Add warning if users want to change the position of video on a timeline later
This happened in the previous version: users annotated a video and the changed the position on the timeline later. Video was moved but annotations remained on their position on the timeline. This is also still possible, because you can edit the "start time" of a video on the timeline. Maybe in the future there could be a feature which allows you to "lock" annotations to a video, so if the video gets moved, the annotations stick to their relative instead of their absolute position. As long as this is not possible we should implement a warning. Can be very simple:
Warning text: "In case you already annotated the video, you should not change the start time and its position on the Timeline! The annotations will lose their link to the video!"