[youtube] Fix relative URLs in description

youtube_dl/extractor/youtube.py

@@ -1630,7 +1630,7 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
                     class="[^"]*"[^>]*>
                 [^<]+\.{3}\s*
                 </a>
-            ''', r'\1', video_description)
+            ''', lambda m: compat_urlparse.urljoin(url, m.group(1)), video_description)
             video_description = clean_html(video_description)
         else:
             fd_mobj = re.search(r'<meta name="description" content="([^"]+)"', video_webpage)