Hello Doug, thanks for your comment and for using Imagination. Unfortunately what you asked is extremely difficult to code as GTK doesn't offer a native timeline widget and building it from scratch is hard indeed. I do not get any donation sadly for Imagination and the time I have to code it is not too much. Anyway, during those "lockdown days" I'm improving it. I recently added a preview timer that gets updated when the user click on a slide with the time the clicked slide starts from when previewing. Also I'm getting rid of ffmpeg run into the background by using avcodec straight away. I attached a small clip showing the preview. Keep safe, all the best to you and your family.