I'm an open source maintainer and I have never been in a situation where someone filing a security issue will withhold indefinitely, nor would I ever think of asking them to withhold forever. If there are some complications maybe we can discuss a delayed disclosure but ffmpeg is just complaining about the whole concept of delayed disclosures which seems really immature to me.

As a user of ffmpeg I would definitely want to know this kind of information. The responsibility the issue filer has is not to the project, but to the public.