[videolecturesnet] Fix rtmp stream glitches (Closes #4968)

youtube_dl/extractor/videolecturesnet.py

@@ -70,6 +70,7 @@ class VideoLecturesNetIE(InfoExtractor):
                 f.update({
                     'url': v.attrib['streamer'],
                     'play_path': src,
+                    'rtmp_real_time': True,
                 })
                 formats.append(f)
         self._sort_formats(formats)