Apparently you can’t, but have to run $ x264 –fullhelp
or some odd.
They fixed it for me!
$ ffmpeg -i something -vcodec libx264 -preset help -tune help -profile:v help yo.avi
[libx264 @ 02142b80] Possible presets: ultrafast superfast veryfast faster fast medium slow slower veryslow placebo
[libx264 @ 02142b80] Possible tunes: film animation grain stillimage psnr ssim fastdecode zerolatency
But not for profile, FWIW.
NB that this isn’t all the possible presets, because there are “some” that are file-based, external still, as well:
like ipod ones.
This cheat sheet might help: