Hexadecimal byte array from a Midi event to int

Question

I'm trying to retrieve the tempo of a midi file through the javax.midi library.

MidiMessage message = event.getMessage();
if(message instanceof MetaMessage)
 MetaMessage mm = (MetaMessage) message;
 System.out.println(Arrays.toString(mm.getData()));
}

What I am expected to receive is an array of three ex, because the Set Tempo meta message (which is this case, has just 3 bytes specifying a miliseconds amount. This is how the midi event returns

0x07 0xA1 0x20

So if you join them you have 0x07A120 which is 500,000 ms, but Java returns in the print

[7, -95, 32]

First of all it is parsing it to decimal, and then I need to get this 500,000 number. I don't know how to do it because first I need to join all the hex, and then I will have the number, but I don't know how to do it.

Anyone can help me, please?

Numbers are numbers. How they're printed is relevant only when... printing them. If you need to pass them around they are just numbers. — Federico klez Culloca, May 01 '22 at 09:03

score 2 · Accepted Answer · answered May 01 '22 at 09:22

MetaMessage.getData() returns a byte array, which you turn into a list of bytes using Arrays.asList(), that's why you print a list of bytes.

Below is a method that compute the tempo in beats per minute from a TEMPO MetaMessage. The mspq variable (milliseconds per quarter) is the value you seek.

/**
 * Get the tempo in BPM coded in a Tempo Midi message.
 *
 * @param tempoMsg Must be a tempo MetaMessage (type=81)
 * @return
 */
static public int getTempoInBPM(MetaMessage tempoMsg)
{
    byte[] data = tempoMsg.getData();
    if (tempoMsg.getType() != 81 || data.length != 3)
    {
        throw new IllegalArgumentException("tempoMsg=" + tempoMsg);   
    }
    int mspq = ((data[0] & 0xff) << 16) | ((data[1] & 0xff) << 8) | (data[2] & 0xff);
    int tempo = Math.round(60000001f / mspq);
    return tempo;
}

Here you'll find some more Midi utilities in java.

score -1 · Answer 2 · answered May 01 '22 at 14:04

-1

int tempo = new BigInteger(mm.getData()).intValue();

would be simpler

answered May 01 '22 at 14:04

g00se

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Hexadecimal byte array from a Midi event to int

2 Answers2