diff --git a/youtube_dl/YoutubeDL.py b/youtube_dl/YoutubeDL.py
index e34b36016..61675d8ec 100755
--- a/youtube_dl/YoutubeDL.py
+++ b/youtube_dl/YoutubeDL.py
@@ -203,6 +203,7 @@ class YoutubeDL(object):
 
                        Progress hooks are guaranteed to be called at least once
                        (with status "finished") if the download is successful.
+    merge_output_format: Extension to use when merging formats.
 
 
     The following parameters are not used by YoutubeDL itself, they are used by
@@ -909,6 +910,10 @@ def process_video_result(self, info_dict, download=True):
                                                   'contain the video, try using '
                                                   '"-f %s+%s"' % (format_2, format_1))
                                 return
+                            output_ext = (
+                                formats_info[0]['ext']
+                                if self.params.get('merge_output_format') is None
+                                else self.params['merge_output_format'])
                             selected_format = {
                                 'requested_formats': formats_info,
                                 'format': rf,
@@ -921,6 +926,7 @@ def process_video_result(self, info_dict, download=True):
                                 'vbr': formats_info[0].get('vbr'),
                                 'acodec': formats_info[1].get('acodec'),
                                 'abr': formats_info[1].get('abr'),
+                                'ext': output_ext,
                             }
                         else:
                             selected_format = None
diff --git a/youtube_dl/__init__.py b/youtube_dl/__init__.py
index 844992d8e..b4ae35a2b 100644
--- a/youtube_dl/__init__.py
+++ b/youtube_dl/__init__.py
@@ -166,6 +166,9 @@ 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)
     else:
@@ -323,6 +326,7 @@ def _real_main(argv=None):
         'encoding': opts.encoding,
         'exec_cmd': opts.exec_cmd,
         'extract_flat': opts.extract_flat,
+        'merge_output_format': opts.merge_output_format,
         'postprocessors': postprocessors,
     }
 
diff --git a/youtube_dl/options.py b/youtube_dl/options.py
index feaca03a3..0ed5e3db4 100644
--- a/youtube_dl/options.py
+++ b/youtube_dl/options.py
@@ -302,6 +302,12 @@ def _hide_login_info(opts):
         '--youtube-skip-dash-manifest',
         action='store_false', dest='youtube_include_dash_manifest',
         help='Do not download the DASH manifest on YouTube videos')
+    video_format.add_option(
+    	'--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) '
+            'Ignored if no merge is required'))
 
     subtitles = optparse.OptionGroup(parser, 'Subtitle Options')
     subtitles.add_option(