I'm attempting to be fastidiously accurate due to all the high emotion.
The video is of the girl talking to media.
SO... she doesn't actually have the video in her possession, and (like most others on scene) is basing her 'eyewitness' description on what Mike's Friend Dorian Johnson said to the media right after the incident.
Remember, this happened in the street, on the way to the apartment complex.
It all happened very quickly so I would seriously question if anyone at all had video of the actual incident.
If there is any, the police have it, and it will eventually come out. Especially if they try to put the officer up on charges. It would and should be kept confidential until that time.