diff --git a/fam-core/src/fam_core/db_layer.py b/fam-core/src/fam_core/db_layer.py
index af00032..a19671c 100644
--- a/fam-core/src/fam_core/db_layer.py
+++ b/fam-core/src/fam_core/db_layer.py
@@ -176,8 +176,28 @@ def get_video_url_exists(video_path: str) -> bool:
 # ============================================================
 
 def _dt_or_none(value):
-    """datetime 字段归一化: 空串/None → NULL（MariaDB 严格模式拒绝 '' 插入 DATETIME 列）"""
-    return value if value else None
+    """datetime 字段归一化（MariaDB 严格模式兼容）
+
+    - 空串/None/'None'/'null' → NULL
+    - ISO 8601（2026-08-20T01:06:44Z / 2026-08-20T01:06:44.123+00:00）→ '2026-08-20 01:06:44'
+    - 已为标准格式则原样返回
+    """
+    if value is None:
+        return None
+    s = str(value).strip()
+    if s in ('', 'None', 'null', 'NaN'):
+        return None
+    # 归一化 ISO 8601 -> 'YYYY-MM-DD HH:MM:SS'
+    s2 = s.replace('T', ' ').replace('Z', '').replace('z', '')
+    if '+' in s2[10:]:
+        s2 = s2[:s2.index('+')]
+    if '.' in s2:
+        s2 = s2[:s2.index('.')]
+    try:
+        dt = datetime.strptime(s2, '%Y-%m-%d %H:%M:%S')
+        return dt.strftime('%Y-%m-%d %H:%M:%S')
+    except Exception:
+        return None
 
 
 def insert_event(task_id: int, event_start_time: str, event_end_time: str,
diff --git a/fam-edge/config/config.yaml b/fam-edge/config/config.yaml
index c7cc96f..848892d 100644
--- a/fam-edge/config/config.yaml
+++ b/fam-edge/config/config.yaml
@@ -72,6 +72,6 @@ models:
     model_name: "qwen2.5:7b"
     base_url: "http://localhost:11434"
     timeout: 300
-    num_predict: 1024
+    num_predict: 512
     circuit_breaker:
       enabled: false