ffmpeg -y -vaapi_device /dev/dri/renderD128 -f x11grab -i :44 -vf 'hwupload,scale_vaapi=format=nv12' -c:v h264_vaapi -bf 0 output.mp4
ffmpeg version N-89674-g57d0c24132 Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 7.2.1 (GCC) 20171128
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-avisynth --enable-avresample --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libass --enable-libbluray --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxvid --enable-shared --enable-version3
  libavutil      56.  7.100 / 56.  7.100
  libavcodec     58.  9.100 / 58.  9.100
  libavformat    58.  3.100 / 58.  3.100
  libavdevice    58.  0.100 / 58.  0.100
  libavfilter     7.  8.100 /  7.  8.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  0.101 /  5.  0.101
  libswresample   3.  0.101 /  3.  0.101
  libpostproc    55.  0.100 / 55.  0.100
Input #0, x11grab, from ':44':
  Duration: N/A, start: 1514998577.359994, bitrate: N/A
    Stream #0:0: Video: rawvideo (BGR[0] / 0x524742), bgr0, 640x480, 29.97 fps, 30 tbr, 1000k tbn, 1000k tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (h264_vaapi))
Press [q] to stop, [?] for help
[h264_vaapi @ 0x55e9bfad3d40] Warning: some packed headers are not supported (want 0xd, got 0).
Output #0, mp4, to 'output.mp4':
  Metadata:
    encoder         : Lavf58.3.100
    Stream #0:0: Video: h264 (h264_vaapi) (High) (avc1 / 0x31637661), vaapi_vld, 640x480, q=0-31, 30 fps, 15360 tbn, 30 tbc
    Metadata:
      encoder         : Lavc58.9.100 h264_vaapi
Past duration 0.966667 too large
frame=  925 fps= 30 q=-0.0 Lsize=     447kB time=00:00:30.80 bitrate= 118.8kbits/s dup=3 drop=1 speed=1.01x
video:442kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.994684%