ffmpeg cheat sheet

process_audio.sh

#!/bin/bash

# Downmix 5.1 to stereo, compress dynamic range and normalize an audio track using ffmpeg.
#
# This comes in handy when you're constantly fiddling with your volume control while watching a movie
# because the dialogues are too silent and the explosions too loud.
#
# Firstly, Surround sound is mixed down to stereo. Then, audio is normalized with the intention to "fit"
# the "points" of the following DRC process using the compand filter. The last step is to ensure that the end
# result is normalized.
#
# See:
# [1] https://superuser.com/a/1219033
# [2] https://forum.videohelp.com/threads/349883-Remixing-DTS-5-1-to-good-AC3-5-1-track#post2202882
# [3] http://sox.sourceforge.net/sox.html
# [4] http://ffmpeg.org/ffmpeg-filters.html#compand
# [5] http://ffmpeg.org/ffmpeg-filters.html#dynaudnorm

DOWNMIX="pan=stereo|FL < 1.0*FL + 0.707*FC + 0.707*BL|FR < 1.0*FR + 0.707*FC + 0.707*BR" # See [1]
COMPAND="compand=.1|.1:.3|.3:-90/-90|-70/-64|-43/-37|-31/-31|-21/-21|0/-20:6:0:0:0.1" # "Film Standard" compand filter from [2]
FILTER_CHAIN="$DOWNMIX, dynaudnorm, $COMPAND, dynaudnorm"

ffmpeg -i "$1" -filter:a:0 "$FILTER_CHAIN" processed_"$1".wav