#!/bin/bash
# twitch_reencode.sh
# 
# requires ffmpeg and fdkaac

VERSION="1.1.0"

# audio variable bitrate setting (1-5)
audio_vbr=3

# h264 rate factor (22-28 recommended range)
video_crf=27

# h264 profile and preset
# https://trac.ffmpeg.org/wiki/Encode/H.264
video_profile="-profile:v high -level 4.2 -pix_fmt yuv420p"

video_preset="veryslow"
video_preset_short="vs"

function usage {
    echo "$(basename "$0") v${VERSION} - Reencode a twitch video file to make much smaller."
    echo "If no output filename is provided, one will be generated automatically."
    echo "Examples:"
    echo "    $(basename "$0") <input.mp4> [output.mp4]" 
    echo "Options:"
    echo "    -h, --help         Print this help message and exit"
    echo "    -v, --version      Print this help message and exit"
    echo "    --video-crf        h264 rate factor (quality, 22-28, default $video_crf)"
}

function parse_args {
    local arg
    
    while (( $# != 0)); do
	arg="$1"
	shift
	
	case "$arg" in
	-h|--help)
	    usage
	    exit 0
	    ;;
	-v|--version)
	    usage
	    exit 0
	    ;;
	--video-crf)
	    [[ -z "$1" ]] && echo "ERROR: --video-crf must specify a rate factor" && exit 1
	    video_crf="$1"
	    echo "Video h264 rate factor set to $video_crf"
	    shift
	    ;;
	*)
	    if [[ -z "$input" ]]; then
		input="$arg"
	    else
		output="$arg"
	    fi
	    ;;
	esac
    done
    
    [[ -z "$input" ]] && usage && exit 1
    
    if [[ -z "$output" ]]; then
	output="${input%.*}-${video_preset_short}-crf${video_crf}-faacm${audio_vbr}.reenc.mp4"
    fi
}

# main

parse_args "$@"

echo "reencoding '$input' to '$output'"

ffmpeg -loglevel 24 -i "$input" -vn -f caf - | fdkaac -S -m "$audio_vbr" - -f 2 -o - | nice -n 20 ffmpeg -i "$input" -i - -c:v h264 ${video_profile} -movflags +faststart -crf "$video_crf" -preset "$video_preset" -c:a copy -map 0:v:0 -map 1:a:0 -y "$output"