anchor.diff: -{ stdenv, fetchurl, pkgconfig, yasm, bzip2, zlib
  +{ stdenv, fetchurl, pkgconfig, yasm, bzip2, zlib, perl
   , mp3Support    ? true,   lame      ? null
   , speexSupport  ? true,   speex     ? null
   , theoraSupport ? true,   libtheora ? null
  
positive.code:       description = "A complete, cross-platform solution to record, convert and stream audio and video (fork of ffmpeg)";
        license = with licenses; if enableUnfree then unfree #ToDo: redistributable or not?
          else if enableGPL then gpl2Plus else lgpl21Plus;
        platforms = platforms.linux;
        maintainers = [ maintainers.vcunat ];
      };
    }; # libavFun
  
  in result
  
  
negative.code:       "--enable-avplay"
        "--enable-shared"
        "--enable-runtime-cpudetect"
        "--cc=cc"
      ]
        ++ optionals enableGPL [ "--enable-gpl" "--enable-swscale" ]
        ++ optional mp3Support "--enable-libmp3lame"
  