[options] PEP8 and simpler --merge-output-format handling (#4673)

youtube_dl/__init__.py

@@ -166,8 +166,6 @@ def _real_main(argv=None):
     if opts.recodevideo is not None:
         if opts.recodevideo not in ['mp4', 'flv', 'webm', 'ogg', 'mkv']:
             parser.error('invalid video recode format specified')
-    if opts.merge_output_format is not None and not '+' in opts.format: #if merge format output is used on videos that don't require merging, ignore
-        opts.merge_output_format = None
 
     if opts.date is not None:
         date = DateRange.day(opts.date)

youtube_dl/options.py

@@ -306,7 +306,7 @@ def parseOpts(overrideArguments=None):
         '--merge-output-format',
         action='store', dest='merge_output_format', metavar='FORMAT', default=None,
         help=(
-            'If a merge is required (e.g. bestvideo+bestaudio), output to given container format (e.g. mkv, mp4, ogg, webm, flv) '
+            'If a merge is required (e.g. bestvideo+bestaudio), output to given container format. One of mkv, mp4, ogg, webm, flv.'
             'Ignored if no merge is required'))
 
     subtitles = optparse.OptionGroup(parser, 'Subtitle Options')