Haven't had time to bisect, but I can't screengrab to mkv any more.
kmsgrab + playing with vsync etc. give the same error as this example,
mp4 works OK.
ffm -loglevel debug -vaapi_device /dev/dri/renderD128 -f x11grab
-video_size 1920x1080 -i :0 -vf 'format=nv12,hwupload' -c:v h264_vaapi
-profile:v 578 -bf 0 -y out.mkv
ffmpeg version N-90148-g0419623cdc Copyright (c) 2000-2018 the FFmpeg
developers
built with gcc 7.3.0 (GCC)
configuration: --prefix=/usr --disable-doc --enable-gpl
--enable-libvpx --enable-libx265 --enable-libx264 --enable-gnutls
--enable-libdrm --enable-libfreetype --enable-libmp3lame
libavutil 56. 7.101 / 56. 7.101
libavcodec 58. 12.102 / 58. 12.102
libavformat58. 9.100 / 58. 9.100
libavdevice58. 2.100 / 58. 2.100
libavfilter 7. 12.100 / 7. 12.100
libswscale 5. 0.101 / 5. 0.101
libswresample 3. 0.101 / 3. 0.101
libpostproc55. 0.100 / 55. 0.100
Splitting the commandline.
Reading option '-loglevel' ... matched as option 'loglevel' (set logging
level) with argument 'debug'.
Reading option '-vaapi_device' ... matched as option 'vaapi_device' (set
VAAPI hardware device (DRM path or X11 display name)) with argument
'/dev/dri/renderD128'.
Reading option '-f' ... matched as option 'f' (force format) with
argument 'x11grab'.
Reading option '-video_size' ... matched as AVOption 'video_size' with
argument '1920x1080'.
Reading option '-i' ... matched as input url with argument ':0'.
Reading option '-vf' ... matched as option 'vf' (set video filters) with
argument 'format=nv12,hwupload'.
Reading option '-c:v' ... matched as option 'c' (codec name) with
argument 'h264_vaapi'.
Reading option '-profile:v' ... matched as option 'profile' (set
profile) with argument '578'.
Reading option '-bf' ... matched as AVOption 'bf' with argument '0'.
Reading option '-y' ... matched as option 'y' (overwrite output files)
with argument '1'.
Reading option 'out.mkv' ... matched as output url.
Finished splitting the commandline.
Parsing a group of options: global .
Applying option loglevel (set logging level) with argument debug.
Applying option vaapi_device (set VAAPI hardware device (DRM path or X11
display name)) with argument /dev/dri/renderD128.
[AVHWDeviceContext @ 0x2152640] Opened VA display via DRM device
/dev/dri/renderD128.
[AVHWDeviceContext @ 0x2152640] libva: VA-API version 1.1.0
[AVHWDeviceContext @ 0x2152640] libva: va_getDriverName() returns 0
[AVHWDeviceContext @ 0x2152640] libva: User requested driver 'radeonsi'
[AVHWDeviceContext @ 0x2152640] libva: Trying to open
/usr/lib/dri/radeonsi_drv_video.so
[AVHWDeviceContext @ 0x2152640] libva: Found init function
__vaDriverInit_1_1
[AVHWDeviceContext @ 0x2152640] libva: va_openDriver() returns 0
[AVHWDeviceContext @ 0x2152640] Initialised VAAPI connection: version 1.1
[AVHWDeviceContext @ 0x2152640] Format 0x3231564e -> nv12.
[AVHWDeviceContext @ 0x2152640] Format 0x30313050 -> p010le.
[AVHWDeviceContext @ 0x2152640] Format 0x36313050 -> unknown.
[AVHWDeviceContext @ 0x2152640] Format 0x32315659 -> yuv420p.
[AVHWDeviceContext @ 0x2152640] Format 0x56595559 -> unknown.
[AVHWDeviceContext @ 0x2152640] Format 0x59565955 -> uyvy422.
[AVHWDeviceContext @ 0x2152640] Format 0x41524742 -> bgra.
[AVHWDeviceContext @ 0x2152640] Format 0x41424752 -> rgba.
[AVHWDeviceContext @ 0x2152640] Format 0x58524742 -> bgr0.
[AVHWDeviceContext @ 0x2152640] Format 0x58424752 -> rgb0.
[AVHWDeviceContext @ 0x2152640] Unknown driver "Mesa Gallium driver
18.1.0-devel for AMD Radeon R9 200 Series (TONGA / DRM 3.25.0 /
4.16.0-rc1-g2693c7e7ca44, LLVM 7.0.0)", assuming standard behaviour.
Applying option y (overwrite output files) with argument 1.
Successfully parsed a group of options.
Parsing a group of options: input url :0.
Applying option f (force format) with argument x11grab.
Successfully parsed a group of options.
Opening an input file: :0.
[x11grab @ 0x223ca00] Probe buffer size limit of 500 bytes reached
[x11grab @ 0x223ca00] Stream #0: not enough frames to estimate rate;
consider increasing probesize
Input #0, x11grab, from ':0':
Duration: N/A, start: 1519432751.575405, bitrate: N/A
Stream #0:0, 1, 1/100: Video: rawvideo, 1 reference frame
(BGR[0] / 0x524742), bgr0, 1920x1080, 0/1, 29.97 fps, 1000k tbr, 1000k
tbn, 1000k tbc
Successfully opened the file.
Parsing a group of options: output url out.mkv.
Applying option vf (set video filters) with argument format=nv12,hwupload.
Applying option c:v (codec name) with argument h264_vaapi.
Applying option profile:v (set profile) with argument 578.
Successfully parsed a group of options.
Opening an output file: out.mkv.
[file @ 0x224ab40] Setting default whitelist 'file,crypto'
Successfully opened the file.
Stream mapping:
Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (h264_vaapi))
Press [q] to stop, [?] for help
cur_dts is invalid (this is harmless if it occurs once at the start per
stream)
[rawvideo @ 0x22467c0]
