Filming is legal. In public spaces (streets, parks), there is no "reasonable expectation of privacy." You do not need permission to point a camera. The exceptions are usually for offensive or harassing type of filming.

Publishing is regulated. In EU, once you share the footage , you are "processing personal data" under GDPR. There are also exceptions where publishing without permission is legal. Legitimate Interest (security footage or incidental background), Public Interest/Journalism, and Artistic Expression.

Generally you must ask permission to publish, not to film. Although asking permission to film is good ethical principle too.