You will need to install a user script manager extension to install this script.
Show the remaining time of a YouTube video right inside the player.
Even works for embedded videos, and videos that last longer than a day!
Unless otherwise configured, the remaining time displayed is the video's duration minus the current time. This does not account for playback rate. If you'd like to show the real remaining time, i.e. display a remaining time 2 times longer when the playback rate is set to 0.5x (for example), edit the configuration line at the top of the script.