ffreplaygain.sh

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

set +e
ffmpeg -version > /dev/null 2>&1
if [[ $? -ne 0 ]]; then
	echo "ffmpeg must be installed"
	exit 1
fi
set -e

function process_file {
	local file=$1

	local info=$(ffmpeg -i "$file" -filter replaygain -f null /dev/null 2>&1)
	track_gain=$(echo $info | sed -n -r 's/.* track_gain = ([-+]?[0-9]+\.[0-9]+ dB).*/\1/p')
	track_peak=$(echo $info | sed -n -r 's/.* track_peak = ([-+]?[0-9]+\.[0-9]+)/\1/p')

	output=$(mktemp --suffix ".${file##*.}")
	function finish {
		rm -rf "$output"
	}
	trap finish EXIT

	ffmpeg -y -loglevel warning \
		-i "$file" \
		-codec copy \
		-metadata REPLAYGAIN_IMPLEMENTATION="ffmpeg" \
		-metadata REPLAYGAIN_TRACK_GAIN="$track_gain" \
		-metadata REPLAYGAIN_TRACK_PEAK="$track_peak" \
		-metadata REPLAYGAIN_ALBUM_GAIN="$track_gain" \
		-metadata REPLAYGAIN_ALBUM_PEAK="$track_peak" \
		$output
	chown --reference="$file" "$output"
        chmod --reference="$file" "$output"
		
	mv "$output" "$file"
}

files=()
compute_album=false
verbose=false
while [[ $# -gt 0 ]]; do
	arg="$1"

	case "$arg" in
		-h|--help)
			echo "ffreplaygain [-v|--verbose] [-a|--album] FILE..."
			exit 0
			;;
		-v|--verbose)
			verbose=true
			shift
			;;
		-a|--album)
			# TODO: compute album gain and peak
			compute_album=true
			shift
			;;
		*)
			files+=("$arg")
			shift
			;;
	esac
done

for file in "${files[@]}"; do
	process_file "$file"
	if [ $verbose = true ]; then
		echo "Finished $file: track_gain = $track_gain, track_peak = $track_peak"
	fi
done