The official lineup for 2013's Bonnaroo festival was announced live via YouTube this afternoon with an exclusive, Weird Al Yankovic-hosted webcast titled "B.L.A.M!," ("Bonnaroo Live Announcement Megathon").

Weird All emceed the New York event, which took on a mock "call-in show"-type atmosphere. Throughout it, Yankovic revealed Bonnaroo 2013's biggest performers through a series of crowd-assisted skits and high jinx.

Bonnaroo 2013 Lineup: Paul McCartney, Mumford & Sons Headlining [1]

Also on hand for a performance were Roo-confirmed indie rockers Portugal. The Man, who re-took the stage in the final moments for an unexpected performance of "Canadian Idiot," with Al singing lead and playing accordion.

The hour-long webcast revealed performers at a rapid-fire pace through ridiculous games (pie eating race, bobbing-for-meat), call-ins from fans and celebrities (including Mumford & Sons and Jimmy Fallon), and a panel of Bonnaroo "staffers" who took calls from festival fans, hoping to get an early look into the lineup.

Some of those "staffers" included Bonnaroo-approved indie comics like Mike Birbiglia and Eugene Mirman.

The telethon-esque vibe had shades of the 1989 cult comedy, "VH1," in which Weird Al plays an imaginative manager trying to save a local TV station.

The biggest festival names, mostly saved for the final minutes of the hour-long web special, included Paul McCartney, Mumford & Sons, Björk, and Tom Petty & the Heartbreakers. Last but certainly not least, Weird Al himself was confirmed for a Bonnaroo performance. For a look at the complete lineup, check out Billboard's coverage of Bonnaroo 2013 [1].

The annual, four-day music-fest is slated for June 13-16 at Manchester, Tenn.