anchor.diff:  assert faacSupport -> faac != null;
   assert flacSupport -> flac != null;
   assert soxSupport -> sox != null;
  -assert vorbisSupport -> vorbisTools != null;
  +assert vorbisSupport -> vorbis-tools != null;
   
   let
     zeroconf = pythonPackages.callPackage ./zeroconf.nix { };
  
positive.code:     ++ stdenv.lib.optional faacSupport faac
      ++ stdenv.lib.optional flacSupport flac
      ++ stdenv.lib.optional soxSupport sox
      ++ stdenv.lib.optional vorbisSupport vorbisTools;
  
    # upstream has no tests
    checkPhase = ''
  
negative.code: , faacSupport ? false, faac ? null
  , flacSupport ? true, flac ? null
  , soxSupport ? true, sox ? null
  , vorbisSupport ? true, vorbis-tools ? null
  }:
  
  assert mp3Support -> lame != null;
  