I was rendering a video in ffmpeg and accidentally pressed "shift" and "+", and the below started happening.
Don't worry, all you did is increase verbosity. The Shift had no effect, but the + increased it. Press - to cycle back to a lower verbosity level.
Press ? to see a list of all available commands.
If you want to not worry about accidental keypresses, you can add
-nostdin to the command. Don't do this if one of your inputs is a pipe.