[YoutubeDL] don't default to 'bestvideo+bestaudio/best' for live videos

Doesn't work currently.

youtube_dl/YoutubeDL.py

@@ -1104,7 +1104,8 @@ class YoutubeDL(object):
         if req_format is None:
             req_format_list = []
             if (self.params.get('outtmpl', DEFAULT_OUTTMPL) != '-' and
-                    info_dict['extractor'] in ['youtube', 'ted']):
+                    info_dict['extractor'] in ['youtube', 'ted'] and
+                    not info_dict.get('is_live')):
                 merger = FFmpegMergerPP(self)
                 if merger.available and merger.can_merge():
                     req_format_list.append('bestvideo+bestaudio')