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/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
  * 

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();
+  }
+}

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;
+  }
+}

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();