diff --git a/youtube_dlc/extractor/dispeak.py b/youtube_dlc/extractor/dispeak.py
index c345e0274..22bdc5635 100644
--- a/youtube_dlc/extractor/dispeak.py
+++ b/youtube_dlc/extractor/dispeak.py
@@ -93,6 +93,7 @@ class DigitallySpeakingIE(InfoExtractor):
             'quality': -2,
             'preference': -2,
             'format_id': 'slides',
+            'acodec': 'none',
         })
         speaker_video_path = xpath_text(metadata, './speakerVideo', fatal=True)
         formats.append({