anchor.diff:  assert amrSupport -> (amrnb != null && amrwb != null);
   assert screenSaverSupport -> libXScrnSaver != null;
   assert vdpauSupport -> libvdpau != null;
  +assert speexSupport -> speex != null;
   
   let
   
  
positive.code:     ++ stdenv.lib.optional pulseSupport pulseaudio
      ++ stdenv.lib.optional screenSaverSupport libXScrnSaver
      ++ stdenv.lib.optional lameSupport lame
      ++ stdenv.lib.optional vdpauSupport libvdpau;
  
    buildNativeInputs = [ yasm ];
  
  
negative.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 ""}
      ${stdenv.lib.optionalString speexSupport "--enable-speex"}
      --disable-xanim
      --disable-ivtv
      --enable-vidix
  