I don't have a video card with ARC ... so I can't test, but based in some search I can recommend reading: https://forum.level1techs.com/t/ffmpeg-av1-encoding-using-intel-arc-gpu-tips/205120/2
When I experimented with atom CPU, I used the following command:
/usr/bin/ffmpeg -hide_banner -hwaccel vaapi -hwaccel_output_format vaapi -i pipe:0 -map 0:v -vf 'deinterlace_vaapi' -c:v h264_vaapi -preset veryslow -profile:v high -qp:v 28 -map 0:a? -c:a aac -b:a 64k -map 0:s? -c:s copy -fflags +nobuffer+discardcorrupt+genpts+flush_packets -avoid_negative_ts disabled -f mpegts pipe:1
You have to combine those two.
I starting point is:
/usr/bin/ffmpeg -i pipe:0 -init_hw_device vaapi=va:/dev/dri/renderD128 -c:v av1_qsv -preset veryslow -extbrc 1 -look_ahead_depth 40 -b:v 1M -bufsize 2M -rc_init_occupancy 512K -low_power 0 -adaptive_i 1 -adaptive_b 1 -b_strategy 1 -bf 7 -map 0:a? -c:a aac -b:a 64k -map 0:s? -c:s copy -fflags +nobuffer+discardcorrupt+genpts+flush_packets -avoid_negative_ts disabled -f mpegts pipe:1
