mp3ify

#!/usr/bin/env sh

set -o errexit

log() {
    if [ "${MP3IFY_LOG}" == "true" ]; then
        echo $1 1>&2
    fi
    if [ "${MP3IFY_LOG_FD1}" == "true" ]; then
        echo $1 1>&2 >> /proc/1/fd/1
    fi
}

USAGE="Usage: `basename $0` input output"

if [ $# -ne 2 ]; then
    echo $USAGE >&2
    exit 1
fi

I=$1
O=$2

[ ! -e "${I}" ] && \
    echo "Input file ${I} does not exist" >&2 && \
    exit 1

stream0=$(ffprobe -select_streams 0 -show_streams "${I}" 2>/dev/null)

codec_type=$(echo "${stream0}" | grep "^codec_type=" | cut -d = -f 2)
if [ "${codec_type}" != "audio" ]; then
    echo "Expected stream 0 to be audio, but is ${codec_type}" >&2
    exit 1
fi

codec_name=$(echo "${stream0}" | grep "^codec_name=" | cut -d = -f 2)
sample_fmt=$(echo "${stream0}" | grep "^sample_fmt=" | cut -d = -f 2)
sample_rate=$(echo "${stream0}" | grep "^sample_rate=" | cut -d = -f 2)

case "${codec_name}" in
    mp3)
        log "mp3ify: mp3 -> mp3"
        ffmpeg \
            -i "${I}" \
            -map 0:a \
            -c:a copy \
            -map_metadata -1 \
            -flush_packets 1 \
            -f mp3 \
            "${O}"
    ;;
    flac|alac|aac)
        log "mp3ify: ${codec_name} -> mp3"
        ffmpeg \
            -i "${I}" \
            -af aresample=resampler=soxr:precision=28 \
            -codec:a libmp3lame \
            -q:a 0 \
            -frame_duration 10 \
            -map_metadata -1 \
            -flush_packets 1 \
            -f mp3 \
            "${O}"
    ;;
    *)
        log "mp3ify: File ${I} has an unsupported codec ${codec_name}"
        exit 1
    ;;
esac