anchor.diff:  assert vpxSupport -> libvpx != null;
   assert x264Support -> x264 != null;
   assert xvidSupport -> xvidcore != null;
  +assert opusSupport -> libopus != null;
   assert vdpauSupport -> libvdpau != null;
   assert vaapiSupport -> libva != null;
   assert faacSupport -> faac != null;
  
positive.code: , vpxSupport ? false, libvpx ? null
  , x264Support ? true, x264 ? null
  , xvidSupport ? true, xvidcore ? null
  , vdpauSupport ? true, libvdpau ? null
  , vaapiSupport ? true, libva ? null
  , faacSupport ? false, faac ? null
  
negative.code:     ++ stdenv.lib.optional vpxSupport libvpx
      ++ stdenv.lib.optional x264Support x264
      ++ stdenv.lib.optional xvidSupport xvidcore
      ++ stdenv.lib.optional opusSupport libopus
      ++ stdenv.lib.optional vdpauSupport libvdpau
      ++ stdenv.lib.optional vaapiSupport libva
      ++ stdenv.lib.optional faacSupport faac
  