--embed-subs now implies --write-sub

--write-sub was needed to generate a video file with embed subtitles anyway, so
we simplify the interface

youtube_dl/__init__.py

@@ -280,6 +280,7 @@ def _real_main(argv=None):
             'format': opts.convertsubtitles,
         })
     if opts.embedsubtitles:
+        opts.writesubtitles = True # Required to generate a final file with embed subtitles
         postprocessors.append({
             'key': 'FFmpegEmbedSubtitle',
         })

youtube_dl/options.py

@@ -805,7 +805,7 @@ def parseOpts(overrideArguments=None):
     postproc.add_option(
         '--embed-subs',
         action='store_true', dest='embedsubtitles', default=False,
-        help='Embed subtitles in the video (only for mp4, webm and mkv videos)')
+        help='Embed subtitles in the video (only for mp4, webm and mkv videos), implies --write-sub')
     postproc.add_option(
         '--embed-thumbnail',
         action='store_true', dest='embedthumbnail', default=False,