#!/bin/bash

MPLAYER="mplayer"
FFMPEG="ffmpeg"

if [ -z "$1" ]; then
    echo "Usage: $0 filename"
    exit 1
fi

INPUT="$1"

acodec="$(
    "$MPLAYER" -identify -vo null -ao null -frames 0 "$INPUT" |
    grep ID_AUDIO_CODEC |
    cut -d= -f2
)"
if [ "$acodec" = "ffaac" ]; then
    ext=".m4a"
else
    echo "Unknown audio codec! $acodec"
    exit 1
fi

OUTPUT="$(basename "$INPUT" | sed 's/\.[a-zA-Z1-9]*$//')${ext}"
"$FFMPEG" -i "$INPUT" -vn -acodec copy "$OUTPUT"