anchor.diff:      (if x264Support then "--enable-x264 --disable-x264-lavc" else "--disable-x264 --enable-x264-lavc")
       (if jackaudioSupport then "" else "--disable-jack")
       (if pulseSupport then "--enable-pulse" else "--disable-pulse")
  +    (if v4lSupport then "--enable-v4l2 --enable-tv-v4l2" else "--disable-v4l2 --disable-tv-v4l2")
       "--disable-xanim"
       "--disable-ivtv"
       "--disable-xvid --disable-xvid-lavc"
  
positive.code: assert bs2bSupport -> libbs2b != null;
  assert libpngSupport -> libpng != null;
  assert libjpegSupport -> libjpeg != null;
  
  let
  
  
negative.code:     ++ optional libpngSupport libpng
      ++ optional libjpegSupport libjpeg
      ++ optional bs2bSupport libbs2b
      ++ optional v4lSupport libv4l
      ++ (with darwin.apple_sdk.frameworks; optionals stdenv.isDarwin [ Cocoa OpenGL ])
      ;
  
  