Convert a rotated video recording (recorded in portrait mode, but plays in landscape mode) to landscape video with the same video blurred as backdrop

convert-rotated-video.sh

#!/bin/bash -eu

INPUT="input.mp4"
OUTPUT="output.mp4"
W=1920
H=1080
OVERLAY_W=1080 # Increase this to remove the bottom part of the portrait recording
OVERLAY_X=$(
  echo "(${W} - (${H} * ${OVERLAY_W} / ${W})) / 2" | bc
)

ffmpeg -i "${INPUT}" \
  -filter_complex "
  [0:v]rotate='-PI/2:${H}:${W}'[rot];
  [rot]split[rotbg][rotfg];
  [rotbg]scale=${W}*2:-1, crop=${W}:${H}, boxblur=luma_radius=20:chroma_radius=20:luma_power=10[blurredbg];
  [rotfg]scale=-1:${OVERLAY_W}[zoomedfg];
  [blurredbg][zoomedfg]overlay=${OVERLAY_X}:0[combine];
  [combine]fade=in:0:75[out];
  [0:a]afade=in:st=0:d=5[audio]
  " \
  -map "[out]" -map "[audio]" "${OUTPUT}"