This question is probably more appropriate over on the Law Stack Exchange. But I'll post the IANAL answer here.

It likely hinges less on model releases and more on what constitutes being "in public." All of this might be different given your state and (if applicable) major metropolitan area, as many have additional restrictions on what constitutes "public" and "private" spaces. (i.e. in NYC, if there is any kind of barrier, you are "in private", even if it's just a piece of rope around an outdoor dining area.)

At least in the US, photos take in public can be used, even for commercial purposes, without an explicit release.

Probably all you need is a notification of public filming (essentially declaring it a public space for photographic/video purposes). This can be on the invitation, tickets, programs, even posted at the entrances to the venue. Merely entering the private space then constitutes consent to having the image used under the terms of that notice.

There are obvious exceptions, for example, you can't film them in any situation where privacy is universally expected—like in a changing area or washroom—without explicit consent.

As always, consult an actual lawyer who is knowledgeable in this area. Also consider the PR risk, as if you suspect your attendees will resent having their images used, you may want to go well above the legal requirements and get permission for each use.