As for the need for LIBVA_DRIVER_NAME iHD I must say when I tested this it was an ivybridge looking at the packges descriptions:
libva-intel-driver-2.3.0_3 VAAPI legacy driver for Intel GMA 4500 (Gen4) or newer
libva-intel-hybrid-driver-1.0.2_1 Hybrid VP8 encoder and VP9 decoder for Intel GPUs
libva-intel-media-driver-18.4.1 VAAPI driver for Intel HD 5000 (Gen8) or newer
looks like for newer we need libva-intel-media-driver and this requires extra setup… I might have access to hardware with a more recent intel cpu, if so I can possibly look into it but not promises on timing
