Forbid context menu if video is not downloadable

templates/lecture.html

@@ -90,7 +90,6 @@
 </div>
 {% endif %}
 
-
 <script>
 function hintchapterclick (src) {
 	$.ajax({
@@ -148,6 +147,12 @@ $(document).ready(function() {
 		videojs('videoplayer').currentTime($(this).data("seek-time"));
 		return false;
 	});
+	var downloadable = {{ ((videos|length > 0 and videos[0].downloadable) or ismod())|tojson }};
+	if (!downloadable) {
+		$("#videoplayer_html5_api").on('contextmenu', function(e) {
+			e.preventDefault();
+		});
+	}
 });
 </script>
 {% endblock %}