Fix stderr print when ffmpeg fails

diff --git a/youtube-dl b/youtube-dl
index f8271a7..9e9be67 100755 (executable)
--- a/youtube-dl
+++ b/youtube-dl
@@ -2676,7 +2676,7 @@ class FFmpegExtractAudioPP(PostProcessor):
                status = self.run_ffmpeg(path, new_path, acodec, more_opts)
 
                if not status:
-                       self._downloader.to_stderr(u'WARNING: error running ffmpeg' % ret)
+                       self._downloader.to_stderr(u'WARNING: error running ffmpeg')
                        return None
 
                try: