@43c Thanks for the info, that workaround is also mentioned in the arch wiki.
But I am not willing to sacrifice security for VAAPI, specially since I don’t know the exact changes with disabling sandbox in firefox.
I got vivaldi working with VAAPI.
EDIT:
If anyone is wondering, this worked for me on vivaldi, it should work on all chromium based browsers with some adjustments.
Launch vivaldi with
vivaldi-stable --use-gl=desktop --disable-features=UseChromeOSDirectVideoDecoder --enable-features=VaapiVideoDecoder --ignore-gpu-blocklist --enable-gpu-rasterization --enable-accelerated-2d-canvas --enable-accelerated-video-decode --enable-zero-copy
or create vivaldi-stable.conf in ~/.config with
–use-gl=desktop
–disable-features=UseChromeOSDirectVideoDecoder
–enable-features=VaapiVideoDecoder
–ignore-gpu-blocklist
–enable-gpu-rasterization
–enable-accelerated-2d-canvas
–enable-accelerated-video-decode
Working on Arch, i3WM, X11, Vivaldi 5.2.2623.39 (Stable channel) stable (64-bit)