#!/bin/sh

# Compresses a video to a target size, for configuration see VARIABLES
# From: https://trac.ffmpeg.org/wiki/Encode/H.264#Two-PassExample
#
# $1: input file

# VARIABLES
video_codec="libx264"
audio_codec="aac"
audio_bitrate="96"
target_size="8"

MEGABIT="8388"

# Main

input="$1"
if [ -z "$input" ]
then
	>&2 printf 'Usage: discord_compress <input>\n'
	exit 1
fi

duration="$(date -u -d @"$(ffprobe -show_entries format=duration -v quiet -of csv="p=0" -i "$input")" +'%s')"

video_bitrate="$(((target_size * MEGABIT / duration) - audio_bitrate))"
[ "$video_bitrate" ] || exit 1

common_args="-hide_banner -v quiet -stats -y -hwaccel auto -i $input -c:v $video_codec -b:v ${video_bitrate}K"

set -ex

ffmpeg $common_args -pass 1 -an -f null /dev/null
ffmpeg $common_args -pass 2 -c:a "$audio_codec" -b:a "${audio_bitrate}K" compressed_"${input%.*}".mp4

rm -f ffmpeg2pass*.log*