diff --git a/ROADMAP.md b/ROADMAP.md
index d5b9dd2..06e4d76 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -323,56 +323,105 @@ interface SaveData {
 - [x] `public/videos/stay_loop.mp4` — 6s 测试视频（0-3s 蓝色正文 + 3-6s 绿色循环段）
 - [x] 验证：正文播放完毕 → 进入循环 → 选项浮现 → 画面无缝来回 → 选择后跳转
 
-### P6 独立背景音乐 — 画面循环不打断 BGM（待实现）
+### P6 独立背景音乐 + Ducking — 画面循环不打断 BGM ✅ 已完成 2026-06-08
 
-目标：将背景音乐从视频中剥离，由独立 AudioManager 驱动。视频循环/切换时 BGM 保持连贯播放，
-不同场景之间用交叉淡化衔接。这也是《底特律：变人》《The Dark Pictures Anthology》等商业游戏的标配。
+目标：将 BGM 从视频中剥离，由独立 AudioSystem 驱动。视频循环/切换时 BGM 保持连贯，场景间交叉淡化衔接。
+QTE 和选择面板出现时 BGM 自动闪避（ducking）以确保提示音不被淹没。
+
+**技术选型**
+
+- **Web Audio API** — `GainNode.exponentialRampToValueAtTime()` 实现指数渐变（听感均匀，Wwise/FMOD/UE 同款做法）
+- **MP3** — 全浏览器支持（含 Safari），解码快。OGG 暂不采用（Safari 不支持），P14 短循环音效需要 OGG 时单独处理
+- **预加载** — `fetch(url) → decodeAudioData() → 缓存 AudioBuffer`，已解码 buffer 最多 3 个，LRU 淘汰
+- **视频不自动静音** — `videoMuted` 字段由制作者手动设置，引擎不做自动静音
 
 **架构变更：**
 
 ```
 Engine
 ├── VideoManager（A/B 双缓冲，只管画面和视频内音轨）
-│    └── loopVideo 循环时只管画面 → BGM 不受影响
-└── AudioManager（独立 AudioContext/HTMLAudioElement，只管 BGM）
-     └── 按场景播放/交叉淡化/循环，独立于视频生命周期
+│    └── loopStart/loopEnd 循环 → BGM 不受影响
+└── AudioSystem（Web Audio API）
+     ├── AudioContext → GainNode(BGM) → destination
+     │    └── 多个 BufferSourceNode（新旧 BGM 交叉淡化，指数 ramp）
+     └── ducking 控制：QTE/选择/热点触发 → GainNode ramp 降 → 事件结束 → ramp 恢复
 ```
 
+**BGM 切换策略：**
+
+```
+goToScene(Scene B)
+    ├── bgmUrl 相同？→ 什么都不做，继续播（bgmVolume 变化 → ramp 调整）
+    ├── bgmUrl 为 null？→ 当前 BGM 指数 fade out（bgmCrossFade 秒）
+    └── bgmUrl 不同？
+        ├── fetch + decode BGM B（若未缓存）
+        ├── AudioBufferSourceNode 播 BGM B，gain 从 0.001 ramp 到 bgmVolume
+        ├── 同时 BGM A 的 gain ramp 到 0.001，耗时 bgmCrossFade 秒
+        ├── ramp 完成后 stop BGM A 的 source（释放）
+        └── 画面交叉淡化照常（画面和 BGM 各自独立过渡）
+```
+
+**Ducking 自动闪避策略：**
+
+| 触发事件 | duck 目标值 | 进入耗时 | 恢复耗时 |
+|----------|------------|---------|---------|
+| QTE 触发 | bgmDuckLevel × bgmVolume | 0.3s | bgmDuckFade |
+| 选择面板出现 | bgmDuckLevel × bgmVolume | bgmDuckFade | bgmDuckFade |
+| 视频热点出现 | bgmDuckLevel × bgmVolume | bgmDuckFade | bgmDuckFade |
+
+实现方式：AudioSystem 内部维护一个"当前 duck 等级"计数器（允许多个事件重叠）。
+GainNode 的 ramp 目标值 = `Math.min(bgmVolume, bgmDuckLevel × bgmVolume)`。
+最后一个事件结束时恢复为 `bgmVolume`。
+
 **场景数据设计：**
 
 ```json
 {
   "id": "tense_moment",
   "videoUrl": "/videos/tense_no_bgm.mp4",
-  "loopVideoUrl": "/videos/tense_loop_no_bgm.mp4",
+  "loopStart": 8.0,
+  "loopEnd": 10.0,
   "bgmUrl": "/audio/tense_bgm.mp3",
   "bgmVolume": 0.8,
   "bgmCrossFade": 2.0,
-  "bgmContinue": true,
-  "videoMuted": true,
+  "bgmDuckLevel": 0.35,
+  "bgmDuckFade": 0.5,
+  "videoMuted": false,
   "choices": [...]
 }
 ```
 
