After I record an mp4, the thumbnail is just black. It doesn't show part of the video like thumbnails have prior. I haven't changed any settings since when it did work. It only seems to do this if I record with, in my scene, my webcam, using the option "Video Capture Device". Why is this, and how can I alleviate this? It never used to do this before. I Googled around and couldn't find a fix to this.