A unit change is involved, but as AVOption parameters are now parsed with
ff_eval2(), you can use the QP2LAMBDA constant to ease the change, f.e.:
ffmpeg -i src.ext -lmin 21*QP2LAMBDA dst.ext


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@6368 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b