Steps to reproduce:
2. Open a video in Thedul player that has no timeline preview images generated by Opencast, e.g. https://presentation.opencast.uni-halle.de/engage/theodul/ui/core.html?id=5d3ff574-38fd-47ed-8864-f9c2173c3917
3. Notice the error message `No valid timelinepreviews image was found. TypeError: "timelinePreview.get(...) is undefined"`
Received an error message.
Received an information or warning message, except if Opencast/Theodul will not support missing timeline preview images in future. In that case, however, how can we regenerate the missing images for all episodes?
Workaround (if any):