Extendscript: get audio file bitrate

getAudioItemkbps.jsx

// This doesn't check that the selection is valid, or that it's an audio file.
// Based on: http://stackoverflow.com/questions/21634091/is-it-possible-to-get-bitrate-of-mp3

(function () {
    var item = app.project.selection[0];
    var duration = item.duration;
    var fileSize = item.file.length;

    var kbit = fileSize/128;
    var kbps = Math.ceil(Math.round(kbit / duration) / 16) * 16;

    $.writeln(kbps + " kbps");
})();