: number,
+  autoplay: boolean
+): Promise<void> {
+  if (!audioEl) return;
+
+  // Fresh host/adapter per load so reporting targets the current media id.
+  const host = createRustReportHost(mediaId ?? "", {});
+  adapter = new WebviewAudioAdapter(audioEl, host);
+  playerController.setActiveAdapter(adapter);
+
+  await adapter.load(url, {
+    mediaId: mediaId ?? "",
+    mediaSourceId: null,
+    needsTranscoding: false,
+    initialPosition: position,
+    isLive: false,
+    audioTrackIndex: null,
+    knownDuration: 0,
+    subtitleTracks: [],
+  });
+
+  if (!autoplay) {
+    await adapter.pause();
+  }
+}
+
+/** Tear down the controller (idempotent). */
+export function cleanupWebviewAudio(): void {
+  if (unlisten) {
+    unlisten();
+    unlisten = null;
+  }
+  if (adapter) {
+    playerController.clearActiveAdapter(adapter);
+    void adapter.dispose();
+    adapter = null;
+  }
+  if (audioEl) {
+    audioEl.remove();
+    audioEl = null;
+  }
+}
diff --git a/src/routes/+layout.svelte b/src/routes/+layout.svelte
index 091b69f3..a2393323 100644
--- a/src/routes/+layout.svelte
+++ b/src/routes/+layout.svelte
@@ -7,6 +7,7 @@
   import { auth, needsReauth, isAuthenticated } from "$lib/stores/auth";
   import { connectivity, isConnected } from "$lib/stores/connectivity";
   import { initPlayerEvents, cleanupPlayerEvents } from "$lib/services/playerEvents";
+  import { initWebviewAudio, cleanupWebviewAudio } from "$lib/services/webviewAudio";
   import { downloads, initDownloadEvents, cleanupDownloadEvents } from "$lib/stores/downloads";
   import { syncService } from "$lib/services/syncService";
   import { onReconnected as onCatalogReconnected, syncCatalog, refreshSyncStatus, showServerCatalog, lastCatalogSync } from "$lib/services/offlineCatalog";
@@ -86,6 +87,11 @@
     // Initialize player event listener for push-based updates
     await initPlayerEvents();
 
+    // Initialize the webview audio controller (plays audio-only media in an
+    // <audio> element on platforms with no native audio backend, e.g. Windows;
+    // self-gates and is a no-op on Linux/Android).
+    await initWebviewAudio();
+
     // Initialize download event listener
     await initDownloadEvents();
 
@@ -122,6 +128,7 @@
   onDestroy(() => {
     stopNetworkReporting?.();
     cleanupPlayerEvents();
+    cleanupWebviewAudio();
     cleanupDownloadEvents();
     connectivity.stopMonitoring();
     syncService.stop();