It depends on which license the code is in already and what each contributor allows. If you own the copyright, completely, you can license under virtually any

It depends on which license the code is in already and what each contributor allows. If you own the copyright, completely, you can license under virtually any license, ever, at any time. Period. But if you have an open-source project with tons of contributors, well, they licensed their work under the terms of a specific license. And in the case of the GPL, it explicitly means that their contributions CANNOT be redistributed under ANY terms that conflict with the “freedoms” guaranteed to end users, etc., by the GPL. However, you can at any time release a BSD-licensed work under the GPL. This is part of why the GPL is sometimes called “viral” — once it touches you, it’s hard/impossible to escape, see? So what would have to happen would be for everyone who ever contributed to VLC to say, “Okay, I’m chill with BSD,” and the code contributed by anyone who refused to do so would need re-written e.g. in a cleanroom to avoid copyright infringement. :-/