Mix byte array android

Question

I would like to mix audio byte array, but I didn't succeed to sum the array.(note i already added some silent bytes of 0 as padding before). I have an ArrayList of byte[] which contains:

the first byte[] is header (44 bytes).
Following byte[] are raw data byte array to be mixed

Here is my code:

ArrayList<byte[]> ListAudio = new ArrayList<byte[]>();
byte[] header= WriteHeader(); //wav header 44 bytes
ListAudio.add(header);
for (byte[] b : audioTreatment.ListDataByte) {
      ListAudio.add(b);
 }
 //calculate total length of audio
 int length = 0;
 for (byte[] array : ListAudio) {
 length += array.length;
 }

 final int len = length;
 final byte[] mixBytes = new byte[len];
 for (byte[] array : ListAudio) {
 for (int i = 44; i < len; ++i) {
     mixBytes[i] += array[i];
   // mixBytes[i]=(byte) ((bytes1[i]+bytes2[i]) / 2);

     }
}

I found somewhere that the method to mix digital byte array is :

mixBytes[i]=(byte) ((bytes1[i]+bytes2[i]) / 2);

I don't arrive to include the calcul above, to sum the byte array. How can i sum the bytes array from my ArrayList ?

uhm, what was the question?

Martin Frank
– Martin Frank

2016-09-21 13:51:16 +00:00
Commented Sep 21, 2016 at 13:51 — Martin Frank
– Martin Frank, Commented Sep 21, 2016 at 13:51
Martin Frank, i edited my question, thanks you

Rocé Tarentula
– Rocé Tarentula

2016-09-21 14:47:06 +00:00
Commented Sep 21, 2016 at 14:47 — Rocé Tarentula
– Rocé Tarentula, Commented Sep 21, 2016 at 14:47

Martin Frank · Accepted Answer · 2016-09-23 08:57:51Z

1

you have to declare your sources to merge them

byte[] source1 = ListAudio.get(0); //first from list
byte[] source2 = ListAudio.get(1); //second from list

int length = Math.min(source1.length, source2.length);//length of new array
length = length - 44; //skipping 44 byte

byte[] dest = new byte[length];
for(int index = 0; index < length; index ++){
    byte b1 = source1[index+44];
    byte b2 = source2[index+44];
    dest[index] = (byte) ((b1+b2) / 2);
}

That would merge the first two byte[] from your list.

If you want to merge other sources you can change them by selecting other byte[] from your List.

HINT
The length of the destination is declared as Math.min(a,b) but you can fill missing bytes with zeros if you want...

if you want to merge all arrays, you have to adjust your merge operation

mixing two bytes: mixBytes[i]=(byte) ((bytes1[i]+bytes2[i]) / 2);

mixing three bytes: mixBytes[i]=(byte) ((bytes1[i]+bytes2[i]+bytes3[i]) / 3);

mixing N bytes: mixBytes[i]=(byte) ((bytes1[i]+bytes2[i]+bytes3[i]+...+bytesN[i]) / N);

ok, for your code snipped it would be:

int length = ...;//length of result, either min or max as mentioned above, see HINT
byte[] mixBytes = new byte[length]; 

int amountAudio = ListAudio.size(); //amount of tracks in your list aka 'N' 

int sum;
for(int index = 0; index < length; index++){
    sum = 0;
    for(byte[] source: ListAudio){
        //adding all byte into one big integer
        sum = sum + source[index]; //NOTE: watch for indexOutOfBoundsException
    }
    //afterward divide the big int through amount of Audio tracks in your list
    mixBytes[index] = (byte)(sum / amountAudio);
}

edited Sep 23, 2016 at 8:57

answered Sep 22, 2016 at 8:38

Martin Frank

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10 Comments

Martin Frank Over a year ago

i'm not sure if the conversion ((byte1+byte2)/2)is working properly, I copy/pastd it from your code

Rocé Tarentula Over a year ago

Thanks you very much, but if my source within the arraylist are dynamic and i can't declare them statically, how could i proceed?

Martin Frank Over a year ago

uhm - i'm not sure what you mean... what is dynamically? the content of the list? the content of the arrays in the list?

Rocé Tarentula Over a year ago

Yes the content of the list is dynamic and can contain 2 or more byte[] to be mixed, so i can't declare : byte[] source1 = ListAudio.get(0); //first from list byte[] source2 = ListAudio.get(1); //second from list

Martin Frank Over a year ago

then how is the list filled? when is the list changed?

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