Add 'm4a' to the default audio formats

youtube_dl_gui/optionsmanager.py

@@ -258,7 +258,7 @@ class OptionsManager(object):
             'main_win_size': (710, 490),
             'opts_win_size': (640, 470),
             'selected_video_formats': ['webm', 'mp4'],
-            'selected_audio_formats': ['mp3', 'vorbis'],
+            'selected_audio_formats': ['mp3', 'm4a', 'vorbis'],
             'selected_format': '0'
         }