YouTube uses a countdown to display when a premiere starts. By looking through the minified client side studio source code, we can find the original video ID used internally for the countdown.
In fact, there are actually multiple countdown videos, because in the future, creators will be able to customize their premieres with trailers and countdown themes.
VIDEO_PREMIERE_INTRO_THEME_DEFAULT #VIDEO_PREMIERE_INTRO_THEME_INSPIRATIONAL #VIDEO_PREMIERE_INTRO_THEME_CALM #VIDEO_PREMIERE_INTRO_THEME_ENTERTAINMENT #VIDEO_PREMIERE_INTRO_THEME_PLAYFUL #VIDEO_PREMIERE_INTRO_THEME_GRUNGE #VIDEO_PREMIERE_INTRO_THEME_NATURE #VIDEO_PREMIERE_INTRO_THEME_TACTILE #VIDEO_PREMIERE_INTRO_THEME_CONTEMPORARY #VIDEO_PREMIERE_INTRO_THEME_TECHNICAL #VIDEO_PREMIERE_INTRO_THEME_MUSIC #