scripts/downmix.sh

#!/bin/bash

# ====================================================================
# Simple script to downmix a 5.0/5.1/5.1 (side) flac file to stereo,
# and optionally resample to cd quality
# 
# Dependencies: ffmpeg (built with libsoxr and flac)
# ====================================================================

read -p 'Gain db [-6]: ' GAIN
if [[ -z "$GAIN" ]]; then
	GAIN=-6
fi

read -p 'Resample to cd quality? [No]: ' RES

mkdir -p down

for file in *.flac; do
	if [[ -z "$RES" ]]; then
		ffmpeg -i "$file" -af "volume=volume=${GAIN}dB:precision=double,pan=stereo| FL = FL + 0.707*FC + 0.707*BL + 0.707*SL + 0.5*LFE | FR = FR + 0.707*FC + 0.707*BR + 0.707*SR + 0.5*LFE" "down/$file"
	else
		ffmpeg -i "$file" -af "volume=volume=${GAIN}dB:precision=double,pan=stereo| FL = FL + 0.707*FC + 0.707*BL + 0.707*SL + 0.5*LFE | FR = FR + 0.707*FC + 0.707*BR + 0.707*SR + 0.5*LFE,aresample=resampler=soxr:precision=33:cutoff=0.96:dither_method=triangular:out_sample_rate=44100:out_sample_fmt=s16" "down/${file/%flac/wav}"
	fi
done