Allow users to specify an age limit (fixes #1545)

With these changes, users can now restrict what videos are downloaded by the intented audience, by specifying their age with --age-limit YEARS .
Add rudimentary support in youtube, pornotube, and youporn.

youtube_dl/extractor/common.py

@@ -54,6 +54,7 @@ class InfoExtractor(object):
     view_count:     How many users have watched the video on the platform.
     urlhandle:      [internal] The urlHandle to be used to download the file,
                     like returned by urllib.request.urlopen
+    age_limit:      Age restriction for the video, as an integer (years)
     formats:        A list of dictionaries for each format available, it must
                     be ordered from worst to best quality. Potential fields:
                     * url       Mandatory. The URL of the video file
@@ -318,6 +319,15 @@ class InfoExtractor(object):
                                         self._og_regex('video')],
                                        html, name, **kargs)
 
+    def _rta_search(self, html):
+        # See http://www.rtalabel.org/index.php?content=howtofaq#single
+        if re.search(r'(?ix)<meta\s+name="rating"\s+'
+                     r'     content="RTA-5042-1996-1400-1577-RTA"',
+                     html):
+            return 18
+        return 0
+
+
 class SearchInfoExtractor(InfoExtractor):
     """
     Base class for paged search queries extractors.

youtube_dl/extractor/pornotube.py

@@ -38,6 +38,7 @@ class PornotubeIE(InfoExtractor):
         VIDEO_UPLOADED_RE = r'<div class="video_added_by">Added (?P<date>[0-9\/]+) by'
         upload_date = self._html_search_regex(VIDEO_UPLOADED_RE, webpage, u'upload date', fatal=False)
         if upload_date: upload_date = unified_strdate(upload_date)
+        age_limit = self._rta_search(webpage)
 
         info = {'id': video_id,
                 'url': video_url,
@@ -45,6 +46,7 @@ class PornotubeIE(InfoExtractor):
                 'upload_date': upload_date,
                 'title': video_title,
                 'ext': 'flv',
-                'format': 'flv'}
+                'format': 'flv',
+                'age_restriction': age_limit}
 
         return [info]

youtube_dl/extractor/youporn.py

@@ -51,6 +51,7 @@ class YouPornIE(InfoExtractor):
         req = compat_urllib_request.Request(url)
         req.add_header('Cookie', 'age_verified=1')
         webpage = self._download_webpage(req, video_id)
+        age_limit = self._rta_search(webpage)
 
         # Get JSON parameters
         json_params = self._search_regex(r'var currentVideo = new Video\((.*)\);', webpage, u'JSON parameters')
@@ -115,7 +116,8 @@ class YouPornIE(InfoExtractor):
                 'ext': extension,
                 'format': format,
                 'thumbnail': thumbnail,
-                'description': video_description
+                'description': video_description,
+                'age_restriction': age_limit,
             })
 
         if self._downloader.params.get('listformats', None):

youtube_dl/extractor/youtube.py

@@ -1495,7 +1495,8 @@ class YoutubeIE(YoutubeBaseInfoExtractor, SubtitlesInfoExtractor):
                 'description':  video_description,
                 'player_url':   player_url,
                 'subtitles':    video_subtitles,
-                'duration':     video_duration
+                'duration':     video_duration,
+                'age_restriction': 18 if age_gate else 0,
             })
         return results