I would honestly put money on a MetallicaFest or something similar. Obviously because in the video it lists every festival they played and why else only list festivals they played at instead of cities? Plus if it ended up being "But you've never seen them... in 3D" it would be stupid because the people that have seen them live actually did see them in 3D.
05/24-05/26 - Maryland Deathfest
06/01 - Bolt Thrower