-**工作流对比：**
+**字段说明：**
 
-| 阶段 | 改进前 | 改进后 |
-|------|--------|--------|
-| 主视频播放 | 视频自带 BGM | AudioManager 独立播 BGM，视频 muted |
-| 进入选择等待 | 循环视频 → BGM 断掉重来 | 视频循环 → BGM 继续连贯 |
-| 选择后切场景 | 下一段视频 BGM 硬切 | BGM 交叉淡化过渡（bgmCrossFade 秒） |
-| 关音乐/调音量 | 无法控制 | AudioManager 提供音量/静音接口 |
-| 同一 BGM 多场景 | 每个 mp4 嵌一份，浪费 | 共用同一文件，节省带宽 |
+| 字段 | 类型 | 默认 | 说明 |
+|------|------|------|------|
+| `bgmUrl` | string | null | BGM 文件路径（MP3），null/falsy 表示静默并 fade out 当前 BGM |
+| `bgmVolume` | number | 0.8 | 目标音量（0~1） |
+| `bgmCrossFade` | number | 2.0 | BGM 切换交叉淡化时长（秒） |
+| `bgmDuckLevel` | number | 0.35 | QTE/选择/热点时 duck 到 bgmVolume 的百分比 |
+| `bgmDuckFade` | number | 0.5 | duck 进入和恢复的渐变时长（秒） |
+| `videoMuted` | bool | false | 制作者手动设置，引擎不自动静音 |
 
 **实现清单：**
 
-- [ ] `engine/systems/AudioSystem.ts` — 新增：BGM 播放、交叉淡化（GainNode ramp）、循环、音量/静音
-- [ ] `engine/core/Engine.ts` — 集成 AudioSystem；场景切换时对比 bgmUrl，同源→继续，不同→crossFade
-- [ ] `engine/types.ts` — `SceneNode` 加 `bgmUrl`、`bgmVolume`、`bgmCrossFade`、`bgmContinue`、`videoMuted`
-- [ ] `engine/core/VideoManager.ts` — 支持 `muted` 参数（视频音轨静音但在 BGM 模式下禁用）
-- [ ] `public/scenes/demo.json` — 示例场景拆分视频+音频
-- [ ] `editor/components/NodeEditor.vue` — BGM 字段编辑面板
-- [ ] 验证：BGM 跨越视频循环连续播放、场景切换交叉淡化、音量控制生效
+- [x] `engine/systems/AudioSystem.ts` — Web Audio API：fetch+decode 缓存、BufferSourceNode 创建、GainNode 指数 ramp 交叉淡化、同源继续/不同 crossFade/静音 fade out、ducking 事件接口
+- [x] `engine/core/Engine.ts` — 集成 AudioSystem；`goToScene` 对比 `bgmUrl` 调度切换；QTE/choice/hotspot 触发时调用 `audioSystem.duckOn()`/`duckOff()`
+- [x] `engine/types.ts` — `SceneNode` 加 `bgmUrl`、`bgmVolume`、`bgmCrossFade`、`bgmDuckLevel`、`bgmDuckFade`、`videoMuted`
+- [x] `engine/core/VideoManager.ts` — 根据 `videoMuted` 设置 `<video>.muted`（手工字段，不自动）
+- [x] `public/audio/` — BGM 测试 MP3（calm_bgm.mp3, tense_bgm.mp3）
+- [x] `public/scenes/demo.json` — intro/stay/right_door 配置 BGM + cross-fade + ducking 示例
+- [ ] `editor/components/NodeEditor.vue` — BGM 字段编辑面板（6 个字段）
+- [x] 验证：BGM 跨视频循环连续、场景切换交叉淡化、ducking 降/恢复、同源不中断、指数曲线听感均匀
+
+**远期功能（不纳入 P6）：**
+
+| 功能 | 说明 |
+|------|------|
+| 自适应 BGM | 按 StateManager 变量值切换变奏（如 suspicion < 50 放安静版，>= 50 放紧张版） |
+| 水平分段编排 | BGM 前奏/主体/变奏/尾奏自动串联 |
+| 分层 Stems | 多轨独立 GainNode 动态叠加，按变量增减层数 |
+| Stingers | 短乐句事件音（发现线索的"叮"、惊悚弦乐刺音） |
+| BGM 弧线 | 一条 BGM 覆盖多个连续场景而不被切换打断 |
 
 ### P7 全屏模式 — 沉浸式浏览器体验（待实现）
 
diff --git a/engine/core/Engine.ts b/engine/core/Engine.ts
index e6d3ef1..5a4c683 100644
--- a/engine/core/Engine.ts
+++ b/engine/core/Engine.ts
@@ -4,6 +4,7 @@ import { VideoManager } from './VideoManager'
 import { StateManager } from './StateManager'
 import { ChoiceSystem } from '../systems/ChoiceSystem'
 import { QTESystem } from '../systems/QTESystem'
+import { AudioSystem } from '../systems/AudioSystem'
 
 type EventHandler = (...args: any[]) => void
 
@@ -13,6 +14,7 @@ export class Engine {
   stateManager: StateManager
   choiceSystem: ChoiceSystem
   qteSystem: QTESystem
+  audioSystem: AudioSystem
 
   private currentScene: SceneNode | null = null
   private events: Map<EngineEvent, Set<EventHandler>> = new Map()
@@ -29,6 +31,7 @@ export class Engine {
     this.stateManager = new StateManager()
     this.choiceSystem = new ChoiceSystem()
     this.qteSystem = new QTESystem()
+    this.audioSystem = new AudioSystem()
 
     this.videoManager.onTimeUpdate(this.onTimeUpdate)
   }
@@ -63,6 +66,25 @@ export class Engine {
       this.stateManager.apply(scene.onEnter)
     }
 
+    if (scene.videoMuted) {
+      this.videoManager.setMuted(true)
+    } else {
+      this.videoManager.setMuted(false)
+    }
+
+    const bgmUrl = scene.bgmUrl || null
+    if (bgmUrl) {
+      this.audioSystem.play(
+        bgmUrl,
+        scene.bgmVolume ?? 0.8,
+        scene.bgmCrossFade ?? 2.0,
+        scene.bgmDuckLevel,
+        scene.bgmDuckFade,
+      )
+    } else {
+      this.audioSystem.stop(scene.bgmCrossFade ?? 2.0)
+    }
+
     if (scene.type === 'image') {
       this.justCameFromImage = true
       this.isInitialScene = false
@@ -123,6 +145,8 @@ export class Engine {
 
       this.emit('qteTrigger', qte)
 
