[YoutubeDL] Do not force bestvideo+bestaudio when outtmpl is stdout (#5627)

youtube_dl/YoutubeDL.py

@@ -1086,7 +1086,9 @@ class YoutubeDL(object):
         req_format = self.params.get('format')
         if req_format is None:
             req_format_list = []
-            if info_dict['extractor'] in ['youtube', 'ted'] and FFmpegMergerPP(self).available:
+            if (self.params.get('outtmpl', DEFAULT_OUTTMPL) != '-'
+                    and info_dict['extractor'] in ['youtube', 'ted']
+                    and FFmpegMergerPP(self).available):
                 req_format_list.append('bestvideo+bestaudio')
             req_format_list.append('best')
             req_format = '/'.join(req_format_list)