Question

I am facing a problem regarding audio decoding. I have the SPIMP3 library for mp3 decoding and I am trying to decode mp3’s and storing them to an array of bytes.

Here is the thing, when I try to decode a 2 minute mp3 song it gives me, for example, the following bytes:

[ -1, 0, 42, -115, -45, 0, 14 … etc].

But when I cut that mp3 in half and try to decode the first half I get the following bytes:

[ 1, 0, 0, 65, -97, 135, -64, 32 …etc]

The weird thing is that they don’t match. The only thing that differs here is the audio length, but I am decoding the first part of both of the mp3 samples which is the same.

Here is my code:

public void testPlay(String mp3) {
    try {
        File file = new File(mp3);
        AudioInputStream in = AudioSystem.getAudioInputStream(file);
        AudioInputStream din = null;
        AudioFormat baseFormat = in.getFormat();
        AudioFormat decodedFormat = new AudioFormat(AudioFormat.Encoding.PCM_SIGNED,
                baseFormat.getSampleRate(),
                16,
                baseFormat.getChannels(),
                baseFormat.getChannels() * 2,
                baseFormat.getSampleRate(),
                false);
        din = AudioSystem.getAudioInputStream(decodedFormat, in);

        play(decodedFormat, din);
        spi(decodedFormat, in);
        in.close();
    } catch (Exception e) {
        System.out.println("MP3");
    }

}

private void play(AudioFormat targetFormat, AudioInputStream din) throws IOException, LineUnavailableException {

    ByteArrayOutputStream out = new ByteArrayOutputStream();
    byte[] data = new byte[4096];
    SourceDataLine line = getLine(targetFormat);

        int nBytesRead = 0, nBytesWritten = 0;
        while (nBytesRead != -1) {
            nBytesRead = din.read(data, 0, data.length);
            if (nBytesRead != -1) {
                nBytesWritten = line.write(data, 0, nBytesRead);
                out.write(data, 0, 4096);
            }

        }

       byte[] audio = out.toByteArray();

}

Is this something to be expected or is there a problem on my code???

How can I change my code to get the same bytes for the matching part of my mp3?

Thank you.

Answer 1

this line should be:

out.write(data, 0, nBytesRead);