Professional actors and wannabe rock legends Jack Black and Jason Segel were filming 'Gulliver's Travels' (opening Dec. 22) when they were apparently overcome with Christmas spirit and decided to go into the recording studio.

It's no glossy 'Glee' duet, but the pair bring gritty gusto to their harmonious cover of Bing Crosby and David Bowie's 1977 single 'Peace on Earth / Little Drummer Boy.' Now on sale via iTunes, the track's proceeds will benefit Blue Star Families, an organization that supports military families.

Black told Spin.com, "The original version is pretty mellow. So we delivered the sweet nectar of the rock gods."

After the jump, check out the animated music video featuring 'How I Met Your Mother' star Segel (currently shooting a new muppet movie with Amy Adams) singing his heart out for the holidays in his new duet with 'Tenacious D' veteran Black.