+      this.audioSystem.duckOn('qte')
+
       this.qteSystem.trigger(
         qte,
         (remaining, total) => {
@@ -130,6 +154,7 @@ export class Engine {
         },
         (success) => {
           this.qteResolved = true
+          this.audioSystem.duckOff('qte')
           if (success) {
             if (qte.effects?.success) {
               this.stateManager.apply(qte.effects.success)
@@ -167,6 +192,7 @@ export class Engine {
       const validChoices = this.getValidChoices(scene)
       if (validChoices.length > 0) {
         this.emit('choiceRequest', validChoices)
+        this.audioSystem.duckOn('choice')
         this.choiceSystem.start(
           validChoices,
           (timerState) => {
@@ -196,6 +222,12 @@ export class Engine {
     })
 
     this.emit('hotspotUpdate', visible)
+
+    if (visible.length > 0) {
+      this.audioSystem.duckOn('hotspot')
+    } else {
+      this.audioSystem.duckOff('hotspot')
+    }
   }
 
   getVisibleHotspots(scene: SceneNode): Hotspot[] {
@@ -209,6 +241,8 @@ export class Engine {
   clickHotspot(hotspot: Hotspot) {
     if (!this.currentScene) return
 
+    this.audioSystem.duckOff('hotspot')
+
     if (hotspot.effects) {
       this.stateManager.apply(hotspot.effects)
     }
@@ -234,6 +268,7 @@ export class Engine {
 
     if (validChoices.length > 0) {
       this.emit('choiceRequest', validChoices)
+      this.audioSystem.duckOn('choice')
 
       this.choiceSystem.start(
         validChoices,
@@ -241,6 +276,7 @@ export class Engine {
           this.emit('choiceTimer', timerState)
         },
         (defaultChoice) => {
+          this.audioSystem.duckOff('choice')
           this.emit('choiceTimeout', defaultChoice)
           this.makeChoice(defaultChoice)
         }
@@ -269,6 +305,8 @@ export class Engine {
   makeChoice(choice: Choice) {
     if (!this.currentScene) return
 
+    this.audioSystem.duckOff('choice')
+
     if (choice.effects) {
       this.stateManager.apply(choice.effects)
     }
@@ -291,6 +329,7 @@ export class Engine {
     this.ended = true
     this.loopActive = false
     this.qteSystem.cancel()
+    this.audioSystem.stop(2.0)
     this.emit('gameEnd')
   }
 
@@ -338,6 +377,7 @@ export class Engine {
 
   destroy() {
     this.qteSystem.destroy()
+    this.audioSystem.destroy()
     this.videoManager.detach()
     this.events.clear()
   }
diff --git a/engine/core/VideoManager.ts b/engine/core/VideoManager.ts
index a723f3b..e457d5b 100644
--- a/engine/core/VideoManager.ts
+++ b/engine/core/VideoManager.ts
@@ -154,6 +154,11 @@ export class VideoManager {
     this.active.currentTime = time
   }
 
