anchor.diff:  assert amrSupport -> (amrnb != null && amrwb != null);
   assert screenSaverSupport -> libXScrnSaver != null;
   assert vdpauSupport -> libvdpau != null;
  +assert speexSupport -> speex != null;
   
   let
   
  
positive.code:     ${if codecs != null then "--codecsdir=${codecs}" else ""}
      ${if (stdenv.isi686 || stdenv.isx86_64) then "--enable-runtime-cpudetection" else ""}
      ${if x11Support then "--enable-x11" else ""}
      --disable-xanim
      --disable-ivtv
      --enable-vidix
  
negative.code: , x264Support ? false, x264 ? null
  , xvidSupport ? false, xvidcore ? null
  , lameSupport ? true, lame ? null
  , speexSupport ? true, speex ? null
  , screenSaverSupport ? true, libXScrnSaver
  , pulseSupport ? false, pulseaudio
  , mesa, pkgconfig, unzip, yasm, freefont_ttf
  