code: private void computeIv(long label, long index) {
  		long key_id;
  
  		if (keyDerivationRate == 0) {
  			key_id = label << 48;
  		} else {
  			key_id = ((label << 48) | (index / keyDerivationRate));
  		}
  		for (int i = 0; i < 7; i++) {
  			ivStore[i] = masterSalt[i];
  		}
  		for (int i = 7; i < 14; i++) {
  			ivStore[i] = (byte) ((byte) (0xFF & (key_id >> (8 * (13 - i)))) ^ masterSalt[i]);
  		}
  		ivStore[14] = ivStore[15] = 0;
  	}
docs: Compute the initialization vector, used later by encryption algorithms,
  based on the lable, the packet index, key derivation rate and master salt
  key.
  
  @param label
  label specified for each type of iv
  @param index
  48bit RTP packet index