Not a lawyer either, but...
It probably makes a difference if you are trying to make money off the video. If not, likely no one will bother you. If so, someone will bother you.
That said, if it is a public event, from a legal standpoint I'm not sure if someone in the audience would have a case. As long as they are just shown as spectators and not, say, portrayed badly (i.e., a caption reading "I'm a fat cow!"), if someone is in public they generally don't have a right to privacy.
However, if they threatened legal action, from a practical standpoint that would probably force you to either hire a lawyer, blur their face, or otherwise edit the video.
I would also keep any literature or print out any page which indicated that taking pictures and video was encouraged. Might mitigate the threat that a model would sue you, they should also have to go after the event promoters.