fix: demuxSegment改为异步，等待onSamples完成后再返回，修复黑屏根因

- demuxSegment 改为 async 函数，返回 Promise<SegmentMeta | null>
- 用 new Promise 包装 MP4Box.js 回调，在 onSamples 完成后 resolve(meta)
- init 中 await demuxSegment 确保 samples 数据就绪后再进入解码
- onReady 无视频轨道、onSamples meta 为空、onError 均 resolve(null)
- 解决 meta.samples 始终为空数组导致 Canvas 黑屏的根本问题

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

@@ -258,8 +258,9 @@ 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 ──
+  // ✅ 关键修复：改为异步函数，等待 MP4Box.js 的 onSamples 回调完成后再返回
   const demuxSegment = useCallback(
-    (buffer: ArrayBuffer, segIndex: number): SegmentMeta | null => {
+    async (buffer: ArrayBuffer, segIndex: number): Promise<SegmentMeta | null> => {
       const segment = segments?.[segIndex]
       if (!segment) {
         console.warn("[useCanvasPlayer] No segment at index", segIndex)
@@ -273,104 +274,113 @@ export function useCanvasPlayer(
       }
 
       const mp4File = createFile()
-      let meta: SegmentMeta | null = null
 
-      mp4File.onReady = (info: Movie) => {
-        const videoTrack = info?.videoTracks?.[0]
-        if (!videoTrack) {
-          console.warn("[useCanvasPlayer] No video track found for segment", segIndex)
-          return
-        }
+      return new Promise<SegmentMeta | null>((resolve) => {
+        let meta: SegmentMeta | null = null
 
-        // 提取编解码器配置数据（HEVC 必需，H.264 也需要）
-        let description = extractCodecDescription(buffer)
-
-        // 如果当前分片没有 description，尝试从缓存获取
-        if (!description) {
-          for (const cached of descriptionCache.current.values()) {
-            description = cached
-            break
+        mp4File.onReady = (info: Movie) => {
+          const videoTrack = info?.videoTracks?.[0]
+          if (!videoTrack) {
+            console.warn("[useCanvasPlayer] No video track found for segment", segIndex)
+            resolve(null)
+            return
           }
-        }
 
-        // 缓存 description 供后续分片使用
-        if (description) {
-          descriptionCache.current.set(segment.assetId, description)
-        }
+          // 提取编解码器配置数据（HEVC 必需，H.264 也需要）
+          let description = extractCodecDescription(buffer)
 
-        meta = {
-          assetId: segment.assetId,
-          videoUrl: segment.videoUrl,
-          globalStartTime: globalStart,
-          globalEndTime: globalStart + (segment.endTime - segment.startTime),
-          trackId: videoTrack.id ?? 1,
-          timescale: videoTrack.timescale ?? 90000,
-          codec: videoTrack.codec ?? "avc1.42E01E",
-          videoWidth: videoTrack.track_width || 1280,
-          videoHeight: videoTrack.track_height || 720,
-          description,
-          samples: [],
-        }
-
-        // 提取所有 samples
-        mp4File.setExtractionOptions(videoTrack.id ?? 1, null, {
-          nbSamples: videoTrack.nb_samples ?? 0,
-        })
-        mp4File.start()
-      }
-
-      mp4File.onSamples = (_trackId: number, _user: unknown, samples: Sample[]) => {
-        if (!meta) return
-
-        // 前端切片：按 [startTime, endTime] 时间范围过滤样本
-        const timescale = meta.timescale
-        const startCts = segment.startTime * timescale
-        const endCts = segment.endTime * timescale
-
-        // 过滤出时间范围内的样本
-        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
-        filtered = filtered.filter((s) => {
-          if (s.is_sync) {
-            foundSync = true
-            return true
+          // 如果当前分片没有 description，尝试从缓存获取
+          if (!description) {
+            for (const cached of descriptionCache.current.values()) {
+              description = cached
+              break
+            }
           }
-          return foundSync
-        })
 
