anchor.diff: -{ stdenv, fetchurl, pkgconfig, yasm, bzip2, zlib, perl
  +{ stdenv, fetchurl, pkgconfig, yasm, bzip2, zlib, perl, bash
   , mp3Support    ? true,   lame      ? null
   , speexSupport  ? true,   speex     ? null
   , theoraSupport ? true,   libtheora ? null
  
positive.code:       ++ optional (vpxSupport && hasPrefix "0.8." version) ./vpxenc-0.8.17-libvpx-1.5.patch
        ;
  
      preConfigure = "patchShebangs doc/texi2pod.pl";
  
      configureFlags =
        assert stdenv.lib.all (x: x!=null) buildInputs;
  
negative.code: 
      # alltools to build smaller tools, incl. aviocat, ismindex, qt-faststart, etc.
      buildFlags = "all alltools install-man";
  
  
      postInstall = ''
        moveToOutput bin "$bin"
  