anchor.diff:  , dc1394Support ? false, libdc1394 ? null
   , x11grabSupport ? false, libXext ? null, libXfixes ? null
   , playSupport ? true, SDL ? null
  +, freetypeSupport ? true, freetype ? null
   }:
   
   assert speexSupport -> speex != null;
  
positive.code:     ++ stdenv.lib.optional faacSupport "--enable-libfaac --enable-nonfree"
      ++ stdenv.lib.optional dc1394Support "--enable-libdc1394"
      ++ stdenv.lib.optional x11grabSupport "--enable-x11grab"
      ++ stdenv.lib.optional playSupport "--enable-ffplay";
  
    buildInputs = [ pkgconfig lame yasm zlib bzip2 alsaLib texinfo perl ]
      ++ stdenv.lib.optional mp3Support lame
  
negative.code: assert faacSupport -> faac != null;
  assert x11grabSupport -> libXext != null && libXfixes != null;
  assert playSupport -> SDL != null;
  assert freetypeSupport -> freetype != null;
  
  stdenv.mkDerivation rec {
    name = "ffmpeg-1.2.3";
  