$ ~/src2/ffmpeg/ffmpeg -loglevel verbose -vaapi_device /dev/dri/renderD128 -f x11grab -video_size 1280x1024 -i :0 -c:v h264_vaapi -vf:v format=nv12,hwupload -profile:v 578 -y output.mp4
ffmpeg version n4.0.2-6-g2be51cbeea Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 7 (Ubuntu 7.3.0-27ubuntu1~18.04)
  configuration: --enable-libpulse --enable-vaapi --enable-libx264 --enable-libx265 --enable-gpl
  libavutil      56. 14.100 / 56. 14.100
  libavcodec     58. 18.100 / 58. 18.100
  libavformat    58. 12.100 / 58. 12.100
  libavdevice    58.  3.100 / 58.  3.100
  libavfilter     7. 16.100 /  7. 16.100
  libswscale      5.  1.100 /  5.  1.100
  libswresample   3.  1.100 /  3.  1.100
  libpostproc    55.  1.100 / 55.  1.100
[AVHWDeviceContext @ 0x562b84fb7440] Opened VA display via DRM device /dev/dri/renderD128.
[AVHWDeviceContext @ 0x562b84fb7440] libva: VA-API version 1.1.0
[AVHWDeviceContext @ 0x562b84fb7440] libva: va_getDriverName() returns 0
[AVHWDeviceContext @ 0x562b84fb7440] libva: Trying to open /usr/lib/x86_64-linux-gnu/dri/radeonsi_drv_video.so
[AVHWDeviceContext @ 0x562b84fb7440] libva: Found init function __vaDriverInit_1_1
[AVHWDeviceContext @ 0x562b84fb7440] libva: va_openDriver() returns 0
[AVHWDeviceContext @ 0x562b84fb7440] Initialised VAAPI connection: version 1.1
[AVHWDeviceContext @ 0x562b84fb7440] Unknown driver "mesa gallium vaapi", assuming standard behaviour.
[x11grab @ 0x562b850a1ec0] Stream #0: not enough frames to estimate rate; consider increasing probesize
Input #0, x11grab, from ':0':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: rawvideo, 1 reference frame (BGR[0] / 0x524742), bgr0, 1280x1024, 29.97 fps, 1000k tbr, 1000k tbn, 1000k tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (h264_vaapi))
Press [q] to stop, [?] for help
[graph 0 input from stream 0:0 @ 0x562b850b4e40] w:1280 h:1024 pixfmt:bgr0 tb:1/1000000 fr:30000/1001 sar:0/1 sws_param:flags=2
[auto_scaler_0 @ 0x562b850b75c0] w:iw h:ih flags:'bicubic' interl:0
[Parsed_format_0 @ 0x562b850b4000] auto-inserting filter 'auto_scaler_0' between the filter 'graph 0 input from stream 0:0' and the filter 'Parsed_format_0'
[auto_scaler_0 @ 0x562b850b75c0] w:1280 h:1024 fmt:bgr0 sar:0/1 -> w:1280 h:1024 fmt:nv12 sar:0/1 flags:0x4
[h264_vaapi @ 0x562b850af540] H.264 constrained baseline profile doesn't support encoding with B frames, disabling them.
[h264_vaapi @ 0x562b850af540] Warning: some packed headers are not supported (want 0xd, got 0).
Output #0, mp4, to 'output.mp4':
  Metadata:
    encoder         : Lavf58.12.100
    Stream #0:0: Video: h264 (h264_vaapi) (Constrained Baseline), 1 reference frame (avc1 / 0x31637661), vaapi_vld, 1280x1024, q=0-31, 29.97 fps, 30k tbn, 29.97 tbc
    Metadata:
      encoder         : Lavc58.18.100 h264_vaapi
*** dropping frame 3 from stream 0 at ts 0
    Last message repeated 13 times
*** dropping frame 3 from stream 0 at ts 0 time=00:00:00.06 bitrate=   5.8kbits/s dup=0 drop=14 speed=0.124x
    Last message repeated 15 times
*** dropping frame 3 from stream 0 at ts 0 time=00:00:00.06 bitrate=   5.8kbits/s dup=0 drop=30 speed=0.0623x
    Last message repeated 14 times
*** dropping frame 3 from stream 0 at ts 0 time=00:00:00.06 bitrate=   5.8kbits/s dup=0 drop=45 speed=0.0424x
    Last message repeated 15 times