HitFix Mix: Pentatonix can't cover Taylor Swift, plus who is the ultimate pop star?

Watch the HitFix Mix episode with Pentatonix: We talk to Avi Kaplan and Mitch Grassi about finding your way into a Taylor Swift song, the truth about Christmas music, avoiding old-school a cappella and more. Check out the three songs they'd recommend, each, for our HitFix Mixtape, the songs "to know."