diff --git a/src/ffx/cli.py b/src/ffx/cli.py
index 1c339a9..5e3b784 100755
--- a/src/ffx/cli.py
+++ b/src/ffx/cli.py
@@ -1394,8 +1394,15 @@ def convert(ctx,
 
         from ffx.attachment_format import AttachmentFormat
 
+        styledAssDetector = getattr(
+            sourceMediaDescriptor,
+            "hasStyledAssSubtitlesWithFontAttachments",
+            None,
+        )
         styledAssSourceDetected = (
-            sourceMediaDescriptor.hasStyledAssSubtitlesWithFontAttachments()
+            bool(styledAssDetector())
+            if callable(styledAssDetector)
+            else False
         )
         if styledAssSourceDetected:
             styledAssMessage = (
diff --git a/src/ffx/media_workflow_screen_base.py b/src/ffx/media_workflow_screen_base.py
index 7968276..6dd882d 100644
--- a/src/ffx/media_workflow_screen_base.py
+++ b/src/ffx/media_workflow_screen_base.py
@@ -209,7 +209,12 @@ class MediaWorkflowScreenBase(Screen):
             return None
 
         targetMediaDescriptor = currentPattern.getMediaDescriptor(self.context)
-        if sourceMediaDescriptor.hasStyledAssSubtitlesWithFontAttachments():
+        styledAssDetector = getattr(
+            sourceMediaDescriptor,
+            "hasStyledAssSubtitlesWithFontAttachments",
+            None,
+        )
+        if callable(styledAssDetector) and styledAssDetector():
             targetMediaDescriptor = targetMediaDescriptor.withSourceAttachmentTracks(
                 sourceMediaDescriptor,
                 AttachmentFormat.TTF,