Also allow qmin/qmax to go up to 69 (the current max value for libx264). This
will have to increase when we add 9/10-bit support.
(cherry picked from commit c7ac200d15)
Not 100% accurate, since not all x264 options have ffmpeg equivalents yet.
Patch by Lou Logan.
Originally committed as revision 22144 to svn://svn.ffmpeg.org/ffmpeg/trunk
