As the 45th annual Comic-Con International 2014 began, Warner Bros. Television hosted their Preview Night event Wednesday, screening pilot episodes of debuting television series. This year, two shows based on comic book characters were screened: "The Flash" and "Constantine."

A third pilot from the new "iZombie" was set for viewing Wednesday, but pulled out of the screening due to casting problems. Warner Bros. publicists assured that a 15-minute clip would be added to the scheduled panel with the show's stars.

To make up for the "iZombie" drop out, Comic-Con organizers played "The Flash" episode twice. The audience seemed receptive to the premise, applauding each time the show paused during a would-be commercial break.

"The Flash," based on the comic book superhero who is the fastest man alive, features Grant Gustin ("Arrow") as the title character, Barry Allen. The show was created by the same team behind the reinterpreted Green Arrow series "Arrow": executive producers Greg Berlanti and Andrew Kreisberg along with director David Nutter.

During the pilot, a cameo from Stephen Amell, the lead actor on "Arrow," and an appearance from the original television Flash, John Wesley Shipp, both drew cheers from the Comic-Con audience. The episode deals a lot in exposition to bring viewers up to speed on characters' backgrounds and superpower abilities.

"The Flash" is set to premiere this fall Tuesdays 8/7c on The CW.

Adapted from the comic book "Hellblazer," Constantine is a darker character than the all-American Flash. The show, starring "Criminal Minds" actor Matt Ryan, follows John Constantine dealing with the supernatural world to investigate issues beyond the human world.

This adaptation of the comic, which was also made into a 2005 film starring Keanu Reeves, had Comic-Con audiences a bit quieter than "The Flash" premiere. According to one attendee, viewers responded well to easter eggs throughout the episode, little story or character details included for devoted fans.

"Constantine" will premiere Fridays 10/9c starting Oct. 24 on NBC.