$ ffmpeg -video_size 3198x1798  -framerate 60 -f x11grab -i :0.0 -c:v libx264 -qp 0 -preset ultrafast -f null -
ffmpeg version 3.1.5-1 Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 6.2.0 (Debian 6.2.0-9) 20161019
  configuration: --prefix=/usr --extra-version=1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --enable-shared --disable-libtesseract --disable-stripping --disable-decoder=libschroedinger --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libebur128 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librubberband --enable-libschroedinger --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-frei0r --enable-chromaprint --enable-libopencv --enable-libx264
  libavutil      55. 28.100 / 55. 28.100
  libavcodec     57. 48.101 / 57. 48.101
  libavformat    57. 41.100 / 57. 41.100
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 47.100 /  6. 47.100
  libavresample   3.  0.  0 /  3.  0.  0
  libswscale      4.  1.100 /  4.  1.100
  libswresample   2.  1.100 /  2.  1.100
  libpostproc    54.  0.100 / 54.  0.100
[x11grab @ 0x56432eb59c80] Stream #0: not enough frames to estimate rate; consider increasing probesize
Input #0, x11grab, from ':0.0':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 3198x1798, 60 fps, 1000k tbr, 1000k tbn, 1000k tbc
No pixel format specified, yuv444p for H.264 encoding chosen.
Use -pix_fmt yuv420p for compatibility with outdated media players.
[libx264 @ 0x56432eb62ce0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 AVX2 LZCNT BMI2
[libx264 @ 0x56432eb62ce0] profile High 4:4:4 Predictive, level 5.2, 4:4:4 8-bit
[null @ 0x56432eb612c0] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.
Output #0, null, to 'pipe:':
  Metadata:
    encoder         : Lavf57.41.100
    Stream #0:0: Video: h264 (libx264), yuv444p, 3198x1798, q=-1--1, 60 fps, 60 tbn, 60 tbc
    Metadata:
      encoder         : Lavc57.48.101 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[swscaler @ 0x56432eb673a0] Warning: data is not aligned! This can lead to a speedloss
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTS
    Last message repeated 7 times
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTSitrate=N/A speed=0.0278x
    Last message repeated 7 times
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTSitrate=N/A speed=0.0149x
    Last message repeated 8 times
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTSitrate=N/A speed=0.0102x
    Last message repeated 5 times
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTSitrate=N/A speed=0.00777x
    Last message repeated 8 times
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTSitrate=N/A speed=0.00623x
    Last message repeated 7 times
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTSitrate=N/A speed=0.0052x
    Last message repeated 8 times
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTSitrate=N/A speed=0.00449x
    Last message repeated 8 times
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTSitrate=N/A speed=0.00394x
    Last message repeated 8 times
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTSitrate=N/A speed=0.00351x
    Last message repeated 8 times
[libx264 @ 0x56432eb62ce0] non-strictly-monotonic PTSitrate=N/A speed=0.00316x
    Last message repeated 7 times
frame=   93 fps= 16 q=-1.0 Lsize=N/A time=00:00:00.01 bitrate=N/A speed=0.00285x
video:7672kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
[libx264 @ 0x56432eb62ce0] frame I:1     Avg QP: 0.00  size:1951588
[libx264 @ 0x56432eb62ce0] frame P:92    Avg QP: 0.00  size: 64178
[libx264 @ 0x56432eb62ce0] mb I  I16..4: 100.0%  0.0%  0.0%
[libx264 @ 0x56432eb62ce0] mb P  I16..4: 65.3%  0.0%  0.0%  P16..4:  0.3%  0.0%  0.0%  0.0%  0.0%    skip:34.4%
[libx264 @ 0x56432eb62ce0] coded y,u,v intra: 1.6% 1.1% 1.2% inter: 0.2% 0.1% 0.1%
[libx264 @ 0x56432eb62ce0] i16 v,h,dc,p: 99%  1%  0%  0%
[libx264 @ 0x56432eb62ce0] kb/s:inf
Exiting normally, received signal 2.