The trailer is basically President Snow giving a speech on Capitol TV saying:
"Since the dark days, our great nation has known only peace. Ours is an elegant system, conceived to nourish and protect. Your districts are the body, the Capitol is the beating heart. Your hard work feeds us, and in return we feed and protect you. But if you resist the system, you starve yourself. If you fight against it, it is you who will bleed. I know you will stand with me, with us, with all of us, together, as one. Panem today, Panem tomorrow, Panem forever."
His speech is actually a threat to Katniss and the districts. "Your districts are the body, the Capitol is the beating heart." Basically he says don't try to get free or you will die. "If you fight against it, it is you who will bleed." In other words "Dear Katniss, I will kill you." By "Panem today, Panem tomorrow, Panem forever." we all know he means Panem will last and reign for all of time.
When the speech starts, we can see only President Snow's face but when the camera turns around we can see a man standing by him. We think it's probably one of the bodyguards but then we see; it's Peeta. Which must mean that they have captured him. What is he doing at the side of Snow? The world knows that he loves Katniss and the world also knows that Katniss is against Snow. This must mean that President Snow wants Panem to think that they divorced, or parted ways in some way or another.
During the broadcast three words appear while Snow is talking. Unity. We can understand that he wants the districts to remain united with Panem. Prosperity. He wants to make people believe that they are in a good economical situation. Even though most districts starve like 12 did when it existed. Sacrifice. Here comes the complicated part. Why the heck would he mention sacrifice? The only sacrifice made was the Hunger Games, something that is hated by the districts.
Something I would also like to point out is the fact that Peeta doesn't look at the camera until the last few seconds of the clip. I'm not really sure what they want to say with this. However I have theory that it's a message to Katniss that he doesn't care anymore, which is probably created by Snow.
Here's the trailer in case you didn't see it:
Dear people who read the book. Please be respectful while commenting and don't spoil the story. Thank you!