I recall seeing a trailer for a film a while back, sometime in the last 2 years, and was wondering which film it was for. I recall it being a found footage-style film, that centered on a group of teenagers using a time machine. The trailer had some sort of party, I think it was a birthday party. I recall the trailer ending with the camera showing one of the time traveling kids seeing themselves in a mirror, which I think was from the camera's point of view. I think the twist was that this was at that person's birthday party, when they were younger, so it was a record that they'd traveled back in time.
Which film was this?