anchor.diff:  
     buildInputs = with stdenv.lib;
       [ freetype pkgconfig ffmpeg libass docutils which ]
  -    ++ optionals x11Support [ libX11 libXext mesa ]
  +    ++ optionals x11Support [ libX11 libXext mesa libXxf86vm ]
       ++ optional alsaSupport alsaLib
       ++ optional xvSupport libXv
       ++ optional theoraSupport libtheora
  
positive.code: , useUnfreeCodecs ? false
  }:
  
  assert x11Support -> (libX11 != null && libXext != null && mesa != null);
  assert xineramaSupport -> (libXinerama != null && x11Support);
  assert xvSupport -> (libXv != null && x11Support);
  assert alsaSupport -> alsaLib != null;
  
negative.code: { stdenv, fetchurl, fetchgit, freetype, pkgconfig, yasm, freefont_ttf, ffmpeg, libass
  , python3, docutils, which
  , x11Support ? true, libX11 ? null, libXext ? null, mesa ? null, libXxf86vm ? null
  , xineramaSupport ? true, libXinerama ? null
  , xvSupport ? true, libXv ? null
  , alsaSupport ? true, alsaLib ? null
  