Pentatonix uploaded its version of "Little Drummer Boy" to YouTube a week ago.
As of Tuesday morning, the video had 8.3 million views.
The five-person a cappella group won the third season of NBC's competition series "The Sing-Off" in 2011 and have since become YouTube stars, with more than 2 million subscribers and more than 14 million people having watched their recent viral Daft Punk cover video.
The group, from Arlington, Texas, is five vocalists: Scott Hoying, Kirstie Maldonado, Mitch Grassi, Avi Kaplan and Kevin Olusola.
The Daft Punk cover video
| Keith Robison, The Star