[ndriscoll]

Static linking means combining compiled object files (e.g. your program and ffmpeg) into a single executable. Loading a .so or .dll file at runtime would be dynamic linking. Invoking through a child process is not linking at all.

Basically you must allow the user to swap out the ffmpeg portion with their own version. So you can dynamically link with a .dll/.so, which the user can replace, and you can invoke a CLI command, which the user can replace. Any modifications you make to the ffmpeg code itself must be provided.