As a side note, this opera has a fantastic German name: Schwanda der Dudelsackpfeifer.
Extensive article on Weinberger at the Orel Foundation, a group dedicated to uncovering neglected works of 20th century composers.
Description and plot synopsis of Schwanda the Bagpiper at boosey.com.
Link to the Naxos CD recording of the opera, as well as a thoughtful article about it and the composer.
Finally, some videos. First, William D. Revelli and the University of Michigan Symphony Band from 1965:
Then a Cincinnati Pops version under Erich Kunzel. Be aware that it’s slightly different in form from what we’re playing and is in a different key with one different modulation in the fugue as well. And of course it’s for orchestra.