diff --git a/doco/src/doco/video_split.py b/doco/src/doco/video_split.py
index 68fc4ed..0411d11 100644
--- a/doco/src/doco/video_split.py
+++ b/doco/src/doco/video_split.py
@@ -132,11 +132,13 @@ def extract_frames(
         raise RuntimeError(f"ffmpeg 抽帧失败: {result.stderr}")
 
     # 收集抽出的帧
+    # frame_index 直接从文件名提取(1-based),与 ffmpeg %04d 编号一致
+    # 避免 enumerate 从 0 计数导致下游清理/自检的 off-by-one 索引错位
     frames = []
-    for i, f in enumerate(sorted(frames_dir.glob("frame_*.png"))):
-        # 时间戳:第 i 帧就是 i 秒
-        timestamp_ms = i * 1000
-        frames.append((i, timestamp_ms, f))
+    for f in sorted(frames_dir.glob("frame_*.png")):
+        frame_index = int(f.stem.split("_")[1])    # 1-based,与文件名编号一致
+        timestamp_ms = (frame_index - 1) * 1000      # frame_0001 → 0ms, frame_0002 → 1000ms
+        frames.append((frame_index, timestamp_ms, f))
 
     return frames