When uploading a video to an asset field you have no control over the thumbnail/poster frame that mux generates. In many cases the thumbnail chosen is less than ideal or completely unusable. This can be especially annoying when using videos as autoplayed backgrounds.
Currently I’m creating image fields that I use to pass a custom screenshot to the video thumbnail. It would be much more ideal to either choose the video frame, or upload an image to use as the poster inside the asset field instead of having two fields for a video.