refactor: 默认使用原生video播放，彻底解决主线程解码卡顿

FrontendPreviewPlayer.tsx:
- useWebCodecs 默认 false，走浏览器原生硬件解码（独立线程）
- 删除 Canvas ResizeObserver useEffect（默认路径不需要）
- video 元素只预加载当前+下一片段，其余 preload=none+不设src，减少并发连接
- 片段指示器统一显示片段序号，不再显示Canvas/降级提示
- isWebCodecsSupported 不再导入，清理 TS6133

useSegmentScheduler.ts:
- tick 进度更新 200ms 节流（5fps），避免 60fps setCurrentTime 触发整树 re-render
- 重播/seek 时重置节流 ref
- switchToSegment 兜底：若 video 无 src 则动态设置并 load()，兼容 seek 到未预加载片段

useCanvasPlayer.ts 不删，保留作为兜底

apps/web/src/pages/generate/components/FrontendPreviewPlayer.tsx

@@ -17,7 +17,7 @@ import {
 import type { AssetItem } from "@/api/assets"
 import type { EditingTemplate } from "@/api/editing-planner"
 import { useSegmentScheduler, type PlaybackSegment } from "../hooks/useSegmentScheduler"
-import { useCanvasPlayer, isWebCodecsSupported } from "../hooks/useCanvasPlayer"
+import { useCanvasPlayer } from "../hooks/useCanvasPlayer"
 
 interface FrontendPreviewPlayerProps {
   assets: AssetItem[]
@@ -82,7 +82,9 @@ const FrontendPreviewPlayer: React.FC<FrontendPreviewPlayerProps> = ({
   titleSettings,
 }) => {
   const segments = useMemo(() => buildPlaybackSegments(assets, template), [assets, template])
-  const useWebCodecs = isWebCodecsSupported()
+  // 默认走原生 video 播放（浏览器硬件解码，独立线程，不阻塞 UI）
+  // WebCodecs 仅在明确需要时启用（保留代码作为兜底）
+  const useWebCodecs = false
 
   // ── 两条路径共用同一个 canvas ref（fallback 路径不使用） ──
   const canvasRef = useRef<HTMLCanvasElement>(null)
@@ -265,32 +267,8 @@ const FrontendPreviewPlayer: React.FC<FrontendPreviewPlayerProps> = ({
 
   const progressPercent = totalDuration > 0 ? (currentTime / totalDuration) * 100 : 0
 
-  // ── Canvas ResizeObserver ──
+  // ── Canvas 容器 ref（保留声明，WebCodecs 兜底路径仍引用） ──
   const canvasContainerRef = useRef<HTMLDivElement>(null)
-  useEffect(() => {
-    if (!effectiveUseWebCodecs || !canPlay) return
-    const container = canvasContainerRef.current
-    const canvas = canvasRef.current
-    if (!container || !canvas) return
-    // 立即设置一次 canvas 像素分辨率，避免默认 300×150 导致首帧变形
-    const initRect = container.getBoundingClientRect()
-    if (initRect.width > 0 && initRect.height > 0) {
-      const dpr = window.devicePixelRatio || 1
-      canvas.width = initRect.width * dpr
-      canvas.height = initRect.height * dpr
-    }
-    const ro = new ResizeObserver((entries) => {
-      for (const entry of entries) {
-        const { width, height } = entry.contentRect
-        if (width > 0 && height > 0) {
-          canvas.width = width * window.devicePixelRatio
-          canvas.height = height * window.devicePixelRatio
-        }
-      }
-    })
-    ro.observe(container)
-    return () => ro.disconnect()
-  }, [effectiveUseWebCodecs, canPlay])
 
   // ── 未就绪 ──
   if (!ready || !assets.length) {
@@ -385,31 +363,35 @@ const FrontendPreviewPlayer: React.FC<FrontendPreviewPlayerProps> = ({
         </div>
       )}
 
-      {/* ── Video 渲染层（fallback 路径，或 WebCodecs 解码失败时自动切换） ── */}
+      {/* ── Video 渲染层（默认路径，浏览器原生硬件解码） ── */}
       {!effectiveUseWebCodecs &&
-        segments.map((seg, i) => (
-          <video
-            key={seg.assetId}
-            muted
-            ref={(el) => {
-              videoRefs.current[i] = el
-            }}
-            preload="auto"
-            src={seg.videoUrl}
-            style={{
-              position: "absolute",
-              inset: 0,
-              width: "100%",
-              height: "100%",
-              objectFit: "contain",
-              background: "#000",
-              zIndex: 1,
-              opacity: i === videoCurrentSegIdx ? 1 : 0,
-              pointerEvents: i === videoCurrentSegIdx ? "auto" : "none",
-            }}
-            playsInline
-          />
-        ))}
+        segments.map((seg, i) => {
+          // 只预加载当前片段和下一个片段，其余延迟加载
+          const shouldPreload = i <= videoCurrentSegIdx + 1
+          return (
+            <video
+              key={seg.assetId}
+              muted
+              ref={(el) => {
+                videoRefs.current[i] = el
+              }}
+              preload={shouldPreload ? "auto" : "none"}
+              src={shouldPreload ? seg.videoUrl : undefined}
+              style={{
+                position: "absolute",
+                inset: 0,
+                width: "100%",
+                height: "100%",
+                objectFit: "contain",
+                background: "#000",
+                zIndex: 1,
+                opacity: i === videoCurrentSegIdx ? 1 : 0,
+                pointerEvents: i === videoCurrentSegIdx ? "auto" : "none",
+              }}
+              playsInline
+            />
+          )
+        })}
 