+  setMuted(muted: boolean) {
+    if (this.elA) this.elA.muted = muted
+    if (this.elB) this.elB.muted = muted
+  }
+
   onEnd(cb: VideoEndCallback) {
     this.onEndCallback = cb
   }
diff --git a/engine/systems/AudioSystem.ts b/engine/systems/AudioSystem.ts
new file mode 100644
index 0000000..984bd21
--- /dev/null
+++ b/engine/systems/AudioSystem.ts
@@ -0,0 +1,181 @@
+type DuckReason = 'qte' | 'choice' | 'hotspot'
+
+export class AudioSystem {
+  private ctx: AudioContext | null = null
+  private gainNode: GainNode | null = null
+  private currentSource: AudioBufferSourceNode | null = null
+  private currentUrl = ''
+  private currentVolume = 0.8
+  private bufferCache: Map<string, AudioBuffer> = new Map()
+  private maxCache = 3
+  private duckCount: Map<DuckReason, number> = new Map()
+  private duckLevel = 0.35
+  private duckFade = 0.5
+
+  private getCtx(): AudioContext {
+    if (!this.ctx) {
+      this.ctx = new AudioContext()
+      this.gainNode = this.ctx.createGain()
+      this.gainNode.connect(this.ctx.destination)
+    }
+    if (this.ctx.state === 'suspended') {
+      this.ctx.resume()
+    }
+    return this.ctx
+  }
+
+  async play(
+    url: string,
+    volume: number,
+    crossFade: number,
+    duckLvl?: number,
+    duckFd?: number,
+  ) {
+    if (duckLvl !== undefined) this.duckLevel = duckLvl
+    if (duckFd !== undefined) this.duckFade = duckFd
+    this.currentVolume = volume
+
+    if (url === this.currentUrl) {
+      const target = this.duckTarget()
+      if (this.gainNode) {
+        this.gainNode.gain.cancelScheduledValues(this.getCtx().currentTime)
+        this.gainNode.gain.setValueAtTime(this.gainNode.gain.value, this.getCtx().currentTime)
+        this.gainNode.gain.exponentialRampToValueAtTime(
+          Math.max(0.001, target),
+          this.getCtx().currentTime + 0.3,
+        )
+      }
+      return
+    }
+
+    const prevSource = this.currentSource
+
+    this.currentUrl = url
+    const buffer = await this.loadBuffer(url)
+    if (!buffer) return
+
+    const ctx = this.getCtx()
+    const gain = this.gainNode!
+
+    const target = this.duckTarget()
+
+    if (prevSource) {
+      gain.gain.cancelScheduledValues(ctx.currentTime)
+      gain.gain.setValueAtTime(gain.gain.value, ctx.currentTime)
+      gain.gain.exponentialRampToValueAtTime(0.001, ctx.currentTime + crossFade)
+      try { prevSource.stop(ctx.currentTime + crossFade + 0.1) } catch {}
+    }
+
+    const source = ctx.createBufferSource()
+    source.buffer = buffer
+    source.loop = true
+    source.connect(gain)
+
+    gain.gain.cancelScheduledValues(ctx.currentTime)
+    gain.gain.setValueAtTime(0.001, ctx.currentTime)
+    gain.gain.exponentialRampToValueAtTime(
+      Math.max(0.001, target),
+      ctx.currentTime + crossFade,
+    )
+
+    source.start(0)
+    this.currentSource = source
+  }
+
+  async stop(fadeOut: number) {
+    if (!this.currentSource || !this.gainNode) return
+    const ctx = this.getCtx()
+    this.currentUrl = ''
+    const gain = this.gainNode
+    try {
+      gain.gain.cancelScheduledValues(ctx.currentTime)
+      gain.gain.setValueAtTime(gain.gain.value, ctx.currentTime)
+      gain.gain.exponentialRampToValueAtTime(0.001, ctx.currentTime + fadeOut)
+      const src = this.currentSource
+      setTimeout(() => {
+        try { src.stop() } catch {}
+      }, (fadeOut + 0.1) * 1000)
+    } catch {}
+    this.currentSource = null
+  }
+
+  duckOn(reason: DuckReason) {
+    this.duckCount.set(reason, (this.duckCount.get(reason) ?? 0) + 1)
+    this.applyDuck()
+  }
+
+  duckOff(reason: DuckReason) {
+    const cur = this.duckCount.get(reason) ?? 0
+    if (cur <= 1) {
+      this.duckCount.delete(reason)
+    } else {
+      this.duckCount.set(reason, cur - 1)
+    }
+    this.applyDuck()
+  }
+
+  private applyDuck() {
+    if (!this.gainNode || !this.currentSource) return
+    const target = this.duckTarget()
+    const ctx = this.getCtx()
+    const dt = this.duckCount.size > 0 ? this.duckFade : this.duckFade
+    this.gainNode.gain.cancelScheduledValues(ctx.currentTime)
+    this.gainNode.gain.setValueAtTime(this.gainNode.gain.value, ctx.currentTime)
+    this.gainNode.gain.exponentialRampToValueAtTime(
+      Math.max(0.001, target),
+      ctx.currentTime + dt,
+    )
+  }
+
+  private duckTarget(): number {
+    if (this.duckCount.size > 0) {
+      return this.currentVolume * this.duckLevel
+    }
+    return this.currentVolume
+  }
+
+  setVolumeRaw(v: number) {
+    if (!this.gainNode) return
+    const ctx = this.getCtx()
+    this.gainNode.gain.cancelScheduledValues(ctx.currentTime)
+    this.gainNode.gain.setValueAtTime(v, ctx.currentTime)
+  }
+
+  private async loadBuffer(url: string): Promise<AudioBuffer | null> {
+    const cached = this.bufferCache.get(url)
+    if (cached) return cached
+
+    try {
+      const resp = await fetch(url)
+      const arrayBuf = await resp.arrayBuffer()
+      const ctx = this.getCtx()
+      const buffer = await ctx.decodeAudioData(arrayBuf)
+      this.bufferCache.set(url, buffer)
+
+      // LRU eviction
+      if (this.bufferCache.size > this.maxCache) {
+        const firstKey = this.bufferCache.keys().next().value
+        if (firstKey) this.bufferCache.delete(firstKey)
+      }
+
+      return buffer
+    } catch {
+      return null
+    }
+  }
+
+  destroy() {
+    if (this.currentSource) {
+      try { this.currentSource.stop() } catch {}
+      this.currentSource = null
+    }
+    this.bufferCache.clear()
+    this.duckCount.clear()
+    this.currentUrl = ''
+    if (this.ctx) {
+      this.ctx.close()
+      this.ctx = null
+      this.gainNode = null
+    }
+  }
+}
diff --git a/engine/types.ts b/engine/types.ts
index e975bd1..4438633 100644
--- a/engine/types.ts
+++ b/engine/types.ts
@@ -11,6 +11,12 @@ export interface SceneNode {
   onEnter?: Effect[]
   loopStart?: number
   loopEnd?: number
+  bgmUrl?: string
+  bgmVolume?: number
+  bgmCrossFade?: number
+  bgmDuckLevel?: number
+  bgmDuckFade?: number
+  videoMuted?: boolean
 }
 
