diff --git a/src/ffx/ffx_controller.py b/src/ffx/ffx_controller.py
index 128c154..d44824f 100644
--- a/src/ffx/ffx_controller.py
+++ b/src/ffx/ffx_controller.py
@@ -60,7 +60,7 @@ class FfxController():
 
         return [f"-c:v:{int(subIndex)}", 'libx264',
                 "-preset", "slow",
-                f"crf={quality}"]
+                '-crf', str(quality)]
 
 
     # -c:v:0 libvpx-vp9 -row-mt 1 -crf 32 -pass 1 -speed 4 -frame-parallel 0 -g 9999 -aq-mode 0