Added new option '--only-srt' to download only the subtitles of a video

Improved option '--srt-lang'
 - it shows the argument in case of missing subtitles
 - added language suffix for non-english languages (e.g. video.it.srt)

test/test_youtube_subtitles.py

@@ -53,5 +53,12 @@ class TestYoutubeSubtitles(unittest.TestCase):
         info_dict = IE.extract('QRS8MkLhQmM')
         self.assertEqual(md5(info_dict[0]['subtitles']), '164a51f16f260476a05b50fe4c2f161d')
 
+    def test_youtube_onlysubtitles(self):
+        DL = FakeDownloader()
+        DL.params['onlysubtitles'] = True
+        IE = YoutubeIE(DL)
+        info_dict = IE.extract('QRS8MkLhQmM')
+        self.assertEqual(md5(info_dict[0]['subtitles']), '4cd9278a35ba2305f47354ee13472260')
+
 if __name__ == '__main__':
     unittest.main()

youtube_dl/FileDownloader.py

@@ -79,6 +79,7 @@ class FileDownloader(object):
     writedescription:  Write the video description to a .description file
     writeinfojson:     Write the video description to a .info.json file
     writesubtitles:    Write the video subtitles to a .srt file
+    onlysubtitles:     Downloads only the subtitles of the video
     subtitleslang:     Language of the subtitles to download
     test:              Download only first bytes to test the downloader.
     keepvideo:         Keep the video file after post-processing
@@ -443,9 +444,13 @@ class FileDownloader(object):
             # that way it will silently go on when used with unsupporting IE
             try:
                 srtfn = filename.rsplit('.', 1)[0] + u'.srt'
+                if self.params.get('subtitleslang', False):
+                    srtfn = filename.rsplit('.', 1)[0] + u'.' + self.params['subtitleslang'] + u'.srt'
                 self.report_writesubtitles(srtfn)
                 with io.open(encodeFilename(srtfn), 'w', encoding='utf-8') as srtfile:
                     srtfile.write(info_dict['subtitles'])
+                if self.params.get('onlysubtitles', False):
+                    return 
             except (OSError, IOError):
                 self.trouble(u'ERROR: Cannot write subtitles file ' + descfn)
                 return

youtube_dl/InfoExtractors.py

@@ -228,6 +228,7 @@ class YoutubeIE(InfoExtractor):
         """Indicate the download will use the RTMP protocol."""
         self._downloader.to_screen(u'[youtube] RTMP download detected')
 
+
     def _extract_subtitles(self, video_id):
         self.report_video_subtitles_download(video_id)
         request = compat_urllib_request.Request('http://video.google.com/timedtext?hl=en&type=list&v=%s' % video_id)
@@ -246,7 +247,7 @@ class YoutubeIE(InfoExtractor):
         else:
             srt_lang = list(srt_lang_list.keys())[0]
         if not srt_lang in srt_lang_list:
-            return (u'WARNING: no closed captions found in the specified language', None)
+            return (u'WARNING: no closed captions found in the specified language "%s"' % srt_lang, None)
         params = compat_urllib_parse.urlencode({
             'lang': srt_lang,
             'name': srt_lang_list[srt_lang].encode('utf-8'),
@@ -483,6 +484,10 @@ class YoutubeIE(InfoExtractor):
 
         # closed captions
         video_subtitles = None
+        if self._downloader.params.get('subtitleslang', False):
+            self._downloader.params['writesubtitles'] = True
+        if self._downloader.params.get('onlysubtitles', False):
+            self._downloader.params['writesubtitles'] = True
         if self._downloader.params.get('writesubtitles', False):
             (srt_error, video_subtitles) = self._extract_subtitles(video_id)
             if srt_error:

youtube_dl/__init__.py

@@ -176,6 +176,9 @@ def parseOpts():
     video_format.add_option('--write-srt',
             action='store_true', dest='writesubtitles',
             help='write video closed captions to a .srt file (currently youtube only)', default=False)
+    video_format.add_option('--only-srt',
+            action='store_true', dest='onlysubtitles',
+            help='downloads only the subtitles of the video (currently youtube only)', default=False)
     video_format.add_option('--srt-lang',
             action='store', dest='subtitleslang', metavar='LANG',
             help='language of the closed captions to download (optional) use IETF language tags like \'en\'')
@@ -450,6 +453,7 @@ def _real_main():
         'writedescription': opts.writedescription,
         'writeinfojson': opts.writeinfojson,
         'writesubtitles': opts.writesubtitles,
+        'onlysubtitles': opts.onlysubtitles,
         'subtitleslang': opts.subtitleslang,
         'matchtitle': decodeOption(opts.matchtitle),
         'rejecttitle': decodeOption(opts.rejecttitle),