       {/* 播放按钮 */}
       {!isPlaying && (
@@ -453,11 +435,7 @@ const FrontendPreviewPlayer: React.FC<FrontendPreviewPlayerProps> = ({
           zIndex: 10,
         }}
       >
-        {effectiveUseWebCodecs
-          ? "Canvas"
-          : forceVideoFallback
-            ? "Canvas 解码失败，已切换原生播放"
-            : `片段 ${videoCurrentSegIdx + 1}/${segments.length}`}
+        {`片段 ${videoCurrentSegIdx + 1}/${segments.length}`}
       </div>
 
       {/* 控制条 */}

apps/web/src/pages/generate/hooks/useSegmentScheduler.ts

@@ -97,6 +97,7 @@ export function useSegmentScheduler(segments: PlaybackSegment[]): SegmentSchedul
   const [isEnded, setIsEnded] = useState(false)
   const rafRef = useRef<number>(0)
   const isSeekingRef = useRef(false)
+  const lastTimeUpdateRef = useRef(0)
 
   // 计算时间线
   const timelineStarts = useMemo(() => buildTimeline(segments), [segments])
@@ -133,6 +134,12 @@ export function useSegmentScheduler(segments: PlaybackSegment[]): SegmentSchedul
         const seg = segments[index]
         const localTime = seekToLocalTime ?? seg.startTime
 
+        // 确保 video 有 src（预加载策略下可能还未设置）
+        if (!video.src && seg.videoUrl) {
+          video.src = seg.videoUrl
+          video.load()
+        }
+
         // 设置播放位置
         video.currentTime = localTime
 
@@ -167,7 +174,7 @@ export function useSegmentScheduler(segments: PlaybackSegment[]): SegmentSchedul
     [segments, currentSegmentIndex],
   )
 
-  /** 播放循环 — 检测片段边界并切换 */
+  /** 播放循环 — 检测片段边界并切换（进度更新 200ms 节流，避免 60fps re-render） */
   const tick = useCallback(() => {
     const video = videoRefs.current[currentSegmentIndex]
     if (!video || isSeekingRef.current) {
@@ -185,7 +192,6 @@ export function useSegmentScheduler(segments: PlaybackSegment[]): SegmentSchedul
       const timeToEnd = seg.endTime - video.currentTime
       if (timeToEnd <= 3 && nextVideo && nextVideo.readyState < 3) {
         const nextSeg = segments[nextIndex]
-        // 只在还没 seek 过时设置（避免反复 seek）
         if (Math.abs(nextVideo.currentTime - nextSeg.startTime) > 1) {
           nextVideo.currentTime = nextSeg.startTime
         }
@@ -226,6 +232,7 @@ export function useSegmentScheduler(segments: PlaybackSegment[]): SegmentSchedul
         })
         const accumulatedTime =
           (timelineStarts[currentSegmentIndex] || 0) + (seg.endTime - seg.startTime)
+        lastTimeUpdateRef.current = 0
         setCurrentTime(accumulatedTime)
       } else {
         setIsPlaying(false)
@@ -236,7 +243,12 @@ export function useSegmentScheduler(segments: PlaybackSegment[]): SegmentSchedul
     } else {
       const globalTime =
         (timelineStarts[currentSegmentIndex] || 0) + (video.currentTime - seg.startTime)
-      setCurrentTime(Math.max(0, Math.min(globalTime, totalDuration)))
+      // 节流：200ms 更新一次进度状态（5fps），避免 60fps re-render 拖慢页面
+      const now = performance.now()
+      if (now - lastTimeUpdateRef.current >= 200) {
+        lastTimeUpdateRef.current = now
+        setCurrentTime(Math.max(0, Math.min(globalTime, totalDuration)))
+      }
     }
 
     rafRef.current = requestAnimationFrame(tick)
@@ -285,6 +297,7 @@ export function useSegmentScheduler(segments: PlaybackSegment[]): SegmentSchedul
       if (isEnded) {
         // 播放结束后再次播放，从头开始
         setIsEnded(false)
+        lastTimeUpdateRef.current = 0
         switchToSegment(0, segments[0]?.startTime).then(() => {
           const video = videoRefs.current[0]
           if (video) {
@@ -317,6 +330,7 @@ export function useSegmentScheduler(segments: PlaybackSegment[]): SegmentSchedul
         if (video) video.currentTime = localTime
       }
 
+      lastTimeUpdateRef.current = 0
       setCurrentTime(clampedTime)
       setIsEnded(false)