ffmpeg -i https://2ch.hk/s/src/1240405/14341441473030.webm -lavfi '[0:v]scale=ih*16/9:-1,boxblur=3:3[bg];[bg][0:v]overlay=(h*16/9-w)/2:(h*W/w-h)/2,crop=h=iw*9/16' -c:v libvpx-vp9 -b:v 0 -crf 20 -c:a copy -threads 8 -y out.webm