diff --git a/youtube_dl/postprocessor/ffmpeg.py b/youtube_dl/postprocessor/ffmpeg.py
index 6955b01f9..380bc6f29 100644
--- a/youtube_dl/postprocessor/ffmpeg.py
+++ b/youtube_dl/postprocessor/ffmpeg.py
@@ -510,7 +510,6 @@ class FFmpegSubtitlesConvertorPP(FFmpegPostProcessor):
                     f.write(srt_data)
                 old_file = srt_file
 
-                ext = 'srt'
                 subs[lang] = {
                     'ext': 'srt',
                     'data': srt_data