Convert a clip of an MP3 file to an AAC encoded ringtone

mp3-to-ringtone.sh

#!/bin/sh

progname=`basename $0`

err()
{
    code="$1"
    if test -z "$code" ; then
        code=1
    fi
    msg="$*"
    if test -z "$msg" ; then
        msg="something funny is going on"
    fi
    echo >&2 "${progname}: error: ${msg}"
    exit $code
}

usage()
{
    echo >&2 "usage: $progname HH:MM HH:MM INFILE.mp3 OFILE.m4r"
    exit 64
}

start="$1"
stop="$2"
input="$3"
output="$4"

test -z "$start"  && echo >&2 'start time not specified'  && usage
test -z "$stop"   && echo >&2 'stop time not specified'   && usage
test -z "$input"  && echo >&2 'input file not specified'  && usage
test -z "$output" && echo >&2 'output file not specified' && usage

if test "$input" = "$output" ; then
    err 1 "input and output cannot be the same file"
fi

case $output in
    *.[mM]4[rR])
        audio=`echo "$output" | sed -e 's/\.[mM]4[rR]$/.m4a/'`
        ;;
    *)
        echo >&2 "output file MUST have an .m4r extension"
        usage
        ;;
esac

ffmpeg -ss "$start" -t "$stop" -i "$input" -vn -c:a aac -vbr 4 "$audio"
if test $? -ne 0 ; then
    rm -f "$audio"
fi
mv "$audio" "$output"