Concatenate audio files into single opus file

concat2opus.sh

#!/bin/bash

TMP=$(mktemp -d)

# syntax check
if [ -z "$3" ]; then
    echo "Syntax: $0 <output>.opus <input1> <input2> ..."
    exit 1
fi

# split arguments (inputs in $@)
output="$1"
shift

# decode inputs
intermediates=""
i=1
for f in "$@"; do
    mkfifo $TMP/fifo_$i
    ffmpeg -y -i "$f" -vn -f u16le -c:a pcm_s16le -ac 2 -ar 48000 $TMP/fifo_$i 2>/dev/null </dev/null &
    intermediates="$intermediates $TMP/fifo_$i"
    let i++
done

# concatenate
mkfifo $TMP/fifo_all
cat $intermediates > $TMP/fifo_all &

# encode
ffmpeg -f u16le -c:a pcm_s16le -ac 2 -ar 48000 -i $TMP/fifo_all -c:a libopus -b:a 48k "$output.opus"

# cleanup
rm $TMP/fifo_*
rmdir $TMP