nnn/plugins/mp3conv

#!/usr/bin/env sh

# Description: Extract audio from multimedia files and convert to mp3
#
# Dependency: ffmpeg compiled with libmp3lame audio codec support
#
# Shell: POSIX compliant
# Author: Arun Prakash Jana

outdir=_mp3files

handle_multimedia() {
    mime="${1}"
    file="${2}"

    case "${mime}" in
        audio/* | video/*)
            ffmpeg -i "${file}" -vn -codec:a libmp3lame -q:a 2 "${outdir}/${file%.*}.mp3"
            ;;
        *)
            ;;
    esac
}

printf "Process 'a'll in directory or 'c'urrent? "
read -r resp

if [ "$resp" = "a" ]; then
    if ! [ -e "${outdir}" ]; then
        mkdir "${outdir}"
    fi

    for f in *; do
        if [ -f "${f}" ]; then
            mimestr="$( file --dereference --brief --mime-type -- "${f}" )"
            handle_multimedia "${mimestr}" "${f}"
        fi
    done
elif [ "$resp" = "c" ] && [ -f "$1" ]; then
    ffmpeg -i "${1}" -vn -codec:a libmp3lame -q:a 2 "${1%.*}.mp3"
fi