it works, but at around 0.8 fps for 720p video

ffmpeg -i MLP_animation_sleepsong_IeIDCNS-VUw.webm -s 1280x720  -an -f yuv4mpegpipe   - | SvtAv1EncApp -i - -b mlp.ivf --passes 1 --rc 1 --tbr 1000

after looking at code I see all asm there is 64bit :)

this explains why it is much faster on x86_64.

Anyway, even 0.8 fps is ok for short (few mins) clips, I guess.