Writer Evan Goldberg, who has worked with the duo on Superbad, Pineapple Express and The Green Hornet, dropped the news at last year's ComicCon, and more details have now emerged.
"It's a movie about sausages in a supermarket that need to get back to their aisle before the fourth of July," Seth told Screenrant.
Evan added: "Sausage Party is our super project. Sausage Party is an idea that me, Seth and Jonah Hill came up with, and we're all going to make it. Seth and Jonah are going to be the stars and Conrad Vernon - who directed Shrek 2 and Monsters Vs Aliens - is producing it with me and Seth.
"It's a rated-R, super dirty, mockery of a Pixar movie about sausages in a supermarket that need to get back to their aisle before the fourth of July. We've written that, we've finished and are going out to studios with it now. We're very passionate about it. Sausage Party is very special to us," he continued.
Seth will next be seen on the big screen as the masked superhero in The Green Hornet alongside Jay Chou and Cameron Diaz.