anchor.diff:      ++ stdenv.lib.optional x11grabSupport "--enable-x11grab";
   
     buildInputs = [ pkgconfig lame yasm zlib bzip2 alsaLib ]
  +    ++ stdenv.lib.optional jackSupport jackaudio
       ++ stdenv.lib.optional mp3Support lame
       ++ stdenv.lib.optional speexSupport speex
       ++ stdenv.lib.optional theoraSupport libtheora
  
positive.code: { stdenv, fetchurl, pkgconfig, yasm, zlib, bzip2, alsaLib
  , mp3Support ? true, lame ? null
  , speexSupport ? true, speex ? null
  , theoraSupport ? true, libtheora ? null
  
negative.code: , x11grabSupport ? false, libXext ? null, libXfixes ? null
  }:
  
  assert jackSupport -> jackaudio != null;
  assert speexSupport -> speex != null;
  assert theoraSupport -> libtheora != null;
  assert vorbisSupport -> libvorbis != null;
  