SPOILERS.
Some scenes might be missing or out of order.
Trailer begins with a shot of the chaotic scenes in the city, just like at the end of the previous movie. People are running and shouting. As we hear Tony Stark's quote from Avengers:
"If we can't protect the Earth, you can be damn well sure we'll avenge it."
We see shots of Hawkeye's house, Hawkeye is looking at something he can't believe.
A brief shot of M'Baku.
In Wakanda, the remaining Avengers are all broken and miserable. Rhodes says, "What's the plan, Cap? What do we do?"
Cap says nothing.
Fade into black, then out to Thanos with the damaged Gauntlet and a sword, looking at something. He says something about his destiny and fate as we move to a close up shot of Tony Stark, looking at something with a fierce expression in his eyes, he looks like he has not slept at all, we see his face, Pepper with a worried expression, and then the camera turns, and we see that he is staring at a whole army of suits in front of him.
Thor walking around a place that is dark and fiery.
Brief shots of Captain Marvel in action.
Then a shot of Ant-Man flying in the Quantum Realm at the high speed, shouting. Someone, probably Tony's voice: "There's no other way. We have to do this..."
THIS MAY
A blast of light, Cap and Thor using the Stormbreaker portal. Brief shots of the Guardians' ship at Vormir cliff.
Rocket, Tony Stark and Shuri are arguing about something where Shuri makes a arrogant statement, Rocket gives her a counter, and then Stark says something which shuts both of them up.
Ant-Man opens his eyes, finds himself near his house. He goes inside, expecting his daughter, but the door is opened by a teenager. "Cassie?"
WITNESS THE CULMINATION
Thor blasts lightning, fights monsters, still in the dark place. Someone's voice is heard off screen. "You're late."
Tony presses a button, and we see what appears to be BARF loading a scene, but it seems to be real, because then we see brief shots from Avengers, including shots of Tony Stark dressed in SWAT gear, and the previous movies shown from different angles including them fighting aliens in the Battle of New York, then robots in Ultron, and then again fighting aliens in Wakanda, similarly framed as in the Captain Marvel trailer.
OF THE UNIVERSE
Brief shots of Black Widow and Rhodey looking at their surroundings in the city.
A very angry Hulk leaping at the camera, towards an armored Thanos in what appears to be the first scene of Infinity War from a different angle.
A slow shot showing off Hawkeye in his new avatar, fighting ninjas.
Captain Marvel fighting someone, using her powers.
Thanos returning to Earth. A scene of a bloody faced Captain America standing alone in front of Thanos, as they are surrounded by fallen heroes, some familiar, some unfamiliar. "Noble sentiments from one who is about to die..." says Thanos.
Thor charging in with his army from Hel.
An older, light haired Tony Stark shouting something in desperation, "NO!"
Loud music, a shot of the fully equipped, but still burnt Gauntlet, presumably in Thanos' hands. As the music builds up, a zooming in, close up shot of Thanos, eyes, transitioning into silhouettes of the Avengers as the theme plays. The Space Stone disappears.
TITLE REVEAL.
The Guardians' Ship lands in Wakanda, as Tony comes out, broken and wounded, he notices Cap.
"Cap?"
"Tony?"
End trailer.