The Comic Book Cast YouTube put these together from what looks to be various sources (reddit, 4chan, speculation, etc).
The Avengers: Infinity War rumors:
The original plan was for The Avengers: Infinity War to be divided into two parts, but Joe and Anthony Russo preferred a standalone movie.
The Avengers: Infinity War centers on the Avengers trying to prevent Thanos from assembling the Infinity Gauntlet.
Thanos arrives on Earth to reclaim the Mind Stone from Vision and the Time Stone from Doctor Strange leading to a "vicious battle."
Black Panther directly leads into The Avengers: Infinity War.
The Avengers will still be split at the start of Avengers: Infinity War and will have to learn to work together to stop Thanos.
Heroes expected include: Captain America, Iron Man, Thor, Hulk, Hawkeye, Black Widow, Scarlet Witch, Vision, Winter Soldier, Black Panther and Doctor Strange.
Guardians of the Galaxy arrive to help the Avengers in the third act of Avengers: Infinity War.
While the rumors don't specifically mention Spider-Man, it's speculated Spider-Man will be featured in some sort of New York battle.
Vision will die early in Avengers: Infinity War and the Mind Stone will be taken.
Carol Danvers gets introduced as a soldier helping the Avengers fending off an attack from Thanos.
The movie ends with Thanos appearing to look defeated, but returns with a fully powered Infinity Gauntlet in Avengers 4.
Tom Hiddleston's Loki will appear in Avengers: Infinity War and Avengers 4 as Thanos' adviser (my note: Maybe taking the role of Mephisto from the comics?) while secretly conspiring against Thanos.
Thanos will have a large army, the Deviants, to battle Earth and the Avengers.
Scarlet Witch will be pivotal in defeating Thanos.
Rumored titles for Avengers 4: Thanos Imperative, Thanos War, Infinity Crusade.
The Avengers: Infinity War and Avengers 4 conclude the stories from the previous phases of the MCU all the way back to Iron Man while planting the seeds for the next Marvel movies.
Watch more of The Avengers: Infinity War rumors below.
The Avengers: Infinity War has a May 4, 2018 release directed by Joe and Anthony Russo starring Josh Brolin as Thanos.