Straight No Chaser is a men's a cappella group from Indiana University, started in 1996. In 2007, a 1998 video of them singing "The 12 Days of Christmas" went viral and subsequently led to a record deal with Atlantic Records.
These are photos from concerts where Straight No Chaser played, so they may be of other bands that played the concert as well.
Straight No Chaser / Scott Bradlee's Postmodern Jukebox Jul 13, 2017 Chicago, Illinois, United States Uploaded by Rob Hanczar