-        // Fallback：如果时间范围内没有样本，使用全部样本从第一个关键帧开始
-        if (filtered.length === 0) {
-          console.warn(
-            `[useCanvasPlayer] No samples in range [${segment.startTime}s, ${segment.endTime}s] for segment ${segIndex}, fallback to all from keyframe`,
-          )
-          let sync = false
-          filtered = samples.filter((s) => {
+          // 缓存 description 供后续分片使用
+          if (description) {
+            descriptionCache.current.set(segment.assetId, description)
+          }
+
+          meta = {
+            assetId: segment.assetId,
+            videoUrl: segment.videoUrl,
+            globalStartTime: globalStart,
+            globalEndTime: globalStart + (segment.endTime - segment.startTime),
+            trackId: videoTrack.id ?? 1,
+            timescale: videoTrack.timescale ?? 90000,
+            codec: videoTrack.codec ?? "avc1.42E01E",
+            videoWidth: videoTrack.track_width || 1280,
+            videoHeight: videoTrack.track_height || 720,
+            description,
+            samples: [],
+          }
+
+          // 提取所有 samples
+          mp4File.setExtractionOptions(videoTrack.id ?? 1, null, {
+            nbSamples: videoTrack.nb_samples ?? 0,
+          })
+          mp4File.start()
+        }
+
+        mp4File.onSamples = (_trackId: number, _user: unknown, samples: Sample[]) => {
+          if (!meta) {
+            resolve(null)
+            return
+          }
+
+          // 前端切片：按 [startTime, endTime] 时间范围过滤样本
+          const timescale = meta.timescale
+          const startCts = segment.startTime * timescale
+          const endCts = segment.endTime * timescale
+
+          // 过滤出时间范围内的样本
+          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
+          filtered = filtered.filter((s) => {
             if (s.is_sync) {
-              sync = true
+              foundSync = true
               return true
             }
-            return sync
+            return foundSync
           })
+
+          // Fallback：如果时间范围内没有样本，使用全部样本从第一个关键帧开始
+          if (filtered.length === 0) {
+            console.warn(
+              `[useCanvasPlayer] No samples in range [${segment.startTime}s, ${segment.endTime}s] for segment ${segIndex}, fallback to all from keyframe`,
+            )
+            let sync = false
+            filtered = samples.filter((s) => {
+              if (s.is_sync) {
+                sync = true
+                return true
+              }
+              return sync
+            })
+          }
+
+          meta.samples = filtered
+          console.log(
+            `[useCanvasPlayer] Segment ${segIndex}: ${filtered.length}/${samples.length} samples (range ${segment.startTime}s-${segment.endTime}s)`,
+          )
+
+          // ✅ 关键修复：等待 onSamples 完成后再返回
+          resolve(meta)
         }
 
-        meta.samples = filtered
-        console.log(
-          `[useCanvasPlayer] Segment ${segIndex}: ${filtered.length}/${samples.length} samples (range ${segment.startTime}s-${segment.endTime}s)`,
-        )
-      }
+        mp4File.onError = (_module: string, message: string) => {
+          console.error(`[useCanvasPlayer] MP4Box error: ${message}`)
+          resolve(null)
+        }
 
-      mp4File.onError = (_module: string, message: string) => {
-        console.error(`[useCanvasPlayer] MP4Box error: ${message}`)
-      }
-
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      ;(buffer as any).fileStart = 0
-      // eslint-disable-next-line @typescript-eslint/no-explicit-any
-      mp4File.appendBuffer(buffer as any)
-
-      return meta
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        ;(buffer as any).fileStart = 0
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        mp4File.appendBuffer(buffer as any)
+      })
     },
     [segments, extractCodecDescription],
   )
@@ -666,12 +676,12 @@ export function useCanvasPlayer(
 
       if (isDestroyedRef.current) return
 
-      // 2. 解析每个片段的轨道元数据
+      // 2. 解析每个片段的轨道元数据（await 等待 onSamples 回调完成）
       const metas: SegmentMeta[] = []
       for (let i = 0; i < segments.length; i++) {
         const buffer = segmentDataRef.current.get(segments[i].assetId)
         if (!buffer) continue
-        const meta = demuxSegment(buffer, i)
+        const meta = await demuxSegment(buffer, i)
         if (meta) metas.push(meta)
       }