About five minutes of new footage was shown at an event in Las Vegas; and it suggests Captain Marvel may play a bigger role than everyone thought.
www.gamespot.com
According to The Hollywood Reporter, Disney showed "several minutes" of the movie, and one scene showed Captain Marvel (Brie Larson) telling the Avengers that they plan to kill Thanos. They might not have succeeded in Infinity War, but Captain Marvel says in the new footage, "Before, you didn't have me."
Captain Marvel the character is incredibly powerful, so she'll no doubt be able to help the Avengers in whatever plan they've come up with. Her debut in the MCU was teased in an after-credits scene of Avengers: Infinity War before getting her own solo film this year--marking Marvel's final movie before the release of Endgame.
Also in the new footage, Captain America (Chris Evans) loses his subdued attitude and bluntly states about Thanos, "Let's get that son of a bitch."
ComicBook also saw the footage, and the site reports that the footage included Nebula saying she knows where Thanos is, and that Captain Marvel has a cocky attitude and believes Thanos has never faced someone as powerful as her. Captain Marvel also apparently talks about wanting to use the Infinity Stones to undo Thanos' snap.