[FFmpeg-user] kmsgrab on non primary card, libva/hwmap advice?

[test]

Hi All. Thanks in advance for any assistance provided.

I've been trying to get kmsgrab to work on my second rx570.
Aim is to record multiple framebuffers on both cards. Both cards are
maxed in terms of CRTC's, so switching all to one card isn't an
option. x11grab has not been performant enough.

I have three "cards":

/dev/dri/card0 -> intel iGPU
/dev/dri/card1 -> rx 570
/dev/dri/card2 -> rx 570

I have card1 working fine, it's the primary card. I haven't tried card0.

/home/test/.local/bin/ffmpeg  -framerate 60 -device /dev/dri/card1  -f
kmsgrab  -i - -vf 'hwmap=derive_device=vaapi,hwdownload,format=bgr0'
/home/test/card1.mp4

Whilst trying for card2 and a similar command I get errors.
I've tried advice under https://trac.ffmpeg.org/wiki/Hardware/VAAPI
regarding device selection.
The error doesn't change?

./ffmpeg -init_hw_device
vaapi=foo:/dev/dri/by-path/pci-0000\:02\:00.0-render
-filter_hw_device foo -framerate 60 -device /dev/dri/card2  -f kmsgrab
 -i - -vf 'hwmap=
derive_device=vaapi,hwdownload,format=bgr0' /home/test/card2.mp4

Any advice would be appreciated.
Cheers.
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