It's my right to demand that.
(This does not mean that everybody conforms to the law. But people that don't would be at least liable for damages.)
Edit, to clarify: Of course you can film in public. But you're required to cut out people who didn't give explicit consent before showing the material in public or handing it over to third parties.
All of this delightful nuance goes to my previous point; there’s plenty to debate and discuss here and the whole idea of an absolute right to privacy in public is comical.
But distributing or handing over such material is limited and requires usually consent.
Please pay special attention to the second sentence of the cited paragraph.
We're talking here about rights that are derived directly form the first sentence of the German constitution!
Such right is very strong. Only in exceptional cases it can be overruled by other constitutional rights.
Details can be found for example here: https://www.prigge-recht.de/wann-darf-ich-bilder-von-anderen...