Merge pull request #1622 from rbrito/fix-extension

extractor: youtube: Set extension of AAC audio formats to m4a.

youtube_dl/extractor/youtube.py

@@ -236,11 +236,13 @@ class YoutubeIE(YoutubeBaseInfoExtractor, SubtitlesInfoExtractor):
         '136': 'mp4',
         '137': 'mp4',
         '138': 'mp4',
-        '139': 'mp4',
-        '140': 'mp4',
-        '141': 'mp4',
         '160': 'mp4',
 
+        # Dash mp4 audio
+        '139': 'm4a',
+        '140': 'm4a',
+        '141': 'm4a',
+
         # Dash webm
         '171': 'webm',
         '172': 'webm',