feat(playback): add browser TTS mute detection and notification

components/stage.tsx

@@ -32,6 +32,7 @@ import {
 } from '@/components/ui/alert-dialog';
 import { AlertTriangle } from 'lucide-react';
 import { VisuallyHidden } from 'radix-ui';
+import { toast } from 'sonner';
 
 /**
  * Stage Component
@@ -528,6 +529,12 @@ export function Stage({
           }, 1500);
         }
       },
+      onBrowserTTSMuted: () => {
+        toast.warning(t('playback.browserTtsMuted'), {
+          duration: 5000,
+          id: 'browser-tts-muted',
+        });
+      },
     });
 
     engineRef.current = engine;

lib/i18n/common.ts

@@ -37,6 +37,9 @@ export const commonZhCN = {
     exportSuccess: '导出成功',
     exportFailed: '导出失败',
   },
+  playback: {
+    browserTtsMuted: '当前浏览器处于静音状态，无法听到语音。请打开系统或浏览器音量。',
+  },
 } as const;
 
 export const commonEnUS = {
@@ -78,4 +81,7 @@ export const commonEnUS = {
     exportSuccess: 'Export successful',
     exportFailed: 'Export failed',
   },
+  playback: {
+    browserTtsMuted: 'Browser is muted. Please unmute your system or browser to hear the audio.',
+  },
 } as const;

lib/playback/engine.ts

@@ -663,7 +663,19 @@ export class PlaybackEngine {
       utterance.lang = cjkRatio > CJK_LANG_THRESHOLD ? 'zh-CN' : 'en-US';
     }
 
+    // Track start time to detect abnormally fast completion (likely due to mute)
+    const startTime = performance.now();
+    const MIN_NORMAL_DURATION = 200; // ms - anything faster is suspicious
+
     utterance.onend = () => {
+      const duration = performance.now() - startTime;
+
+      // Detect abnormally fast completion - likely browser/system is muted
+      if (duration < MIN_NORMAL_DURATION && chunkText.trim().length > 0) {
+        log.warn(`Browser TTS chunk ended too quickly (${duration}ms) - possible mute state`);
+        this.callbacks.onBrowserTTSMuted?.();
+      }
+
       this.browserTTSChunkIndex++;
       if (this.mode === 'playing') {
         this.playBrowserTTSChunk(); // next chunk

lib/playback/types.ts

@@ -59,4 +59,7 @@ export interface PlaybackEngineCallbacks {
   getPlaybackSpeed?: () => number;
 
   onComplete?: () => void;
+
+  /** Browser TTS is muted - prompt user to unmute */
+  onBrowserTTSMuted?: () => void;
 }