fix: HEVC description偏移修正(70→78)+调试日志

- findCodecConfig: VisualSampleEntry偏移从70改为78字节（ISO 14496-12）
- extractCodecDescription: 添加调试日志（moovOffset/moovSize/searchRange/found/resultByteLength）
- findCodecConfig: 添加stsd和entry的调试日志（entryCount/entryOffset/entrySize/entryType）

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

@@ -36,15 +36,27 @@ function findCodecConfig(buffer: ArrayBuffer, start: number, end: number): Array
       // SampleDescriptionBox 是 fullbox: 8 header + 4 version/flags + 4 entry_count
       const entryCount = view.getUint32(offset + 12)
       let entryOffset = offset + 16
+      console.log("[findCodecConfig] stsd found:", {
+        entryCount,
+        stsdOffset: offset,
+        stsdSize: size,
+      })
       for (let i = 0; i < entryCount && entryOffset < offset + size; i++) {
         const entrySize = view.getUint32(entryOffset)
+        const entryType = String.fromCharCode(
+          view.getUint8(entryOffset + 4),
+          view.getUint8(entryOffset + 5),
+          view.getUint8(entryOffset + 6),
+          view.getUint8(entryOffset + 7),
+        )
+        console.log("[findCodecConfig] entry:", { index: i, entryOffset, entrySize, entryType })
         // 视觉样本条目: 8 header + 6 reserved + 2 data_ref_index + remaining
         // 子 box 从 entryOffset + 16 + 62 开始 (skip reserved + data_ref_index + predefined)
         // 实际结构: 8(header) + 6(reserved) + 2(data_ref_index) + 16(predefined+reserved) + 2(width) + 2(height) + ...
         // 子 box 从 entryOffset + 8 + 6 + 2 + 16 + 2 + 2 + 2 + 2 + 4 + 2 + 2 + 2 + 2 = entryOffset + 78
         // 更简单的做法：扫描 entry 内的子 box
         const entryEnd = entryOffset + entrySize
-        const subBoxStart = entryOffset + 8 + 70 // VisualSampleEntry 固定字段共 70 字节
+        const subBoxStart = entryOffset + 8 + 78 // VisualSampleEntry 固定字段共 78 字节（ISO 14496-12）
         const result = findCodecConfig(buffer, subBoxStart, entryEnd)
         if (result) return result
         entryOffset += entrySize
@@ -246,7 +258,15 @@ export function useCanvasPlayer(
           view.getUint8(offset + 7),
         )
         if (type === "moov") {
-          return findCodecConfig(buffer, offset + 8, offset + size)
+          const result = findCodecConfig(buffer, offset + 8, offset + size)
+          console.log("[useCanvasPlayer] extractCodecDescription:", {
+            moovOffset: offset,
+            moovSize: size,
+            searchRange: [offset + 8, offset + size],
+            found: !!result,
+            resultByteLength: result?.byteLength,
+          })
+          return result
         }
         if (size === 0) break
         offset += size