fix: Canvas播放器全量修复 - nbSamples/description/调试日志

- Fix 1: nbSamples 为 0 时传入 10000，确保 MP4Box 提取所有样本
- Fix 2: description 缺失时直接 resolve(null)，避免无效解码
- Fix 3: 添加 demuxSegment 详细调试日志（segIndex/startTime/endTime/nbSamples/codec/videoWidth/videoHeight）

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

@@ -292,6 +292,17 @@ export function useCanvasPlayer(
 
         mp4File.onReady = (info: Movie) => {
           const videoTrack = info?.videoTracks?.[0]
+
+          console.log("[useCanvasPlayer] demuxSegment:", {
+            segIndex,
+            startTime: segment.startTime,
+            endTime: segment.endTime,
+            nbSamples: videoTrack?.nb_samples,
+            codec: videoTrack?.codec,
+            videoWidth: videoTrack?.track_width,
+            videoHeight: videoTrack?.track_height,
+          })
+
           if (!videoTrack) {
             console.warn("[useCanvasPlayer] No video track found for segment", segIndex)
             clearTimeout(timeout)
@@ -311,11 +322,20 @@ export function useCanvasPlayer(
             }
           }
 
-          // 缓存 description 供后续分片使用
-          if (description) {
-            descriptionCache.current.set(segment.assetId, description)
+          // ✅ 如果 description 缺失，无法解码 HEVC
+          if (!description) {
+            console.error(
+              `[useCanvasPlayer] No description found for segment ${segIndex}, cannot decode HEVC`,
+            )
+            clearTimeout(timeout)
+            resolved = true
+            resolve(null)
+            return
           }
 
+          // 缓存 description 供后续分片使用
+          descriptionCache.current.set(segment.assetId, description)
+
           meta = {
             assetId: segment.assetId,
             videoUrl: segment.videoUrl,
@@ -332,7 +352,7 @@ export function useCanvasPlayer(
 
           // 提取所有 samples
           mp4File.setExtractionOptions(videoTrack.id ?? 1, null, {
-            nbSamples: videoTrack.nb_samples ?? 0,
+            nbSamples: videoTrack.nb_samples || 10000,
           })
           mp4File.start()
         }