diff --git a/filter.php b/filter.php
index bc2f70852383d9d3a580d969b0f90cef63ad0982..17971e4cd2bc848119e23bca4e5bb8b825b192fb 100644
--- a/filter.php
+++ b/filter.php
@@ -119,6 +119,10 @@ class filter_opencast extends moodle_text_filter
                             $mustachedata = new stdClass();
                             $mustachedata->playerid = 'ocplayer_' . $i++;
                             $mustachedata->configurl = get_config('filter_opencast', 'configurl_' . $ocinstance->id);
+                            if (strpos($mustachedata->configurl, 'http') === false) {
+                                $mustachedata->configurl = (new moodle_url($mustachedata->configurl))->out();
+                            }
+
                             $mustachedata->data = json_encode($data);
                             $mustachedata->width = $width;
                             $mustachedata->height = $height;