> can I express "any version of ffmpeg"? No, this would go against the goals of Guix: packages can't depend on properties of the environment they'll end up in (if any).
They must be self-contained, or use standard features like $PATH et al to find optional dependencies at run time, but these will have to be provided by the user/manifest/whatever. Sorry, T G-R Sent on the go. Excuse or enjoy my brevity.
