#!/bin/bash

# See : 
# https://stackoverflow.com/questions/49955100/how-do-i-split-a-video-to-2-separate-files-for-odd-and-even-fields-using-ffmpeg
# Et : 
# https://korben.info/ffmpeg-pour-les-nuls.html


# Split the 1 video in 2

ffmpeg -i $1 -filter_complex "[0]il=l=d:c=d,split[o][e];[o]crop=iw:ih/2:0:0[odd];[e]crop=iw:ih/2:0:ih/2[even]" -map "[odd]" odd.mp4 -map "[even]" even.mp4


# Rotate the 2 videos clockwise

ffmpeg -i odd.mp4 -vf "transpose=1" odd_90cw.mp4
ffmpeg -i even.mp4 -vf "transpose=1" even_90cw.mp4


# Split each of the 2 videos in 2
# We now have 4 videos

ffmpeg -i odd_90cw.mp4 -filter_complex "[0]il=l=d:c=d,split[o][e];[o]crop=iw:ih/2:0:0[odd];[e]crop=iw:ih/2:0:ih/2[even]" -map "[odd]" odd_90cw_odd.mp4 -map "[even]" odd_90cw_even.mp4
ffmpeg -i even_90cw.mp4 -filter_complex "[0]il=l=d:c=d,split[o][e];[o]crop=iw:ih/2:0:0[odd];[e]crop=iw:ih/2:0:ih/2[even]" -map "[odd]" even_90cw_odd.mp4 -map "[even]" even_90cw_even.mp4

# Rotate these 4 video back to normal (counter-clockwise)

ffmpeg -i even_90cw_odd.mp4 -vf "transpose=2" even_odd.mp4
ffmpeg -i even_90cw_even.mp4 -vf "transpose=2" even_even.mp4
ffmpeg -i odd_90cw_odd.mp4 -vf "transpose=2" odd_odd.mp4
ffmpeg -i odd_90cw_even.mp4 -vf "transpose=2" odd_even.mp4

# Get filename

filename=$(basename -- "$1")
extension="${filename##*.}"
filename="${filename%.*}"

# Extract audio from original file

ffmpeg -i $1 -acodec copy $filename.aac

# Merge audio track into each one of the 4 videos

ffmpeg -i $filename.aac -i even_odd.mp4 $filename.part1.$extension
ffmpeg -i $filename.aac -i even_even.mp4 $filename.part2.$extension
ffmpeg -i $filename.aac -i odd_odd.mp4 $filename.part3.$extension
ffmpeg -i $filename.aac -i odd_even.mp4 $filename.part4.$extension

# Remove useless files

rm odd.mp4 even.mp4 odd_90cw.mp4 even_90cw.mp4 even_90cw_odd.mp4 even_90cw_even.mp4 odd_90cw_odd.mp4 odd_90cw_even.mp4 even_odd.mp4 even_even.mp4 odd_odd.mp4 odd_even.mp4 $filename.aac