#!/usr/bin/env bash
set -x
INPUT=$1 # input file
OUTPUT=$2 # target file
SIZE=$3 # [0-9]+[GgMmKk]
TEMP=$(mktemp)
DURATION=$(mediainfo --Inform="Video;%Duration%" $INPUT)
durS=$(($DURATION/1000))
if [[ "$SIZE" =~ [0-9]+[Gg] ]]; then
    gb=${SIZE/[Gg]/}
    kb=$(($gb * 8 * 1024 * 1024))
fi
if [[ "$SIZE" =~ [0-9]+[Mm] ]]; then
    mb=${SIZE/[Mm]/}
    kb=$(($mb * 8 * 1024)) # doing 1M = 1000K just to build in some overhead
fi
if [[ "$SIZE" =~ [0-9]+[Kk] ]]; then
    k=${SIZE/[Kk]/}
    kb=$((k * 8))

fi
if [ ! $kb ]; then
    echo "unable to calculate bitrate"
    exit
fi
audiosize=$((160*durS))
target=$(($kb-$audiosize))
bitrate=$(($target/$durS))


ffmpeg -i $1 \
       -y \
       -f mp4 \
       -g 15 \
       -movflags +faststart \
       -preset ultrafast \
       -threads 9 \
       -c:v libx264 \
       -b:v ${bitrate}k \
       -pass 1 \
       -an \
       -passlogfile $TEMP \
       /dev/null

ffmpeg -i $1 \
       -y \
       -b:a 160k \
       -c:a aac \
       -ac 2 \
       -f mp4 \
       -g 15 \
       -movflags +faststart \
       -preset ultrafast \
       -threads 9 \
       -c:v libx264 \
       -b:v ${bitrate}k \
       -pass 2 \
       -passlogfile $TEMP \
       $2