SAN DIEGO (CNS) - Oscar award-winning director Steven Spielberg will be in downtown San Diego Friday to discuss his forthcoming film when he makes his first-ever appearance at a session of Comic-Con International.

Spielberg is scheduled to attend the wildly popular annual trade show to discuss his forthcoming motion-capture release, "The Adventures of Tintin."

The project -- based on one of the most popular European comics of the 20th century -- uses a technique in which actors' movements are recorded and translated into digital animation, such as in the 2009 film, "Avatar."

Comic-Con Thursday kicked off its sold-out four-day run, during which time it is expected to attract 126,000 people.

Other highlights on tap for today include a forum on the HBO program, "True Blood;" appearances by the developers of the"Lego Star Wars" video game; William Shatner and the captains of "Star Trek;" and a presentation on the state of the comic book industry.

Comic-Con started in 1970 as a modest comic book fair and has since grown into a premier pop culture extravaganza for the fantasy-minded.

Due to Comic-Con's popularity, the Metropolitan Transit Service is offering extra trolley service through Sunday. The agency is also offering two special four-day rider passes, one for $15 that includes unlimited trolley and bus service and one for $50 that also includes unlimited access to the Coaster train.