res.writeHead(200, {
        'Content-Type': 'audio/mpeg',
        'Content-Length': size - startByte,
        'Transfer-Encoding': 'chuncked',
        'Cache-Control': "no-cache",
        'Connection': 'Keep-Alive'
    });

    ffmpeg(assetUrl)
    //.withDuration(60)
    //.seek(30)
    .format("mp3")
    .audioQuality(5)
    .withNoVideo()
    .audioBitrate(96)
    .audioChannels(2)
    .audioFrequency(44100)
    .audioFilters([
        {
            filter: 'volume',
            options: ['0.4']
        },
        {
            filter: 'silencedetect',
            options: { n: '-50dB', d: 5 }
        }
    ])
    .on('end', function(err) {
        console.log('done!', err)
    })
    .on('error', function(err) {
        console.log('an error: ' + err);
    })
    .stream().pipe(res, { end: true })