Movie split FAT32 size limit

ffmpeg -i "SOURCE.mkv" -map 0:v:0 -map 0:a:0 -c:v copy -ac 2 -clev 2dB -slev -3dB -c:a libfdk_aac -b:a 192k "TARGET-temp.mp4"

fSIZE=$(du -k "TARGET-temp.mp4" | awk '{print $1}')

if [ $fSIZE -ge 4194303 ]; then
    SpliT=$(( ( $fSIZE / 2 ) + 51200 ))
    [ $fSIZE -ge 8388606 ] && SpliT=$(( $SpliT / 2 ))
    MP4Box -new -add "TARGET-temp.mp4" -splits $SpliT "TARGET.mp4"
fi