#!/bin/bash
# http://redsymbol.net/articles/unofficial-bash-strict-mode/
set -euo pipefail

# Source: https://rentry.co/n4ost

f="$1"
t=$(mktemp)
mp4extract-bento4 moov/trak/mdia/minf/stbl/stsd/mp4a/esds \
    "$f" /dev/stdout | xxd -p | tr -d '\n' > $t

magic=$(sed -re 's/^.*0580808002(....).*$/\1/' $t)

if [ "$magic" != "1212" ]; then
    rm "$t"
    exit 0
fi

t2=`mktemp`
new=$(sed -re 's/05808080021212/05808080021210/' $t | xxd -r -p >$t2)
rm $t
old="${f}.pre-fix"
mv -v "$f" "$old"
mp4edit --replace \
    moov/trak/mdia/minf/stbl/stsd/mp4a/esds:"$t2" \
    "$old" \
    "$f"

rm "$old"