diff --git a/render.py b/render.py
index 38591e4..b8ba4e7 100644
--- a/render.py
+++ b/render.py
@@ -592,16 +592,27 @@ def render_all(options):
                     print(" ".join([str(x) for x in cmd]))
                 subprocess.call(cmd)
 
+            if options.get("debug"):
+                for a, b in (
+                    ("back-audio.mp4", "back.mp4"),
+                    ("front-mixed.mp4", "front.mp4"),
+                ):
+                    duration_a = ox.avinfo(str(fragment_prefix / a))['duration']
+                    duration_b = ox.avinfo(str(fragment_prefix / b))['duration']
+                    if duration_a != duration_b:
+                        print('!!', duration_a, fragment_prefix / a)
+                        print('!!', duration_b, fragment_prefix / b)
+                        sys.exit(-1)
+
             for a, b in (
-                ("back-audio.mp4", "back.mp4"),
-                ("front-mixed.mp4", "front.mp4"),
+                ("back-audio.mp4", "front-mixed.mp4"),
             ):
                 duration_a = ox.avinfo(str(fragment_prefix / a))['duration']
                 duration_b = ox.avinfo(str(fragment_prefix / b))['duration']
                 if duration_a != duration_b:
                     print('!!', duration_a, fragment_prefix / a)
                     print('!!', duration_b, fragment_prefix / b)
-                    sys.exit(-1)
+
             shutil.move(fragment_prefix / "back-audio.mp4", fragment_prefix / "back.mp4")
             shutil.move(fragment_prefix / "front-mixed.mp4", fragment_prefix / "front.mp4")
             if options["keep_audio"]: