tomp3normvol

#!/usr/bin/env bash

# problem: my recorders often produce audio streams with volume level far lower than ideal
# ffmpeg (and bash and perl) to the rescue!  Catalyst https://superuser.com/questions/323119/how-can-i-normalize-audio-using-ffmpeg

die() { printf %s "${@+$@$'\n'}" 1>&2 ; exit 1 ; }

command -v ffmpeg || die "ffmpeg not in PATH"

read_mean_volume_neg_db() (
   ffmpeg -i "$1" -vn -sn -dn -af "volumedetect" -f null /dev/null 2>&1 >/dev/null | perl -lne '/mean_volume: \-(\d+)\.\d+ dB/ && print $1'
   )

destext=mp3

outfnm_suffix="_normvol.$destext"

normvol_to_mp3() (
   # set -x
   outfnm="${1%.*}$outfnm_suffix"
   [[ -f "$outfnm" && "$outfnm" -nt "$1" ]] && die "exists $outfnm"
   dbadj="$(read_mean_volume_neg_db "$1")" || die "read_mean_volume_neg_db failed on $1"
   printf "+%3ddB %s\n" "$dbadj" "$outfnm"
   ffmpeg -i "$1" -y -f "$destext" -q:a 0 -af "volume=${dbadj}dB" "$outfnm" 2> /dev/null || die "normvol failed on $1"
   )

for fnm in "$@"; do
   if [[ -f "$fnm" ]]; then
      case "$fnm" in
         *"$outfnm_suffix") echo "!recnv $fnm" ;;
         *)                 normvol_to_mp3 "$fnm" ;;
      esac
   fi
done