diff --git a/fam-core/src/fam_core/dispatcher/dispatcher.py b/fam-core/src/fam_core/dispatcher/dispatcher.py
index 81562ab..ff74167 100644
--- a/fam-core/src/fam_core/dispatcher/dispatcher.py
+++ b/fam-core/src/fam_core/dispatcher/dispatcher.py
@@ -178,6 +178,7 @@ class Dispatcher:
                      'scale=trunc(iw/2)*2:trunc(ih/2)*2'),
             '-c:v', 'libx264', '-preset', 'veryfast', '-crf', '28',
             '-an',
+            '-f', 'mp4',  # .tmp 扩展名无法推断 muxer，必须显式指定
             tmp_path,
         ]
         try: