From Mile High mystery: UFO sightings in sky over Denver

Video link.

He said, “The flying objects appear around noon or 1:00 p.m. at least a couple of times a week.” The strangest part is they are flying too fast to see with the naked eye, but when we slowed down the video, several UFOs appear.
We altered the color contrast to make it easier to see. You can take a look for yourself by watching the video clip.
We wanted to verify the video we saw was legitimate and not doctored in anyway. So our photojournalist set up his camera in the same spot, and shot video from just before noon until just after 1:00 p.m. He also captured something unexplained on video.

(emphasis mine)