diff --git a/yt_dlp/postprocessor/ffmpeg.py b/yt_dlp/postprocessor/ffmpeg.py
index d986d12b8..616af58d8 100644
--- a/yt_dlp/postprocessor/ffmpeg.py
+++ b/yt_dlp/postprocessor/ffmpeg.py
@@ -649,7 +649,7 @@ def run(self, info):
                 mp4_ass_warn = True
                 self.report_warning('ASS subtitles cannot be properly embedded in mp4 files; expect issues')
 
-        if not sub_langs:
+        if not sub_langs and not json_subs:
             return [], info
 
         input_files = [filename, *sub_filenames]