currently, for some bizarre reason, if a user uploads, a video to dropbox, the thumbnail attached to the video becomes a random screen frame approximately eight seconds into the video, rather than the first image of the video. Thus, if you make a video and wish to share it with others from your dropbox, the thumbnail that attaches to it will be some random unintended thumbnail. This is sub optimal programming, and dropbox says that they will correct it if enough users request it. please vote to make the thumbnail assigned as the first frame of an uploaded video.