$ ffmpeg -f x11grab -r 25 -s 1920x1080 -i :0.0 -vcodec libx264 -vcodec libx264 -crf 0 -preset ultrafast -threads 0 -t 10 -y -f null -
ffmpeg version 1.1.3 Copyright (c) 2000-2013 the FFmpeg developers
  built on Mar 12 2013 20:42:55 with gcc 4.6.3 (Gentoo 4.6.3 p1.11, pie-0.5.2)
  configuration: --prefix=/usr --libdir=/usr/lib64 --shlibdir=/usr/lib64 --mandir=/usr/share/man --enable-shared --cc=x86_64-pc-linux-gnu-gcc --cxx=x86_64-pc-linux-gnu-g++ --ar=x86_64-pc-linux-gnu-ar --optflags='-march=athlon64 -O2 -pipe -msse -msse2 -msse3 -mmmx -m3dnow' --extra-cflags='-march=athlon64 -O2 -pipe -msse -msse2 -msse3 -mmmx -m3dnow' --extra-cxxflags='-march=athlon64 -O2 -pipe -msse -msse2 -msse3 -mmmx -m3dnow' --disable-static --enable-gpl --enable-version3 --enable-postproc --enable-avfilter --disable-stripping --disable-debug --disable-doc --disable-network --disable-vaapi --disable-ffplay --disable-runtime-cpudetect --enable-libmp3lame --enable-libvo-amrwbenc --enable-libx264 --disable-indev=oss --disable-indev=jack --enable-x11grab --disable-outdev=oss --disable-outdev=sdl --enable-libopencore-amrwb --enable-libopencore-amrnb --disable-amd3dnow --disable-amd3dnowext --disable-altivec --disable-avx --disable-mmxext --disable-ssse3 --disable-vis --disable-neon --cpu=athlon64 --enable-hardcod  libavutil      52. 13.100 / 52. 13.100
  libavcodec     54. 86.100 / 54. 86.100
  libavformat    54. 59.106 / 54. 59.106
  libavdevice    54.  3.102 / 54.  3.102
  libavfilter     3. 32.100 /  3. 32.100
  libswscale      2.  1.103 /  2.  1.103
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
[x11grab @ 0x1fdb7d0] device: :0.0 -> display: :0.0 x: 0 y: 0 width: 1920 height: 1080
[x11grab @ 0x1fdb7d0] shared memory extension found
[x11grab @ 0x1fdb7d0] Estimating duration from bitrate, this may be inaccurate
Input #0, x11grab, from ':0.0':
  Duration: N/A, start: 1363122098.944934, bitrate: 1658880 kb/s
    Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 1920x1080, 1658880 kb/s, 25 tbr, 1000k tbn, 25 tbc
[libx264 @ 0x2005260] using cpu capabilities: MMX2 SSE2Fast SSSE3 FastShuffle SSE4.1 Cache64
[libx264 @ 0x2005260] profile High 4:4:4 Predictive, level 4.0, 4:4:4 8-bit
Output #0, null, to 'pipe:':
  Metadata:
    encoder         : Lavf54.59.106
    Stream #0:0: Video: h264, yuv444p, 1920x1080, q=-1--1, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo -> libx264)
Press [q] to stop, [?] for help
frame=  250 fps= 10 q=32766.0 Lsize=N/A time=00:00:10.00 bitrate=N/A    
video:3639kB audio:0kB subtitle:0 global headers:0kB muxing overhead -100.000590%
[libx264 @ 0x2005260] frame I:1     Avg QP: 0.00  size:2249100
[libx264 @ 0x2005260] frame P:249   Avg QP: 0.00  size:  5932
[libx264 @ 0x2005260] mb I  I16..4: 100.0%  0.0%  0.0%
[libx264 @ 0x2005260] mb P  I16..4:  8.6%  0.0%  0.0%  P16..4:  0.1%  0.0%  0.0%  0.0%  0.0%    skip:91.3%
[libx264 @ 0x2005260] coded y,u,v intra: 5.4% 5.0% 5.4% inter: 0.0% 0.0% 0.0%
[libx264 @ 0x2005260] i16 v,h,dc,p: 96%  4%  0%  0%
[libx264 @ 0x2005260] kb/s:2980.93