m3u generator with relative paths

#!/bin/bash
#Dependencies: ffmpeg or ffprobe, standard gnu utils (including bc)
#
#april 21 2014 edited to also work with locales that
#use , instead of .for decimal position (thanks to Tina Keil).
#march 20 2013 edited to accommodate opus files and to fix error in fetching
#durations, caused by changes in ffprobe.
#june 07 2012 edited to remove unwanted \ in regex expression which
#prevented ogg files from being parsed.

#also work with locales that use , instead of .for decimal position.
LC_NUMERIC=C LC_COLLATE=C

function usage ()
{
    printf "\nUSAGE:
\t$(basename "$0") [options] {-o out} <directory>\n
OPTIONS:
\t-D  Don't overwrite existing playlist (default is to replace)\n
\t-s  Simple m3u8 playlist instead of extended m3u8\n
\t-p  writes the file names in .m3u with full path\n\
\t    (default is simple file name without path)\n
\t-d  Set the recursion depth (default is 1)\n
\t-r  Recurses through subdirectories and writes file names with
\t    full path\n
\t-R  Recurses through subdirectories and writes file names with
\t    relative path\n
\t-c  Format playlist for Sansa Clip+ Internal Memory (implies -p)
\t
\t-C  Format playlist for Sansa Clip+ MicroSDHC (implies -p)
\t
\t-H  Format playlist for iriver H10/100/300 series players (implies -p)
\t    You MUST change the MicroSDHC card label and mount point in
\t    the sed expressions to the ACTUAL MicroSDHC card label and
\t    mount point on your OS.  The Clip internal storage and iRiver H
\t    values are quite generic but Clip external storage values could be
\t    anything - user must check this.\n
\t-o <output directory>  (default is target directory)\n
\t$(basename "$0") finds the audio files in the directory, parses
\tthe metadata, then writes an extended .m3u playlist\n
\t$(basename "$0") understands the same files as  your
\tinstalled version of ffmpeg.\n
\tIf $(basename "$0") fails please check output directory exists
\tand is writeable.\n\n"
}

#dump file data;grep metadata relevant to extm3u.
#extm3u spec states that stated time MUST be equal to or greater than
#track duration so all times are rounded UP to integer i.e. 38.00 secs
#becomes 38 seconds but 38.10 secs or 38.95 seconds become 39 seconds.
function getdata ()
{
ffprobe -v quiet -show_format -show_streams "$f">"$DATA"

PERF=$(grep -m 1 -i tag:artist "$DATA" |\
awk -F "=" '{$1="";$0=substr($0,2)}1' |cleantag)
TIT=$(grep -m 1 -i tag:title "$DATA" |\
awk -F "=" '{$1="";$0=substr($0,2)}1' |cleantag)
SEC=$(printf %.2f\\n $(grep -m 1 -i -e "^duration=" "$DATA" |\
awk -F "=" '{print $2}'))
SEC=$(printf %0.f\\n $(echo "$SEC+0.5"|bc))
}

#remove problematic characters from metadata.
function cleantag ()
{
    sed 's/[;]/-/g;s/[/]/-/g;s/[<]/-/g;s/[>]/-/g;s/[:]/-/g;s/[|]/-/g'
}

function relpath ()
{
        source=$1
        target=$2
        common_part=$source
        back=
        while [ "${target#$common_part}" = "${target}" ]; do
                common_part=$(dirname $common_part)
                back="../${back}"
        done
        echo ${back}${target#$common_part/}
}

#user options
while getopts 'CcDHo:prRs' OPTION
do
    case $OPTION in
    o)  oflag=1
        oval=$OPTARG
        ;;
    p)  pflag=1
        ;;
    r)  rflag=1
        pflag=1
        ;;
    R)  rflag=1
        relpathflag=1
        ;;
    c)  cflag=1
        ;;
    C)  Cflag=1
        pflag=1
        ;;
    H)  Hflag=1
        pflag=1
        ;;
    s)  sflag=1
        ;;
    D)  Dflag=1
        ;;
    esac
done
shift $(($OPTIND-1))

if [ $# -lt 1 ]; then
    usage
    exit 1
fi

#recurse?
if [ $rflag ]; then
    DEPTH=''
else
    DEPTH="-maxdepth 1"
fi

for i in "$@" ; do
#ensure .m3u name is not dot file if script run within target directory.
PN=$(basename "$(readlink -f "$i")").m3u

#some simple error checking
if [ ! -d "$i" ]; then
    usage
    exit
fi

#set output destination. Output dir exists and writeable?
if [ $oflag ]; then
    if [ ! -d "$oval" -o ! -w "$oval" ]; then
    usage
    exit
    fi
    PL=$oval/"$PN"
    else
    PL="$i"/"$PN"
fi

#playlist exists? overwrite?
if [ $Dflag ] && [ -f "$PL" ]; then
    printf "\n$PL already exists.\n"
    continue
    else
    > "$PL"
fi

if [ ! $sflag ]; then
    #write mandatory extm3u8 header
    printf "#EXTM3U">"$PL"
    WRITE=xlist
    else
    WRITE=slist
fi

#find all audio files to be referenced in .m3u
find "$i" $DEPTH -iregex ".*\(flac\|ape\|wv\|wav\|mpc\|aac\|m4a\|wma\|\
mp3\|ogg\|oga\|mka\|ac3\|opus\)$" |sort |while read f ; do

#use full path or simple names?
if [ $pflag ]; then
    if [ $cflag ]; then
        FILENAME=$(readlink -f "$f"|sed 's/\/media\/SANSA\ CLIPP//')
    elif [ $Cflag ]; then
        FILENAME=$(readlink -f "$f"|sed 's/media\/LEX/\<microSD1\>/')
    elif [ $Hflag ]; then
        FILENAME=$(readlink -f "$f"|sed 's/media\/H[0-9]*.//')
    else
        FILENAME=$(readlink -f "$f")
    fi
elif [ $relpathflag ]; then
    FILENAME=$(readlink -f "$f")
    FILENAME=$(relpath $PWD $FILENAME)
else
    FILENAME="${f##*/}"
fi

#where to dump ffprobe's file info
DATA="${f%.*}"_data

#run getdata silently (ffprobe generates much unwanted text)
getdata>/dev/null 2>&1

#write to the playlist, clean up.
printf "\n#EXTINF:$SEC,$PERF - $TIT\n$FILENAME">>"$PL"
rm "$DATA"
done

#confirm to user, quit.
echo "Wrote "$PL""
done
exit 0