create mpeg_encode parameter file on the fly


git-svn-id: https://geuz.org/svn/gmsh/trunk@16735 59c8cabf-10d6-4a28-b43f-3936b85956c4


git-svn-id: https://geuz.org/svn/gmsh/trunk@16736 59c8cabf-10d6-4a28-b43f-3936b85956c4