anchor.diff:  { stdenv, fetchurl, pkgconfig, perl, texinfo, yasm
   , alsaLib, bzip2, fontconfig, freetype, gnutls, libiconv, lame, libass, libogg
   , libtheora, libva, libvdpau, libvorbis, libvpx, lzma, libpulseaudio, SDL, soxr
  -, x264, xvidcore, zlib
  +, x264, xvidcore, zlib, libopus
   , openglSupport ? false, mesa ? null
   # Build options
   , runtimeCpuDetectBuild ? true # Detect CPU capabilities at runtime
  
positive.code:       "--enable-libx264"
        "--enable-libxvid"
        "--enable-zlib"
      # Developer flags
        (enableFeature debugDeveloper "debug")
        (enableFeature optimizationsDeveloper "optimizations")
  
negative.code: 
    buildInputs = [
      bzip2 fontconfig freetype gnutls libiconv lame libass libogg libtheora
      libvdpau libvorbis lzma SDL soxr x264 xvidcore zlib libopus
    ] ++ optional openglSupport mesa
      ++ optionals (!isDarwin) [ libvpx libpulseaudio ] # Need to be fixed on Darwin
      ++ optional (isLinux || isFreeBSD) libva
  