diff --git a/apps/api/app/api/routes/templates_editor/cover.py b/apps/api/app/api/routes/templates_editor/cover.py
index a112942d7..59a5a6ad9 100755
--- a/apps/api/app/api/routes/templates_editor/cover.py
+++ b/apps/api/app/api/routes/templates_editor/cover.py
@@ -137,6 +137,12 @@ def editor_generate_cover(
 
             storage_svc = get_shared_storage_service()
             primary_video_url = storage_svc.get_url(rendered_storage_key)
+        # 防御性规范化：合并路径中的双斜杠（// -> /），但保留协议头的 ://
+        # 历史数据中 project_id 为空时会产生 projects//tasks/ 路径，
+        # MediaKit 的 HTTP 客户端会规范化 URL 导致 404
+        if primary_video_url:
+            import re as _re
+            primary_video_url = _re.sub(r'(?<!:)//', '/', primary_video_url)
         logger.info(
             "获取预览视频URL用于封面生成: plan_id=%s url=%s",
             plan_id,
diff --git a/apps/api/app/api/routes/templates_editor/generation.py b/apps/api/app/api/routes/templates_editor/generation.py
index 84107e7d4..804b66a14 100755
--- a/apps/api/app/api/routes/templates_editor/generation.py
+++ b/apps/api/app/api/routes/templates_editor/generation.py
@@ -223,7 +223,12 @@ def _get_task_output_url(task, gen_task_repo, db) -> str:
         use_case = ListGeneratedVideosByTaskUseCase(video_repo)
         videos = use_case.execute(task.id)
         if videos:
-            return getattr(videos[0], "file_url", "") or ""
+            url = getattr(videos[0], "file_url", "") or ""
+            # 规范化：合并路径中的双斜杠（保留协议头 ://）
+            if url:
+                import re as _re
+                url = _re.sub(r"(?<!:)//", "/", url)
+            return url
     except Exception:
         pass
     return ""
diff --git a/apps/worker/worker_app/tasks/generation.py b/apps/worker/worker_app/tasks/generation.py
index 62be2f660..f641e66c6 100644
--- a/apps/worker/worker_app/tasks/generation.py
+++ b/apps/worker/worker_app/tasks/generation.py
@@ -1262,7 +1262,9 @@ def _upload_and_record(
     Returns:
         (file_url, duration, file_size, video_count)
     """
-    storage_key = f"generated/projects/{project_id}/tasks/{task_id}/{output_path.name}"
+    # project_id 可能为空（模板编辑器草稿不属于任何项目），过滤空段避免 OSS key 出现 //
+    path_parts = [p for p in ("generated", "projects", project_id, "tasks", task_id, output_path.name) if p]
+    storage_key = "/".join(path_parts)
     file_size = output_path.stat().st_size
 
     # 上传 OSS
diff --git a/packages/shared/ai_service.py b/packages/shared/ai_service.py
index 70a9ed55b..b5e7f0ff3 100755
--- a/packages/shared/ai_service.py
+++ b/packages/shared/ai_service.py
@@ -396,6 +396,12 @@ def _call_ai_cover_service(
 
     # ai_frame / ai_regenerate - 尝试调用 MediaKit
     if primary_video_url:
+        # 规范化 URL：合并路径中的双斜杠（保留协议头 ://）
+        # 历史数据中 project_id 为空时 OSS key 会出现 projects//tasks/ 路径
+        import re as _re
+
+        primary_video_url = _re.sub(r"(?<!:)//", "/", primary_video_url)
+
         from packages.shared.mediakit_client import get_mediakit_client
 
         client = get_mediakit_client()
diff --git a/tests/unit/test_mediakit_cover.py b/tests/unit/test_mediakit_cover.py
index d48d65834..287e2c0ef 100755
--- a/tests/unit/test_mediakit_cover.py
+++ b/tests/unit/test_mediakit_cover.py
@@ -191,6 +191,33 @@ class TestAICoverService:
                 primary_video_url="https://example.com/nonexistent.mp4",
             )
 
+    @patch("packages.shared.ai_service.http_requests.head")
+    @patch("packages.shared.mediakit_client.get_mediakit_client")
+    def test_call_ai_cover_url_double_slash_normalized(self, mock_get_client, mock_head):
+        """URL 路径中的双斜杠应被规范化，避免 MediaKit 404."""
+        dirty_url = "https://oss.example.com/generated/projects//tasks/abc123/rendered.mp4"
+        clean_url = "https://oss.example.com/generated/projects/tasks/abc123/rendered.mp4"
+
+        mock_head.return_value.status_code = 200
+        mock_client = Mock()
+        mock_client.is_available = True
+        mock_client.extract_frames.return_value = []
+        mock_get_client.return_value = mock_client
+
+        from packages.shared.ai_service import _call_ai_cover_service
+
+        with pytest.raises(RuntimeError):
+            _call_ai_cover_service(
+                plan_id="plan-1",
+                asset_ids=["a1"],
+                cover_type="ai_frame",
+                primary_video_url=dirty_url,
+            )
+
+        # HEAD 请求使用规范化后的 URL
+        mock_head.assert_called_once()
+        assert mock_head.call_args[0][0] == clean_url
+
     @patch("packages.shared.ai_service.http_requests.head")
     @patch("packages.shared.mediakit_client.get_mediakit_client")
     def test_call_ai_cover_with_mediakit_failure_raises(self, mock_get_client, mock_head):