It will depend on lots of factors. Commercial filming for advertising or movies will normally require a permit. If you have to inconvenience the public, you may have to get some permits and pay for crowd control and security. You may also need film releases for people who are on screen. Check the local laws for the place you are going to be.
For news and private use there is normally no license required.
The duration of Private Fears in Public Places - film - is 2 hours.
Private Fears in Public Places - film - was created on 2006-11-22.
The duration of Cops - film - is 1080.0 seconds.
Shooting the Police Cops on Film - 2006 TV was released on: USA: 1 July 2006
It depends. You can film people without their knowledge in public places or places where there is no expectation of privacy. Filming a person in their home without their knowledge would probably be considered criminal stalking.
The duration of In Public - film - is 1800.0 seconds.
That's illegal
Script Cops - 2007 was released on: USA: 1 March 2007 (Beverly Hills Shorts Film Festival) USA: 15 April 2007 (Wisconsin Film Festival)
In Public - film - was created on 2001-04-28.
Campus Cops - 2010 was released on: USA: 17 April 2010 (LA Comedy Shorts Film Festival)
The duration of The Public Eye - film - is 1.65 hours.
The duration of Public Domain - film - is 1.5 hours.