Thanks for the posting.
At the moment, there's no thumbnail modification yet available for the exported videos. Though it may be part of a future update.
If you have any suggestions or feature requests that you would want to see in the software in the future, just head on over to the link below and send over your suggestions to our developers:
Hi, if you upload direct to FB you can select the slide you want to display as the Thumbnail.
Alan T. Richardson
Is there a way to include a stile frame of a video clip? When I created my first video and emailed/posted (on FB), the video appears as a black box. It would be nice to be able to have a visual heading or a shot of the first or last frame so that it doesn't appear as a huge black rectangle. Any advice or is there a workaround to accomplishing my request?