diff --git a/server.py b/server.py
index abf6f4eb6f1aed1af5f2aca9505fd26c8116269d..acb24bd063e4bad3a502ff1a018af12d290ae77e 100644
--- a/server.py
+++ b/server.py
@@ -14,6 +14,7 @@ from socket import gethostname
 from ipaddress import ip_address, ip_network
 import math
 import locale
+import base64
 
 locale.setlocale(locale.LC_ALL, 'de_DE.utf8')
 
@@ -28,6 +29,7 @@ app.add_template_global(gethostname, name='gethostname')
 app.add_template_global(min, name='min')
 app.add_template_global(max, name='max')
 
+
 scheduler = sched.scheduler()
 def run_scheduler():
 	import time
@@ -132,6 +134,10 @@ def evalperm(perms):
 		return cperms
 	return [{'type': 'public'}]
 
+@app.template_filter()
+def base64encode(str):
+	return base64.b64encode(str.encode('UTF-8')).decode('UTF-8')
+
 @app.template_filter()
 def checkperm(perms, username=None, password=None):
 	if ismod():
diff --git a/templates/changelog.html b/templates/changelog.html
index ec76f038edc3d029c09f26a59bd09bdd8e1fe89f..87db02fbf6d8071905153c5ad486fb83fd37ebae 100644
--- a/templates/changelog.html
+++ b/templates/changelog.html
@@ -47,7 +47,7 @@
 						<td style="white-space: nowrap;">{{i.path}}</td>
 						<td>"{{i.value_old}}"</td>
 						<td>"{{i.value_new}}"</td>
-						<td><button onclick="moderator.api.set('{{i.path}}','{{i.value_old}}');alert('done');" class="btn btn-default">undo</button></td>
+						<td><button onclick="moderator.api.set('{{i.path}}',atob('{{i.value_old|base64encode }}'));alert('done');" class="btn btn-default">undo</button></td>
 					</tr>
 				{% endfor %}
 			</table>
diff --git a/templates/lecture.html b/templates/lecture.html
index a5e0a07c6515b8be76e875393441b26ca590aab3..c7d38a3bdf7b8d210fdfb7da9a84a16d36c30199 100644
--- a/templates/lecture.html
+++ b/templates/lecture.html
@@ -13,7 +13,7 @@
 {% block header %}
 {{ super() }}
 
-	<meta property="og:image" content="{{ config.VIDEOPREFIX }}/{{ lecture['titlefile'] }}" />
+	<meta property="og:image" content="{{ config.VIDEOPREFIX }}/thumbnail/l_{{lecture.id}}.jpg" />
 	<meta property="og:title" content="{{ course.title }}: {{ lecture.title}}" />
 	<meta property="og:description" content="{{ lecture.comment }}" />
 {% endblock %}