diff --git a/yt_dlp/postprocessor/ffmpeg.py b/yt_dlp/postprocessor/ffmpeg.py
index b29cd1d938..b029f12899 100644
--- a/yt_dlp/postprocessor/ffmpeg.py
+++ b/yt_dlp/postprocessor/ffmpeg.py
@@ -826,6 +826,8 @@ class FFmpegMetadataPP(FFmpegPostProcessor):
         self.to_screen(f'Adding metadata to "{filename}"')
         try:
             f = mutagen.File(filename)
+            if f is None:
+                raise TypeError(f'Mutagen unable to determine type of file: {info["ext"]}')
             self._assemble_metadata(f, metadata)
             f.save()
         except Exception as err: