diff --git a/server/main.py b/server/main.py
index 1e4b02a..416d62f 100644
--- a/server/main.py
+++ b/server/main.py
@@ -188,6 +188,23 @@ def process_video_task(task_id: str, req: GenerateRequest):
             # Clear buffer
             frame_buffer.clear()
 
+        # Seek once to the starting frame. Avoid random-access seek on every frame.
+        if req.start_frame > 0:
+            seek_ok = cap.set(cv2.CAP_PROP_POS_FRAMES, req.start_frame)
+            if not seek_ok:
+                print(
+                    f"[FaceMask] Warning: CAP_PROP_POS_FRAMES seek failed, "
+                    f"fallback to sequential skip ({req.start_frame} frames)"
+                )
+                for _ in range(req.start_frame):
+                    ret, _ = cap.read()
+                    if not ret:
+                        tasks[task_id].status = TaskStatus.FAILED
+                        tasks[task_id].message = (
+                            f"Failed to seek to start frame: {req.start_frame}"
+                        )
+                        return
+
         # Process loop with batching
         current_count = 0
         for frame_idx in range(req.start_frame, end_frame + 1):
@@ -196,8 +213,7 @@ def process_video_task(task_id: str, req: GenerateRequest):
                 tasks[task_id].message = "Cancelled by user"
                 break
 
-            # Read frame
-            cap.set(cv2.CAP_PROP_POS_FRAMES, frame_idx)
+            # Read next frame sequentially (after one-time initial seek)
             ret, frame = cap.read()
 
             if ret: