vp8enc always fails on: Error: Input colorspace YUV420 not supported, exit

Hello,

the libva-utils vp8enc always fails with error:

Error: Input colorspace YUV420 not supported, exit

I have tried all the different input types - always with the same result

other encoders such as jpegenc or h264encode have no problem at all

testing on skylake i6700, followed this guide to setup my environment: https://gist.github.com/Brainiarc7/24de2edef08866c304080504877239a3

Thanks