Whedon and Spurlock's film will focus on a group of 'superfans', following them for a few months before the convention and at the event itself, reports E! Online.
Whedon is a regular attendee at Comic-Con and Spurlock was also present last year, recruiting fans for his Simpsons 20th anniversary documentary.
Spurlock is also currently working on a comic titled Supersized: Strange Tales From a Fast Food Culture for Dark Horse.
The documentary's superfans have yet to be cast.