Prior to the libx264 and x264 packages being merged, it was possible to compile a headless version of ffmpeg by depending solely on libx264. Now that libx264 is part of the x264 package, there is a circular dependency between ffmpeg and x264, and it isn't possible to compile ffmpeg manually (such as to compile a headless version) without bringing in potentially unwanted graphical packages, or compiling libx264 as well.

Basically, it doesn't seem to make much sense that in order to be able to compile ffmpeg, one must already have ffmpeg installed, or be willing to also manually compile some of its dependencies.