Check out Sam Tsui & Kurt Schneider's cover of "I Knew You Were Trouble."

Watch the original video from Taylor Swift:

Check out Against The Current's pop-rock cover of "All I Want For Christmas Is You":

Watch the original video from Mariah Carey:

Check out Tyler Ward and Alex G's cover of "Ho Hey":

Watch the original video from the Lumineers below.

Check out Peter's innovative one-man cover of Philllip Phillips' hit song:

Watch the original video from Phillip Phillips:

Check out Hollywood Ending's cover of Justin Bieber:

Check out the original video from Justin Bieber and Nicki Minaj: