anchor.diff:  assert bs2bSupport -> libbs2b != null;
   assert libpngSupport -> libpng != null;
   assert libjpegSupport -> libjpeg != null;
  +assert v4lSupport -> libv4l != null;
   
   let
   
  
positive.code:     ++ optional libpngSupport libpng
      ++ optional libjpegSupport libjpeg
      ++ optional bs2bSupport libbs2b
      ++ (with darwin.apple_sdk.frameworks; optionals stdenv.isDarwin [ Cocoa OpenGL ])
      ;
  
  
negative.code:     (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"
  