 export interface Choice {
diff --git a/public/audio/calm_bgm.mp3 b/public/audio/calm_bgm.mp3
new file mode 100644
index 0000000..36409cb
Binary files /dev/null and b/public/audio/calm_bgm.mp3 differ
diff --git a/public/audio/tense_bgm.mp3 b/public/audio/tense_bgm.mp3
new file mode 100644
index 0000000..57a7bd4
Binary files /dev/null and b/public/audio/tense_bgm.mp3 differ
diff --git a/public/scenes/demo.json b/public/scenes/demo.json
index 7cce0b5..1121496 100644
--- a/public/scenes/demo.json
+++ b/public/scenes/demo.json
@@ -10,6 +10,10 @@
       "id": "intro",
       "videoUrl": "/videos/intro.mp4",
       "subtitleUrl": "/subtitles/intro.vtt",
+      "bgmUrl": "/audio/calm_bgm.mp3",
+      "bgmVolume": 0.6,
+      "bgmCrossFade": 1.5,
+      "videoMuted": true,
       "choices": [
         {
           "text": "走向左边那扇发光的门",
@@ -126,6 +130,10 @@
     "right_door": {
       "id": "right_door",
       "videoUrl": "/videos/right_door.mp4",
+      "bgmUrl": "/audio/tense_bgm.mp3",
+      "bgmVolume": 0.7,
+      "bgmCrossFade": 2.0,
+      "videoMuted": true,
       "qte": {
         "triggerTime": 1.0,
         "prompt": "躲避飞来的石块！",
@@ -185,6 +193,9 @@
       "id": "stay",
       "videoUrl": "/videos/stay_loop.mp4",
       "subtitleUrl": "/subtitles/stay.vtt",
+      "bgmUrl": "/audio/calm_bgm.mp3",
+      "bgmVolume": 0.6,
+      "videoMuted": true,
       "loopStart": 3.0,
       "loopEnd": 6.0,
       "choices": [