fix: 全量可选链+空值兜底，杜绝 TypeError

- info?.videoTracks?.[0] 安全访问视频轨道
- videoTrack 属性加 fallback 默认值（id=1, timescale=90000, codec=avc1.42E01E）
- segments?.[segIndex] 安全索引
- sample.cts/duration 可选链
- EncodedVideoChunk 构建加 sample.data 空值检查
- meta.timescale 除零保护

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

@@ -260,8 +260,11 @@ export function useCanvasPlayer(
   // ── 解封装单个片段，提取轨道元数据 + 按时间范围过滤样本 ──
   const demuxSegment = useCallback(
     (buffer: ArrayBuffer, segIndex: number): SegmentMeta | null => {
-      const segment = segments[segIndex]
-      if (!segment) return null
+      const segment = segments?.[segIndex]
+      if (!segment) {
+        console.warn("[useCanvasPlayer] No segment at index", segIndex)
+        return null
+      }
 
       // 计算全局偏移
       let globalStart = 0
@@ -273,9 +276,9 @@ export function useCanvasPlayer(
       let meta: SegmentMeta | null = null
 
       mp4File.onReady = (info: Movie) => {
-        const videoTrack = info.videoTracks[0]
+        const videoTrack = info?.videoTracks?.[0]
         if (!videoTrack) {
-          console.error("[useCanvasPlayer] No video track found for segment", segIndex)
+          console.warn("[useCanvasPlayer] No video track found for segment", segIndex)
           return
         }
 
@@ -300,9 +303,9 @@ export function useCanvasPlayer(
           videoUrl: segment.videoUrl,
           globalStartTime: globalStart,
           globalEndTime: globalStart + (segment.endTime - segment.startTime),
-          trackId: videoTrack.id,
-          timescale: videoTrack.timescale,
-          codec: videoTrack.codec,
+          trackId: videoTrack.id ?? 1,
+          timescale: videoTrack.timescale ?? 90000,
+          codec: videoTrack.codec ?? "avc1.42E01E",
           videoWidth: videoTrack.track_width || 1280,
           videoHeight: videoTrack.track_height || 720,
           description,
@@ -310,8 +313,8 @@ export function useCanvasPlayer(
         }
 
         // 提取所有 samples
-        mp4File.setExtractionOptions(videoTrack.id, null, {
-          nbSamples: videoTrack.nb_samples,
+        mp4File.setExtractionOptions(videoTrack.id ?? 1, null, {
+          nbSamples: videoTrack.nb_samples ?? 0,
         })
         mp4File.start()
       }
@@ -325,7 +328,7 @@ export function useCanvasPlayer(
         const endCts = segment.endTime * timescale
 
         // 过滤出时间范围内的样本
-        let filtered = samples.filter((s) => s.cts >= startCts && s.cts < endCts)
+        let filtered = samples.filter((s) => (s?.cts ?? 0) >= startCts && (s?.cts ?? 0) < endCts)
 
         // 确保从关键帧开始（跳过第一个 sync 之前的非关键帧）
         let foundSync = false
@@ -436,10 +439,11 @@ export function useCanvasPlayer(
         if (!sample.data || isDestroyedRef.current) continue
         if (decoder.state === "closed") break
 
+        if (!sample.data) continue
         const chunk = new EncodedVideoChunk({
           type: sample.is_sync ? "key" : "delta",
-          timestamp: (sample.cts / meta.timescale) * 1_000_000,
-          duration: (sample.duration / meta.timescale) * 1_000_000,
+          timestamp: ((sample.cts ?? 0) / (meta.timescale || 90000)) * 1_000_000,
+          duration: ((sample.duration ?? 0) / (meta.timescale || 90000)) * 1_000_000,
           data: sample.data,
         })