This comes from a live performance of the 1998 Broadway review of the show, that starred Brent Spiner (who most people best-known as Lt. Commander Data on Star Trek: The Next Generation) as John Adams. It's not just the opening song, "Sit Down, John," but the first five minutes of the show, including the brief overture. The footage is taken from the audience, so hardly perfect, but it's actually pretty watchable. And if you only have seen the movie, which is very well done, this nonetheless captures the vibrancy of the stage show. (The original production, in 1969, I believe, with William Daniels in the lead role is the first musical I ever saw on Broadway.)
So, curtain up. With music and lyrics by Sherman Edwards.