If you are posting from YouTube, Vimeo, Dailymotion or other WordPress supported website then there is no need to upload Thumbnail. But if you are going to upload .mp4 video then you must need to upload video thumbnail.
If you are posting from YouTube, Vimeo, Dailymotion or other WordPress supported website then there is no need to upload Thumbnail. But if you are going to upload .mp4 video then you must need to upload video thumbnail.