A self-described "throwback carnival" that has toured the world on the popularity of its music videos that have given the band huge followings on YouTube and Facebook, Scott Bradlee’s Postmodern Jukebox offers a range of clever covers, including a woozy take on “All About That Bass” and a particularly soulful rendition of Beyonce's "Halo." The group performs tonight at 7 at the Agora.